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inode.c

/*
 *  linux/fs/ext4/inode.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card (card@masi.ibp.fr)
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/inode.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Goal-directed block allocation by Stephen Tweedie
 *    (sct@redhat.com), 1993, 1998
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller (davem@caip.rutgers.edu), 1995
 *  64-bit file support on 64-bit platforms by Jakub Jelinek
 *    (jj@sunsite.ms.mff.cuni.cz)
 *
 *  Assorted race fixes, rewrite of ext4_get_block() by Al Viro, 2000
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/time.h>
#include <linux/jbd2.h>
#include <linux/highuid.h>
#include <linux/pagemap.h>
#include <linux/quotaops.h>
#include <linux/string.h>
#include <linux/buffer_head.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/mpage.h>
#include <linux/namei.h>
#include <linux/uio.h>
#include <linux/bio.h>

#include "ext4_jbd2.h"
#include "xattr.h"
#include "acl.h"
#include "ext4_extents.h"

#include <trace/events/ext4.h>

#define MPAGE_DA_EXTENT_TAIL 0x01

static inline int ext4_begin_ordered_truncate(struct inode *inode,
                                    loff_t new_size)
{
      return jbd2_journal_begin_ordered_truncate(
                              EXT4_SB(inode->i_sb)->s_journal,
                              &EXT4_I(inode)->jinode,
                              new_size);
}

static void ext4_invalidatepage(struct page *page, unsigned long offset);

/*
 * Test whether an inode is a fast symlink.
 */
static int ext4_inode_is_fast_symlink(struct inode *inode)
{
      int ea_blocks = EXT4_I(inode)->i_file_acl ?
            (inode->i_sb->s_blocksize >> 9) : 0;

      return (S_ISLNK(inode->i_mode) && inode->i_blocks - ea_blocks == 0);
}

/*
 * The ext4 forget function must perform a revoke if we are freeing data
 * which has been journaled.  Metadata (eg. indirect blocks) must be
 * revoked in all cases.
 *
 * "bh" may be NULL: a metadata block may have been freed from memory
 * but there may still be a record of it in the journal, and that record
 * still needs to be revoked.
 *
 * If the handle isn't valid we're not journaling, but we still need to
 * call into ext4_journal_revoke() to put the buffer head.
 */
int ext4_forget(handle_t *handle, int is_metadata, struct inode *inode,
            struct buffer_head *bh, ext4_fsblk_t blocknr)
{
      int err;

      might_sleep();

      BUFFER_TRACE(bh, "enter");

      jbd_debug(4, "forgetting bh %p: is_metadata = %d, mode %o, "
              "data mode %x\n",
              bh, is_metadata, inode->i_mode,
              test_opt(inode->i_sb, DATA_FLAGS));

      /* Never use the revoke function if we are doing full data
       * journaling: there is no need to, and a V1 superblock won't
       * support it.  Otherwise, only skip the revoke on un-journaled
       * data blocks. */

      if (test_opt(inode->i_sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA ||
          (!is_metadata && !ext4_should_journal_data(inode))) {
            if (bh) {
                  BUFFER_TRACE(bh, "call jbd2_journal_forget");
                  return ext4_journal_forget(handle, bh);
            }
            return 0;
      }

      /*
       * data!=journal && (is_metadata || should_journal_data(inode))
       */
      BUFFER_TRACE(bh, "call ext4_journal_revoke");
      err = ext4_journal_revoke(handle, blocknr, bh);
      if (err)
            ext4_abort(inode->i_sb, __func__,
                     "error %d when attempting revoke", err);
      BUFFER_TRACE(bh, "exit");
      return err;
}

/*
 * Work out how many blocks we need to proceed with the next chunk of a
 * truncate transaction.
 */
static unsigned long blocks_for_truncate(struct inode *inode)
{
      ext4_lblk_t needed;

      needed = inode->i_blocks >> (inode->i_sb->s_blocksize_bits - 9);

      /* Give ourselves just enough room to cope with inodes in which
       * i_blocks is corrupt: we've seen disk corruptions in the past
       * which resulted in random data in an inode which looked enough
       * like a regular file for ext4 to try to delete it.  Things
       * will go a bit crazy if that happens, but at least we should
       * try not to panic the whole kernel. */
      if (needed < 2)
            needed = 2;

      /* But we need to bound the transaction so we don't overflow the
       * journal. */
      if (needed > EXT4_MAX_TRANS_DATA)
            needed = EXT4_MAX_TRANS_DATA;

      return EXT4_DATA_TRANS_BLOCKS(inode->i_sb) + needed;
}

/*
 * Truncate transactions can be complex and absolutely huge.  So we need to
 * be able to restart the transaction at a conventient checkpoint to make
 * sure we don't overflow the journal.
 *
 * start_transaction gets us a new handle for a truncate transaction,
 * and extend_transaction tries to extend the existing one a bit.  If
 * extend fails, we need to propagate the failure up and restart the
 * transaction in the top-level truncate loop. --sct
 */
static handle_t *start_transaction(struct inode *inode)
{
      handle_t *result;

      result = ext4_journal_start(inode, blocks_for_truncate(inode));
      if (!IS_ERR(result))
            return result;

      ext4_std_error(inode->i_sb, PTR_ERR(result));
      return result;
}

/*
 * Try to extend this transaction for the purposes of truncation.
 *
 * Returns 0 if we managed to create more room.  If we can't create more
 * room, and the transaction must be restarted we return 1.
 */
static int try_to_extend_transaction(handle_t *handle, struct inode *inode)
{
      if (!ext4_handle_valid(handle))
            return 0;
      if (ext4_handle_has_enough_credits(handle, EXT4_RESERVE_TRANS_BLOCKS+1))
            return 0;
      if (!ext4_journal_extend(handle, blocks_for_truncate(inode)))
            return 0;
      return 1;
}

/*
 * Restart the transaction associated with *handle.  This does a commit,
 * so before we call here everything must be consistently dirtied against
 * this transaction.
 */
static int ext4_journal_test_restart(handle_t *handle, struct inode *inode)
{
      BUG_ON(EXT4_JOURNAL(inode) == NULL);
      jbd_debug(2, "restarting handle %p\n", handle);
      return ext4_journal_restart(handle, blocks_for_truncate(inode));
}

/*
 * Called at the last iput() if i_nlink is zero.
 */
void ext4_delete_inode(struct inode *inode)
{
      handle_t *handle;
      int err;

      if (ext4_should_order_data(inode))
            ext4_begin_ordered_truncate(inode, 0);
      truncate_inode_pages(&inode->i_data, 0);

      if (is_bad_inode(inode))
            goto no_delete;

      handle = ext4_journal_start(inode, blocks_for_truncate(inode)+3);
      if (IS_ERR(handle)) {
            ext4_std_error(inode->i_sb, PTR_ERR(handle));
            /*
             * If we're going to skip the normal cleanup, we still need to
             * make sure that the in-core orphan linked list is properly
             * cleaned up.
             */
            ext4_orphan_del(NULL, inode);
            goto no_delete;
      }

      if (IS_SYNC(inode))
            ext4_handle_sync(handle);
      inode->i_size = 0;
      err = ext4_mark_inode_dirty(handle, inode);
      if (err) {
            ext4_warning(inode->i_sb, __func__,
                       "couldn't mark inode dirty (err %d)", err);
            goto stop_handle;
      }
      if (inode->i_blocks)
            ext4_truncate(inode);

      /*
       * ext4_ext_truncate() doesn't reserve any slop when it
       * restarts journal transactions; therefore there may not be
       * enough credits left in the handle to remove the inode from
       * the orphan list and set the dtime field.
       */
      if (!ext4_handle_has_enough_credits(handle, 3)) {
            err = ext4_journal_extend(handle, 3);
            if (err > 0)
                  err = ext4_journal_restart(handle, 3);
            if (err != 0) {
                  ext4_warning(inode->i_sb, __func__,
                             "couldn't extend journal (err %d)", err);
            stop_handle:
                  ext4_journal_stop(handle);
                  goto no_delete;
            }
      }

      /*
       * Kill off the orphan record which ext4_truncate created.
       * AKPM: I think this can be inside the above `if'.
       * Note that ext4_orphan_del() has to be able to cope with the
       * deletion of a non-existent orphan - this is because we don't
       * know if ext4_truncate() actually created an orphan record.
       * (Well, we could do this if we need to, but heck - it works)
       */
      ext4_orphan_del(handle, inode);
      EXT4_I(inode)->i_dtime  = get_seconds();

      /*
       * One subtle ordering requirement: if anything has gone wrong
       * (transaction abort, IO errors, whatever), then we can still
       * do these next steps (the fs will already have been marked as
       * having errors), but we can't free the inode if the mark_dirty
       * fails.
       */
      if (ext4_mark_inode_dirty(handle, inode))
            /* If that failed, just do the required in-core inode clear. */
            clear_inode(inode);
      else
            ext4_free_inode(handle, inode);
      ext4_journal_stop(handle);
      return;
no_delete:
      clear_inode(inode);     /* We must guarantee clearing of inode... */
}

typedef struct {
      __le32      *p;
      __le32      key;
      struct buffer_head *bh;
} Indirect;

static inline void add_chain(Indirect *p, struct buffer_head *bh, __le32 *v)
{
      p->key = *(p->p = v);
      p->bh = bh;
}

/**
 *    ext4_block_to_path - parse the block number into array of offsets
 *    @inode: inode in question (we are only interested in its superblock)
 *    @i_block: block number to be parsed
 *    @offsets: array to store the offsets in
 *    @boundary: set this non-zero if the referred-to block is likely to be
 *           followed (on disk) by an indirect block.
 *
 *    To store the locations of file's data ext4 uses a data structure common
 *    for UNIX filesystems - tree of pointers anchored in the inode, with
 *    data blocks at leaves and indirect blocks in intermediate nodes.
 *    This function translates the block number into path in that tree -
 *    return value is the path length and @offsets[n] is the offset of
 *    pointer to (n+1)th node in the nth one. If @block is out of range
 *    (negative or too large) warning is printed and zero returned.
 *
 *    Note: function doesn't find node addresses, so no IO is needed. All
 *    we need to know is the capacity of indirect blocks (taken from the
 *    inode->i_sb).
 */

/*
 * Portability note: the last comparison (check that we fit into triple
 * indirect block) is spelled differently, because otherwise on an
 * architecture with 32-bit longs and 8Kb pages we might get into trouble
 * if our filesystem had 8Kb blocks. We might use long long, but that would
 * kill us on x86. Oh, well, at least the sign propagation does not matter -
 * i_block would have to be negative in the very beginning, so we would not
 * get there at all.
 */

static int ext4_block_to_path(struct inode *inode,
                        ext4_lblk_t i_block,
                        ext4_lblk_t offsets[4], int *boundary)
{
      int ptrs = EXT4_ADDR_PER_BLOCK(inode->i_sb);
      int ptrs_bits = EXT4_ADDR_PER_BLOCK_BITS(inode->i_sb);
      const long direct_blocks = EXT4_NDIR_BLOCKS,
            indirect_blocks = ptrs,
            double_blocks = (1 << (ptrs_bits * 2));
      int n = 0;
      int final = 0;

      if (i_block < 0) {
            ext4_warning(inode->i_sb, "ext4_block_to_path", "block < 0");
      } else if (i_block < direct_blocks) {
            offsets[n++] = i_block;
            final = direct_blocks;
      } else if ((i_block -= direct_blocks) < indirect_blocks) {
            offsets[n++] = EXT4_IND_BLOCK;
            offsets[n++] = i_block;
            final = ptrs;
      } else if ((i_block -= indirect_blocks) < double_blocks) {
            offsets[n++] = EXT4_DIND_BLOCK;
            offsets[n++] = i_block >> ptrs_bits;
            offsets[n++] = i_block & (ptrs - 1);
            final = ptrs;
      } else if (((i_block -= double_blocks) >> (ptrs_bits * 2)) < ptrs) {
            offsets[n++] = EXT4_TIND_BLOCK;
            offsets[n++] = i_block >> (ptrs_bits * 2);
            offsets[n++] = (i_block >> ptrs_bits) & (ptrs - 1);
            offsets[n++] = i_block & (ptrs - 1);
            final = ptrs;
      } else {
            ext4_warning(inode->i_sb, "ext4_block_to_path",
                       "block %lu > max in inode %lu",
                       i_block + direct_blocks +
                       indirect_blocks + double_blocks, inode->i_ino);
      }
      if (boundary)
            *boundary = final - 1 - (i_block & (ptrs - 1));
      return n;
}

static int __ext4_check_blockref(const char *function, struct inode *inode,
                         __le32 *p, unsigned int max)
{
      __le32 *bref = p;
      unsigned int blk;

      while (bref < p+max) {
            blk = le32_to_cpu(*bref++);
            if (blk &&
                unlikely(!ext4_data_block_valid(EXT4_SB(inode->i_sb),
                                        blk, 1))) {
                  ext4_error(inode->i_sb, function,
                           "invalid block reference %u "
                           "in inode #%lu", blk, inode->i_ino);
                  return -EIO;
            }
      }
      return 0;
}


#define ext4_check_indirect_blockref(inode, bh)                         \
      __ext4_check_blockref(__func__, inode, (__le32 *)(bh)->b_data,  \
                        EXT4_ADDR_PER_BLOCK((inode)->i_sb))

#define ext4_check_inode_blockref(inode)                                \
      __ext4_check_blockref(__func__, inode, EXT4_I(inode)->i_data,   \
                        EXT4_NDIR_BLOCKS)

/**
 *    ext4_get_branch - read the chain of indirect blocks leading to data
 *    @inode: inode in question
 *    @depth: depth of the chain (1 - direct pointer, etc.)
 *    @offsets: offsets of pointers in inode/indirect blocks
 *    @chain: place to store the result
 *    @err: here we store the error value
 *
 *    Function fills the array of triples <key, p, bh> and returns %NULL
 *    if everything went OK or the pointer to the last filled triple
 *    (incomplete one) otherwise. Upon the return chain[i].key contains
 *    the number of (i+1)-th block in the chain (as it is stored in memory,
 *    i.e. little-endian 32-bit), chain[i].p contains the address of that
 *    number (it points into struct inode for i==0 and into the bh->b_data
 *    for i>0) and chain[i].bh points to the buffer_head of i-th indirect
 *    block for i>0 and NULL for i==0. In other words, it holds the block
 *    numbers of the chain, addresses they were taken from (and where we can
 *    verify that chain did not change) and buffer_heads hosting these
 *    numbers.
 *
 *    Function stops when it stumbles upon zero pointer (absent block)
 *          (pointer to last triple returned, *@err == 0)
 *    or when it gets an IO error reading an indirect block
 *          (ditto, *@err == -EIO)
 *    or when it reads all @depth-1 indirect blocks successfully and finds
 *    the whole chain, all way to the data (returns %NULL, *err == 0).
 *
 *      Need to be called with
 *      down_read(&EXT4_I(inode)->i_data_sem)
 */
static Indirect *ext4_get_branch(struct inode *inode, int depth,
                         ext4_lblk_t  *offsets,
                         Indirect chain[4], int *err)
{
      struct super_block *sb = inode->i_sb;
      Indirect *p = chain;
      struct buffer_head *bh;

      *err = 0;
      /* i_data is not going away, no lock needed */
      add_chain(chain, NULL, EXT4_I(inode)->i_data + *offsets);
      if (!p->key)
            goto no_block;
      while (--depth) {
            bh = sb_getblk(sb, le32_to_cpu(p->key));
            if (unlikely(!bh))
                  goto failure;

            if (!bh_uptodate_or_lock(bh)) {
                  if (bh_submit_read(bh) < 0) {
                        put_bh(bh);
                        goto failure;
                  }
                  /* validate block references */
                  if (ext4_check_indirect_blockref(inode, bh)) {
                        put_bh(bh);
                        goto failure;
                  }
            }

            add_chain(++p, bh, (__le32 *)bh->b_data + *++offsets);
            /* Reader: end */
            if (!p->key)
                  goto no_block;
      }
      return NULL;

failure:
      *err = -EIO;
no_block:
      return p;
}

/**
 *    ext4_find_near - find a place for allocation with sufficient locality
 *    @inode: owner
 *    @ind: descriptor of indirect block.
 *
 *    This function returns the preferred place for block allocation.
 *    It is used when heuristic for sequential allocation fails.
 *    Rules are:
 *      + if there is a block to the left of our position - allocate near it.
 *      + if pointer will live in indirect block - allocate near that block.
 *      + if pointer will live in inode - allocate in the same
 *        cylinder group.
 *
 * In the latter case we colour the starting block by the callers PID to
 * prevent it from clashing with concurrent allocations for a different inode
 * in the same block group.   The PID is used here so that functionally related
 * files will be close-by on-disk.
 *
 *    Caller must make sure that @ind is valid and will stay that way.
 */
static ext4_fsblk_t ext4_find_near(struct inode *inode, Indirect *ind)
{
      struct ext4_inode_info *ei = EXT4_I(inode);
      __le32 *start = ind->bh ? (__le32 *) ind->bh->b_data : ei->i_data;
      __le32 *p;
      ext4_fsblk_t bg_start;
      ext4_fsblk_t last_block;
      ext4_grpblk_t colour;
      ext4_group_t block_group;
      int flex_size = ext4_flex_bg_size(EXT4_SB(inode->i_sb));

      /* Try to find previous block */
      for (p = ind->p - 1; p >= start; p--) {
            if (*p)
                  return le32_to_cpu(*p);
      }

      /* No such thing, so let's try location of indirect block */
      if (ind->bh)
            return ind->bh->b_blocknr;

      /*
       * It is going to be referred to from the inode itself? OK, just put it
       * into the same cylinder group then.
       */
      block_group = ei->i_block_group;
      if (flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) {
            block_group &= ~(flex_size-1);
            if (S_ISREG(inode->i_mode))
                  block_group++;
      }
      bg_start = ext4_group_first_block_no(inode->i_sb, block_group);
      last_block = ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es) - 1;

      /*
       * If we are doing delayed allocation, we don't need take
       * colour into account.
       */
      if (test_opt(inode->i_sb, DELALLOC))
            return bg_start;

      if (bg_start + EXT4_BLOCKS_PER_GROUP(inode->i_sb) <= last_block)
            colour = (current->pid % 16) *
                  (EXT4_BLOCKS_PER_GROUP(inode->i_sb) / 16);
      else
            colour = (current->pid % 16) * ((last_block - bg_start) / 16);
      return bg_start + colour;
}

/**
 *    ext4_find_goal - find a preferred place for allocation.
 *    @inode: owner
 *    @block:  block we want
 *    @partial: pointer to the last triple within a chain
 *
 *    Normally this function find the preferred place for block allocation,
 *    returns it.
 */
static ext4_fsblk_t ext4_find_goal(struct inode *inode, ext4_lblk_t block,
                           Indirect *partial)
{
      /*
       * XXX need to get goal block from mballoc's data structures
       */

      return ext4_find_near(inode, partial);
}

/**
 *    ext4_blks_to_allocate: Look up the block map and count the number
 *    of direct blocks need to be allocated for the given branch.
 *
 *    @branch: chain of indirect blocks
 *    @k: number of blocks need for indirect blocks
 *    @blks: number of data blocks to be mapped.
 *    @blocks_to_boundary:  the offset in the indirect block
 *
 *    return the total number of blocks to be allocate, including the
 *    direct and indirect blocks.
 */
static int ext4_blks_to_allocate(Indirect *branch, int k, unsigned int blks,
                         int blocks_to_boundary)
{
      unsigned int count = 0;

      /*
       * Simple case, [t,d]Indirect block(s) has not allocated yet
       * then it's clear blocks on that path have not allocated
       */
      if (k > 0) {
            /* right now we don't handle cross boundary allocation */
            if (blks < blocks_to_boundary + 1)
                  count += blks;
            else
                  count += blocks_to_boundary + 1;
            return count;
      }

      count++;
      while (count < blks && count <= blocks_to_boundary &&
            le32_to_cpu(*(branch[0].p + count)) == 0) {
            count++;
      }
      return count;
}

/**
 *    ext4_alloc_blocks: multiple allocate blocks needed for a branch
 *    @indirect_blks: the number of blocks need to allocate for indirect
 *                blocks
 *
 *    @new_blocks: on return it will store the new block numbers for
 *    the indirect blocks(if needed) and the first direct block,
 *    @blks:      on return it will store the total number of allocated
 *          direct blocks
 */
static int ext4_alloc_blocks(handle_t *handle, struct inode *inode,
                       ext4_lblk_t iblock, ext4_fsblk_t goal,
                       int indirect_blks, int blks,
                       ext4_fsblk_t new_blocks[4], int *err)
{
      struct ext4_allocation_request ar;
      int target, i;
      unsigned long count = 0, blk_allocated = 0;
      int index = 0;
      ext4_fsblk_t current_block = 0;
      int ret = 0;

      /*
       * Here we try to allocate the requested multiple blocks at once,
       * on a best-effort basis.
       * To build a branch, we should allocate blocks for
       * the indirect blocks(if not allocated yet), and at least
       * the first direct block of this branch.  That's the
       * minimum number of blocks need to allocate(required)
       */
      /* first we try to allocate the indirect blocks */
      target = indirect_blks;
      while (target > 0) {
            count = target;
            /* allocating blocks for indirect blocks and direct blocks */
            current_block = ext4_new_meta_blocks(handle, inode,
                                          goal, &count, err);
            if (*err)
                  goto failed_out;

            target -= count;
            /* allocate blocks for indirect blocks */
            while (index < indirect_blks && count) {
                  new_blocks[index++] = current_block++;
                  count--;
            }
            if (count > 0) {
                  /*
                   * save the new block number
                   * for the first direct block
                   */
                  new_blocks[index] = current_block;
                  printk(KERN_INFO "%s returned more blocks than "
                                    "requested\n", __func__);
                  WARN_ON(1);
                  break;
            }
      }

      target = blks - count ;
      blk_allocated = count;
      if (!target)
            goto allocated;
      /* Now allocate data blocks */
      memset(&ar, 0, sizeof(ar));
      ar.inode = inode;
      ar.goal = goal;
      ar.len = target;
      ar.logical = iblock;
      if (S_ISREG(inode->i_mode))
            /* enable in-core preallocation only for regular files */
            ar.flags = EXT4_MB_HINT_DATA;

      current_block = ext4_mb_new_blocks(handle, &ar, err);

      if (*err && (target == blks)) {
            /*
             * if the allocation failed and we didn't allocate
             * any blocks before
             */
            goto failed_out;
      }
      if (!*err) {
            if (target == blks) {
                  /*
                   * save the new block number
                   * for the first direct block
                   */
                  new_blocks[index] = current_block;
            }
            blk_allocated += ar.len;
      }
allocated:
      /* total number of blocks allocated for direct blocks */
      ret = blk_allocated;
      *err = 0;
      return ret;
failed_out:
      for (i = 0; i < index; i++)
            ext4_free_blocks(handle, inode, new_blocks[i], 1, 0);
      return ret;
}

/**
 *    ext4_alloc_branch - allocate and set up a chain of blocks.
 *    @inode: owner
 *    @indirect_blks: number of allocated indirect blocks
 *    @blks: number of allocated direct blocks
 *    @offsets: offsets (in the blocks) to store the pointers to next.
 *    @branch: place to store the chain in.
 *
 *    This function allocates blocks, zeroes out all but the last one,
 *    links them into chain and (if we are synchronous) writes them to disk.
 *    In other words, it prepares a branch that can be spliced onto the
 *    inode. It stores the information about that chain in the branch[], in
 *    the same format as ext4_get_branch() would do. We are calling it after
 *    we had read the existing part of chain and partial points to the last
 *    triple of that (one with zero ->key). Upon the exit we have the same
 *    picture as after the successful ext4_get_block(), except that in one
 *    place chain is disconnected - *branch->p is still zero (we did not
 *    set the last link), but branch->key contains the number that should
 *    be placed into *branch->p to fill that gap.
 *
 *    If allocation fails we free all blocks we've allocated (and forget
 *    their buffer_heads) and return the error value the from failed
 *    ext4_alloc_block() (normally -ENOSPC). Otherwise we set the chain
 *    as described above and return 0.
 */
static int ext4_alloc_branch(handle_t *handle, struct inode *inode,
                       ext4_lblk_t iblock, int indirect_blks,
                       int *blks, ext4_fsblk_t goal,
                       ext4_lblk_t *offsets, Indirect *branch)
{
      int blocksize = inode->i_sb->s_blocksize;
      int i, n = 0;
      int err = 0;
      struct buffer_head *bh;
      int num;
      ext4_fsblk_t new_blocks[4];
      ext4_fsblk_t current_block;

      num = ext4_alloc_blocks(handle, inode, iblock, goal, indirect_blks,
                        *blks, new_blocks, &err);
      if (err)
            return err;

      branch[0].key = cpu_to_le32(new_blocks[0]);
      /*
       * metadata blocks and data blocks are allocated.
       */
      for (n = 1; n <= indirect_blks;  n++) {
            /*
             * Get buffer_head for parent block, zero it out
             * and set the pointer to new one, then send
             * parent to disk.
             */
            bh = sb_getblk(inode->i_sb, new_blocks[n-1]);
            branch[n].bh = bh;
            lock_buffer(bh);
            BUFFER_TRACE(bh, "call get_create_access");
            err = ext4_journal_get_create_access(handle, bh);
            if (err) {
                  unlock_buffer(bh);
                  brelse(bh);
                  goto failed;
            }

            memset(bh->b_data, 0, blocksize);
            branch[n].p = (__le32 *) bh->b_data + offsets[n];
            branch[n].key = cpu_to_le32(new_blocks[n]);
            *branch[n].p = branch[n].key;
            if (n == indirect_blks) {
                  current_block = new_blocks[n];
                  /*
                   * End of chain, update the last new metablock of
                   * the chain to point to the new allocated
                   * data blocks numbers
                   */
                  for (i = 1; i < num; i++)
                        *(branch[n].p + i) = cpu_to_le32(++current_block);
            }
            BUFFER_TRACE(bh, "marking uptodate");
            set_buffer_uptodate(bh);
            unlock_buffer(bh);

            BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
            err = ext4_handle_dirty_metadata(handle, inode, bh);
            if (err)
                  goto failed;
      }
      *blks = num;
      return err;
failed:
      /* Allocation failed, free what we already allocated */
      for (i = 1; i <= n ; i++) {
            BUFFER_TRACE(branch[i].bh, "call jbd2_journal_forget");
            ext4_journal_forget(handle, branch[i].bh);
      }
      for (i = 0; i < indirect_blks; i++)
            ext4_free_blocks(handle, inode, new_blocks[i], 1, 0);

      ext4_free_blocks(handle, inode, new_blocks[i], num, 0);

      return err;
}

/**
 * ext4_splice_branch - splice the allocated branch onto inode.
 * @inode: owner
 * @block: (logical) number of block we are adding
 * @chain: chain of indirect blocks (with a missing link - see
 *    ext4_alloc_branch)
 * @where: location of missing link
 * @num:   number of indirect blocks we are adding
 * @blks:  number of direct blocks we are adding
 *
 * This function fills the missing link and does all housekeeping needed in
 * inode (->i_blocks, etc.). In case of success we end up with the full
 * chain to new block and return 0.
 */
static int ext4_splice_branch(handle_t *handle, struct inode *inode,
                        ext4_lblk_t block, Indirect *where, int num,
                        int blks)
{
      int i;
      int err = 0;
      ext4_fsblk_t current_block;

      /*
       * If we're splicing into a [td]indirect block (as opposed to the
       * inode) then we need to get write access to the [td]indirect block
       * before the splice.
       */
      if (where->bh) {
            BUFFER_TRACE(where->bh, "get_write_access");
            err = ext4_journal_get_write_access(handle, where->bh);
            if (err)
                  goto err_out;
      }
      /* That's it */

      *where->p = where->key;

      /*
       * Update the host buffer_head or inode to point to more just allocated
       * direct blocks blocks
       */
      if (num == 0 && blks > 1) {
            current_block = le32_to_cpu(where->key) + 1;
            for (i = 1; i < blks; i++)
                  *(where->p + i) = cpu_to_le32(current_block++);
      }

      /* We are done with atomic stuff, now do the rest of housekeeping */
      /* had we spliced it onto indirect block? */
      if (where->bh) {
            /*
             * If we spliced it onto an indirect block, we haven't
             * altered the inode.  Note however that if it is being spliced
             * onto an indirect block at the very end of the file (the
             * file is growing) then we *will* alter the inode to reflect
             * the new i_size.  But that is not done here - it is done in
             * generic_commit_write->__mark_inode_dirty->ext4_dirty_inode.
             */
            jbd_debug(5, "splicing indirect only\n");
            BUFFER_TRACE(where->bh, "call ext4_handle_dirty_metadata");
            err = ext4_handle_dirty_metadata(handle, inode, where->bh);
            if (err)
                  goto err_out;
      } else {
            /*
             * OK, we spliced it into the inode itself on a direct block.
             */
            ext4_mark_inode_dirty(handle, inode);
            jbd_debug(5, "splicing direct\n");
      }
      return err;

err_out:
      for (i = 1; i <= num; i++) {
            BUFFER_TRACE(where[i].bh, "call jbd2_journal_forget");
            ext4_journal_forget(handle, where[i].bh);
            ext4_free_blocks(handle, inode,
                              le32_to_cpu(where[i-1].key), 1, 0);
      }
      ext4_free_blocks(handle, inode, le32_to_cpu(where[num].key), blks, 0);

      return err;
}

/*
 * The ext4_ind_get_blocks() function handles non-extents inodes
 * (i.e., using the traditional indirect/double-indirect i_blocks
 * scheme) for ext4_get_blocks().
 *
 * Allocation strategy is simple: if we have to allocate something, we will
 * have to go the whole way to leaf. So let's do it before attaching anything
 * to tree, set linkage between the newborn blocks, write them if sync is
 * required, recheck the path, free and repeat if check fails, otherwise
 * set the last missing link (that will protect us from any truncate-generated
 * removals - all blocks on the path are immune now) and possibly force the
 * write on the parent block.
 * That has a nice additional property: no special recovery from the failed
 * allocations is needed - we simply release blocks and do not touch anything
 * reachable from inode.
 *
 * `handle' can be NULL if create == 0.
 *
 * return > 0, # of blocks mapped or allocated.
 * return = 0, if plain lookup failed.
 * return < 0, error case.
 *
 * The ext4_ind_get_blocks() function should be called with
 * down_write(&EXT4_I(inode)->i_data_sem) if allocating filesystem
 * blocks (i.e., flags has EXT4_GET_BLOCKS_CREATE set) or
 * down_read(&EXT4_I(inode)->i_data_sem) if not allocating file system
 * blocks.
 */
static int ext4_ind_get_blocks(handle_t *handle, struct inode *inode,
                         ext4_lblk_t iblock, unsigned int maxblocks,
                         struct buffer_head *bh_result,
                         int flags)
{
      int err = -EIO;
      ext4_lblk_t offsets[4];
      Indirect chain[4];
      Indirect *partial;
      ext4_fsblk_t goal;
      int indirect_blks;
      int blocks_to_boundary = 0;
      int depth;
      int count = 0;
      ext4_fsblk_t first_block = 0;

      J_ASSERT(!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL));
      J_ASSERT(handle != NULL || (flags & EXT4_GET_BLOCKS_CREATE) == 0);
      depth = ext4_block_to_path(inode, iblock, offsets,
                           &blocks_to_boundary);

      if (depth == 0)
            goto out;

      partial = ext4_get_branch(inode, depth, offsets, chain, &err);

      /* Simplest case - block found, no allocation needed */
      if (!partial) {
            first_block = le32_to_cpu(chain[depth - 1].key);
            clear_buffer_new(bh_result);
            count++;
            /*map more blocks*/
            while (count < maxblocks && count <= blocks_to_boundary) {
                  ext4_fsblk_t blk;

                  blk = le32_to_cpu(*(chain[depth-1].p + count));

                  if (blk == first_block + count)
                        count++;
                  else
                        break;
            }
            goto got_it;
      }

      /* Next simple case - plain lookup or failed read of indirect block */
      if ((flags & EXT4_GET_BLOCKS_CREATE) == 0 || err == -EIO)
            goto cleanup;

      /*
       * Okay, we need to do block allocation.
      */
      goal = ext4_find_goal(inode, iblock, partial);

      /* the number of blocks need to allocate for [d,t]indirect blocks */
      indirect_blks = (chain + depth) - partial - 1;

      /*
       * Next look up the indirect map to count the totoal number of
       * direct blocks to allocate for this branch.
       */
      count = ext4_blks_to_allocate(partial, indirect_blks,
                              maxblocks, blocks_to_boundary);
      /*
       * Block out ext4_truncate while we alter the tree
       */
      err = ext4_alloc_branch(handle, inode, iblock, indirect_blks,
                        &count, goal,
                        offsets + (partial - chain), partial);

      /*
       * The ext4_splice_branch call will free and forget any buffers
       * on the new chain if there is a failure, but that risks using
       * up transaction credits, especially for bitmaps where the
       * credits cannot be returned.  Can we handle this somehow?  We
       * may need to return -EAGAIN upwards in the worst case.  --sct
       */
      if (!err)
            err = ext4_splice_branch(handle, inode, iblock,
                               partial, indirect_blks, count);
      else
            goto cleanup;

      set_buffer_new(bh_result);
got_it:
      map_bh(bh_result, inode->i_sb, le32_to_cpu(chain[depth-1].key));
      if (count > blocks_to_boundary)
            set_buffer_boundary(bh_result);
      err = count;
      /* Clean up and exit */
      partial = chain + depth - 1;  /* the whole chain */
cleanup:
      while (partial > chain) {
            BUFFER_TRACE(partial->bh, "call brelse");
            brelse(partial->bh);
            partial--;
      }
      BUFFER_TRACE(bh_result, "returned");
out:
      return err;
}

qsize_t ext4_get_reserved_space(struct inode *inode)
{
      unsigned long long total;

      spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
      total = EXT4_I(inode)->i_reserved_data_blocks +
            EXT4_I(inode)->i_reserved_meta_blocks;
      spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

      return total;
}
/*
 * Calculate the number of metadata blocks need to reserve
 * to allocate @blocks for non extent file based file
 */
static int ext4_indirect_calc_metadata_amount(struct inode *inode, int blocks)
{
      int icap = EXT4_ADDR_PER_BLOCK(inode->i_sb);
      int ind_blks, dind_blks, tind_blks;

      /* number of new indirect blocks needed */
      ind_blks = (blocks + icap - 1) / icap;

      dind_blks = (ind_blks + icap - 1) / icap;

      tind_blks = 1;

      return ind_blks + dind_blks + tind_blks;
}

/*
 * Calculate the number of metadata blocks need to reserve
 * to allocate given number of blocks
 */
static int ext4_calc_metadata_amount(struct inode *inode, int blocks)
{
      if (!blocks)
            return 0;

      if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL)
            return ext4_ext_calc_metadata_amount(inode, blocks);

      return ext4_indirect_calc_metadata_amount(inode, blocks);
}

static void ext4_da_update_reserve_space(struct inode *inode, int used)
{
      struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
      int total, mdb, mdb_free;

      spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
      /* recalculate the number of metablocks still need to be reserved */
      total = EXT4_I(inode)->i_reserved_data_blocks - used;
      mdb = ext4_calc_metadata_amount(inode, total);

      /* figure out how many metablocks to release */
      BUG_ON(mdb > EXT4_I(inode)->i_reserved_meta_blocks);
      mdb_free = EXT4_I(inode)->i_reserved_meta_blocks - mdb;

      if (mdb_free) {
            /* Account for allocated meta_blocks */
            mdb_free -= EXT4_I(inode)->i_allocated_meta_blocks;

            /* update fs dirty blocks counter */
            percpu_counter_sub(&sbi->s_dirtyblocks_counter, mdb_free);
            EXT4_I(inode)->i_allocated_meta_blocks = 0;
            EXT4_I(inode)->i_reserved_meta_blocks = mdb;
      }

      /* update per-inode reservations */
      BUG_ON(used  > EXT4_I(inode)->i_reserved_data_blocks);
      EXT4_I(inode)->i_reserved_data_blocks -= used;
      spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

      /*
       * free those over-booking quota for metadata blocks
       */
      if (mdb_free)
            vfs_dq_release_reservation_block(inode, mdb_free);

      /*
       * If we have done all the pending block allocations and if
       * there aren't any writers on the inode, we can discard the
       * inode's preallocations.
       */
      if (!total && (atomic_read(&inode->i_writecount) == 0))
            ext4_discard_preallocations(inode);
}

static int check_block_validity(struct inode *inode, sector_t logical,
                        sector_t phys, int len)
{
      if (!ext4_data_block_valid(EXT4_SB(inode->i_sb), phys, len)) {
            ext4_error(inode->i_sb, "check_block_validity",
                     "inode #%lu logical block %llu mapped to %llu "
                     "(size %d)", inode->i_ino,
                     (unsigned long long) logical,
                     (unsigned long long) phys, len);
            WARN_ON(1);
            return -EIO;
      }
      return 0;
}

/*
 * The ext4_get_blocks() function tries to look up the requested blocks,
 * and returns if the blocks are already mapped.
 *
 * Otherwise it takes the write lock of the i_data_sem and allocate blocks
 * and store the allocated blocks in the result buffer head and mark it
 * mapped.
 *
 * If file type is extents based, it will call ext4_ext_get_blocks(),
 * Otherwise, call with ext4_ind_get_blocks() to handle indirect mapping
 * based files
 *
 * On success, it returns the number of blocks being mapped or allocate.
 * if create==0 and the blocks are pre-allocated and uninitialized block,
 * the result buffer head is unmapped. If the create ==1, it will make sure
 * the buffer head is mapped.
 *
 * It returns 0 if plain look up failed (blocks have not been allocated), in
 * that casem, buffer head is unmapped
 *
 * It returns the error in case of allocation failure.
 */
int ext4_get_blocks(handle_t *handle, struct inode *inode, sector_t block,
                unsigned int max_blocks, struct buffer_head *bh,
                int flags)
{
      int retval;

      clear_buffer_mapped(bh);
      clear_buffer_unwritten(bh);

      /*
       * Try to see if we can get the block without requesting a new
       * file system block.
       */
      down_read((&EXT4_I(inode)->i_data_sem));
      if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
            retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
                        bh, 0);
      } else {
            retval = ext4_ind_get_blocks(handle, inode, block, max_blocks,
                                   bh, 0);
      }
      up_read((&EXT4_I(inode)->i_data_sem));

      if (retval > 0 && buffer_mapped(bh)) {
            int ret = check_block_validity(inode, block,
                                     bh->b_blocknr, retval);
            if (ret != 0)
                  return ret;
      }

      /* If it is only a block(s) look up */
      if ((flags & EXT4_GET_BLOCKS_CREATE) == 0)
            return retval;

      /*
       * Returns if the blocks have already allocated
       *
       * Note that if blocks have been preallocated
       * ext4_ext_get_block() returns th create = 0
       * with buffer head unmapped.
       */
      if (retval > 0 && buffer_mapped(bh))
            return retval;

      /*
       * When we call get_blocks without the create flag, the
       * BH_Unwritten flag could have gotten set if the blocks
       * requested were part of a uninitialized extent.  We need to
       * clear this flag now that we are committed to convert all or
       * part of the uninitialized extent to be an initialized
       * extent.  This is because we need to avoid the combination
       * of BH_Unwritten and BH_Mapped flags being simultaneously
       * set on the buffer_head.
       */
      clear_buffer_unwritten(bh);

      /*
       * New blocks allocate and/or writing to uninitialized extent
       * will possibly result in updating i_data, so we take
       * the write lock of i_data_sem, and call get_blocks()
       * with create == 1 flag.
       */
      down_write((&EXT4_I(inode)->i_data_sem));

      /*
       * if the caller is from delayed allocation writeout path
       * we have already reserved fs blocks for allocation
       * let the underlying get_block() function know to
       * avoid double accounting
       */
      if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
            EXT4_I(inode)->i_delalloc_reserved_flag = 1;
      /*
       * We need to check for EXT4 here because migrate
       * could have changed the inode type in between
       */
      if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
            retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
                                    bh, flags);
      } else {
            retval = ext4_ind_get_blocks(handle, inode, block,
                                   max_blocks, bh, flags);

            if (retval > 0 && buffer_new(bh)) {
                  /*
                   * We allocated new blocks which will result in
                   * i_data's format changing.  Force the migrate
                   * to fail by clearing migrate flags
                   */
                  EXT4_I(inode)->i_flags = EXT4_I(inode)->i_flags &
                                          ~EXT4_EXT_MIGRATE;
            }
      }

      if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
            EXT4_I(inode)->i_delalloc_reserved_flag = 0;

      /*
       * Update reserved blocks/metadata blocks after successful
       * block allocation which had been deferred till now.
       */
      if ((retval > 0) && (flags & EXT4_GET_BLOCKS_UPDATE_RESERVE_SPACE))
            ext4_da_update_reserve_space(inode, retval);

      up_write((&EXT4_I(inode)->i_data_sem));
      if (retval > 0 && buffer_mapped(bh)) {
            int ret = check_block_validity(inode, block,
                                     bh->b_blocknr, retval);
            if (ret != 0)
                  return ret;
      }
      return retval;
}

/* Maximum number of blocks we map for direct IO at once. */
#define DIO_MAX_BLOCKS 4096

int ext4_get_block(struct inode *inode, sector_t iblock,
               struct buffer_head *bh_result, int create)
{
      handle_t *handle = ext4_journal_current_handle();
      int ret = 0, started = 0;
      unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
      int dio_credits;

      if (create && !handle) {
            /* Direct IO write... */
            if (max_blocks > DIO_MAX_BLOCKS)
                  max_blocks = DIO_MAX_BLOCKS;
            dio_credits = ext4_chunk_trans_blocks(inode, max_blocks);
            handle = ext4_journal_start(inode, dio_credits);
            if (IS_ERR(handle)) {
                  ret = PTR_ERR(handle);
                  goto out;
            }
            started = 1;
      }

      ret = ext4_get_blocks(handle, inode, iblock, max_blocks, bh_result,
                        create ? EXT4_GET_BLOCKS_CREATE : 0);
      if (ret > 0) {
            bh_result->b_size = (ret << inode->i_blkbits);
            ret = 0;
      }
      if (started)
            ext4_journal_stop(handle);
out:
      return ret;
}

/*
 * `handle' can be NULL if create is zero
 */
struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
                        ext4_lblk_t block, int create, int *errp)
{
      struct buffer_head dummy;
      int fatal = 0, err;
      int flags = 0;

      J_ASSERT(handle != NULL || create == 0);

      dummy.b_state = 0;
      dummy.b_blocknr = -1000;
      buffer_trace_init(&dummy.b_history);
      if (create)
            flags |= EXT4_GET_BLOCKS_CREATE;
      err = ext4_get_blocks(handle, inode, block, 1, &dummy, flags);
      /*
       * ext4_get_blocks() returns number of blocks mapped. 0 in
       * case of a HOLE.
       */
      if (err > 0) {
            if (err > 1)
                  WARN_ON(1);
            err = 0;
      }
      *errp = err;
      if (!err && buffer_mapped(&dummy)) {
            struct buffer_head *bh;
            bh = sb_getblk(inode->i_sb, dummy.b_blocknr);
            if (!bh) {
                  *errp = -EIO;
                  goto err;
            }
            if (buffer_new(&dummy)) {
                  J_ASSERT(create != 0);
                  J_ASSERT(handle != NULL);

                  /*
                   * Now that we do not always journal data, we should
                   * keep in mind whether this should always journal the
                   * new buffer as metadata.  For now, regular file
                   * writes use ext4_get_block instead, so it's not a
                   * problem.
                   */
                  lock_buffer(bh);
                  BUFFER_TRACE(bh, "call get_create_access");
                  fatal = ext4_journal_get_create_access(handle, bh);
                  if (!fatal && !buffer_uptodate(bh)) {
                        memset(bh->b_data, 0, inode->i_sb->s_blocksize);
                        set_buffer_uptodate(bh);
                  }
                  unlock_buffer(bh);
                  BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
                  err = ext4_handle_dirty_metadata(handle, inode, bh);
                  if (!fatal)
                        fatal = err;
            } else {
                  BUFFER_TRACE(bh, "not a new buffer");
            }
            if (fatal) {
                  *errp = fatal;
                  brelse(bh);
                  bh = NULL;
            }
            return bh;
      }
err:
      return NULL;
}

struct buffer_head *ext4_bread(handle_t *handle, struct inode *inode,
                         ext4_lblk_t block, int create, int *err)
{
      struct buffer_head *bh;

      bh = ext4_getblk(handle, inode, block, create, err);
      if (!bh)
            return bh;
      if (buffer_uptodate(bh))
            return bh;
      ll_rw_block(READ_META, 1, &bh);
      wait_on_buffer(bh);
      if (buffer_uptodate(bh))
            return bh;
      put_bh(bh);
      *err = -EIO;
      return NULL;
}

static int walk_page_buffers(handle_t *handle,
                       struct buffer_head *head,
                       unsigned from,
                       unsigned to,
                       int *partial,
                       int (*fn)(handle_t *handle,
                               struct buffer_head *bh))
{
      struct buffer_head *bh;
      unsigned block_start, block_end;
      unsigned blocksize = head->b_size;
      int err, ret = 0;
      struct buffer_head *next;

      for (bh = head, block_start = 0;
           ret == 0 && (bh != head || !block_start);
           block_start = block_end, bh = next) {
            next = bh->b_this_page;
            block_end = block_start + blocksize;
            if (block_end <= from || block_start >= to) {
                  if (partial && !buffer_uptodate(bh))
                        *partial = 1;
                  continue;
            }
            err = (*fn)(handle, bh);
            if (!ret)
                  ret = err;
      }
      return ret;
}

/*
 * To preserve ordering, it is essential that the hole instantiation and
 * the data write be encapsulated in a single transaction.  We cannot
 * close off a transaction and start a new one between the ext4_get_block()
 * and the commit_write().  So doing the jbd2_journal_start at the start of
 * prepare_write() is the right place.
 *
 * Also, this function can nest inside ext4_writepage() ->
 * block_write_full_page(). In that case, we *know* that ext4_writepage()
 * has generated enough buffer credits to do the whole page.  So we won't
 * block on the journal in that case, which is good, because the caller may
 * be PF_MEMALLOC.
 *
 * By accident, ext4 can be reentered when a transaction is open via
 * quota file writes.  If we were to commit the transaction while thus
 * reentered, there can be a deadlock - we would be holding a quota
 * lock, and the commit would never complete if another thread had a
 * transaction open and was blocking on the quota lock - a ranking
 * violation.
 *
 * So what we do is to rely on the fact that jbd2_journal_stop/journal_start
 * will _not_ run commit under these circumstances because handle->h_ref
 * is elevated.  We'll still have enough credits for the tiny quotafile
 * write.
 */
static int do_journal_get_write_access(handle_t *handle,
                               struct buffer_head *bh)
{
      if (!buffer_mapped(bh) || buffer_freed(bh))
            return 0;
      return ext4_journal_get_write_access(handle, bh);
}

static int ext4_write_begin(struct file *file, struct address_space *mapping,
                      loff_t pos, unsigned len, unsigned flags,
                      struct page **pagep, void **fsdata)
{
      struct inode *inode = mapping->host;
      int ret, needed_blocks;
      handle_t *handle;
      int retries = 0;
      struct page *page;
      pgoff_t index;
      unsigned from, to;

      trace_ext4_write_begin(inode, pos, len, flags);
      /*
       * Reserve one block more for addition to orphan list in case
       * we allocate blocks but write fails for some reason
       */
      needed_blocks = ext4_writepage_trans_blocks(inode) + 1;
      index = pos >> PAGE_CACHE_SHIFT;
      from = pos & (PAGE_CACHE_SIZE - 1);
      to = from + len;

retry:
      handle = ext4_journal_start(inode, needed_blocks);
      if (IS_ERR(handle)) {
            ret = PTR_ERR(handle);
            goto out;
      }

      /* We cannot recurse into the filesystem as the transaction is already
       * started */
      flags |= AOP_FLAG_NOFS;

      page = grab_cache_page_write_begin(mapping, index, flags);
      if (!page) {
            ext4_journal_stop(handle);
            ret = -ENOMEM;
            goto out;
      }
      *pagep = page;

      ret = block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
                        ext4_get_block);

      if (!ret && ext4_should_journal_data(inode)) {
            ret = walk_page_buffers(handle, page_buffers(page),
                        from, to, NULL, do_journal_get_write_access);
      }

      if (ret) {
            unlock_page(page);
            page_cache_release(page);
            /*
             * block_write_begin may have instantiated a few blocks
             * outside i_size.  Trim these off again. Don't need
             * i_size_read because we hold i_mutex.
             *
             * Add inode to orphan list in case we crash before
             * truncate finishes
             */
            if (pos + len > inode->i_size && ext4_can_truncate(inode))
                  ext4_orphan_add(handle, inode);

            ext4_journal_stop(handle);
            if (pos + len > inode->i_size) {
                  ext4_truncate(inode);
                  /*
                   * If truncate failed early the inode might
                   * still be on the orphan list; we need to
                   * make sure the inode is removed from the
                   * orphan list in that case.
                   */
                  if (inode->i_nlink)
                        ext4_orphan_del(NULL, inode);
            }
      }

      if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
            goto retry;
out:
      return ret;
}

/* For write_end() in data=journal mode */
static int write_end_fn(handle_t *handle, struct buffer_head *bh)
{
      if (!buffer_mapped(bh) || buffer_freed(bh))
            return 0;
      set_buffer_uptodate(bh);
      return ext4_handle_dirty_metadata(handle, NULL, bh);
}

static int ext4_generic_write_end(struct file *file,
                          struct address_space *mapping,
                          loff_t pos, unsigned len, unsigned copied,
                          struct page *page, void *fsdata)
{
      int i_size_changed = 0;
      struct inode *inode = mapping->host;
      handle_t *handle = ext4_journal_current_handle();

      copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);

      /*
       * No need to use i_size_read() here, the i_size
       * cannot change under us because we hold i_mutex.
       *
       * But it's important to update i_size while still holding page lock:
       * page writeout could otherwise come in and zero beyond i_size.
       */
      if (pos + copied > inode->i_size) {
            i_size_write(inode, pos + copied);
            i_size_changed = 1;
      }

      if (pos + copied >  EXT4_I(inode)->i_disksize) {
            /* We need to mark inode dirty even if
             * new_i_size is less that inode->i_size
             * bu greater than i_disksize.(hint delalloc)
             */
            ext4_update_i_disksize(inode, (pos + copied));
            i_size_changed = 1;
      }
      unlock_page(page);
      page_cache_release(page);

      /*
       * Don't mark the inode dirty under page lock. First, it unnecessarily
       * makes the holding time of page lock longer. Second, it forces lock
       * ordering of page lock and transaction start for journaling
       * filesystems.
       */
      if (i_size_changed)
            ext4_mark_inode_dirty(handle, inode);

      return copied;
}

/*
 * We need to pick up the new inode size which generic_commit_write gave us
 * `file' can be NULL - eg, when called from page_symlink().
 *
 * ext4 never places buffers on inode->i_mapping->private_list.  metadata
 * buffers are managed internally.
 */
static int ext4_ordered_write_end(struct file *file,
                          struct address_space *mapping,
                          loff_t pos, unsigned len, unsigned copied,
                          struct page *page, void *fsdata)
{
      handle_t *handle = ext4_journal_current_handle();
      struct inode *inode = mapping->host;
      int ret = 0, ret2;

      trace_ext4_ordered_write_end(inode, pos, len, copied);
      ret = ext4_jbd2_file_inode(handle, inode);

      if (ret == 0) {
            ret2 = ext4_generic_write_end(file, mapping, pos, len, copied,
                                          page, fsdata);
            copied = ret2;
            if (pos + len > inode->i_size && ext4_can_truncate(inode))
                  /* if we have allocated more blocks and copied
                   * less. We will have blocks allocated outside
                   * inode->i_size. So truncate them
                   */
                  ext4_orphan_add(handle, inode);
            if (ret2 < 0)
                  ret = ret2;
      }
      ret2 = ext4_journal_stop(handle);
      if (!ret)
            ret = ret2;

      if (pos + len > inode->i_size) {
            ext4_truncate(inode);
            /*
             * If truncate failed early the inode might still be
             * on the orphan list; we need to make sure the inode
             * is removed from the orphan list in that case.
             */
            if (inode->i_nlink)
                  ext4_orphan_del(NULL, inode);
      }


      return ret ? ret : copied;
}

static int ext4_writeback_write_end(struct file *file,
                            struct address_space *mapping,
                            loff_t pos, unsigned len, unsigned copied,
                            struct page *page, void *fsdata)
{
      handle_t *handle = ext4_journal_current_handle();
      struct inode *inode = mapping->host;
      int ret = 0, ret2;

      trace_ext4_writeback_write_end(inode, pos, len, copied);
      ret2 = ext4_generic_write_end(file, mapping, pos, len, copied,
                                          page, fsdata);
      copied = ret2;
      if (pos + len > inode->i_size && ext4_can_truncate(inode))
            /* if we have allocated more blocks and copied
             * less. We will have blocks allocated outside
             * inode->i_size. So truncate them
             */
            ext4_orphan_add(handle, inode);

      if (ret2 < 0)
            ret = ret2;

      ret2 = ext4_journal_stop(handle);
      if (!ret)
            ret = ret2;

      if (pos + len > inode->i_size) {
            ext4_truncate(inode);
            /*
             * If truncate failed early the inode might still be
             * on the orphan list; we need to make sure the inode
             * is removed from the orphan list in that case.
             */
            if (inode->i_nlink)
                  ext4_orphan_del(NULL, inode);
      }

      return ret ? ret : copied;
}

static int ext4_journalled_write_end(struct file *file,
                             struct address_space *mapping,
                             loff_t pos, unsigned len, unsigned copied,
                             struct page *page, void *fsdata)
{
      handle_t *handle = ext4_journal_current_handle();
      struct inode *inode = mapping->host;
      int ret = 0, ret2;
      int partial = 0;
      unsigned from, to;
      loff_t new_i_size;

      trace_ext4_journalled_write_end(inode, pos, len, copied);
      from = pos & (PAGE_CACHE_SIZE - 1);
      to = from + len;

      if (copied < len) {
            if (!PageUptodate(page))
                  copied = 0;
            page_zero_new_buffers(page, from+copied, to);
      }

      ret = walk_page_buffers(handle, page_buffers(page), from,
                        to, &partial, write_end_fn);
      if (!partial)
            SetPageUptodate(page);
      new_i_size = pos + copied;
      if (new_i_size > inode->i_size)
            i_size_write(inode, pos+copied);
      EXT4_I(inode)->i_state |= EXT4_STATE_JDATA;
      if (new_i_size > EXT4_I(inode)->i_disksize) {
            ext4_update_i_disksize(inode, new_i_size);
            ret2 = ext4_mark_inode_dirty(handle, inode);
            if (!ret)
                  ret = ret2;
      }

      unlock_page(page);
      page_cache_release(page);
      if (pos + len > inode->i_size && ext4_can_truncate(inode))
            /* if we have allocated more blocks and copied
             * less. We will have blocks allocated outside
             * inode->i_size. So truncate them
             */
            ext4_orphan_add(handle, inode);

      ret2 = ext4_journal_stop(handle);
      if (!ret)
            ret = ret2;
      if (pos + len > inode->i_size) {
            ext4_truncate(inode);
            /*
             * If truncate failed early the inode might still be
             * on the orphan list; we need to make sure the inode
             * is removed from the orphan list in that case.
             */
            if (inode->i_nlink)
                  ext4_orphan_del(NULL, inode);
      }

      return ret ? ret : copied;
}

static int ext4_da_reserve_space(struct inode *inode, int nrblocks)
{
      int retries = 0;
      struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
      unsigned long md_needed, mdblocks, total = 0;

      /*
       * recalculate the amount of metadata blocks to reserve
       * in order to allocate nrblocks
       * worse case is one extent per block
       */
repeat:
      spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
      total = EXT4_I(inode)->i_reserved_data_blocks + nrblocks;
      mdblocks = ext4_calc_metadata_amount(inode, total);
      BUG_ON(mdblocks < EXT4_I(inode)->i_reserved_meta_blocks);

      md_needed = mdblocks - EXT4_I(inode)->i_reserved_meta_blocks;
      total = md_needed + nrblocks;

      /*
       * Make quota reservation here to prevent quota overflow
       * later. Real quota accounting is done at pages writeout
       * time.
       */
      if (vfs_dq_reserve_block(inode, total)) {
            spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
            return -EDQUOT;
      }

      if (ext4_claim_free_blocks(sbi, total)) {
            spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
            if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
                  yield();
                  goto repeat;
            }
            vfs_dq_release_reservation_block(inode, total);
            return -ENOSPC;
      }
      EXT4_I(inode)->i_reserved_data_blocks += nrblocks;
      EXT4_I(inode)->i_reserved_meta_blocks = mdblocks;

      spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
      return 0;       /* success */
}

static void ext4_da_release_space(struct inode *inode, int to_free)
{
      struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
      int total, mdb, mdb_free, release;

      if (!to_free)
            return;           /* Nothing to release, exit */

      spin_lock(&EXT4_I(inode)->i_block_reservation_lock);

      if (!EXT4_I(inode)->i_reserved_data_blocks) {
            /*
             * if there is no reserved blocks, but we try to free some
             * then the counter is messed up somewhere.
             * but since this function is called from invalidate
             * page, it's harmless to return without any action
             */
            printk(KERN_INFO "ext4 delalloc try to release %d reserved "
                      "blocks for inode %lu, but there is no reserved "
                      "data blocks\n", to_free, inode->i_ino);
            spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
            return;
      }

      /* recalculate the number of metablocks still need to be reserved */
      total = EXT4_I(inode)->i_reserved_data_blocks - to_free;
      mdb = ext4_calc_metadata_amount(inode, total);

      /* figure out how many metablocks to release */
      BUG_ON(mdb > EXT4_I(inode)->i_reserved_meta_blocks);
      mdb_free = EXT4_I(inode)->i_reserved_meta_blocks - mdb;

      release = to_free + mdb_free;

      /* update fs dirty blocks counter for truncate case */
      percpu_counter_sub(&sbi->s_dirtyblocks_counter, release);

      /* update per-inode reservations */
      BUG_ON(to_free > EXT4_I(inode)->i_reserved_data_blocks);
      EXT4_I(inode)->i_reserved_data_blocks -= to_free;

      BUG_ON(mdb > EXT4_I(inode)->i_reserved_meta_blocks);
      EXT4_I(inode)->i_reserved_meta_blocks = mdb;
      spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

      vfs_dq_release_reservation_block(inode, release);
}

static void ext4_da_page_release_reservation(struct page *page,
                                   unsigned long offset)
{
      int to_release = 0;
      struct buffer_head *head, *bh;
      unsigned int curr_off = 0;

      head = page_buffers(page);
      bh = head;
      do {
            unsigned int next_off = curr_off + bh->b_size;

            if ((offset <= curr_off) && (buffer_delay(bh))) {
                  to_release++;
                  clear_buffer_delay(bh);
            }
            curr_off = next_off;
      } while ((bh = bh->b_this_page) != head);
      ext4_da_release_space(page->mapping->host, to_release);
}

/*
 * Delayed allocation stuff
 */

01866 struct mpage_da_data {
      struct inode *inode;
      sector_t b_blocknr;           /* start block number of extent */
      size_t b_size;                /* size of extent */
      unsigned long b_state;        /* state of the extent */
      unsigned long first_page, next_page;      /* extent of pages */
      struct writeback_control *wbc;
      int io_done;
      int pages_written;
      int retval;
};

/*
 * mpage_da_submit_io - walks through extent of pages and try to write
 * them with writepage() call back
 *
 * @mpd->inode: inode
 * @mpd->first_page: first page of the extent
 * @mpd->next_page: page after the last page of the extent
 *
 * By the time mpage_da_submit_io() is called we expect all blocks
 * to be allocated. this may be wrong if allocation failed.
 *
 * As pages are already locked by write_cache_pages(), we can't use it
 */
static int mpage_da_submit_io(struct mpage_da_data *mpd)
{
      long pages_skipped;
      struct pagevec pvec;
      unsigned long index, end;
      int ret = 0, err, nr_pages, i;
      struct inode *inode = mpd->inode;
      struct address_space *mapping = inode->i_mapping;

      BUG_ON(mpd->next_page <= mpd->first_page);
      /*
       * We need to start from the first_page to the next_page - 1
       * to make sure we also write the mapped dirty buffer_heads.
       * If we look at mpd->b_blocknr we would only be looking
       * at the currently mapped buffer_heads.
       */
      index = mpd->first_page;
      end = mpd->next_page - 1;

      pagevec_init(&pvec, 0);
      while (index <= end) {
            nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
            if (nr_pages == 0)
                  break;
            for (i = 0; i < nr_pages; i++) {
                  struct page *page = pvec.pages[i];

                  index = page->index;
                  if (index > end)
                        break;
                  index++;

                  BUG_ON(!PageLocked(page));
                  BUG_ON(PageWriteback(page));

                  pages_skipped = mpd->wbc->pages_skipped;
                  err = mapping->a_ops->writepage(page, mpd->wbc);
                  if (!err && (pages_skipped == mpd->wbc->pages_skipped))
                        /*
                         * have successfully written the page
                         * without skipping the same
                         */
                        mpd->pages_written++;
                  /*
                   * In error case, we have to continue because
                   * remaining pages are still locked
                   * XXX: unlock and re-dirty them?
                   */
                  if (ret == 0)
                        ret = err;
            }
            pagevec_release(&pvec);
      }
      return ret;
}

/*
 * mpage_put_bnr_to_bhs - walk blocks and assign them actual numbers
 *
 * @mpd->inode - inode to walk through
 * @exbh->b_blocknr - first block on a disk
 * @exbh->b_size - amount of space in bytes
 * @logical - first logical block to start assignment with
 *
 * the function goes through all passed space and put actual disk
 * block numbers into buffer heads, dropping BH_Delay and BH_Unwritten
 */
static void mpage_put_bnr_to_bhs(struct mpage_da_data *mpd, sector_t logical,
                         struct buffer_head *exbh)
{
      struct inode *inode = mpd->inode;
      struct address_space *mapping = inode->i_mapping;
      int blocks = exbh->b_size >> inode->i_blkbits;
      sector_t pblock = exbh->b_blocknr, cur_logical;
      struct buffer_head *head, *bh;
      pgoff_t index, end;
      struct pagevec pvec;
      int nr_pages, i;

      index = logical >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
      end = (logical + blocks - 1) >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
      cur_logical = index << (PAGE_CACHE_SHIFT - inode->i_blkbits);

      pagevec_init(&pvec, 0);

      while (index <= end) {
            /* XXX: optimize tail */
            nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
            if (nr_pages == 0)
                  break;
            for (i = 0; i < nr_pages; i++) {
                  struct page *page = pvec.pages[i];

                  index = page->index;
                  if (index > end)
                        break;
                  index++;

                  BUG_ON(!PageLocked(page));
                  BUG_ON(PageWriteback(page));
                  BUG_ON(!page_has_buffers(page));

                  bh = page_buffers(page);
                  head = bh;

                  /* skip blocks out of the range */
                  do {
                        if (cur_logical >= logical)
                              break;
                        cur_logical++;
                  } while ((bh = bh->b_this_page) != head);

                  do {
                        if (cur_logical >= logical + blocks)
                              break;

                        if (buffer_delay(bh) ||
                                    buffer_unwritten(bh)) {

                              BUG_ON(bh->b_bdev != inode->i_sb->s_bdev);

                              if (buffer_delay(bh)) {
                                    clear_buffer_delay(bh);
                                    bh->b_blocknr = pblock;
                              } else {
                                    /*
                                     * unwritten already should have
                                     * blocknr assigned. Verify that
                                     */
                                    clear_buffer_unwritten(bh);
                                    BUG_ON(bh->b_blocknr != pblock);
                              }

                        } else if (buffer_mapped(bh))
                              BUG_ON(bh->b_blocknr != pblock);

                        cur_logical++;
                        pblock++;
                  } while ((bh = bh->b_this_page) != head);
            }
            pagevec_release(&pvec);
      }
}


/*
 * __unmap_underlying_blocks - just a helper function to unmap
 * set of blocks described by @bh
 */
static inline void __unmap_underlying_blocks(struct inode *inode,
                                   struct buffer_head *bh)
{
      struct block_device *bdev = inode->i_sb->s_bdev;
      int blocks, i;

      blocks = bh->b_size >> inode->i_blkbits;
      for (i = 0; i < blocks; i++)
            unmap_underlying_metadata(bdev, bh->b_blocknr + i);
}

static void ext4_da_block_invalidatepages(struct mpage_da_data *mpd,
                              sector_t logical, long blk_cnt)
{
      int nr_pages, i;
      pgoff_t index, end;
      struct pagevec pvec;
      struct inode *inode = mpd->inode;
      struct address_space *mapping = inode->i_mapping;

      index = logical >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
      end   = (logical + blk_cnt - 1) >>
                        (PAGE_CACHE_SHIFT - inode->i_blkbits);
      while (index <= end) {
            nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
            if (nr_pages == 0)
                  break;
            for (i = 0; i < nr_pages; i++) {
                  struct page *page = pvec.pages[i];
                  index = page->index;
                  if (index > end)
                        break;
                  index++;

                  BUG_ON(!PageLocked(page));
                  BUG_ON(PageWriteback(page));
                  block_invalidatepage(page, 0);
                  ClearPageUptodate(page);
                  unlock_page(page);
            }
      }
      return;
}

static void ext4_print_free_blocks(struct inode *inode)
{
      struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
      printk(KERN_EMERG "Total free blocks count %lld\n",
                  ext4_count_free_blocks(inode->i_sb));
      printk(KERN_EMERG "Free/Dirty block details\n");
      printk(KERN_EMERG "free_blocks=%lld\n",
                  (long long)percpu_counter_sum(&sbi->s_freeblocks_counter));
      printk(KERN_EMERG "dirty_blocks=%lld\n",
                  (long long)percpu_counter_sum(&sbi->s_dirtyblocks_counter));
      printk(KERN_EMERG "Block reservation details\n");
      printk(KERN_EMERG "i_reserved_data_blocks=%u\n",
                  EXT4_I(inode)->i_reserved_data_blocks);
      printk(KERN_EMERG "i_reserved_meta_blocks=%u\n",
                  EXT4_I(inode)->i_reserved_meta_blocks);
      return;
}

/*
 * mpage_da_map_blocks - go through given space
 *
 * @mpd - bh describing space
 *
 * The function skips space we know is already mapped to disk blocks.
 *
 */
static int mpage_da_map_blocks(struct mpage_da_data *mpd)
{
      int err, blks, get_blocks_flags;
      struct buffer_head new;
      sector_t next = mpd->b_blocknr;
      unsigned max_blocks = mpd->b_size >> mpd->inode->i_blkbits;
      loff_t disksize = EXT4_I(mpd->inode)->i_disksize;
      handle_t *handle = NULL;

      /*
       * We consider only non-mapped and non-allocated blocks
       */
      if ((mpd->b_state  & (1 << BH_Mapped)) &&
            !(mpd->b_state & (1 << BH_Delay)) &&
            !(mpd->b_state & (1 << BH_Unwritten)))
            return 0;

      /*
       * If we didn't accumulate anything to write simply return
       */
      if (!mpd->b_size)
            return 0;

      handle = ext4_journal_current_handle();
      BUG_ON(!handle);

      /*
       * Call ext4_get_blocks() to allocate any delayed allocation
       * blocks, or to convert an uninitialized extent to be
       * initialized (in the case where we have written into
       * one or more preallocated blocks).
       *
       * We pass in the magic EXT4_GET_BLOCKS_DELALLOC_RESERVE to
       * indicate that we are on the delayed allocation path.  This
       * affects functions in many different parts of the allocation
       * call path.  This flag exists primarily because we don't
       * want to change *many* call functions, so ext4_get_blocks()
       * will set the magic i_delalloc_reserved_flag once the
       * inode's allocation semaphore is taken.
       *
       * If the blocks in questions were delalloc blocks, set
       * EXT4_GET_BLOCKS_DELALLOC_RESERVE so the delalloc accounting
       * variables are updated after the blocks have been allocated.
       */
      new.b_state = 0;
      get_blocks_flags = (EXT4_GET_BLOCKS_CREATE |
                      EXT4_GET_BLOCKS_DELALLOC_RESERVE);
      if (mpd->b_state & (1 << BH_Delay))
            get_blocks_flags |= EXT4_GET_BLOCKS_UPDATE_RESERVE_SPACE;
      blks = ext4_get_blocks(handle, mpd->inode, next, max_blocks,
                         &new, get_blocks_flags);
      if (blks < 0) {
            err = blks;
            /*
             * If get block returns with error we simply
             * return. Later writepage will redirty the page and
             * writepages will find the dirty page again
             */
            if (err == -EAGAIN)
                  return 0;

            if (err == -ENOSPC &&
                ext4_count_free_blocks(mpd->inode->i_sb)) {
                  mpd->retval = err;
                  return 0;
            }

            /*
             * get block failure will cause us to loop in
             * writepages, because a_ops->writepage won't be able
             * to make progress. The page will be redirtied by
             * writepage and writepages will again try to write
             * the same.
             */
            printk(KERN_EMERG "%s block allocation failed for inode %lu "
                          "at logical offset %llu with max blocks "
                          "%zd with error %d\n",
                          __func__, mpd->inode->i_ino,
                          (unsigned long long)next,
                          mpd->b_size >> mpd->inode->i_blkbits, err);
            printk(KERN_EMERG "This should not happen.!! "
                              "Data will be lost\n");
            if (err == -ENOSPC) {
                  ext4_print_free_blocks(mpd->inode);
            }
            /* invalidate all the pages */
            ext4_da_block_invalidatepages(mpd, next,
                        mpd->b_size >> mpd->inode->i_blkbits);
            return err;
      }
      BUG_ON(blks == 0);

      new.b_size = (blks << mpd->inode->i_blkbits);

      if (buffer_new(&new))
            __unmap_underlying_blocks(mpd->inode, &new);

      /*
       * If blocks are delayed marked, we need to
       * put actual blocknr and drop delayed bit
       */
      if ((mpd->b_state & (1 << BH_Delay)) ||
          (mpd->b_state & (1 << BH_Unwritten)))
            mpage_put_bnr_to_bhs(mpd, next, &new);

      if (ext4_should_order_data(mpd->inode)) {
            err = ext4_jbd2_file_inode(handle, mpd->inode);
            if (err)
                  return err;
      }

      /*
       * Update on-disk size along with block allocation.
       */
      disksize = ((loff_t) next + blks) << mpd->inode->i_blkbits;
      if (disksize > i_size_read(mpd->inode))
            disksize = i_size_read(mpd->inode);
      if (disksize > EXT4_I(mpd->inode)->i_disksize) {
            ext4_update_i_disksize(mpd->inode, disksize);
            return ext4_mark_inode_dirty(handle, mpd->inode);
      }

      return 0;
}

#define BH_FLAGS ((1 << BH_Uptodate) | (1 << BH_Mapped) | \
            (1 << BH_Delay) | (1 << BH_Unwritten))

/*
 * mpage_add_bh_to_extent - try to add one more block to extent of blocks
 *
 * @mpd->lbh - extent of blocks
 * @logical - logical number of the block in the file
 * @bh - bh of the block (used to access block's state)
 *
 * the function is used to collect contig. blocks in same state
 */
static void mpage_add_bh_to_extent(struct mpage_da_data *mpd,
                           sector_t logical, size_t b_size,
                           unsigned long b_state)
{
      sector_t next;
      int nrblocks = mpd->b_size >> mpd->inode->i_blkbits;

      /* check if thereserved journal credits might overflow */
      if (!(EXT4_I(mpd->inode)->i_flags & EXT4_EXTENTS_FL)) {
            if (nrblocks >= EXT4_MAX_TRANS_DATA) {
                  /*
                   * With non-extent format we are limited by the journal
                   * credit available.  Total credit needed to insert
                   * nrblocks contiguous blocks is dependent on the
                   * nrblocks.  So limit nrblocks.
                   */
                  goto flush_it;
            } else if ((nrblocks + (b_size >> mpd->inode->i_blkbits)) >
                        EXT4_MAX_TRANS_DATA) {
                  /*
                   * Adding the new buffer_head would make it cross the
                   * allowed limit for which we have journal credit
                   * reserved. So limit the new bh->b_size
                   */
                  b_size = (EXT4_MAX_TRANS_DATA - nrblocks) <<
                                    mpd->inode->i_blkbits;
                  /* we will do mpage_da_submit_io in the next loop */
            }
      }
      /*
       * First block in the extent
       */
      if (mpd->b_size == 0) {
            mpd->b_blocknr = logical;
            mpd->b_size = b_size;
            mpd->b_state = b_state & BH_FLAGS;
            return;
      }

      next = mpd->b_blocknr + nrblocks;
      /*
       * Can we merge the block to our big extent?
       */
      if (logical == next && (b_state & BH_FLAGS) == mpd->b_state) {
            mpd->b_size += b_size;
            return;
      }

flush_it:
      /*
       * We couldn't merge the block to our extent, so we
       * need to flush current  extent and start new one
       */
      if (mpage_da_map_blocks(mpd) == 0)
            mpage_da_submit_io(mpd);
      mpd->io_done = 1;
      return;
}

static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh)
{
      return (buffer_delay(bh) || buffer_unwritten(bh)) && buffer_dirty(bh);
}

/*
 * __mpage_da_writepage - finds extent of pages and blocks
 *
 * @page: page to consider
 * @wbc: not used, we just follow rules
 * @data: context
 *
 * The function finds extents of pages and scan them for all blocks.
 */
static int __mpage_da_writepage(struct page *page,
                        struct writeback_control *wbc, void *data)
{
      struct mpage_da_data *mpd = data;
      struct inode *inode = mpd->inode;
      struct buffer_head *bh, *head;
      sector_t logical;

      if (mpd->io_done) {
            /*
             * Rest of the page in the page_vec
             * redirty then and skip then. We will
             * try to to write them again after
             * starting a new transaction
             */
            redirty_page_for_writepage(wbc, page);
            unlock_page(page);
            return MPAGE_DA_EXTENT_TAIL;
      }
      /*
       * Can we merge this page to current extent?
       */
      if (mpd->next_page != page->index) {
            /*
             * Nope, we can't. So, we map non-allocated blocks
             * and start IO on them using writepage()
             */
            if (mpd->next_page != mpd->first_page) {
                  if (mpage_da_map_blocks(mpd) == 0)
                        mpage_da_submit_io(mpd);
                  /*
                   * skip rest of the page in the page_vec
                   */
                  mpd->io_done = 1;
                  redirty_page_for_writepage(wbc, page);
                  unlock_page(page);
                  return MPAGE_DA_EXTENT_TAIL;
            }

            /*
             * Start next extent of pages ...
             */
            mpd->first_page = page->index;

            /*
             * ... and blocks
             */
            mpd->b_size = 0;
            mpd->b_state = 0;
            mpd->b_blocknr = 0;
      }

      mpd->next_page = page->index + 1;
      logical = (sector_t) page->index <<
              (PAGE_CACHE_SHIFT - inode->i_blkbits);

      if (!page_has_buffers(page)) {
            mpage_add_bh_to_extent(mpd, logical, PAGE_CACHE_SIZE,
                               (1 << BH_Dirty) | (1 << BH_Uptodate));
            if (mpd->io_done)
                  return MPAGE_DA_EXTENT_TAIL;
      } else {
            /*
             * Page with regular buffer heads, just add all dirty ones
             */
            head = page_buffers(page);
            bh = head;
            do {
                  BUG_ON(buffer_locked(bh));
                  /*
                   * We need to try to allocate
                   * unmapped blocks in the same page.
                   * Otherwise we won't make progress
                   * with the page in ext4_writepage
                   */
                  if (ext4_bh_delay_or_unwritten(NULL, bh)) {
                        mpage_add_bh_to_extent(mpd, logical,
                                           bh->b_size,
                                           bh->b_state);
                        if (mpd->io_done)
                              return MPAGE_DA_EXTENT_TAIL;
                  } else if (buffer_dirty(bh) && (buffer_mapped(bh))) {
                        /*
                         * mapped dirty buffer. We need to update
                         * the b_state because we look at
                         * b_state in mpage_da_map_blocks. We don't
                         * update b_size because if we find an
                         * unmapped buffer_head later we need to
                         * use the b_state flag of that buffer_head.
                         */
                        if (mpd->b_size == 0)
                              mpd->b_state = bh->b_state & BH_FLAGS;
                  }
                  logical++;
            } while ((bh = bh->b_this_page) != head);
      }

      return 0;
}

/*
 * This is a special get_blocks_t callback which is used by
 * ext4_da_write_begin().  It will either return mapped block or
 * reserve space for a single block.
 *
 * For delayed buffer_head we have BH_Mapped, BH_New, BH_Delay set.
 * We also have b_blocknr = -1 and b_bdev initialized properly
 *
 * For unwritten buffer_head we have BH_Mapped, BH_New, BH_Unwritten set.
 * We also have b_blocknr = physicalblock mapping unwritten extent and b_bdev
 * initialized properly.
 */
static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
                          struct buffer_head *bh_result, int create)
{
      int ret = 0;
      sector_t invalid_block = ~((sector_t) 0xffff);

      if (invalid_block < ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es))
            invalid_block = ~0;

      BUG_ON(create == 0);
      BUG_ON(bh_result->b_size != inode->i_sb->s_blocksize);

      /*
       * first, we need to know whether the block is allocated already
       * preallocated blocks are unmapped but should treated
       * the same as allocated blocks.
       */
      ret = ext4_get_blocks(NULL, inode, iblock, 1,  bh_result, 0);
      if ((ret == 0) && !buffer_delay(bh_result)) {
            /* the block isn't (pre)allocated yet, let's reserve space */
            /*
             * XXX: __block_prepare_write() unmaps passed block,
             * is it OK?
             */
            ret = ext4_da_reserve_space(inode, 1);
            if (ret)
                  /* not enough space to reserve */
                  return ret;

            map_bh(bh_result, inode->i_sb, invalid_block);
            set_buffer_new(bh_result);
            set_buffer_delay(bh_result);
      } else if (ret > 0) {
            bh_result->b_size = (ret << inode->i_blkbits);
            if (buffer_unwritten(bh_result)) {
                  /* A delayed write to unwritten bh should
                   * be marked new and mapped.  Mapped ensures
                   * that we don't do get_block multiple times
                   * when we write to the same offset and new
                   * ensures that we do proper zero out for
                   * partial write.
                   */
                  set_buffer_new(bh_result);
                  set_buffer_mapped(bh_result);
            }
            ret = 0;
      }

      return ret;
}

/*
 * This function is used as a standard get_block_t calback function
 * when there is no desire to allocate any blocks.  It is used as a
 * callback function for block_prepare_write(), nobh_writepage(), and
 * block_write_full_page().  These functions should only try to map a
 * single block at a time.
 *
 * Since this function doesn't do block allocations even if the caller
 * requests it by passing in create=1, it is critically important that
 * any caller checks to make sure that any buffer heads are returned
 * by this function are either all already mapped or marked for
 * delayed allocation before calling nobh_writepage() or
 * block_write_full_page().  Otherwise, b_blocknr could be left
 * unitialized, and the page write functions will be taken by
 * surprise.
 */
static int noalloc_get_block_write(struct inode *inode, sector_t iblock,
                           struct buffer_head *bh_result, int create)
{
      int ret = 0;
      unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;

      BUG_ON(bh_result->b_size != inode->i_sb->s_blocksize);

      /*
       * we don't want to do block allocation in writepage
       * so call get_block_wrap with create = 0
       */
      ret = ext4_get_blocks(NULL, inode, iblock, max_blocks, bh_result, 0);
      if (ret > 0) {
            bh_result->b_size = (ret << inode->i_blkbits);
            ret = 0;
      }
      return ret;
}

static int bget_one(handle_t *handle, struct buffer_head *bh)
{
      get_bh(bh);
      return 0;
}

static int bput_one(handle_t *handle, struct buffer_head *bh)
{
      put_bh(bh);
      return 0;
}

static int __ext4_journalled_writepage(struct page *page,
                               struct writeback_control *wbc,
                               unsigned int len)
{
      struct address_space *mapping = page->mapping;
      struct inode *inode = mapping->host;
      struct buffer_head *page_bufs;
      handle_t *handle = NULL;
      int ret = 0;
      int err;

      page_bufs = page_buffers(page);
      BUG_ON(!page_bufs);
      walk_page_buffers(handle, page_bufs, 0, len, NULL, bget_one);
      /* As soon as we unlock the page, it can go away, but we have
       * references to buffers so we are safe */
      unlock_page(page);

      handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
      if (IS_ERR(handle)) {
            ret = PTR_ERR(handle);
            goto out;
      }

      ret = walk_page_buffers(handle, page_bufs, 0, len, NULL,
                        do_journal_get_write_access);

      err = walk_page_buffers(handle, page_bufs, 0, len, NULL,
                        write_end_fn);
      if (ret == 0)
            ret = err;
      err = ext4_journal_stop(handle);
      if (!ret)
            ret = err;

      walk_page_buffers(handle, page_bufs, 0, len, NULL, bput_one);
      EXT4_I(inode)->i_state |= EXT4_STATE_JDATA;
out:
      return ret;
}

/*
 * Note that we don't need to start a transaction unless we're journaling data
 * because we should have holes filled from ext4_page_mkwrite(). We even don't
 * need to file the inode to the transaction's list in ordered mode because if
 * we are writing back data added by write(), the inode is already there and if
 * we are writing back data modified via mmap(), noone guarantees in which
 * transaction the data will hit the disk. In case we are journaling data, we
 * cannot start transaction directly because transaction start ranks above page
 * lock so we have to do some magic.
 *
 * This function can get called via...
 *   - ext4_da_writepages after taking page lock (have journal handle)
 *   - journal_submit_inode_data_buffers (no journal handle)
 *   - shrink_page_list via pdflush (no journal handle)
 *   - grab_page_cache when doing write_begin (have journal handle)
 *
 * We don't do any block allocation in this function. If we have page with
 * multiple blocks we need to write those buffer_heads that are mapped. This
 * is important for mmaped based write. So if we do with blocksize 1K
 * truncate(f, 1024);
 * a = mmap(f, 0, 4096);
 * a[0] = 'a';
 * truncate(f, 4096);
 * we have in the page first buffer_head mapped via page_mkwrite call back
 * but other bufer_heads would be unmapped but dirty(dirty done via the
 * do_wp_page). So writepage should write the first block. If we modify
 * the mmap area beyond 1024 we will again get a page_fault and the
 * page_mkwrite callback will do the block allocation and mark the
 * buffer_heads mapped.
 *
 * We redirty the page if we have any buffer_heads that is either delay or
 * unwritten in the page.
 *
 * We can get recursively called as show below.
 *
 *    ext4_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
 *          ext4_writepage()
 *
 * But since we don't do any block allocation we should not deadlock.
 * Page also have the dirty flag cleared so we don't get recurive page_lock.
 */
static int ext4_writepage(struct page *page,
                    struct writeback_control *wbc)
{
      int ret = 0;
      loff_t size;
      unsigned int len;
      struct buffer_head *page_bufs;
      struct inode *inode = page->mapping->host;

      trace_ext4_writepage(inode, page);
      size = i_size_read(inode);
      if (page->index == size >> PAGE_CACHE_SHIFT)
            len = size & ~PAGE_CACHE_MASK;
      else
            len = PAGE_CACHE_SIZE;

      if (page_has_buffers(page)) {
            page_bufs = page_buffers(page);
            if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
                              ext4_bh_delay_or_unwritten)) {
                  /*
                   * We don't want to do  block allocation
                   * So redirty the page and return
                   * We may reach here when we do a journal commit
                   * via journal_submit_inode_data_buffers.
                   * If we don't have mapping block we just ignore
                   * them. We can also reach here via shrink_page_list
                   */
                  redirty_page_for_writepage(wbc, page);
                  unlock_page(page);
                  return 0;
            }
      } else {
            /*
             * The test for page_has_buffers() is subtle:
             * We know the page is dirty but it lost buffers. That means
             * that at some moment in time after write_begin()/write_end()
             * has been called all buffers have been clean and thus they
             * must have been written at least once. So they are all
             * mapped and we can happily proceed with mapping them
             * and writing the page.
             *
             * Try to initialize the buffer_heads and check whether
             * all are mapped and non delay. We don't want to
             * do block allocation here.
             */
            ret = block_prepare_write(page, 0, len,
                                noalloc_get_block_write);
            if (!ret) {
                  page_bufs = page_buffers(page);
                  /* check whether all are mapped and non delay */
                  if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
                                    ext4_bh_delay_or_unwritten)) {
                        redirty_page_for_writepage(wbc, page);
                        unlock_page(page);
                        return 0;
                  }
            } else {
                  /*
                   * We can't do block allocation here
                   * so just redity the page and unlock
                   * and return
                   */
                  redirty_page_for_writepage(wbc, page);
                  unlock_page(page);
                  return 0;
            }
            /* now mark the buffer_heads as dirty and uptodate */
            block_commit_write(page, 0, len);
      }

      if (PageChecked(page) && ext4_should_journal_data(inode)) {
            /*
             * It's mmapped pagecache.  Add buffers and journal it.  There
             * doesn't seem much point in redirtying the page here.
             */
            ClearPageChecked(page);
            return __ext4_journalled_writepage(page, wbc, len);
      }

      if (test_opt(inode->i_sb, NOBH) && ext4_should_writeback_data(inode))
            ret = nobh_writepage(page, noalloc_get_block_write, wbc);
      else
            ret = block_write_full_page(page, noalloc_get_block_write,
                                  wbc);

      return ret;
}

/*
 * This is called via ext4_da_writepages() to
 * calulate the total number of credits to reserve to fit
 * a single extent allocation into a single transaction,
 * ext4_da_writpeages() will loop calling this before
 * the block allocation.
 */

static int ext4_da_writepages_trans_blocks(struct inode *inode)
{
      int max_blocks = EXT4_I(inode)->i_reserved_data_blocks;

      /*
       * With non-extent format the journal credit needed to
       * insert nrblocks contiguous block is dependent on
       * number of contiguous block. So we will limit
       * number of contiguous block to a sane value
       */
      if (!(inode->i_flags & EXT4_EXTENTS_FL) &&
          (max_blocks > EXT4_MAX_TRANS_DATA))
            max_blocks = EXT4_MAX_TRANS_DATA;

      return ext4_chunk_trans_blocks(inode, max_blocks);
}

static int ext4_da_writepages(struct address_space *mapping,
                        struct writeback_control *wbc)
{
      pgoff_t     index;
      int range_whole = 0;
      handle_t *handle = NULL;
      struct mpage_da_data mpd;
      struct inode *inode = mapping->host;
      int no_nrwrite_index_update;
      int pages_written = 0;
      long pages_skipped;
      int range_cyclic, cycled = 1, io_done = 0;
      int needed_blocks, ret = 0, nr_to_writebump = 0;
      struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);

      trace_ext4_da_writepages(inode, wbc);

      /*
       * No pages to write? This is mainly a kludge to avoid starting
       * a transaction for special inodes like journal inode on last iput()
       * because that could violate lock ordering on umount
       */
      if (!mapping->nrpages || !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
            return 0;

      /*
       * If the filesystem has aborted, it is read-only, so return
       * right away instead of dumping stack traces later on that
       * will obscure the real source of the problem.  We test
       * EXT4_MF_FS_ABORTED instead of sb->s_flag's MS_RDONLY because
       * the latter could be true if the filesystem is mounted
       * read-only, and in that case, ext4_da_writepages should
       * *never* be called, so if that ever happens, we would want
       * the stack trace.
       */
      if (unlikely(sbi->s_mount_flags & EXT4_MF_FS_ABORTED))
            return -EROFS;

      /*
       * Make sure nr_to_write is >= sbi->s_mb_stream_request
       * This make sure small files blocks are allocated in
       * single attempt. This ensure that small files
       * get less fragmented.
       */
      if (wbc->nr_to_write < sbi->s_mb_stream_request) {
            nr_to_writebump = sbi->s_mb_stream_request - wbc->nr_to_write;
            wbc->nr_to_write = sbi->s_mb_stream_request;
      }
      if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
            range_whole = 1;

      range_cyclic = wbc->range_cyclic;
      if (wbc->range_cyclic) {
            index = mapping->writeback_index;
            if (index)
                  cycled = 0;
            wbc->range_start = index << PAGE_CACHE_SHIFT;
            wbc->range_end  = LLONG_MAX;
            wbc->range_cyclic = 0;
      } else
            index = wbc->range_start >> PAGE_CACHE_SHIFT;

      mpd.wbc = wbc;
      mpd.inode = mapping->host;

      /*
       * we don't want write_cache_pages to update
       * nr_to_write and writeback_index
       */
      no_nrwrite_index_update = wbc->no_nrwrite_index_update;
      wbc->no_nrwrite_index_update = 1;
      pages_skipped = wbc->pages_skipped;

retry:
      while (!ret && wbc->nr_to_write > 0) {

            /*
             * we  insert one extent at a time. So we need
             * credit needed for single extent allocation.
             * journalled mode is currently not supported
             * by delalloc
             */
            BUG_ON(ext4_should_journal_data(inode));
            needed_blocks = ext4_da_writepages_trans_blocks(inode);

            /* start a new transaction*/
            handle = ext4_journal_start(inode, needed_blocks);
            if (IS_ERR(handle)) {
                  ret = PTR_ERR(handle);
                  printk(KERN_CRIT "%s: jbd2_start: "
                         "%ld pages, ino %lu; err %d\n", __func__,
                        wbc->nr_to_write, inode->i_ino, ret);
                  dump_stack();
                  goto out_writepages;
            }

            /*
             * Now call __mpage_da_writepage to find the next
             * contiguous region of logical blocks that need
             * blocks to be allocated by ext4.  We don't actually
             * submit the blocks for I/O here, even though
             * write_cache_pages thinks it will, and will set the
             * pages as clean for write before calling
             * __mpage_da_writepage().
             */
            mpd.b_size = 0;
            mpd.b_state = 0;
            mpd.b_blocknr = 0;
            mpd.first_page = 0;
            mpd.next_page = 0;
            mpd.io_done = 0;
            mpd.pages_written = 0;
            mpd.retval = 0;
            ret = write_cache_pages(mapping, wbc, __mpage_da_writepage,
                              &mpd);
            /*
             * If we have a contigous extent of pages and we
             * haven't done the I/O yet, map the blocks and submit
             * them for I/O.
             */
            if (!mpd.io_done && mpd.next_page != mpd.first_page) {
                  if (mpage_da_map_blocks(&mpd) == 0)
                        mpage_da_submit_io(&mpd);
                  mpd.io_done = 1;
                  ret = MPAGE_DA_EXTENT_TAIL;
            }
            wbc->nr_to_write -= mpd.pages_written;

            ext4_journal_stop(handle);

            if ((mpd.retval == -ENOSPC) && sbi->s_journal) {
                  /* commit the transaction which would
                   * free blocks released in the transaction
                   * and try again
                   */
                  jbd2_journal_force_commit_nested(sbi->s_journal);
                  wbc->pages_skipped = pages_skipped;
                  ret = 0;
            } else if (ret == MPAGE_DA_EXTENT_TAIL) {
                  /*
                   * got one extent now try with
                   * rest of the pages
                   */
                  pages_written += mpd.pages_written;
                  wbc->pages_skipped = pages_skipped;
                  ret = 0;
                  io_done = 1;
            } else if (wbc->nr_to_write)
                  /*
                   * There is no more writeout needed
                   * or we requested for a noblocking writeout
                   * and we found the device congested
                   */
                  break;
      }
      if (!io_done && !cycled) {
            cycled = 1;
            index = 0;
            wbc->range_start = index << PAGE_CACHE_SHIFT;
            wbc->range_end  = mapping->writeback_index - 1;
            goto retry;
      }
      if (pages_skipped != wbc->pages_skipped)
            printk(KERN_EMERG "This should not happen leaving %s "
                        "with nr_to_write = %ld ret = %d\n",
                        __func__, wbc->nr_to_write, ret);

      /* Update index */
      index += pages_written;
      wbc->range_cyclic = range_cyclic;
      if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
            /*
             * set the writeback_index so that range_cyclic
             * mode will write it back later
             */
            mapping->writeback_index = index;

out_writepages:
      if (!no_nrwrite_index_update)
            wbc->no_nrwrite_index_update = 0;
      wbc->nr_to_write -= nr_to_writebump;
      trace_ext4_da_writepages_result(inode, wbc, ret, pages_written);
      return ret;
}

#define FALL_BACK_TO_NONDELALLOC 1
static int ext4_nonda_switch(struct super_block *sb)
{
      s64 free_blocks, dirty_blocks;
      struct ext4_sb_info *sbi = EXT4_SB(sb);

      /*
       * switch to non delalloc mode if we are running low
       * on free block. The free block accounting via percpu
       * counters can get slightly wrong with percpu_counter_batch getting
       * accumulated on each CPU without updating global counters
       * Delalloc need an accurate free block accounting. So switch
       * to non delalloc when we are near to error range.
       */
      free_blocks  = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
      dirty_blocks = percpu_counter_read_positive(&sbi->s_dirtyblocks_counter);
      if (2 * free_blocks < 3 * dirty_blocks ||
            free_blocks < (dirty_blocks + EXT4_FREEBLOCKS_WATERMARK)) {
            /*
             * free block count is less that 150% of dirty blocks
             * or free blocks is less that watermark
             */
            return 1;
      }
      return 0;
}

static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
                         loff_t pos, unsigned len, unsigned flags,
                         struct page **pagep, void **fsdata)
{
      int ret, retries = 0;
      struct page *page;
      pgoff_t index;
      unsigned from, to;
      struct inode *inode = mapping->host;
      handle_t *handle;

      index = pos >> PAGE_CACHE_SHIFT;
      from = pos & (PAGE_CACHE_SIZE - 1);
      to = from + len;

      if (ext4_nonda_switch(inode->i_sb)) {
            *fsdata = (void *)FALL_BACK_TO_NONDELALLOC;
            return ext4_write_begin(file, mapping, pos,
                              len, flags, pagep, fsdata);
      }
      *fsdata = (void *)0;
      trace_ext4_da_write_begin(inode, pos, len, flags);
retry:
      /*
       * With delayed allocation, we don't log the i_disksize update
       * if there is delayed block allocation. But we still need
       * to journalling the i_disksize update if writes to the end
       * of file which has an already mapped buffer.
       */
      handle = ext4_journal_start(inode, 1);
      if (IS_ERR(handle)) {
            ret = PTR_ERR(handle);
            goto out;
      }
      /* We cannot recurse into the filesystem as the transaction is already
       * started */
      flags |= AOP_FLAG_NOFS;

      page = grab_cache_page_write_begin(mapping, index, flags);
      if (!page) {
            ext4_journal_stop(handle);
            ret = -ENOMEM;
            goto out;
      }
      *pagep = page;

      ret = block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
                        ext4_da_get_block_prep);
      if (ret < 0) {
            unlock_page(page);
            ext4_journal_stop(handle);
            page_cache_release(page);
            /*
             * block_write_begin may have instantiated a few blocks
             * outside i_size.  Trim these off again. Don't need
             * i_size_read because we hold i_mutex.
             */
            if (pos + len > inode->i_size)
                  ext4_truncate(inode);
      }

      if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
            goto retry;
out:
      return ret;
}

/*
 * Check if we should update i_disksize
 * when write to the end of file but not require block allocation
 */
static int ext4_da_should_update_i_disksize(struct page *page,
                                  unsigned long offset)
{
      struct buffer_head *bh;
      struct inode *inode = page->mapping->host;
      unsigned int idx;
      int i;

      bh = page_buffers(page);
      idx = offset >> inode->i_blkbits;

      for (i = 0; i < idx; i++)
            bh = bh->b_this_page;

      if (!buffer_mapped(bh) || (buffer_delay(bh)) || buffer_unwritten(bh))
            return 0;
      return 1;
}

static int ext4_da_write_end(struct file *file,
                       struct address_space *mapping,
                       loff_t pos, unsigned len, unsigned copied,
                       struct page *page, void *fsdata)
{
      struct inode *inode = mapping->host;
      int ret = 0, ret2;
      handle_t *handle = ext4_journal_current_handle();
      loff_t new_i_size;
      unsigned long start, end;
      int write_mode = (int)(unsigned long)fsdata;

      if (write_mode == FALL_BACK_TO_NONDELALLOC) {
            if (ext4_should_order_data(inode)) {
                  return ext4_ordered_write_end(file, mapping, pos,
                              len, copied, page, fsdata);
            } else if (ext4_should_writeback_data(inode)) {
                  return ext4_writeback_write_end(file, mapping, pos,
                              len, copied, page, fsdata);
            } else {
                  BUG();
            }
      }

      trace_ext4_da_write_end(inode, pos, len, copied);
      start = pos & (PAGE_CACHE_SIZE - 1);
      end = start + copied - 1;

      /*
       * generic_write_end() will run mark_inode_dirty() if i_size
       * changes.  So let's piggyback the i_disksize mark_inode_dirty
       * into that.
       */

      new_i_size = pos + copied;
      if (new_i_size > EXT4_I(inode)->i_disksize) {
            if (ext4_da_should_update_i_disksize(page, end)) {
                  down_write(&EXT4_I(inode)->i_data_sem);
                  if (new_i_size > EXT4_I(inode)->i_disksize) {
                        /*
                         * Updating i_disksize when extending file
                         * without needing block allocation
                         */
                        if (ext4_should_order_data(inode))
                              ret = ext4_jbd2_file_inode(handle,
                                                   inode);

                        EXT4_I(inode)->i_disksize = new_i_size;
                  }
                  up_write(&EXT4_I(inode)->i_data_sem);
                  /* We need to mark inode dirty even if
                   * new_i_size is less that inode->i_size
                   * bu greater than i_disksize.(hint delalloc)
                   */
                  ext4_mark_inode_dirty(handle, inode);
            }
      }
      ret2 = generic_write_end(file, mapping, pos, len, copied,
                                          page, fsdata);
      copied = ret2;
      if (ret2 < 0)
            ret = ret2;
      ret2 = ext4_journal_stop(handle);
      if (!ret)
            ret = ret2;

      return ret ? ret : copied;
}

static void ext4_da_invalidatepage(struct page *page, unsigned long offset)
{
      /*
       * Drop reserved blocks
       */
      BUG_ON(!PageLocked(page));
      if (!page_has_buffers(page))
            goto out;

      ext4_da_page_release_reservation(page, offset);

out:
      ext4_invalidatepage(page, offset);

      return;
}

/*
 * Force all delayed allocation blocks to be allocated for a given inode.
 */
int ext4_alloc_da_blocks(struct inode *inode)
{
      if (!EXT4_I(inode)->i_reserved_data_blocks &&
          !EXT4_I(inode)->i_reserved_meta_blocks)
            return 0;

      /*
       * We do something simple for now.  The filemap_flush() will
       * also start triggering a write of the data blocks, which is
       * not strictly speaking necessary (and for users of
       * laptop_mode, not even desirable).  However, to do otherwise
       * would require replicating code paths in:
       *
       * ext4_da_writepages() ->
       *    write_cache_pages() ---> (via passed in callback function)
       *        __mpage_da_writepage() -->
       *           mpage_add_bh_to_extent()
       *           mpage_da_map_blocks()
       *
       * The problem is that write_cache_pages(), located in
       * mm/page-writeback.c, marks pages clean in preparation for
       * doing I/O, which is not desirable if we're not planning on
       * doing I/O at all.
       *
       * We could call write_cache_pages(), and then redirty all of
       * the pages by calling redirty_page_for_writeback() but that
       * would be ugly in the extreme.  So instead we would need to
       * replicate parts of the code in the above functions,
       * simplifying them becuase we wouldn't actually intend to
       * write out the pages, but rather only collect contiguous
       * logical block extents, call the multi-block allocator, and
       * then update the buffer heads with the block allocations.
       *
       * For now, though, we'll cheat by calling filemap_flush(),
       * which will map the blocks, and start the I/O, but not
       * actually wait for the I/O to complete.
       */
      return filemap_flush(inode->i_mapping);
}

/*
 * bmap() is special.  It gets used by applications such as lilo and by
 * the swapper to find the on-disk block of a specific piece of data.
 *
 * Naturally, this is dangerous if the block concerned is still in the
 * journal.  If somebody makes a swapfile on an ext4 data-journaling
 * filesystem and enables swap, then they may get a nasty shock when the
 * data getting swapped to that swapfile suddenly gets overwritten by
 * the original zero's written out previously to the journal and
 * awaiting writeback in the kernel's buffer cache.
 *
 * So, if we see any bmap calls here on a modified, data-journaled file,
 * take extra steps to flush any blocks which might be in the cache.
 */
static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
{
      struct inode *inode = mapping->host;
      journal_t *journal;
      int err;

      if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
                  test_opt(inode->i_sb, DELALLOC)) {
            /*
             * With delalloc we want to sync the file
             * so that we can make sure we allocate
             * blocks for file
             */
            filemap_write_and_wait(mapping);
      }

      if (EXT4_JOURNAL(inode) && EXT4_I(inode)->i_state & EXT4_STATE_JDATA) {
            /*
             * This is a REALLY heavyweight approach, but the use of
             * bmap on dirty files is expected to be extremely rare:
             * only if we run lilo or swapon on a freshly made file
             * do we expect this to happen.
             *
             * (bmap requires CAP_SYS_RAWIO so this does not
             * represent an unprivileged user DOS attack --- we'd be
             * in trouble if mortal users could trigger this path at
             * will.)
             *
             * NB. EXT4_STATE_JDATA is not set on files other than
             * regular files.  If somebody wants to bmap a directory
             * or symlink and gets confused because the buffer
             * hasn't yet been flushed to disk, they deserve
             * everything they get.
             */

            EXT4_I(inode)->i_state &= ~EXT4_STATE_JDATA;
            journal = EXT4_JOURNAL(inode);
            jbd2_journal_lock_updates(journal);
            err = jbd2_journal_flush(journal);
            jbd2_journal_unlock_updates(journal);

            if (err)
                  return 0;
      }

      return generic_block_bmap(mapping, block, ext4_get_block);
}

static int ext4_readpage(struct file *file, struct page *page)
{
      return mpage_readpage(page, ext4_get_block);
}

static int
ext4_readpages(struct file *file, struct address_space *mapping,
            struct list_head *pages, unsigned nr_pages)
{
      return mpage_readpages(mapping, pages, nr_pages, ext4_get_block);
}

static void ext4_invalidatepage(struct page *page, unsigned long offset)
{
      journal_t *journal = EXT4_JOURNAL(page->mapping->host);

      /*
       * If it's a full truncate we just forget about the pending dirtying
       */
      if (offset == 0)
            ClearPageChecked(page);

      if (journal)
            jbd2_journal_invalidatepage(journal, page, offset);
      else
            block_invalidatepage(page, offset);
}

static int ext4_releasepage(struct page *page, gfp_t wait)
{
      journal_t *journal = EXT4_JOURNAL(page->mapping->host);

      WARN_ON(PageChecked(page));
      if (!page_has_buffers(page))
            return 0;
      if (journal)
            return jbd2_journal_try_to_free_buffers(journal, page, wait);
      else
            return try_to_free_buffers(page);
}

/*
 * If the O_DIRECT write will extend the file then add this inode to the
 * orphan list.  So recovery will truncate it back to the original size
 * if the machine crashes during the write.
 *
 * If the O_DIRECT write is intantiating holes inside i_size and the machine
 * crashes then stale disk data _may_ be exposed inside the file. But current
 * VFS code falls back into buffered path in that case so we are safe.
 */
static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb,
                        const struct iovec *iov, loff_t offset,
                        unsigned long nr_segs)
{
      struct file *file = iocb->ki_filp;
      struct inode *inode = file->f_mapping->host;
      struct ext4_inode_info *ei = EXT4_I(inode);
      handle_t *handle;
      ssize_t ret;
      int orphan = 0;
      size_t count = iov_length(iov, nr_segs);

      if (rw == WRITE) {
            loff_t final_size = offset + count;

            if (final_size > inode->i_size) {
                  /* Credits for sb + inode write */
                  handle = ext4_journal_start(inode, 2);
                  if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        goto out;
                  }
                  ret = ext4_orphan_add(handle, inode);
                  if (ret) {
                        ext4_journal_stop(handle);
                        goto out;
                  }
                  orphan = 1;
                  ei->i_disksize = inode->i_size;
                  ext4_journal_stop(handle);
            }
      }

      ret = blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov,
                         offset, nr_segs,
                         ext4_get_block, NULL);

      if (orphan) {
            int err;

            /* Credits for sb + inode write */
            handle = ext4_journal_start(inode, 2);
            if (IS_ERR(handle)) {
                  /* This is really bad luck. We've written the data
                   * but cannot extend i_size. Bail out and pretend
                   * the write failed... */
                  ret = PTR_ERR(handle);
                  goto out;
            }
            if (inode->i_nlink)
                  ext4_orphan_del(handle, inode);
            if (ret > 0) {
                  loff_t end = offset + ret;
                  if (end > inode->i_size) {
                        ei->i_disksize = end;
                        i_size_write(inode, end);
                        /*
                         * We're going to return a positive `ret'
                         * here due to non-zero-length I/O, so there's
                         * no way of reporting error returns from
                         * ext4_mark_inode_dirty() to userspace.  So
                         * ignore it.
                         */
                        ext4_mark_inode_dirty(handle, inode);
                  }
            }
            err = ext4_journal_stop(handle);
            if (ret == 0)
                  ret = err;
      }
out:
      return ret;
}

/*
 * Pages can be marked dirty completely asynchronously from ext4's journalling
 * activity.  By filemap_sync_pte(), try_to_unmap_one(), etc.  We cannot do
 * much here because ->set_page_dirty is called under VFS locks.  The page is
 * not necessarily locked.
 *
 * We cannot just dirty the page and leave attached buffers clean, because the
 * buffers' dirty state is "definitive".  We cannot just set the buffers dirty
 * or jbddirty because all the journalling code will explode.
 *
 * So what we do is to mark the page "pending dirty" and next time writepage
 * is called, propagate that into the buffers appropriately.
 */
static int ext4_journalled_set_page_dirty(struct page *page)
{
      SetPageChecked(page);
      return __set_page_dirty_nobuffers(page);
}

static const struct address_space_operations ext4_ordered_aops = {
      .readpage         = ext4_readpage,
      .readpages        = ext4_readpages,
      .writepage        = ext4_writepage,
      .sync_page        = block_sync_page,
      .write_begin            = ext4_write_begin,
      .write_end        = ext4_ordered_write_end,
      .bmap             = ext4_bmap,
      .invalidatepage         = ext4_invalidatepage,
      .releasepage            = ext4_releasepage,
      .direct_IO        = ext4_direct_IO,
      .migratepage            = buffer_migrate_page,
      .is_partially_uptodate  = block_is_partially_uptodate,
};

static const struct address_space_operations ext4_writeback_aops = {
      .readpage         = ext4_readpage,
      .readpages        = ext4_readpages,
      .writepage        = ext4_writepage,
      .sync_page        = block_sync_page,
      .write_begin            = ext4_write_begin,
      .write_end        = ext4_writeback_write_end,
      .bmap             = ext4_bmap,
      .invalidatepage         = ext4_invalidatepage,
      .releasepage            = ext4_releasepage,
      .direct_IO        = ext4_direct_IO,
      .migratepage            = buffer_migrate_page,
      .is_partially_uptodate  = block_is_partially_uptodate,
};

static const struct address_space_operations ext4_journalled_aops = {
      .readpage         = ext4_readpage,
      .readpages        = ext4_readpages,
      .writepage        = ext4_writepage,
      .sync_page        = block_sync_page,
      .write_begin            = ext4_write_begin,
      .write_end        = ext4_journalled_write_end,
      .set_page_dirty         = ext4_journalled_set_page_dirty,
      .bmap             = ext4_bmap,
      .invalidatepage         = ext4_invalidatepage,
      .releasepage            = ext4_releasepage,
      .is_partially_uptodate  = block_is_partially_uptodate,
};

static const struct address_space_operations ext4_da_aops = {
      .readpage         = ext4_readpage,
      .readpages        = ext4_readpages,
      .writepage        = ext4_writepage,
      .writepages       = ext4_da_writepages,
      .sync_page        = block_sync_page,
      .write_begin            = ext4_da_write_begin,
      .write_end        = ext4_da_write_end,
      .bmap             = ext4_bmap,
      .invalidatepage         = ext4_da_invalidatepage,
      .releasepage            = ext4_releasepage,
      .direct_IO        = ext4_direct_IO,
      .migratepage            = buffer_migrate_page,
      .is_partially_uptodate  = block_is_partially_uptodate,
};

void ext4_set_aops(struct inode *inode)
{
      if (ext4_should_order_data(inode) &&
            test_opt(inode->i_sb, DELALLOC))
            inode->i_mapping->a_ops = &ext4_da_aops;
      else if (ext4_should_order_data(inode))
            inode->i_mapping->a_ops = &ext4_ordered_aops;
      else if (ext4_should_writeback_data(inode) &&
             test_opt(inode->i_sb, DELALLOC))
            inode->i_mapping->a_ops = &ext4_da_aops;
      else if (ext4_should_writeback_data(inode))
            inode->i_mapping->a_ops = &ext4_writeback_aops;
      else
            inode->i_mapping->a_ops = &ext4_journalled_aops;
}

/*
 * ext4_block_truncate_page() zeroes out a mapping from file offset `from'
 * up to the end of the block which corresponds to `from'.
 * This required during truncate. We need to physically zero the tail end
 * of that block so it doesn't yield old data if the file is later grown.
 */
int ext4_block_truncate_page(handle_t *handle,
            struct address_space *mapping, loff_t from)
{
      ext4_fsblk_t index = from >> PAGE_CACHE_SHIFT;
      unsigned offset = from & (PAGE_CACHE_SIZE-1);
      unsigned blocksize, length, pos;
      ext4_lblk_t iblock;
      struct inode *inode = mapping->host;
      struct buffer_head *bh;
      struct page *page;
      int err = 0;

      page = find_or_create_page(mapping, from >> PAGE_CACHE_SHIFT,
                           mapping_gfp_mask(mapping) & ~__GFP_FS);
      if (!page)
            return -EINVAL;

      blocksize = inode->i_sb->s_blocksize;
      length = blocksize - (offset & (blocksize - 1));
      iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);

      /*
       * For "nobh" option,  we can only work if we don't need to
       * read-in the page - otherwise we create buffers to do the IO.
       */
      if (!page_has_buffers(page) && test_opt(inode->i_sb, NOBH) &&
           ext4_should_writeback_data(inode) && PageUptodate(page)) {
            zero_user(page, offset, length);
            set_page_dirty(page);
            goto unlock;
      }

      if (!page_has_buffers(page))
            create_empty_buffers(page, blocksize, 0);

      /* Find the buffer that contains "offset" */
      bh = page_buffers(page);
      pos = blocksize;
      while (offset >= pos) {
            bh = bh->b_this_page;
            iblock++;
            pos += blocksize;
      }

      err = 0;
      if (buffer_freed(bh)) {
            BUFFER_TRACE(bh, "freed: skip");
            goto unlock;
      }

      if (!buffer_mapped(bh)) {
            BUFFER_TRACE(bh, "unmapped");
            ext4_get_block(inode, iblock, bh, 0);
            /* unmapped? It's a hole - nothing to do */
            if (!buffer_mapped(bh)) {
                  BUFFER_TRACE(bh, "still unmapped");
                  goto unlock;
            }
      }

      /* Ok, it's mapped. Make sure it's up-to-date */
      if (PageUptodate(page))
            set_buffer_uptodate(bh);

      if (!buffer_uptodate(bh)) {
            err = -EIO;
            ll_rw_block(READ, 1, &bh);
            wait_on_buffer(bh);
            /* Uhhuh. Read error. Complain and punt. */
            if (!buffer_uptodate(bh))
                  goto unlock;
      }

      if (ext4_should_journal_data(inode)) {
            BUFFER_TRACE(bh, "get write access");
            err = ext4_journal_get_write_access(handle, bh);
            if (err)
                  goto unlock;
      }

      zero_user(page, offset, length);

      BUFFER_TRACE(bh, "zeroed end of block");

      err = 0;
      if (ext4_should_journal_data(inode)) {
            err = ext4_handle_dirty_metadata(handle, inode, bh);
      } else {
            if (ext4_should_order_data(inode))
                  err = ext4_jbd2_file_inode(handle, inode);
            mark_buffer_dirty(bh);
      }

unlock:
      unlock_page(page);
      page_cache_release(page);
      return err;
}

/*
 * Probably it should be a library function... search for first non-zero word
 * or memcmp with zero_page, whatever is better for particular architecture.
 * Linus?
 */
static inline int all_zeroes(__le32 *p, __le32 *q)
{
      while (p < q)
            if (*p++)
                  return 0;
      return 1;
}

/**
 *    ext4_find_shared - find the indirect blocks for partial truncation.
 *    @inode:       inode in question
 *    @depth:       depth of the affected branch
 *    @offsets: offsets of pointers in that branch (see ext4_block_to_path)
 *    @chain:       place to store the pointers to partial indirect blocks
 *    @top:   place to the (detached) top of branch
 *
 *    This is a helper function used by ext4_truncate().
 *
 *    When we do truncate() we may have to clean the ends of several
 *    indirect blocks but leave the blocks themselves alive. Block is
 *    partially truncated if some data below the new i_size is refered
 *    from it (and it is on the path to the first completely truncated
 *    data block, indeed).  We have to free the top of that path along
 *    with everything to the right of the path. Since no allocation
 *    past the truncation point is possible until ext4_truncate()
 *    finishes, we may safely do the latter, but top of branch may
 *    require special attention - pageout below the truncation point
 *    might try to populate it.
 *
 *    We atomically detach the top of branch from the tree, store the
 *    block number of its root in *@top, pointers to buffer_heads of
 *    partially truncated blocks - in @chain[].bh and pointers to
 *    their last elements that should not be removed - in
 *    @chain[].p. Return value is the pointer to last filled element
 *    of @chain.
 *
 *    The work left to caller to do the actual freeing of subtrees:
 *          a) free the subtree starting from *@top
 *          b) free the subtrees whose roots are stored in
 *                (@chain[i].p+1 .. end of @chain[i].bh->b_data)
 *          c) free the subtrees growing from the inode past the @chain[0].
 *                (no partially truncated stuff there).  */

static Indirect *ext4_find_shared(struct inode *inode, int depth,
                          ext4_lblk_t offsets[4], Indirect chain[4],
                          __le32 *top)
{
      Indirect *partial, *p;
      int k, err;

      *top = 0;
      /* Make k index the deepest non-null offest + 1 */
      for (k = depth; k > 1 && !offsets[k-1]; k--)
            ;
      partial = ext4_get_branch(inode, k, offsets, chain, &err);
      /* Writer: pointers */
      if (!partial)
            partial = chain + k-1;
      /*
       * If the branch acquired continuation since we've looked at it -
       * fine, it should all survive and (new) top doesn't belong to us.
       */
      if (!partial->key && *partial->p)
            /* Writer: end */
            goto no_top;
      for (p = partial; (p > chain) && all_zeroes((__le32 *) p->bh->b_data, p->p); p--)
            ;
      /*
       * OK, we've found the last block that must survive. The rest of our
       * branch should be detached before unlocking. However, if that rest
       * of branch is all ours and does not grow immediately from the inode
       * it's easier to cheat and just decrement partial->p.
       */
      if (p == chain + k - 1 && p > chain) {
            p->p--;
      } else {
            *top = *p->p;
            /* Nope, don't do this in ext4.  Must leave the tree intact */
#if 0
            *p->p = 0;
#endif
      }
      /* Writer: end */

      while (partial > p) {
            brelse(partial->bh);
            partial--;
      }
no_top:
      return partial;
}

/*
 * Zero a number of block pointers in either an inode or an indirect block.
 * If we restart the transaction we must again get write access to the
 * indirect block for further modification.
 *
 * We release `count' blocks on disk, but (last - first) may be greater
 * than `count' because there can be holes in there.
 */
static void ext4_clear_blocks(handle_t *handle, struct inode *inode,
                        struct buffer_head *bh,
                        ext4_fsblk_t block_to_free,
                        unsigned long count, __le32 *first,
                        __le32 *last)
{
      __le32 *p;
      if (try_to_extend_transaction(handle, inode)) {
            if (bh) {
                  BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
                  ext4_handle_dirty_metadata(handle, inode, bh);
            }
            ext4_mark_inode_dirty(handle, inode);
            ext4_journal_test_restart(handle, inode);
            if (bh) {
                  BUFFER_TRACE(bh, "retaking write access");
                  ext4_journal_get_write_access(handle, bh);
            }
      }

      /*
       * Any buffers which are on the journal will be in memory. We
       * find them on the hash table so jbd2_journal_revoke() will
       * run jbd2_journal_forget() on them.  We've already detached
       * each block from the file, so bforget() in
       * jbd2_journal_forget() should be safe.
       *
       * AKPM: turn on bforget in jbd2_journal_forget()!!!
       */
      for (p = first; p < last; p++) {
            u32 nr = le32_to_cpu(*p);
            if (nr) {
                  struct buffer_head *tbh;

                  *p = 0;
                  tbh = sb_find_get_block(inode->i_sb, nr);
                  ext4_forget(handle, 0, inode, tbh, nr);
            }
      }

      ext4_free_blocks(handle, inode, block_to_free, count, 0);
}

/**
 * ext4_free_data - free a list of data blocks
 * @handle: handle for this transaction
 * @inode:  inode we are dealing with
 * @this_bh:      indirect buffer_head which contains *@first and *@last
 * @first:  array of block numbers
 * @last:   points immediately past the end of array
 *
 * We are freeing all blocks refered from that array (numbers are stored as
 * little-endian 32-bit) and updating @inode->i_blocks appropriately.
 *
 * We accumulate contiguous runs of blocks to free.  Conveniently, if these
 * blocks are contiguous then releasing them at one time will only affect one
 * or two bitmap blocks (+ group descriptor(s) and superblock) and we won't
 * actually use a lot of journal space.
 *
 * @this_bh will be %NULL if @first and @last point into the inode's direct
 * block pointers.
 */
static void ext4_free_data(handle_t *handle, struct inode *inode,
                     struct buffer_head *this_bh,
                     __le32 *first, __le32 *last)
{
      ext4_fsblk_t block_to_free = 0;    /* Starting block # of a run */
      unsigned long count = 0;          /* Number of blocks in the run */
      __le32 *block_to_free_p = NULL;         /* Pointer into inode/ind
                                     corresponding to
                                     block_to_free */
      ext4_fsblk_t nr;            /* Current block # */
      __le32 *p;                  /* Pointer into inode/ind
                                     for current block */
      int err;

      if (this_bh) {                      /* For indirect block */
            BUFFER_TRACE(this_bh, "get_write_access");
            err = ext4_journal_get_write_access(handle, this_bh);
            /* Important: if we can't update the indirect pointers
             * to the blocks, we can't free them. */
            if (err)
                  return;
      }

      for (p = first; p < last; p++) {
            nr = le32_to_cpu(*p);
            if (nr) {
                  /* accumulate blocks to free if they're contiguous */
                  if (count == 0) {
                        block_to_free = nr;
                        block_to_free_p = p;
                        count = 1;
                  } else if (nr == block_to_free + count) {
                        count++;
                  } else {
                        ext4_clear_blocks(handle, inode, this_bh,
                                      block_to_free,
                                      count, block_to_free_p, p);
                        block_to_free = nr;
                        block_to_free_p = p;
                        count = 1;
                  }
            }
      }

      if (count > 0)
            ext4_clear_blocks(handle, inode, this_bh, block_to_free,
                          count, block_to_free_p, p);

      if (this_bh) {
            BUFFER_TRACE(this_bh, "call ext4_handle_dirty_metadata");

            /*
             * The buffer head should have an attached journal head at this
             * point. However, if the data is corrupted and an indirect
             * block pointed to itself, it would have been detached when
             * the block was cleared. Check for this instead of OOPSing.
             */
            if ((EXT4_JOURNAL(inode) == NULL) || bh2jh(this_bh))
                  ext4_handle_dirty_metadata(handle, inode, this_bh);
            else
                  ext4_error(inode->i_sb, __func__,
                           "circular indirect block detected, "
                           "inode=%lu, block=%llu",
                           inode->i_ino,
                           (unsigned long long) this_bh->b_blocknr);
      }
}

/**
 *    ext4_free_branches - free an array of branches
 *    @handle: JBD handle for this transaction
 *    @inode:     inode we are dealing with
 *    @parent_bh: the buffer_head which contains *@first and *@last
 *    @first:     array of block numbers
 *    @last:      pointer immediately past the end of array
 *    @depth:     depth of the branches to free
 *
 *    We are freeing all blocks refered from these branches (numbers are
 *    stored as little-endian 32-bit) and updating @inode->i_blocks
 *    appropriately.
 */
static void ext4_free_branches(handle_t *handle, struct inode *inode,
                         struct buffer_head *parent_bh,
                         __le32 *first, __le32 *last, int depth)
{
      ext4_fsblk_t nr;
      __le32 *p;

      if (ext4_handle_is_aborted(handle))
            return;

      if (depth--) {
            struct buffer_head *bh;
            int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
            p = last;
            while (--p >= first) {
                  nr = le32_to_cpu(*p);
                  if (!nr)
                        continue;         /* A hole */

                  /* Go read the buffer for the next level down */
                  bh = sb_bread(inode->i_sb, nr);

                  /*
                   * A read failure? Report error and clear slot
                   * (should be rare).
                   */
                  if (!bh) {
                        ext4_error(inode->i_sb, "ext4_free_branches",
                                 "Read failure, inode=%lu, block=%llu",
                                 inode->i_ino, nr);
                        continue;
                  }

                  /* This zaps the entire block.  Bottom up. */
                  BUFFER_TRACE(bh, "free child branches");
                  ext4_free_branches(handle, inode, bh,
                              (__le32 *) bh->b_data,
                              (__le32 *) bh->b_data + addr_per_block,
                              depth);

                  /*
                   * We've probably journalled the indirect block several
                   * times during the truncate.  But it's no longer
                   * needed and we now drop it from the transaction via
                   * jbd2_journal_revoke().
                   *
                   * That's easy if it's exclusively part of this
                   * transaction.  But if it's part of the committing
                   * transaction then jbd2_journal_forget() will simply
                   * brelse() it.  That means that if the underlying
                   * block is reallocated in ext4_get_block(),
                   * unmap_underlying_metadata() will find this block
                   * and will try to get rid of it.  damn, damn.
                   *
                   * If this block has already been committed to the
                   * journal, a revoke record will be written.  And
                   * revoke records must be emitted *before* clearing
                   * this block's bit in the bitmaps.
                   */
                  ext4_forget(handle, 1, inode, bh, bh->b_blocknr);

                  /*
                   * Everything below this this pointer has been
                   * released.  Now let this top-of-subtree go.
                   *
                   * We want the freeing of this indirect block to be
                   * atomic in the journal with the updating of the
                   * bitmap block which owns it.  So make some room in
                   * the journal.
                   *
                   * We zero the parent pointer *after* freeing its
                   * pointee in the bitmaps, so if extend_transaction()
                   * for some reason fails to put the bitmap changes and
                   * the release into the same transaction, recovery
                   * will merely complain about releasing a free block,
                   * rather than leaking blocks.
                   */
                  if (ext4_handle_is_aborted(handle))
                        return;
                  if (try_to_extend_transaction(handle, inode)) {
                        ext4_mark_inode_dirty(handle, inode);
                        ext4_journal_test_restart(handle, inode);
                  }

                  ext4_free_blocks(handle, inode, nr, 1, 1);

                  if (parent_bh) {
                        /*
                         * The block which we have just freed is
                         * pointed to by an indirect block: journal it
                         */
                        BUFFER_TRACE(parent_bh, "get_write_access");
                        if (!ext4_journal_get_write_access(handle,
                                                   parent_bh)){
                              *p = 0;
                              BUFFER_TRACE(parent_bh,
                              "call ext4_handle_dirty_metadata");
                              ext4_handle_dirty_metadata(handle,
                                                   inode,
                                                   parent_bh);
                        }
                  }
            }
      } else {
            /* We have reached the bottom of the tree. */
            BUFFER_TRACE(parent_bh, "free data blocks");
            ext4_free_data(handle, inode, parent_bh, first, last);
      }
}

int ext4_can_truncate(struct inode *inode)
{
      if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
            return 0;
      if (S_ISREG(inode->i_mode))
            return 1;
      if (S_ISDIR(inode->i_mode))
            return 1;
      if (S_ISLNK(inode->i_mode))
            return !ext4_inode_is_fast_symlink(inode);
      return 0;
}

/*
 * ext4_truncate()
 *
 * We block out ext4_get_block() block instantiations across the entire
 * transaction, and VFS/VM ensures that ext4_truncate() cannot run
 * simultaneously on behalf of the same inode.
 *
 * As we work through the truncate and commmit bits of it to the journal there
 * is one core, guiding principle: the file's tree must always be consistent on
 * disk.  We must be able to restart the truncate after a crash.
 *
 * The file's tree may be transiently inconsistent in memory (although it
 * probably isn't), but whenever we close off and commit a journal transaction,
 * the contents of (the filesystem + the journal) must be consistent and
 * restartable.  It's pretty simple, really: bottom up, right to left (although
 * left-to-right works OK too).
 *
 * Note that at recovery time, journal replay occurs *before* the restart of
 * truncate against the orphan inode list.
 *
 * The committed inode has the new, desired i_size (which is the same as
 * i_disksize in this case).  After a crash, ext4_orphan_cleanup() will see
 * that this inode's truncate did not complete and it will again call
 * ext4_truncate() to have another go.  So there will be instantiated blocks
 * to the right of the truncation point in a crashed ext4 filesystem.  But
 * that's fine - as long as they are linked from the inode, the post-crash
 * ext4_truncate() run will find them and release them.
 */
void ext4_truncate(struct inode *inode)
{
      handle_t *handle;
      struct ext4_inode_info *ei = EXT4_I(inode);
      __le32 *i_data = ei->i_data;
      int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
      struct address_space *mapping = inode->i_mapping;
      ext4_lblk_t offsets[4];
      Indirect chain[4];
      Indirect *partial;
      __le32 nr = 0;
      int n;
      ext4_lblk_t last_block;
      unsigned blocksize = inode->i_sb->s_blocksize;

      if (!ext4_can_truncate(inode))
            return;

      if (ei->i_disksize && inode->i_size == 0 &&
          !test_opt(inode->i_sb, NO_AUTO_DA_ALLOC))
            ei->i_state |= EXT4_STATE_DA_ALLOC_CLOSE;

      if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
            ext4_ext_truncate(inode);
            return;
      }

      handle = start_transaction(inode);
      if (IS_ERR(handle))
            return;           /* AKPM: return what? */

      last_block = (inode->i_size + blocksize-1)
                              >> EXT4_BLOCK_SIZE_BITS(inode->i_sb);

      if (inode->i_size & (blocksize - 1))
            if (ext4_block_truncate_page(handle, mapping, inode->i_size))
                  goto out_stop;

      n = ext4_block_to_path(inode, last_block, offsets, NULL);
      if (n == 0)
            goto out_stop;    /* error */

      /*
       * OK.  This truncate is going to happen.  We add the inode to the
       * orphan list, so that if this truncate spans multiple transactions,
       * and we crash, we will resume the truncate when the filesystem
       * recovers.  It also marks the inode dirty, to catch the new size.
       *
       * Implication: the file must always be in a sane, consistent
       * truncatable state while each transaction commits.
       */
      if (ext4_orphan_add(handle, inode))
            goto out_stop;

      /*
       * From here we block out all ext4_get_block() callers who want to
       * modify the block allocation tree.
       */
      down_write(&ei->i_data_sem);

      ext4_discard_preallocations(inode);

      /*
       * The orphan list entry will now protect us from any crash which
       * occurs before the truncate completes, so it is now safe to propagate
       * the new, shorter inode size (held for now in i_size) into the
       * on-disk inode. We do this via i_disksize, which is the value which
       * ext4 *really* writes onto the disk inode.
       */
      ei->i_disksize = inode->i_size;

      if (n == 1) {           /* direct blocks */
            ext4_free_data(handle, inode, NULL, i_data+offsets[0],
                         i_data + EXT4_NDIR_BLOCKS);
            goto do_indirects;
      }

      partial = ext4_find_shared(inode, n, offsets, chain, &nr);
      /* Kill the top of shared branch (not detached) */
      if (nr) {
            if (partial == chain) {
                  /* Shared branch grows from the inode */
                  ext4_free_branches(handle, inode, NULL,
                                 &nr, &nr+1, (chain+n-1) - partial);
                  *partial->p = 0;
                  /*
                   * We mark the inode dirty prior to restart,
                   * and prior to stop.  No need for it here.
                   */
            } else {
                  /* Shared branch grows from an indirect block */
                  BUFFER_TRACE(partial->bh, "get_write_access");
                  ext4_free_branches(handle, inode, partial->bh,
                              partial->p,
                              partial->p+1, (chain+n-1) - partial);
            }
      }
      /* Clear the ends of indirect blocks on the shared branch */
      while (partial > chain) {
            ext4_free_branches(handle, inode, partial->bh, partial->p + 1,
                           (__le32*)partial->bh->b_data+addr_per_block,
                           (chain+n-1) - partial);
            BUFFER_TRACE(partial->bh, "call brelse");
            brelse(partial->bh);
            partial--;
      }
do_indirects:
      /* Kill the remaining (whole) subtrees */
      switch (offsets[0]) {
      default:
            nr = i_data[EXT4_IND_BLOCK];
            if (nr) {
                  ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 1);
                  i_data[EXT4_IND_BLOCK] = 0;
            }
      case EXT4_IND_BLOCK:
            nr = i_data[EXT4_DIND_BLOCK];
            if (nr) {
                  ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 2);
                  i_data[EXT4_DIND_BLOCK] = 0;
            }
      case EXT4_DIND_BLOCK:
            nr = i_data[EXT4_TIND_BLOCK];
            if (nr) {
                  ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 3);
                  i_data[EXT4_TIND_BLOCK] = 0;
            }
      case EXT4_TIND_BLOCK:
            ;
      }

      up_write(&ei->i_data_sem);
      inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
      ext4_mark_inode_dirty(handle, inode);

      /*
       * In a multi-transaction truncate, we only make the final transaction
       * synchronous
       */
      if (IS_SYNC(inode))
            ext4_handle_sync(handle);
out_stop:
      /*
       * If this was a simple ftruncate(), and the file will remain alive
       * then we need to clear up the orphan record which we created above.
       * However, if this was a real unlink then we were called by
       * ext4_delete_inode(), and we allow that function to clean up the
       * orphan info for us.
       */
      if (inode->i_nlink)
            ext4_orphan_del(handle, inode);

      ext4_journal_stop(handle);
}

/*
 * ext4_get_inode_loc returns with an extra refcount against the inode's
 * underlying buffer_head on success. If 'in_mem' is true, we have all
 * data in memory that is needed to recreate the on-disk version of this
 * inode.
 */
static int __ext4_get_inode_loc(struct inode *inode,
                        struct ext4_iloc *iloc, int in_mem)
{
      struct ext4_group_desc  *gdp;
      struct buffer_head      *bh;
      struct super_block      *sb = inode->i_sb;
      ext4_fsblk_t            block;
      int               inodes_per_block, inode_offset;

      iloc->bh = NULL;
      if (!ext4_valid_inum(sb, inode->i_ino))
            return -EIO;

      iloc->block_group = (inode->i_ino - 1) / EXT4_INODES_PER_GROUP(sb);
      gdp = ext4_get_group_desc(sb, iloc->block_group, NULL);
      if (!gdp)
            return -EIO;

      /*
       * Figure out the offset within the block group inode table
       */
      inodes_per_block = (EXT4_BLOCK_SIZE(sb) / EXT4_INODE_SIZE(sb));
      inode_offset = ((inode->i_ino - 1) %
                  EXT4_INODES_PER_GROUP(sb));
      block = ext4_inode_table(sb, gdp) + (inode_offset / inodes_per_block);
      iloc->offset = (inode_offset % inodes_per_block) * EXT4_INODE_SIZE(sb);

      bh = sb_getblk(sb, block);
      if (!bh) {
            ext4_error(sb, "ext4_get_inode_loc", "unable to read "
                     "inode block - inode=%lu, block=%llu",
                     inode->i_ino, block);
            return -EIO;
      }
      if (!buffer_uptodate(bh)) {
            lock_buffer(bh);

            /*
             * If the buffer has the write error flag, we have failed
             * to write out another inode in the same block.  In this
             * case, we don't have to read the block because we may
             * read the old inode data successfully.
             */
            if (buffer_write_io_error(bh) && !buffer_uptodate(bh))
                  set_buffer_uptodate(bh);

            if (buffer_uptodate(bh)) {
                  /* someone brought it uptodate while we waited */
                  unlock_buffer(bh);
                  goto has_buffer;
            }

            /*
             * If we have all information of the inode in memory and this
             * is the only valid inode in the block, we need not read the
             * block.
             */
            if (in_mem) {
                  struct buffer_head *bitmap_bh;
                  int i, start;

                  start = inode_offset & ~(inodes_per_block - 1);

                  /* Is the inode bitmap in cache? */
                  bitmap_bh = sb_getblk(sb, ext4_inode_bitmap(sb, gdp));
                  if (!bitmap_bh)
                        goto make_io;

                  /*
                   * If the inode bitmap isn't in cache then the
                   * optimisation may end up performing two reads instead
                   * of one, so skip it.
                   */
                  if (!buffer_uptodate(bitmap_bh)) {
                        brelse(bitmap_bh);
                        goto make_io;
                  }
                  for (i = start; i < start + inodes_per_block; i++) {
                        if (i == inode_offset)
                              continue;
                        if (ext4_test_bit(i, bitmap_bh->b_data))
                              break;
                  }
                  brelse(bitmap_bh);
                  if (i == start + inodes_per_block) {
                        /* all other inodes are free, so skip I/O */
                        memset(bh->b_data, 0, bh->b_size);
                        set_buffer_uptodate(bh);
                        unlock_buffer(bh);
                        goto has_buffer;
                  }
            }

make_io:
            /*
             * If we need to do any I/O, try to pre-readahead extra
             * blocks from the inode table.
             */
            if (EXT4_SB(sb)->s_inode_readahead_blks) {
                  ext4_fsblk_t b, end, table;
                  unsigned num;

                  table = ext4_inode_table(sb, gdp);
                  /* s_inode_readahead_blks is always a power of 2 */
                  b = block & ~(EXT4_SB(sb)->s_inode_readahead_blks-1);
                  if (table > b)
                        b = table;
                  end = b + EXT4_SB(sb)->s_inode_readahead_blks;
                  num = EXT4_INODES_PER_GROUP(sb);
                  if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
                               EXT4_FEATURE_RO_COMPAT_GDT_CSUM))
                        num -= ext4_itable_unused_count(sb, gdp);
                  table += num / inodes_per_block;
                  if (end > table)
                        end = table;
                  while (b <= end)
                        sb_breadahead(sb, b++);
            }

            /*
             * There are other valid inodes in the buffer, this inode
             * has in-inode xattrs, or we don't have this inode in memory.
             * Read the block from disk.
             */
            get_bh(bh);
            bh->b_end_io = end_buffer_read_sync;
            submit_bh(READ_META, bh);
            wait_on_buffer(bh);
            if (!buffer_uptodate(bh)) {
                  ext4_error(sb, __func__,
                           "unable to read inode block - inode=%lu, "
                           "block=%llu", inode->i_ino, block);
                  brelse(bh);
                  return -EIO;
            }
      }
has_buffer:
      iloc->bh = bh;
      return 0;
}

int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc)
{
      /* We have all inode data except xattrs in memory here. */
      return __ext4_get_inode_loc(inode, iloc,
            !(EXT4_I(inode)->i_state & EXT4_STATE_XATTR));
}

void ext4_set_inode_flags(struct inode *inode)
{
      unsigned int flags = EXT4_I(inode)->i_flags;

      inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
      if (flags & EXT4_SYNC_FL)
            inode->i_flags |= S_SYNC;
      if (flags & EXT4_APPEND_FL)
            inode->i_flags |= S_APPEND;
      if (flags & EXT4_IMMUTABLE_FL)
            inode->i_flags |= S_IMMUTABLE;
      if (flags & EXT4_NOATIME_FL)
            inode->i_flags |= S_NOATIME;
      if (flags & EXT4_DIRSYNC_FL)
            inode->i_flags |= S_DIRSYNC;
}

/* Propagate flags from i_flags to EXT4_I(inode)->i_flags */
void ext4_get_inode_flags(struct ext4_inode_info *ei)
{
      unsigned int flags = ei->vfs_inode.i_flags;

      ei->i_flags &= ~(EXT4_SYNC_FL|EXT4_APPEND_FL|
                  EXT4_IMMUTABLE_FL|EXT4_NOATIME_FL|EXT4_DIRSYNC_FL);
      if (flags & S_SYNC)
            ei->i_flags |= EXT4_SYNC_FL;
      if (flags & S_APPEND)
            ei->i_flags |= EXT4_APPEND_FL;
      if (flags & S_IMMUTABLE)
            ei->i_flags |= EXT4_IMMUTABLE_FL;
      if (flags & S_NOATIME)
            ei->i_flags |= EXT4_NOATIME_FL;
      if (flags & S_DIRSYNC)
            ei->i_flags |= EXT4_DIRSYNC_FL;
}

static blkcnt_t ext4_inode_blocks(struct ext4_inode *raw_inode,
                          struct ext4_inode_info *ei)
{
      blkcnt_t i_blocks ;
      struct inode *inode = &(ei->vfs_inode);
      struct super_block *sb = inode->i_sb;

      if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
                        EXT4_FEATURE_RO_COMPAT_HUGE_FILE)) {
            /* we are using combined 48 bit field */
            i_blocks = ((u64)le16_to_cpu(raw_inode->i_blocks_high)) << 32 |
                              le32_to_cpu(raw_inode->i_blocks_lo);
            if (ei->i_flags & EXT4_HUGE_FILE_FL) {
                  /* i_blocks represent file system block size */
                  return i_blocks  << (inode->i_blkbits - 9);
            } else {
                  return i_blocks;
            }
      } else {
            return le32_to_cpu(raw_inode->i_blocks_lo);
      }
}

struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
{
      struct ext4_iloc iloc;
      struct ext4_inode *raw_inode;
      struct ext4_inode_info *ei;
      struct buffer_head *bh;
      struct inode *inode;
      long ret;
      int block;

      inode = iget_locked(sb, ino);
      if (!inode)
            return ERR_PTR(-ENOMEM);
      if (!(inode->i_state & I_NEW))
            return inode;

      ei = EXT4_I(inode);

      ret = __ext4_get_inode_loc(inode, &iloc, 0);
      if (ret < 0)
            goto bad_inode;
      bh = iloc.bh;
      raw_inode = ext4_raw_inode(&iloc);
      inode->i_mode = le16_to_cpu(raw_inode->i_mode);
      inode->i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
      inode->i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
      if (!(test_opt(inode->i_sb, NO_UID32))) {
            inode->i_uid |= le16_to_cpu(raw_inode->i_uid_high) << 16;
            inode->i_gid |= le16_to_cpu(raw_inode->i_gid_high) << 16;
      }
      inode->i_nlink = le16_to_cpu(raw_inode->i_links_count);

      ei->i_state = 0;
      ei->i_dir_start_lookup = 0;
      ei->i_dtime = le32_to_cpu(raw_inode->i_dtime);
      /* We now have enough fields to check if the inode was active or not.
       * This is needed because nfsd might try to access dead inodes
       * the test is that same one that e2fsck uses
       * NeilBrown 1999oct15
       */
      if (inode->i_nlink == 0) {
            if (inode->i_mode == 0 ||
                !(EXT4_SB(inode->i_sb)->s_mount_state & EXT4_ORPHAN_FS)) {
                  /* this inode is deleted */
                  brelse(bh);
                  ret = -ESTALE;
                  goto bad_inode;
            }
            /* The only unlinked inodes we let through here have
             * valid i_mode and are being read by the orphan
             * recovery code: that's fine, we're about to complete
             * the process of deleting those. */
      }
      ei->i_flags = le32_to_cpu(raw_inode->i_flags);
      inode->i_blocks = ext4_inode_blocks(raw_inode, ei);
      ei->i_file_acl = le32_to_cpu(raw_inode->i_file_acl_lo);
      if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_64BIT))
            ei->i_file_acl |=
                  ((__u64)le16_to_cpu(raw_inode->i_file_acl_high)) << 32;
      inode->i_size = ext4_isize(raw_inode);
      ei->i_disksize = inode->i_size;
      inode->i_generation = le32_to_cpu(raw_inode->i_generation);
      ei->i_block_group = iloc.block_group;
      ei->i_last_alloc_group = ~0;
      /*
       * NOTE! The in-memory inode i_data array is in little-endian order
       * even on big-endian machines: we do NOT byteswap the block numbers!
       */
      for (block = 0; block < EXT4_N_BLOCKS; block++)
            ei->i_data[block] = raw_inode->i_block[block];
      INIT_LIST_HEAD(&ei->i_orphan);

      if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
            ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize);
            if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize >
                EXT4_INODE_SIZE(inode->i_sb)) {
                  brelse(bh);
                  ret = -EIO;
                  goto bad_inode;
            }
            if (ei->i_extra_isize == 0) {
                  /* The extra space is currently unused. Use it. */
                  ei->i_extra_isize = sizeof(struct ext4_inode) -
                                  EXT4_GOOD_OLD_INODE_SIZE;
            } else {
                  __le32 *magic = (void *)raw_inode +
                              EXT4_GOOD_OLD_INODE_SIZE +
                              ei->i_extra_isize;
                  if (*magic == cpu_to_le32(EXT4_XATTR_MAGIC))
                        ei->i_state |= EXT4_STATE_XATTR;
            }
      } else
            ei->i_extra_isize = 0;

      EXT4_INODE_GET_XTIME(i_ctime, inode, raw_inode);
      EXT4_INODE_GET_XTIME(i_mtime, inode, raw_inode);
      EXT4_INODE_GET_XTIME(i_atime, inode, raw_inode);
      EXT4_EINODE_GET_XTIME(i_crtime, ei, raw_inode);

      inode->i_version = le32_to_cpu(raw_inode->i_disk_version);
      if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
            if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
                  inode->i_version |=
                  (__u64)(le32_to_cpu(raw_inode->i_version_hi)) << 32;
      }

      ret = 0;
      if (ei->i_file_acl &&
          ((ei->i_file_acl <
            (le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block) +
             EXT4_SB(sb)->s_gdb_count)) ||
           (ei->i_file_acl >= ext4_blocks_count(EXT4_SB(sb)->s_es)))) {
            ext4_error(sb, __func__,
                     "bad extended attribute block %llu in inode #%lu",
                     ei->i_file_acl, inode->i_ino);
            ret = -EIO;
            goto bad_inode;
      } else if (ei->i_flags & EXT4_EXTENTS_FL) {
            if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
                (S_ISLNK(inode->i_mode) &&
                 !ext4_inode_is_fast_symlink(inode)))
                  /* Validate extent which is part of inode */
                  ret = ext4_ext_check_inode(inode);
      } else if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
               (S_ISLNK(inode->i_mode) &&
                !ext4_inode_is_fast_symlink(inode))) {
            /* Validate block references which are part of inode */
            ret = ext4_check_inode_blockref(inode);
      }
      if (ret) {
            brelse(bh);
            goto bad_inode;
      }

      if (S_ISREG(inode->i_mode)) {
            inode->i_op = &ext4_file_inode_operations;
            inode->i_fop = &ext4_file_operations;
            ext4_set_aops(inode);
      } else if (S_ISDIR(inode->i_mode)) {
            inode->i_op = &ext4_dir_inode_operations;
            inode->i_fop = &ext4_dir_operations;
      } else if (S_ISLNK(inode->i_mode)) {
            if (ext4_inode_is_fast_symlink(inode)) {
                  inode->i_op = &ext4_fast_symlink_inode_operations;
                  nd_terminate_link(ei->i_data, inode->i_size,
                        sizeof(ei->i_data) - 1);
            } else {
                  inode->i_op = &ext4_symlink_inode_operations;
                  ext4_set_aops(inode);
            }
      } else if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode) ||
            S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) {
            inode->i_op = &ext4_special_inode_operations;
            if (raw_inode->i_block[0])
                  init_special_inode(inode, inode->i_mode,
                     old_decode_dev(le32_to_cpu(raw_inode->i_block[0])));
            else
                  init_special_inode(inode, inode->i_mode,
                     new_decode_dev(le32_to_cpu(raw_inode->i_block[1])));
      } else {
            brelse(bh);
            ret = -EIO;
            ext4_error(inode->i_sb, __func__,
                     "bogus i_mode (%o) for inode=%lu",
                     inode->i_mode, inode->i_ino);
            goto bad_inode;
      }
      brelse(iloc.bh);
      ext4_set_inode_flags(inode);
      unlock_new_inode(inode);
      return inode;

bad_inode:
      iget_failed(inode);
      return ERR_PTR(ret);
}

static int ext4_inode_blocks_set(handle_t *handle,
                        struct ext4_inode *raw_inode,
                        struct ext4_inode_info *ei)
{
      struct inode *inode = &(ei->vfs_inode);
      u64 i_blocks = inode->i_blocks;
      struct super_block *sb = inode->i_sb;

      if (i_blocks <= ~0U) {
            /*
             * i_blocks can be represnted in a 32 bit variable
             * as multiple of 512 bytes
             */
            raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
            raw_inode->i_blocks_high = 0;
            ei->i_flags &= ~EXT4_HUGE_FILE_FL;
            return 0;
      }
      if (!EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_HUGE_FILE))
            return -EFBIG;

      if (i_blocks <= 0xffffffffffffULL) {
            /*
             * i_blocks can be represented in a 48 bit variable
             * as multiple of 512 bytes
             */
            raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
            raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
            ei->i_flags &= ~EXT4_HUGE_FILE_FL;
      } else {
            ei->i_flags |= EXT4_HUGE_FILE_FL;
            /* i_block is stored in file system block size */
            i_blocks = i_blocks >> (inode->i_blkbits - 9);
            raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
            raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
      }
      return 0;
}

/*
 * Post the struct inode info into an on-disk inode location in the
 * buffer-cache.  This gobbles the caller's reference to the
 * buffer_head in the inode location struct.
 *
 * The caller must have write access to iloc->bh.
 */
static int ext4_do_update_inode(handle_t *handle,
                        struct inode *inode,
                        struct ext4_iloc *iloc)
{
      struct ext4_inode *raw_inode = ext4_raw_inode(iloc);
      struct ext4_inode_info *ei = EXT4_I(inode);
      struct buffer_head *bh = iloc->bh;
      int err = 0, rc, block;

      /* For fields not not tracking in the in-memory inode,
       * initialise them to zero for new inodes. */
      if (ei->i_state & EXT4_STATE_NEW)
            memset(raw_inode, 0, EXT4_SB(inode->i_sb)->s_inode_size);

      ext4_get_inode_flags(ei);
      raw_inode->i_mode = cpu_to_le16(inode->i_mode);
      if (!(test_opt(inode->i_sb, NO_UID32))) {
            raw_inode->i_uid_low = cpu_to_le16(low_16_bits(inode->i_uid));
            raw_inode->i_gid_low = cpu_to_le16(low_16_bits(inode->i_gid));
/*
 * Fix up interoperability with old kernels. Otherwise, old inodes get
 * re-used with the upper 16 bits of the uid/gid intact
 */
            if (!ei->i_dtime) {
                  raw_inode->i_uid_high =
                        cpu_to_le16(high_16_bits(inode->i_uid));
                  raw_inode->i_gid_high =
                        cpu_to_le16(high_16_bits(inode->i_gid));
            } else {
                  raw_inode->i_uid_high = 0;
                  raw_inode->i_gid_high = 0;
            }
      } else {
            raw_inode->i_uid_low =
                  cpu_to_le16(fs_high2lowuid(inode->i_uid));
            raw_inode->i_gid_low =
                  cpu_to_le16(fs_high2lowgid(inode->i_gid));
            raw_inode->i_uid_high = 0;
            raw_inode->i_gid_high = 0;
      }
      raw_inode->i_links_count = cpu_to_le16(inode->i_nlink);

      EXT4_INODE_SET_XTIME(i_ctime, inode, raw_inode);
      EXT4_INODE_SET_XTIME(i_mtime, inode, raw_inode);
      EXT4_INODE_SET_XTIME(i_atime, inode, raw_inode);
      EXT4_EINODE_SET_XTIME(i_crtime, ei, raw_inode);

      if (ext4_inode_blocks_set(handle, raw_inode, ei))
            goto out_brelse;
      raw_inode->i_dtime = cpu_to_le32(ei->i_dtime);
      /* clear the migrate flag in the raw_inode */
      raw_inode->i_flags = cpu_to_le32(ei->i_flags & ~EXT4_EXT_MIGRATE);
      if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
          cpu_to_le32(EXT4_OS_HURD))
            raw_inode->i_file_acl_high =
                  cpu_to_le16(ei->i_file_acl >> 32);
      raw_inode->i_file_acl_lo = cpu_to_le32(ei->i_file_acl);
      ext4_isize_set(raw_inode, ei->i_disksize);
      if (ei->i_disksize > 0x7fffffffULL) {
            struct super_block *sb = inode->i_sb;
            if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
                        EXT4_FEATURE_RO_COMPAT_LARGE_FILE) ||
                        EXT4_SB(sb)->s_es->s_rev_level ==
                        cpu_to_le32(EXT4_GOOD_OLD_REV)) {
                  /* If this is the first large file
                   * created, add a flag to the superblock.
                   */
                  err = ext4_journal_get_write_access(handle,
                              EXT4_SB(sb)->s_sbh);
                  if (err)
                        goto out_brelse;
                  ext4_update_dynamic_rev(sb);
                  EXT4_SET_RO_COMPAT_FEATURE(sb,
                              EXT4_FEATURE_RO_COMPAT_LARGE_FILE);
                  sb->s_dirt = 1;
                  ext4_handle_sync(handle);
                  err = ext4_handle_dirty_metadata(handle, inode,
                              EXT4_SB(sb)->s_sbh);
            }
      }
      raw_inode->i_generation = cpu_to_le32(inode->i_generation);
      if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode)) {
            if (old_valid_dev(inode->i_rdev)) {
                  raw_inode->i_block[0] =
                        cpu_to_le32(old_encode_dev(inode->i_rdev));
                  raw_inode->i_block[1] = 0;
            } else {
                  raw_inode->i_block[0] = 0;
                  raw_inode->i_block[1] =
                        cpu_to_le32(new_encode_dev(inode->i_rdev));
                  raw_inode->i_block[2] = 0;
            }
      } else
            for (block = 0; block < EXT4_N_BLOCKS; block++)
                  raw_inode->i_block[block] = ei->i_data[block];

      raw_inode->i_disk_version = cpu_to_le32(inode->i_version);
      if (ei->i_extra_isize) {
            if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
                  raw_inode->i_version_hi =
                  cpu_to_le32(inode->i_version >> 32);
            raw_inode->i_extra_isize = cpu_to_le16(ei->i_extra_isize);
      }

      BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
      rc = ext4_handle_dirty_metadata(handle, inode, bh);
      if (!err)
            err = rc;
      ei->i_state &= ~EXT4_STATE_NEW;

out_brelse:
      brelse(bh);
      ext4_std_error(inode->i_sb, err);
      return err;
}

/*
 * ext4_write_inode()
 *
 * We are called from a few places:
 *
 * - Within generic_file_write() for O_SYNC files.
 *   Here, there will be no transaction running. We wait for any running
 *   trasnaction to commit.
 *
 * - Within sys_sync(), kupdate and such.
 *   We wait on commit, if tol to.
 *
 * - Within prune_icache() (PF_MEMALLOC == true)
 *   Here we simply return.  We can't afford to block kswapd on the
 *   journal commit.
 *
 * In all cases it is actually safe for us to return without doing anything,
 * because the inode has been copied into a raw inode buffer in
 * ext4_mark_inode_dirty().  This is a correctness thing for O_SYNC and for
 * knfsd.
 *
 * Note that we are absolutely dependent upon all inode dirtiers doing the
 * right thing: they *must* call mark_inode_dirty() after dirtying info in
 * which we are interested.
 *
 * It would be a bug for them to not do this.  The code:
 *
 *    mark_inode_dirty(inode)
 *    stuff();
 *    inode->i_size = expr;
 *
 * is in error because a kswapd-driven write_inode() could occur while
 * `stuff()' is running, and the new i_size will be lost.  Plus the inode
 * will no longer be on the superblock's dirty inode list.
 */
int ext4_write_inode(struct inode *inode, int wait)
{
      if (current->flags & PF_MEMALLOC)
            return 0;

      if (ext4_journal_current_handle()) {
            jbd_debug(1, "called recursively, non-PF_MEMALLOC!\n");
            dump_stack();
            return -EIO;
      }

      if (!wait)
            return 0;

      return ext4_force_commit(inode->i_sb);
}

/*
 * ext4_setattr()
 *
 * Called from notify_change.
 *
 * We want to trap VFS attempts to truncate the file as soon as
 * possible.  In particular, we want to make sure that when the VFS
 * shrinks i_size, we put the inode on the orphan list and modify
 * i_disksize immediately, so that during the subsequent flushing of
 * dirty pages and freeing of disk blocks, we can guarantee that any
 * commit will leave the blocks being flushed in an unused state on
 * disk.  (On recovery, the inode will get truncated and the blocks will
 * be freed, so we have a strong guarantee that no future commit will
 * leave these blocks visible to the user.)
 *
 * Another thing we have to assure is that if we are in ordered mode
 * and inode is still attached to the committing transaction, we must
 * we start writeout of all the dirty pages which are being truncated.
 * This way we are sure that all the data written in the previous
 * transaction are already on disk (truncate waits for pages under
 * writeback).
 *
 * Called with inode->i_mutex down.
 */
int ext4_setattr(struct dentry *dentry, struct iattr *attr)
{
      struct inode *inode = dentry->d_inode;
      int error, rc = 0;
      const unsigned int ia_valid = attr->ia_valid;

      error = inode_change_ok(inode, attr);
      if (error)
            return error;

      if ((ia_valid & ATTR_UID && attr->ia_uid != inode->i_uid) ||
            (ia_valid & ATTR_GID && attr->ia_gid != inode->i_gid)) {
            handle_t *handle;

            /* (user+group)*(old+new) structure, inode write (sb,
             * inode block, ? - but truncate inode update has it) */
            handle = ext4_journal_start(inode, 2*(EXT4_QUOTA_INIT_BLOCKS(inode->i_sb)+
                              EXT4_QUOTA_DEL_BLOCKS(inode->i_sb))+3);
            if (IS_ERR(handle)) {
                  error = PTR_ERR(handle);
                  goto err_out;
            }
            error = vfs_dq_transfer(inode, attr) ? -EDQUOT : 0;
            if (error) {
                  ext4_journal_stop(handle);
                  return error;
            }
            /* Update corresponding info in inode so that everything is in
             * one transaction */
            if (attr->ia_valid & ATTR_UID)
                  inode->i_uid = attr->ia_uid;
            if (attr->ia_valid & ATTR_GID)
                  inode->i_gid = attr->ia_gid;
            error = ext4_mark_inode_dirty(handle, inode);
            ext4_journal_stop(handle);
      }

      if (attr->ia_valid & ATTR_SIZE) {
            if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL)) {
                  struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);

                  if (attr->ia_size > sbi->s_bitmap_maxbytes) {
                        error = -EFBIG;
                        goto err_out;
                  }
            }
      }

      if (S_ISREG(inode->i_mode) &&
          attr->ia_valid & ATTR_SIZE && attr->ia_size < inode->i_size) {
            handle_t *handle;

            handle = ext4_journal_start(inode, 3);
            if (IS_ERR(handle)) {
                  error = PTR_ERR(handle);
                  goto err_out;
            }

            error = ext4_orphan_add(handle, inode);
            EXT4_I(inode)->i_disksize = attr->ia_size;
            rc = ext4_mark_inode_dirty(handle, inode);
            if (!error)
                  error = rc;
            ext4_journal_stop(handle);

            if (ext4_should_order_data(inode)) {
                  error = ext4_begin_ordered_truncate(inode,
                                              attr->ia_size);
                  if (error) {
                        /* Do as much error cleanup as possible */
                        handle = ext4_journal_start(inode, 3);
                        if (IS_ERR(handle)) {
                              ext4_orphan_del(NULL, inode);
                              goto err_out;
                        }
                        ext4_orphan_del(handle, inode);
                        ext4_journal_stop(handle);
                        goto err_out;
                  }
            }
      }

      rc = inode_setattr(inode, attr);

      /* If inode_setattr's call to ext4_truncate failed to get a
       * transaction handle at all, we need to clean up the in-core
       * orphan list manually. */
      if (inode->i_nlink)
            ext4_orphan_del(NULL, inode);

      if (!rc && (ia_valid & ATTR_MODE))
            rc = ext4_acl_chmod(inode);

err_out:
      ext4_std_error(inode->i_sb, error);
      if (!error)
            error = rc;
      return error;
}

int ext4_getattr(struct vfsmount *mnt, struct dentry *dentry,
             struct kstat *stat)
{
      struct inode *inode;
      unsigned long delalloc_blocks;

      inode = dentry->d_inode;
      generic_fillattr(inode, stat);

      /*
       * We can't update i_blocks if the block allocation is delayed
       * otherwise in the case of system crash before the real block
       * allocation is done, we will have i_blocks inconsistent with
       * on-disk file blocks.
       * We always keep i_blocks updated together with real
       * allocation. But to not confuse with user, stat
       * will return the blocks that include the delayed allocation
       * blocks for this file.
       */
      spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
      delalloc_blocks = EXT4_I(inode)->i_reserved_data_blocks;
      spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

      stat->blocks += (delalloc_blocks << inode->i_sb->s_blocksize_bits)>>9;
      return 0;
}

static int ext4_indirect_trans_blocks(struct inode *inode, int nrblocks,
                              int chunk)
{
      int indirects;

      /* if nrblocks are contiguous */
      if (chunk) {
            /*
             * With N contiguous data blocks, it need at most
             * N/EXT4_ADDR_PER_BLOCK(inode->i_sb) indirect blocks
             * 2 dindirect blocks
             * 1 tindirect block
             */
            indirects = nrblocks / EXT4_ADDR_PER_BLOCK(inode->i_sb);
            return indirects + 3;
      }
      /*
       * if nrblocks are not contiguous, worse case, each block touch
       * a indirect block, and each indirect block touch a double indirect
       * block, plus a triple indirect block
       */
      indirects = nrblocks * 2 + 1;
      return indirects;
}

static int ext4_index_trans_blocks(struct inode *inode, int nrblocks, int chunk)
{
      if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
            return ext4_indirect_trans_blocks(inode, nrblocks, chunk);
      return ext4_ext_index_trans_blocks(inode, nrblocks, chunk);
}

/*
 * Account for index blocks, block groups bitmaps and block group
 * descriptor blocks if modify datablocks and index blocks
 * worse case, the indexs blocks spread over different block groups
 *
 * If datablocks are discontiguous, they are possible to spread over
 * different block groups too. If they are contiugous, with flexbg,
 * they could still across block group boundary.
 *
 * Also account for superblock, inode, quota and xattr blocks
 */
int ext4_meta_trans_blocks(struct inode *inode, int nrblocks, int chunk)
{
      ext4_group_t groups, ngroups = ext4_get_groups_count(inode->i_sb);
      int gdpblocks;
      int idxblocks;
      int ret = 0;

      /*
       * How many index blocks need to touch to modify nrblocks?
       * The "Chunk" flag indicating whether the nrblocks is
       * physically contiguous on disk
       *
       * For Direct IO and fallocate, they calls get_block to allocate
       * one single extent at a time, so they could set the "Chunk" flag
       */
      idxblocks = ext4_index_trans_blocks(inode, nrblocks, chunk);

      ret = idxblocks;

      /*
       * Now let's see how many group bitmaps and group descriptors need
       * to account
       */
      groups = idxblocks;
      if (chunk)
            groups += 1;
      else
            groups += nrblocks;

      gdpblocks = groups;
      if (groups > ngroups)
            groups = ngroups;
      if (groups > EXT4_SB(inode->i_sb)->s_gdb_count)
            gdpblocks = EXT4_SB(inode->i_sb)->s_gdb_count;

      /* bitmaps and block group descriptor blocks */
      ret += groups + gdpblocks;

      /* Blocks for super block, inode, quota and xattr blocks */
      ret += EXT4_META_TRANS_BLOCKS(inode->i_sb);

      return ret;
}

/*
 * Calulate the total number of credits to reserve to fit
 * the modification of a single pages into a single transaction,
 * which may include multiple chunks of block allocations.
 *
 * This could be called via ext4_write_begin()
 *
 * We need to consider the worse case, when
 * one new block per extent.
 */
int ext4_writepage_trans_blocks(struct inode *inode)
{
      int bpp = ext4_journal_blocks_per_page(inode);
      int ret;

      ret = ext4_meta_trans_blocks(inode, bpp, 0);

      /* Account for data blocks for journalled mode */
      if (ext4_should_journal_data(inode))
            ret += bpp;
      return ret;
}

/*
 * Calculate the journal credits for a chunk of data modification.
 *
 * This is called from DIO, fallocate or whoever calling
 * ext4_get_blocks() to map/allocate a chunk of contigous disk blocks.
 *
 * journal buffers for data blocks are not included here, as DIO
 * and fallocate do no need to journal data buffers.
 */
int ext4_chunk_trans_blocks(struct inode *inode, int nrblocks)
{
      return ext4_meta_trans_blocks(inode, nrblocks, 1);
}

/*
 * The caller must have previously called ext4_reserve_inode_write().
 * Give this, we know that the caller already has write access to iloc->bh.
 */
int ext4_mark_iloc_dirty(handle_t *handle,
                   struct inode *inode, struct ext4_iloc *iloc)
{
      int err = 0;

      if (test_opt(inode->i_sb, I_VERSION))
            inode_inc_iversion(inode);

      /* the do_update_inode consumes one bh->b_count */
      get_bh(iloc->bh);

      /* ext4_do_update_inode() does jbd2_journal_dirty_metadata */
      err = ext4_do_update_inode(handle, inode, iloc);
      put_bh(iloc->bh);
      return err;
}

/*
 * On success, We end up with an outstanding reference count against
 * iloc->bh.  This _must_ be cleaned up later.
 */

int
ext4_reserve_inode_write(handle_t *handle, struct inode *inode,
                   struct ext4_iloc *iloc)
{
      int err;

      err = ext4_get_inode_loc(inode, iloc);
      if (!err) {
            BUFFER_TRACE(iloc->bh, "get_write_access");
            err = ext4_journal_get_write_access(handle, iloc->bh);
            if (err) {
                  brelse(iloc->bh);
                  iloc->bh = NULL;
            }
      }
      ext4_std_error(inode->i_sb, err);
      return err;
}

/*
 * Expand an inode by new_extra_isize bytes.
 * Returns 0 on success or negative error number on failure.
 */
static int ext4_expand_extra_isize(struct inode *inode,
                           unsigned int new_extra_isize,
                           struct ext4_iloc iloc,
                           handle_t *handle)
{
      struct ext4_inode *raw_inode;
      struct ext4_xattr_ibody_header *header;
      struct ext4_xattr_entry *entry;

      if (EXT4_I(inode)->i_extra_isize >= new_extra_isize)
            return 0;

      raw_inode = ext4_raw_inode(&iloc);

      header = IHDR(inode, raw_inode);
      entry = IFIRST(header);

      /* No extended attributes present */
      if (!(EXT4_I(inode)->i_state & EXT4_STATE_XATTR) ||
            header->h_magic != cpu_to_le32(EXT4_XATTR_MAGIC)) {
            memset((void *)raw_inode + EXT4_GOOD_OLD_INODE_SIZE, 0,
                  new_extra_isize);
            EXT4_I(inode)->i_extra_isize = new_extra_isize;
            return 0;
      }

      /* try to expand with EAs present */
      return ext4_expand_extra_isize_ea(inode, new_extra_isize,
                                raw_inode, handle);
}

/*
 * What we do here is to mark the in-core inode as clean with respect to inode
 * dirtiness (it may still be data-dirty).
 * This means that the in-core inode may be reaped by prune_icache
 * without having to perform any I/O.  This is a very good thing,
 * because *any* task may call prune_icache - even ones which
 * have a transaction open against a different journal.
 *
 * Is this cheating?  Not really.  Sure, we haven't written the
 * inode out, but prune_icache isn't a user-visible syncing function.
 * Whenever the user wants stuff synced (sys_sync, sys_msync, sys_fsync)
 * we start and wait on commits.
 *
 * Is this efficient/effective?  Well, we're being nice to the system
 * by cleaning up our inodes proactively so they can be reaped
 * without I/O.  But we are potentially leaving up to five seconds'
 * worth of inodes floating about which prune_icache wants us to
 * write out.  One way to fix that would be to get prune_icache()
 * to do a write_super() to free up some memory.  It has the desired
 * effect.
 */
int ext4_mark_inode_dirty(handle_t *handle, struct inode *inode)
{
      struct ext4_iloc iloc;
      struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
      static unsigned int mnt_count;
      int err, ret;

      might_sleep();
      err = ext4_reserve_inode_write(handle, inode, &iloc);
      if (ext4_handle_valid(handle) &&
          EXT4_I(inode)->i_extra_isize < sbi->s_want_extra_isize &&
          !(EXT4_I(inode)->i_state & EXT4_STATE_NO_EXPAND)) {
            /*
             * We need extra buffer credits since we may write into EA block
             * with this same handle. If journal_extend fails, then it will
             * only result in a minor loss of functionality for that inode.
             * If this is felt to be critical, then e2fsck should be run to
             * force a large enough s_min_extra_isize.
             */
            if ((jbd2_journal_extend(handle,
                       EXT4_DATA_TRANS_BLOCKS(inode->i_sb))) == 0) {
                  ret = ext4_expand_extra_isize(inode,
                                          sbi->s_want_extra_isize,
                                          iloc, handle);
                  if (ret) {
                        EXT4_I(inode)->i_state |= EXT4_STATE_NO_EXPAND;
                        if (mnt_count !=
                              le16_to_cpu(sbi->s_es->s_mnt_count)) {
                              ext4_warning(inode->i_sb, __func__,
                              "Unable to expand inode %lu. Delete"
                              " some EAs or run e2fsck.",
                              inode->i_ino);
                              mnt_count =
                                le16_to_cpu(sbi->s_es->s_mnt_count);
                        }
                  }
            }
      }
      if (!err)
            err = ext4_mark_iloc_dirty(handle, inode, &iloc);
      return err;
}

/*
 * ext4_dirty_inode() is called from __mark_inode_dirty()
 *
 * We're really interested in the case where a file is being extended.
 * i_size has been changed by generic_commit_write() and we thus need
 * to include the updated inode in the current transaction.
 *
 * Also, vfs_dq_alloc_block() will always dirty the inode when blocks
 * are allocated to the file.
 *
 * If the inode is marked synchronous, we don't honour that here - doing
 * so would cause a commit on atime updates, which we don't bother doing.
 * We handle synchronous inodes at the highest possible level.
 */
void ext4_dirty_inode(struct inode *inode)
{
      handle_t *current_handle = ext4_journal_current_handle();
      handle_t *handle;

      if (!ext4_handle_valid(current_handle)) {
            ext4_mark_inode_dirty(current_handle, inode);
            return;
      }

      handle = ext4_journal_start(inode, 2);
      if (IS_ERR(handle))
            goto out;
      if (current_handle &&
            current_handle->h_transaction != handle->h_transaction) {
            /* This task has a transaction open against a different fs */
            printk(KERN_EMERG "%s: transactions do not match!\n",
                   __func__);
      } else {
            jbd_debug(5, "marking dirty.  outer handle=%p\n",
                        current_handle);
            ext4_mark_inode_dirty(handle, inode);
      }
      ext4_journal_stop(handle);
out:
      return;
}

#if 0
/*
 * Bind an inode's backing buffer_head into this transaction, to prevent
 * it from being flushed to disk early.  Unlike
 * ext4_reserve_inode_write, this leaves behind no bh reference and
 * returns no iloc structure, so the caller needs to repeat the iloc
 * lookup to mark the inode dirty later.
 */
static int ext4_pin_inode(handle_t *handle, struct inode *inode)
{
      struct ext4_iloc iloc;

      int err = 0;
      if (handle) {
            err = ext4_get_inode_loc(inode, &iloc);
            if (!err) {
                  BUFFER_TRACE(iloc.bh, "get_write_access");
                  err = jbd2_journal_get_write_access(handle, iloc.bh);
                  if (!err)
                        err = ext4_handle_dirty_metadata(handle,
                                                 inode,
                                                 iloc.bh);
                  brelse(iloc.bh);
            }
      }
      ext4_std_error(inode->i_sb, err);
      return err;
}
#endif

int ext4_change_inode_journal_flag(struct inode *inode, int val)
{
      journal_t *journal;
      handle_t *handle;
      int err;

      /*
       * We have to be very careful here: changing a data block's
       * journaling status dynamically is dangerous.  If we write a
       * data block to the journal, change the status and then delete
       * that block, we risk forgetting to revoke the old log record
       * from the journal and so a subsequent replay can corrupt data.
       * So, first we make sure that the journal is empty and that
       * nobody is changing anything.
       */

      journal = EXT4_JOURNAL(inode);
      if (!journal)
            return 0;
      if (is_journal_aborted(journal))
            return -EROFS;

      jbd2_journal_lock_updates(journal);
      jbd2_journal_flush(journal);

      /*
       * OK, there are no updates running now, and all cached data is
       * synced to disk.  We are now in a completely consistent state
       * which doesn't have anything in the journal, and we know that
       * no filesystem updates are running, so it is safe to modify
       * the inode's in-core data-journaling state flag now.
       */

      if (val)
            EXT4_I(inode)->i_flags |= EXT4_JOURNAL_DATA_FL;
      else
            EXT4_I(inode)->i_flags &= ~EXT4_JOURNAL_DATA_FL;
      ext4_set_aops(inode);

      jbd2_journal_unlock_updates(journal);

      /* Finally we can mark the inode as dirty. */

      handle = ext4_journal_start(inode, 1);
      if (IS_ERR(handle))
            return PTR_ERR(handle);

      err = ext4_mark_inode_dirty(handle, inode);
      ext4_handle_sync(handle);
      ext4_journal_stop(handle);
      ext4_std_error(inode->i_sb, err);

      return err;
}

static int ext4_bh_unmapped(handle_t *handle, struct buffer_head *bh)
{
      return !buffer_mapped(bh);
}

int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
{
      struct page *page = vmf->page;
      loff_t size;
      unsigned long len;
      int ret = -EINVAL;
      void *fsdata;
      struct file *file = vma->vm_file;
      struct inode *inode = file->f_path.dentry->d_inode;
      struct address_space *mapping = inode->i_mapping;

      /*
       * Get i_alloc_sem to stop truncates messing with the inode. We cannot
       * get i_mutex because we are already holding mmap_sem.
       */
      down_read(&inode->i_alloc_sem);
      size = i_size_read(inode);
      if (page->mapping != mapping || size <= page_offset(page)
          || !PageUptodate(page)) {
            /* page got truncated from under us? */
            goto out_unlock;
      }
      ret = 0;
      if (PageMappedToDisk(page))
            goto out_unlock;

      if (page->index == size >> PAGE_CACHE_SHIFT)
            len = size & ~PAGE_CACHE_MASK;
      else
            len = PAGE_CACHE_SIZE;

      if (page_has_buffers(page)) {
            /* return if we have all the buffers mapped */
            if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
                               ext4_bh_unmapped))
                  goto out_unlock;
      }
      /*
       * OK, we need to fill the hole... Do write_begin write_end
       * to do block allocation/reservation.We are not holding
       * inode.i__mutex here. That allow * parallel write_begin,
       * write_end call. lock_page prevent this from happening
       * on the same page though
       */
      ret = mapping->a_ops->write_begin(file, mapping, page_offset(page),
                  len, AOP_FLAG_UNINTERRUPTIBLE, &page, &fsdata);
      if (ret < 0)
            goto out_unlock;
      ret = mapping->a_ops->write_end(file, mapping, page_offset(page),
                  len, len, page, fsdata);
      if (ret < 0)
            goto out_unlock;
      ret = 0;
out_unlock:
      if (ret)
            ret = VM_FAULT_SIGBUS;
      up_read(&inode->i_alloc_sem);
      return ret;
}

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