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ring_buffer.c

/*
 * Generic ring buffer
 *
 * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
 */
#include <linux/ring_buffer.h>
#include <linux/trace_clock.h>
#include <linux/ftrace_irq.h>
#include <linux/spinlock.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/hardirq.h>
#include <linux/kmemcheck.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/mutex.h>
#include <linux/init.h>
#include <linux/hash.h>
#include <linux/list.h>
#include <linux/cpu.h>
#include <linux/fs.h>

#include "trace.h"

/*
 * The ring buffer header is special. We must manually up keep it.
 */
int ring_buffer_print_entry_header(struct trace_seq *s)
{
      int ret;

      ret = trace_seq_printf(s, "# compressed entry header\n");
      ret = trace_seq_printf(s, "\ttype_len    :    5 bits\n");
      ret = trace_seq_printf(s, "\ttime_delta  :   27 bits\n");
      ret = trace_seq_printf(s, "\tarray       :   32 bits\n");
      ret = trace_seq_printf(s, "\n");
      ret = trace_seq_printf(s, "\tpadding     : type == %d\n",
                         RINGBUF_TYPE_PADDING);
      ret = trace_seq_printf(s, "\ttime_extend : type == %d\n",
                         RINGBUF_TYPE_TIME_EXTEND);
      ret = trace_seq_printf(s, "\tdata max type_len  == %d\n",
                         RINGBUF_TYPE_DATA_TYPE_LEN_MAX);

      return ret;
}

/*
 * The ring buffer is made up of a list of pages. A separate list of pages is
 * allocated for each CPU. A writer may only write to a buffer that is
 * associated with the CPU it is currently executing on.  A reader may read
 * from any per cpu buffer.
 *
 * The reader is special. For each per cpu buffer, the reader has its own
 * reader page. When a reader has read the entire reader page, this reader
 * page is swapped with another page in the ring buffer.
 *
 * Now, as long as the writer is off the reader page, the reader can do what
 * ever it wants with that page. The writer will never write to that page
 * again (as long as it is out of the ring buffer).
 *
 * Here's some silly ASCII art.
 *
 *   +------+
 *   |reader|          RING BUFFER
 *   |page  |
 *   +------+        +---+   +---+   +---+
 *                   |   |-->|   |-->|   |
 *                   +---+   +---+   +---+
 *                     ^               |
 *                     |               |
 *                     +---------------+
 *
 *
 *   +------+
 *   |reader|          RING BUFFER
 *   |page  |------------------v
 *   +------+        +---+   +---+   +---+
 *                   |   |-->|   |-->|   |
 *                   +---+   +---+   +---+
 *                     ^               |
 *                     |               |
 *                     +---------------+
 *
 *
 *   +------+
 *   |reader|          RING BUFFER
 *   |page  |------------------v
 *   +------+        +---+   +---+   +---+
 *      ^            |   |-->|   |-->|   |
 *      |            +---+   +---+   +---+
 *      |                              |
 *      |                              |
 *      +------------------------------+
 *
 *
 *   +------+
 *   |buffer|          RING BUFFER
 *   |page  |------------------v
 *   +------+        +---+   +---+   +---+
 *      ^            |   |   |   |-->|   |
 *      |   New      +---+   +---+   +---+
 *      |  Reader------^               |
 *      |   page                       |
 *      +------------------------------+
 *
 *
 * After we make this swap, the reader can hand this page off to the splice
 * code and be done with it. It can even allocate a new page if it needs to
 * and swap that into the ring buffer.
 *
 * We will be using cmpxchg soon to make all this lockless.
 *
 */

/*
 * A fast way to enable or disable all ring buffers is to
 * call tracing_on or tracing_off. Turning off the ring buffers
 * prevents all ring buffers from being recorded to.
 * Turning this switch on, makes it OK to write to the
 * ring buffer, if the ring buffer is enabled itself.
 *
 * There's three layers that must be on in order to write
 * to the ring buffer.
 *
 * 1) This global flag must be set.
 * 2) The ring buffer must be enabled for recording.
 * 3) The per cpu buffer must be enabled for recording.
 *
 * In case of an anomaly, this global flag has a bit set that
 * will permantly disable all ring buffers.
 */

/*
 * Global flag to disable all recording to ring buffers
 *  This has two bits: ON, DISABLED
 *
 *  ON   DISABLED
 * ---- ----------
 *   0      0        : ring buffers are off
 *   1      0        : ring buffers are on
 *   X      1        : ring buffers are permanently disabled
 */

enum {
      RB_BUFFERS_ON_BIT = 0,
      RB_BUFFERS_DISABLED_BIT = 1,
};

enum {
      RB_BUFFERS_ON           = 1 << RB_BUFFERS_ON_BIT,
      RB_BUFFERS_DISABLED     = 1 << RB_BUFFERS_DISABLED_BIT,
};

static unsigned long ring_buffer_flags __read_mostly = RB_BUFFERS_ON;

#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)

/**
 * tracing_on - enable all tracing buffers
 *
 * This function enables all tracing buffers that may have been
 * disabled with tracing_off.
 */
void tracing_on(void)
{
      set_bit(RB_BUFFERS_ON_BIT, &ring_buffer_flags);
}
EXPORT_SYMBOL_GPL(tracing_on);

/**
 * tracing_off - turn off all tracing buffers
 *
 * This function stops all tracing buffers from recording data.
 * It does not disable any overhead the tracers themselves may
 * be causing. This function simply causes all recording to
 * the ring buffers to fail.
 */
void tracing_off(void)
{
      clear_bit(RB_BUFFERS_ON_BIT, &ring_buffer_flags);
}
EXPORT_SYMBOL_GPL(tracing_off);

/**
 * tracing_off_permanent - permanently disable ring buffers
 *
 * This function, once called, will disable all ring buffers
 * permanently.
 */
void tracing_off_permanent(void)
{
      set_bit(RB_BUFFERS_DISABLED_BIT, &ring_buffer_flags);
}

/**
 * tracing_is_on - show state of ring buffers enabled
 */
int tracing_is_on(void)
{
      return ring_buffer_flags == RB_BUFFERS_ON;
}
EXPORT_SYMBOL_GPL(tracing_is_on);

#include "trace.h"

#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
#define RB_ALIGNMENT          4U
#define RB_MAX_SMALL_DATA     (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
#define RB_EVNT_MIN_SIZE      8U    /* two 32bit words */

/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX

enum {
      RB_LEN_TIME_EXTEND = 8,
      RB_LEN_TIME_STAMP = 16,
};

static inline int rb_null_event(struct ring_buffer_event *event)
{
      return event->type_len == RINGBUF_TYPE_PADDING
                  && event->time_delta == 0;
}

static inline int rb_discarded_event(struct ring_buffer_event *event)
{
      return event->type_len == RINGBUF_TYPE_PADDING && event->time_delta;
}

static void rb_event_set_padding(struct ring_buffer_event *event)
{
      event->type_len = RINGBUF_TYPE_PADDING;
      event->time_delta = 0;
}

static unsigned
rb_event_data_length(struct ring_buffer_event *event)
{
      unsigned length;

      if (event->type_len)
            length = event->type_len * RB_ALIGNMENT;
      else
            length = event->array[0];
      return length + RB_EVNT_HDR_SIZE;
}

/* inline for ring buffer fast paths */
static unsigned
rb_event_length(struct ring_buffer_event *event)
{
      switch (event->type_len) {
      case RINGBUF_TYPE_PADDING:
            if (rb_null_event(event))
                  /* undefined */
                  return -1;
            return  event->array[0] + RB_EVNT_HDR_SIZE;

      case RINGBUF_TYPE_TIME_EXTEND:
            return RB_LEN_TIME_EXTEND;

      case RINGBUF_TYPE_TIME_STAMP:
            return RB_LEN_TIME_STAMP;

      case RINGBUF_TYPE_DATA:
            return rb_event_data_length(event);
      default:
            BUG();
      }
      /* not hit */
      return 0;
}

/**
 * ring_buffer_event_length - return the length of the event
 * @event: the event to get the length of
 */
unsigned ring_buffer_event_length(struct ring_buffer_event *event)
{
      unsigned length = rb_event_length(event);
      if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
            return length;
      length -= RB_EVNT_HDR_SIZE;
      if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
                length -= sizeof(event->array[0]);
      return length;
}
EXPORT_SYMBOL_GPL(ring_buffer_event_length);

/* inline for ring buffer fast paths */
static void *
rb_event_data(struct ring_buffer_event *event)
{
      BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
      /* If length is in len field, then array[0] has the data */
      if (event->type_len)
            return (void *)&event->array[0];
      /* Otherwise length is in array[0] and array[1] has the data */
      return (void *)&event->array[1];
}

/**
 * ring_buffer_event_data - return the data of the event
 * @event: the event to get the data from
 */
void *ring_buffer_event_data(struct ring_buffer_event *event)
{
      return rb_event_data(event);
}
EXPORT_SYMBOL_GPL(ring_buffer_event_data);

#define for_each_buffer_cpu(buffer, cpu)        \
      for_each_cpu(cpu, buffer->cpumask)

#define TS_SHIFT  27
#define TS_MASK         ((1ULL << TS_SHIFT) - 1)
#define TS_DELTA_TEST   (~TS_MASK)

00319 struct buffer_data_page {
      u64          time_stamp;      /* page time stamp */
      local_t            commit;    /* write committed index */
      unsigned char      data[];    /* data of buffer page */
};

00325 struct buffer_page {
      struct list_head list;        /* list of buffer pages */
      local_t            write;           /* index for next write */
      unsigned     read;            /* index for next read */
      local_t            entries;   /* entries on this page */
      struct buffer_data_page *page;      /* Actual data page */
};

static void rb_init_page(struct buffer_data_page *bpage)
{
      local_set(&bpage->commit, 0);
}

/**
 * ring_buffer_page_len - the size of data on the page.
 * @page: The page to read
 *
 * Returns the amount of data on the page, including buffer page header.
 */
size_t ring_buffer_page_len(void *page)
{
      return local_read(&((struct buffer_data_page *)page)->commit)
            + BUF_PAGE_HDR_SIZE;
}

/*
 * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
 * this issue out.
 */
static void free_buffer_page(struct buffer_page *bpage)
{
      free_page((unsigned long)bpage->page);
      kfree(bpage);
}

/*
 * We need to fit the time_stamp delta into 27 bits.
 */
static inline int test_time_stamp(u64 delta)
{
      if (delta & TS_DELTA_TEST)
            return 1;
      return 0;
}

#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)

/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))

/* Max number of timestamps that can fit on a page */
#define RB_TIMESTAMPS_PER_PAGE      (BUF_PAGE_SIZE / RB_LEN_TIME_STAMP)

int ring_buffer_print_page_header(struct trace_seq *s)
{
      struct buffer_data_page field;
      int ret;

      ret = trace_seq_printf(s, "\tfield: u64 timestamp;\t"
                         "offset:0;\tsize:%u;\n",
                         (unsigned int)sizeof(field.time_stamp));

      ret = trace_seq_printf(s, "\tfield: local_t commit;\t"
                         "offset:%u;\tsize:%u;\n",
                         (unsigned int)offsetof(typeof(field), commit),
                         (unsigned int)sizeof(field.commit));

      ret = trace_seq_printf(s, "\tfield: char data;\t"
                         "offset:%u;\tsize:%u;\n",
                         (unsigned int)offsetof(typeof(field), data),
                         (unsigned int)BUF_PAGE_SIZE);

      return ret;
}

/*
 * head_page == tail_page && head == tail then buffer is empty.
 */
00403 struct ring_buffer_per_cpu {
      int                     cpu;
      struct ring_buffer            *buffer;
      spinlock_t              reader_lock; /* serialize readers */
      raw_spinlock_t                lock;
      struct lock_class_key         lock_key;
      struct list_head        pages;
      struct buffer_page            *head_page; /* read from head */
      struct buffer_page            *tail_page; /* write to tail */
      struct buffer_page            *commit_page;     /* committed pages */
      struct buffer_page            *reader_page;
      unsigned long                 nmi_dropped;
      unsigned long                 commit_overrun;
      unsigned long                 overrun;
      unsigned long                 read;
      local_t                       entries;
      local_t                       committing;
      local_t                       commits;
      u64                     write_stamp;
      u64                     read_stamp;
      atomic_t                record_disabled;
};

struct ring_buffer {
      unsigned                pages;
      unsigned                flags;
      int                     cpus;
      atomic_t                record_disabled;
      cpumask_var_t                 cpumask;

      struct lock_class_key         *reader_lock_key;

      struct mutex                  mutex;

      struct ring_buffer_per_cpu    **buffers;

#ifdef CONFIG_HOTPLUG_CPU
      struct notifier_block         cpu_notify;
#endif
      u64                     (*clock)(void);
};

00445 struct ring_buffer_iter {
      struct ring_buffer_per_cpu    *cpu_buffer;
      unsigned long                 head;
      struct buffer_page            *head_page;
      u64                     read_stamp;
};

/* buffer may be either ring_buffer or ring_buffer_per_cpu */
#define RB_WARN_ON(buffer, cond)                      \
      ({                                        \
            int _____ret = unlikely(cond);                  \
            if (_____ret) {                           \
                  atomic_inc(&buffer->record_disabled);     \
                  WARN_ON(1);                   \
            }                                   \
            _____ret;                           \
      })

/* Up this if you want to test the TIME_EXTENTS and normalization */
#define DEBUG_SHIFT 0

static inline u64 rb_time_stamp(struct ring_buffer *buffer, int cpu)
{
      /* shift to debug/test normalization and TIME_EXTENTS */
      return buffer->clock() << DEBUG_SHIFT;
}

u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
{
      u64 time;

      preempt_disable_notrace();
      time = rb_time_stamp(buffer, cpu);
      preempt_enable_no_resched_notrace();

      return time;
}
EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);

void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
                              int cpu, u64 *ts)
{
      /* Just stupid testing the normalize function and deltas */
      *ts >>= DEBUG_SHIFT;
}
EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);

/**
 * check_pages - integrity check of buffer pages
 * @cpu_buffer: CPU buffer with pages to test
 *
 * As a safety measure we check to make sure the data pages have not
 * been corrupted.
 */
static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
{
      struct list_head *head = &cpu_buffer->pages;
      struct buffer_page *bpage, *tmp;

      if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
            return -1;
      if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
            return -1;

      list_for_each_entry_safe(bpage, tmp, head, list) {
            if (RB_WARN_ON(cpu_buffer,
                         bpage->list.next->prev != &bpage->list))
                  return -1;
            if (RB_WARN_ON(cpu_buffer,
                         bpage->list.prev->next != &bpage->list))
                  return -1;
      }

      return 0;
}

static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
                       unsigned nr_pages)
{
      struct list_head *head = &cpu_buffer->pages;
      struct buffer_page *bpage, *tmp;
      unsigned long addr;
      LIST_HEAD(pages);
      unsigned i;

      for (i = 0; i < nr_pages; i++) {
            bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
                            GFP_KERNEL, cpu_to_node(cpu_buffer->cpu));
            if (!bpage)
                  goto free_pages;
            list_add(&bpage->list, &pages);

            addr = __get_free_page(GFP_KERNEL);
            if (!addr)
                  goto free_pages;
            bpage->page = (void *)addr;
            rb_init_page(bpage->page);
      }

      list_splice(&pages, head);

      rb_check_pages(cpu_buffer);

      return 0;

 free_pages:
      list_for_each_entry_safe(bpage, tmp, &pages, list) {
            list_del_init(&bpage->list);
            free_buffer_page(bpage);
      }
      return -ENOMEM;
}

static struct ring_buffer_per_cpu *
rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      struct buffer_page *bpage;
      unsigned long addr;
      int ret;

      cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
                          GFP_KERNEL, cpu_to_node(cpu));
      if (!cpu_buffer)
            return NULL;

      cpu_buffer->cpu = cpu;
      cpu_buffer->buffer = buffer;
      spin_lock_init(&cpu_buffer->reader_lock);
      lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
      cpu_buffer->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
      INIT_LIST_HEAD(&cpu_buffer->pages);

      bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
                      GFP_KERNEL, cpu_to_node(cpu));
      if (!bpage)
            goto fail_free_buffer;

      cpu_buffer->reader_page = bpage;
      addr = __get_free_page(GFP_KERNEL);
      if (!addr)
            goto fail_free_reader;
      bpage->page = (void *)addr;
      rb_init_page(bpage->page);

      INIT_LIST_HEAD(&cpu_buffer->reader_page->list);

      ret = rb_allocate_pages(cpu_buffer, buffer->pages);
      if (ret < 0)
            goto fail_free_reader;

      cpu_buffer->head_page
            = list_entry(cpu_buffer->pages.next, struct buffer_page, list);
      cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;

      return cpu_buffer;

 fail_free_reader:
      free_buffer_page(cpu_buffer->reader_page);

 fail_free_buffer:
      kfree(cpu_buffer);
      return NULL;
}

static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
{
      struct list_head *head = &cpu_buffer->pages;
      struct buffer_page *bpage, *tmp;

      free_buffer_page(cpu_buffer->reader_page);

      list_for_each_entry_safe(bpage, tmp, head, list) {
            list_del_init(&bpage->list);
            free_buffer_page(bpage);
      }
      kfree(cpu_buffer);
}

#ifdef CONFIG_HOTPLUG_CPU
static int rb_cpu_notify(struct notifier_block *self,
                   unsigned long action, void *hcpu);
#endif

/**
 * ring_buffer_alloc - allocate a new ring_buffer
 * @size: the size in bytes per cpu that is needed.
 * @flags: attributes to set for the ring buffer.
 *
 * Currently the only flag that is available is the RB_FL_OVERWRITE
 * flag. This flag means that the buffer will overwrite old data
 * when the buffer wraps. If this flag is not set, the buffer will
 * drop data when the tail hits the head.
 */
struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
                              struct lock_class_key *key)
{
      struct ring_buffer *buffer;
      int bsize;
      int cpu;

      /* keep it in its own cache line */
      buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
                   GFP_KERNEL);
      if (!buffer)
            return NULL;

      if (!alloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
            goto fail_free_buffer;

      buffer->pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
      buffer->flags = flags;
      buffer->clock = trace_clock_local;
      buffer->reader_lock_key = key;

      /* need at least two pages */
      if (buffer->pages < 2)
            buffer->pages = 2;

      /*
       * In case of non-hotplug cpu, if the ring-buffer is allocated
       * in early initcall, it will not be notified of secondary cpus.
       * In that off case, we need to allocate for all possible cpus.
       */
#ifdef CONFIG_HOTPLUG_CPU
      get_online_cpus();
      cpumask_copy(buffer->cpumask, cpu_online_mask);
#else
      cpumask_copy(buffer->cpumask, cpu_possible_mask);
#endif
      buffer->cpus = nr_cpu_ids;

      bsize = sizeof(void *) * nr_cpu_ids;
      buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
                          GFP_KERNEL);
      if (!buffer->buffers)
            goto fail_free_cpumask;

      for_each_buffer_cpu(buffer, cpu) {
            buffer->buffers[cpu] =
                  rb_allocate_cpu_buffer(buffer, cpu);
            if (!buffer->buffers[cpu])
                  goto fail_free_buffers;
      }

#ifdef CONFIG_HOTPLUG_CPU
      buffer->cpu_notify.notifier_call = rb_cpu_notify;
      buffer->cpu_notify.priority = 0;
      register_cpu_notifier(&buffer->cpu_notify);
#endif

      put_online_cpus();
      mutex_init(&buffer->mutex);

      return buffer;

 fail_free_buffers:
      for_each_buffer_cpu(buffer, cpu) {
            if (buffer->buffers[cpu])
                  rb_free_cpu_buffer(buffer->buffers[cpu]);
      }
      kfree(buffer->buffers);

 fail_free_cpumask:
      free_cpumask_var(buffer->cpumask);
      put_online_cpus();

 fail_free_buffer:
      kfree(buffer);
      return NULL;
}
EXPORT_SYMBOL_GPL(__ring_buffer_alloc);

/**
 * ring_buffer_free - free a ring buffer.
 * @buffer: the buffer to free.
 */
void
ring_buffer_free(struct ring_buffer *buffer)
{
      int cpu;

      get_online_cpus();

#ifdef CONFIG_HOTPLUG_CPU
      unregister_cpu_notifier(&buffer->cpu_notify);
#endif

      for_each_buffer_cpu(buffer, cpu)
            rb_free_cpu_buffer(buffer->buffers[cpu]);

      put_online_cpus();

      kfree(buffer->buffers);
      free_cpumask_var(buffer->cpumask);

      kfree(buffer);
}
EXPORT_SYMBOL_GPL(ring_buffer_free);

void ring_buffer_set_clock(struct ring_buffer *buffer,
                     u64 (*clock)(void))
{
      buffer->clock = clock;
}

static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);

static void
rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
{
      struct buffer_page *bpage;
      struct list_head *p;
      unsigned i;

      atomic_inc(&cpu_buffer->record_disabled);
      synchronize_sched();

      for (i = 0; i < nr_pages; i++) {
            if (RB_WARN_ON(cpu_buffer, list_empty(&cpu_buffer->pages)))
                  return;
            p = cpu_buffer->pages.next;
            bpage = list_entry(p, struct buffer_page, list);
            list_del_init(&bpage->list);
            free_buffer_page(bpage);
      }
      if (RB_WARN_ON(cpu_buffer, list_empty(&cpu_buffer->pages)))
            return;

      rb_reset_cpu(cpu_buffer);

      rb_check_pages(cpu_buffer);

      atomic_dec(&cpu_buffer->record_disabled);

}

static void
rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
            struct list_head *pages, unsigned nr_pages)
{
      struct buffer_page *bpage;
      struct list_head *p;
      unsigned i;

      atomic_inc(&cpu_buffer->record_disabled);
      synchronize_sched();

      for (i = 0; i < nr_pages; i++) {
            if (RB_WARN_ON(cpu_buffer, list_empty(pages)))
                  return;
            p = pages->next;
            bpage = list_entry(p, struct buffer_page, list);
            list_del_init(&bpage->list);
            list_add_tail(&bpage->list, &cpu_buffer->pages);
      }
      rb_reset_cpu(cpu_buffer);

      rb_check_pages(cpu_buffer);

      atomic_dec(&cpu_buffer->record_disabled);
}

/**
 * ring_buffer_resize - resize the ring buffer
 * @buffer: the buffer to resize.
 * @size: the new size.
 *
 * The tracer is responsible for making sure that the buffer is
 * not being used while changing the size.
 * Note: We may be able to change the above requirement by using
 *  RCU synchronizations.
 *
 * Minimum size is 2 * BUF_PAGE_SIZE.
 *
 * Returns -1 on failure.
 */
int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      unsigned nr_pages, rm_pages, new_pages;
      struct buffer_page *bpage, *tmp;
      unsigned long buffer_size;
      unsigned long addr;
      LIST_HEAD(pages);
      int i, cpu;

      /*
       * Always succeed at resizing a non-existent buffer:
       */
      if (!buffer)
            return size;

      size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
      size *= BUF_PAGE_SIZE;
      buffer_size = buffer->pages * BUF_PAGE_SIZE;

      /* we need a minimum of two pages */
      if (size < BUF_PAGE_SIZE * 2)
            size = BUF_PAGE_SIZE * 2;

      if (size == buffer_size)
            return size;

      mutex_lock(&buffer->mutex);
      get_online_cpus();

      nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);

      if (size < buffer_size) {

            /* easy case, just free pages */
            if (RB_WARN_ON(buffer, nr_pages >= buffer->pages))
                  goto out_fail;

            rm_pages = buffer->pages - nr_pages;

            for_each_buffer_cpu(buffer, cpu) {
                  cpu_buffer = buffer->buffers[cpu];
                  rb_remove_pages(cpu_buffer, rm_pages);
            }
            goto out;
      }

      /*
       * This is a bit more difficult. We only want to add pages
       * when we can allocate enough for all CPUs. We do this
       * by allocating all the pages and storing them on a local
       * link list. If we succeed in our allocation, then we
       * add these pages to the cpu_buffers. Otherwise we just free
       * them all and return -ENOMEM;
       */
      if (RB_WARN_ON(buffer, nr_pages <= buffer->pages))
            goto out_fail;

      new_pages = nr_pages - buffer->pages;

      for_each_buffer_cpu(buffer, cpu) {
            for (i = 0; i < new_pages; i++) {
                  bpage = kzalloc_node(ALIGN(sizeof(*bpage),
                                      cache_line_size()),
                                  GFP_KERNEL, cpu_to_node(cpu));
                  if (!bpage)
                        goto free_pages;
                  list_add(&bpage->list, &pages);
                  addr = __get_free_page(GFP_KERNEL);
                  if (!addr)
                        goto free_pages;
                  bpage->page = (void *)addr;
                  rb_init_page(bpage->page);
            }
      }

      for_each_buffer_cpu(buffer, cpu) {
            cpu_buffer = buffer->buffers[cpu];
            rb_insert_pages(cpu_buffer, &pages, new_pages);
      }

      if (RB_WARN_ON(buffer, !list_empty(&pages)))
            goto out_fail;

 out:
      buffer->pages = nr_pages;
      put_online_cpus();
      mutex_unlock(&buffer->mutex);

      return size;

 free_pages:
      list_for_each_entry_safe(bpage, tmp, &pages, list) {
            list_del_init(&bpage->list);
            free_buffer_page(bpage);
      }
      put_online_cpus();
      mutex_unlock(&buffer->mutex);
      return -ENOMEM;

      /*
       * Something went totally wrong, and we are too paranoid
       * to even clean up the mess.
       */
 out_fail:
      put_online_cpus();
      mutex_unlock(&buffer->mutex);
      return -1;
}
EXPORT_SYMBOL_GPL(ring_buffer_resize);

static inline void *
__rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
{
      return bpage->data + index;
}

static inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
{
      return bpage->page->data + index;
}

static inline struct ring_buffer_event *
rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
{
      return __rb_page_index(cpu_buffer->reader_page,
                         cpu_buffer->reader_page->read);
}

static inline struct ring_buffer_event *
rb_head_event(struct ring_buffer_per_cpu *cpu_buffer)
{
      return __rb_page_index(cpu_buffer->head_page,
                         cpu_buffer->head_page->read);
}

static inline struct ring_buffer_event *
rb_iter_head_event(struct ring_buffer_iter *iter)
{
      return __rb_page_index(iter->head_page, iter->head);
}

static inline unsigned rb_page_write(struct buffer_page *bpage)
{
      return local_read(&bpage->write);
}

static inline unsigned rb_page_commit(struct buffer_page *bpage)
{
      return local_read(&bpage->page->commit);
}

/* Size is determined by what has been commited */
static inline unsigned rb_page_size(struct buffer_page *bpage)
{
      return rb_page_commit(bpage);
}

static inline unsigned
rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
{
      return rb_page_commit(cpu_buffer->commit_page);
}

static inline unsigned rb_head_size(struct ring_buffer_per_cpu *cpu_buffer)
{
      return rb_page_commit(cpu_buffer->head_page);
}

static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
                         struct buffer_page **bpage)
{
      struct list_head *p = (*bpage)->list.next;

      if (p == &cpu_buffer->pages)
            p = p->next;

      *bpage = list_entry(p, struct buffer_page, list);
}

static inline unsigned
rb_event_index(struct ring_buffer_event *event)
{
      unsigned long addr = (unsigned long)event;

      return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
}

static inline int
rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
               struct ring_buffer_event *event)
{
      unsigned long addr = (unsigned long)event;
      unsigned long index;

      index = rb_event_index(event);
      addr &= PAGE_MASK;

      return cpu_buffer->commit_page->page == (void *)addr &&
            rb_commit_index(cpu_buffer) == index;
}

static void
rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
{
      /*
       * We only race with interrupts and NMIs on this CPU.
       * If we own the commit event, then we can commit
       * all others that interrupted us, since the interruptions
       * are in stack format (they finish before they come
       * back to us). This allows us to do a simple loop to
       * assign the commit to the tail.
       */
 again:
      while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
            cpu_buffer->commit_page->page->commit =
                  cpu_buffer->commit_page->write;
            rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
            cpu_buffer->write_stamp =
                  cpu_buffer->commit_page->page->time_stamp;
            /* add barrier to keep gcc from optimizing too much */
            barrier();
      }
      while (rb_commit_index(cpu_buffer) !=
             rb_page_write(cpu_buffer->commit_page)) {
            cpu_buffer->commit_page->page->commit =
                  cpu_buffer->commit_page->write;
            barrier();
      }

      /* again, keep gcc from optimizing */
      barrier();

      /*
       * If an interrupt came in just after the first while loop
       * and pushed the tail page forward, we will be left with
       * a dangling commit that will never go forward.
       */
      if (unlikely(cpu_buffer->commit_page != cpu_buffer->tail_page))
            goto again;
}

static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
{
      cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
      cpu_buffer->reader_page->read = 0;
}

static void rb_inc_iter(struct ring_buffer_iter *iter)
{
      struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;

      /*
       * The iterator could be on the reader page (it starts there).
       * But the head could have moved, since the reader was
       * found. Check for this case and assign the iterator
       * to the head page instead of next.
       */
      if (iter->head_page == cpu_buffer->reader_page)
            iter->head_page = cpu_buffer->head_page;
      else
            rb_inc_page(cpu_buffer, &iter->head_page);

      iter->read_stamp = iter->head_page->page->time_stamp;
      iter->head = 0;
}

/**
 * ring_buffer_update_event - update event type and data
 * @event: the even to update
 * @type: the type of event
 * @length: the size of the event field in the ring buffer
 *
 * Update the type and data fields of the event. The length
 * is the actual size that is written to the ring buffer,
 * and with this, we can determine what to place into the
 * data field.
 */
static void
rb_update_event(struct ring_buffer_event *event,
                   unsigned type, unsigned length)
{
      event->type_len = type;

      switch (type) {

      case RINGBUF_TYPE_PADDING:
      case RINGBUF_TYPE_TIME_EXTEND:
      case RINGBUF_TYPE_TIME_STAMP:
            break;

      case 0:
            length -= RB_EVNT_HDR_SIZE;
            if (length > RB_MAX_SMALL_DATA)
                  event->array[0] = length;
            else
                  event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
            break;
      default:
            BUG();
      }
}

static unsigned rb_calculate_event_length(unsigned length)
{
      struct ring_buffer_event event; /* Used only for sizeof array */

      /* zero length can cause confusions */
      if (!length)
            length = 1;

      if (length > RB_MAX_SMALL_DATA)
            length += sizeof(event.array[0]);

      length += RB_EVNT_HDR_SIZE;
      length = ALIGN(length, RB_ALIGNMENT);

      return length;
}

static inline void
rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
            struct buffer_page *tail_page,
            unsigned long tail, unsigned long length)
{
      struct ring_buffer_event *event;

      /*
       * Only the event that crossed the page boundary
       * must fill the old tail_page with padding.
       */
      if (tail >= BUF_PAGE_SIZE) {
            local_sub(length, &tail_page->write);
            return;
      }

      event = __rb_page_index(tail_page, tail);
      kmemcheck_annotate_bitfield(event, bitfield);

      /*
       * If this event is bigger than the minimum size, then
       * we need to be careful that we don't subtract the
       * write counter enough to allow another writer to slip
       * in on this page.
       * We put in a discarded commit instead, to make sure
       * that this space is not used again.
       *
       * If we are less than the minimum size, we don't need to
       * worry about it.
       */
      if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
            /* No room for any events */

            /* Mark the rest of the page with padding */
            rb_event_set_padding(event);

            /* Set the write back to the previous setting */
            local_sub(length, &tail_page->write);
            return;
      }

      /* Put in a discarded event */
      event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
      event->type_len = RINGBUF_TYPE_PADDING;
      /* time delta must be non zero */
      event->time_delta = 1;
      /* Account for this as an entry */
      local_inc(&tail_page->entries);
      local_inc(&cpu_buffer->entries);

      /* Set write to end of buffer */
      length = (tail + length) - BUF_PAGE_SIZE;
      local_sub(length, &tail_page->write);
}

static struct ring_buffer_event *
rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
           unsigned long length, unsigned long tail,
           struct buffer_page *commit_page,
           struct buffer_page *tail_page, u64 *ts)
{
      struct buffer_page *next_page, *head_page, *reader_page;
      struct ring_buffer *buffer = cpu_buffer->buffer;
      bool lock_taken = false;
      unsigned long flags;

      next_page = tail_page;

      local_irq_save(flags);
      /*
       * Since the write to the buffer is still not
       * fully lockless, we must be careful with NMIs.
       * The locks in the writers are taken when a write
       * crosses to a new page. The locks protect against
       * races with the readers (this will soon be fixed
       * with a lockless solution).
       *
       * Because we can not protect against NMIs, and we
       * want to keep traces reentrant, we need to manage
       * what happens when we are in an NMI.
       *
       * NMIs can happen after we take the lock.
       * If we are in an NMI, only take the lock
       * if it is not already taken. Otherwise
       * simply fail.
       */
      if (unlikely(in_nmi())) {
            if (!__raw_spin_trylock(&cpu_buffer->lock)) {
                  cpu_buffer->nmi_dropped++;
                  goto out_reset;
            }
      } else
            __raw_spin_lock(&cpu_buffer->lock);

      lock_taken = true;

      rb_inc_page(cpu_buffer, &next_page);

      head_page = cpu_buffer->head_page;
      reader_page = cpu_buffer->reader_page;

      /* we grabbed the lock before incrementing */
      if (RB_WARN_ON(cpu_buffer, next_page == reader_page))
            goto out_reset;

      /*
       * If for some reason, we had an interrupt storm that made
       * it all the way around the buffer, bail, and warn
       * about it.
       */
      if (unlikely(next_page == commit_page)) {
            cpu_buffer->commit_overrun++;
            goto out_reset;
      }

      if (next_page == head_page) {
            if (!(buffer->flags & RB_FL_OVERWRITE))
                  goto out_reset;

            /* tail_page has not moved yet? */
            if (tail_page == cpu_buffer->tail_page) {
                  /* count overflows */
                  cpu_buffer->overrun +=
                        local_read(&head_page->entries);

                  rb_inc_page(cpu_buffer, &head_page);
                  cpu_buffer->head_page = head_page;
                  cpu_buffer->head_page->read = 0;
            }
      }

      /*
       * If the tail page is still the same as what we think
       * it is, then it is up to us to update the tail
       * pointer.
       */
      if (tail_page == cpu_buffer->tail_page) {
            local_set(&next_page->write, 0);
            local_set(&next_page->entries, 0);
            local_set(&next_page->page->commit, 0);
            cpu_buffer->tail_page = next_page;

            /* reread the time stamp */
            *ts = rb_time_stamp(buffer, cpu_buffer->cpu);
            cpu_buffer->tail_page->page->time_stamp = *ts;
      }

      rb_reset_tail(cpu_buffer, tail_page, tail, length);

      __raw_spin_unlock(&cpu_buffer->lock);
      local_irq_restore(flags);

      /* fail and let the caller try again */
      return ERR_PTR(-EAGAIN);

 out_reset:
      /* reset write */
      rb_reset_tail(cpu_buffer, tail_page, tail, length);

      if (likely(lock_taken))
            __raw_spin_unlock(&cpu_buffer->lock);
      local_irq_restore(flags);
      return NULL;
}

static struct ring_buffer_event *
__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
              unsigned type, unsigned long length, u64 *ts)
{
      struct buffer_page *tail_page, *commit_page;
      struct ring_buffer_event *event;
      unsigned long tail, write;

      commit_page = cpu_buffer->commit_page;
      /* we just need to protect against interrupts */
      barrier();
      tail_page = cpu_buffer->tail_page;
      write = local_add_return(length, &tail_page->write);
      tail = write - length;

      /* See if we shot pass the end of this buffer page */
      if (write > BUF_PAGE_SIZE)
            return rb_move_tail(cpu_buffer, length, tail,
                            commit_page, tail_page, ts);

      /* We reserved something on the buffer */

      event = __rb_page_index(tail_page, tail);
      kmemcheck_annotate_bitfield(event, bitfield);
      rb_update_event(event, type, length);

      /* The passed in type is zero for DATA */
      if (likely(!type))
            local_inc(&tail_page->entries);

      /*
       * If this is the first commit on the page, then update
       * its timestamp.
       */
      if (!tail)
            tail_page->page->time_stamp = *ts;

      return event;
}

static inline int
rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
              struct ring_buffer_event *event)
{
      unsigned long new_index, old_index;
      struct buffer_page *bpage;
      unsigned long index;
      unsigned long addr;

      new_index = rb_event_index(event);
      old_index = new_index + rb_event_length(event);
      addr = (unsigned long)event;
      addr &= PAGE_MASK;

      bpage = cpu_buffer->tail_page;

      if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
            /*
             * This is on the tail page. It is possible that
             * a write could come in and move the tail page
             * and write to the next page. That is fine
             * because we just shorten what is on this page.
             */
            index = local_cmpxchg(&bpage->write, old_index, new_index);
            if (index == old_index)
                  return 1;
      }

      /* could not discard */
      return 0;
}

static int
rb_add_time_stamp(struct ring_buffer_per_cpu *cpu_buffer,
              u64 *ts, u64 *delta)
{
      struct ring_buffer_event *event;
      static int once;
      int ret;

      if (unlikely(*delta > (1ULL << 59) && !once++)) {
            printk(KERN_WARNING "Delta way too big! %llu"
                   " ts=%llu write stamp = %llu\n",
                   (unsigned long long)*delta,
                   (unsigned long long)*ts,
                   (unsigned long long)cpu_buffer->write_stamp);
            WARN_ON(1);
      }

      /*
       * The delta is too big, we to add a
       * new timestamp.
       */
      event = __rb_reserve_next(cpu_buffer,
                          RINGBUF_TYPE_TIME_EXTEND,
                          RB_LEN_TIME_EXTEND,
                          ts);
      if (!event)
            return -EBUSY;

      if (PTR_ERR(event) == -EAGAIN)
            return -EAGAIN;

      /* Only a commited time event can update the write stamp */
      if (rb_event_is_commit(cpu_buffer, event)) {
            /*
             * If this is the first on the page, then it was
             * updated with the page itself. Try to discard it
             * and if we can't just make it zero.
             */
            if (rb_event_index(event)) {
                  event->time_delta = *delta & TS_MASK;
                  event->array[0] = *delta >> TS_SHIFT;
            } else {
                  /* try to discard, since we do not need this */
                  if (!rb_try_to_discard(cpu_buffer, event)) {
                        /* nope, just zero it */
                        event->time_delta = 0;
                        event->array[0] = 0;
                  }
            }
            cpu_buffer->write_stamp = *ts;
            /* let the caller know this was the commit */
            ret = 1;
      } else {
            /* Try to discard the event */
            if (!rb_try_to_discard(cpu_buffer, event)) {
                  /* Darn, this is just wasted space */
                  event->time_delta = 0;
                  event->array[0] = 0;
            }
            ret = 0;
      }

      *delta = 0;

      return ret;
}

static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
{
      local_inc(&cpu_buffer->committing);
      local_inc(&cpu_buffer->commits);
}

static void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
{
      unsigned long commits;

      if (RB_WARN_ON(cpu_buffer,
                   !local_read(&cpu_buffer->committing)))
            return;

 again:
      commits = local_read(&cpu_buffer->commits);
      /* synchronize with interrupts */
      barrier();
      if (local_read(&cpu_buffer->committing) == 1)
            rb_set_commit_to_write(cpu_buffer);

      local_dec(&cpu_buffer->committing);

      /* synchronize with interrupts */
      barrier();

      /*
       * Need to account for interrupts coming in between the
       * updating of the commit page and the clearing of the
       * committing counter.
       */
      if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
          !local_read(&cpu_buffer->committing)) {
            local_inc(&cpu_buffer->committing);
            goto again;
      }
}

static struct ring_buffer_event *
rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
                  unsigned long length)
{
      struct ring_buffer_event *event;
      u64 ts, delta = 0;
      int commit = 0;
      int nr_loops = 0;

      rb_start_commit(cpu_buffer);

      length = rb_calculate_event_length(length);
 again:
      /*
       * We allow for interrupts to reenter here and do a trace.
       * If one does, it will cause this original code to loop
       * back here. Even with heavy interrupts happening, this
       * should only happen a few times in a row. If this happens
       * 1000 times in a row, there must be either an interrupt
       * storm or we have something buggy.
       * Bail!
       */
      if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
            goto out_fail;

      ts = rb_time_stamp(cpu_buffer->buffer, cpu_buffer->cpu);

      /*
       * Only the first commit can update the timestamp.
       * Yes there is a race here. If an interrupt comes in
       * just after the conditional and it traces too, then it
       * will also check the deltas. More than one timestamp may
       * also be made. But only the entry that did the actual
       * commit will be something other than zero.
       */
      if (likely(cpu_buffer->tail_page == cpu_buffer->commit_page &&
               rb_page_write(cpu_buffer->tail_page) ==
               rb_commit_index(cpu_buffer))) {
            u64 diff;

            diff = ts - cpu_buffer->write_stamp;

            /* make sure this diff is calculated here */
            barrier();

            /* Did the write stamp get updated already? */
            if (unlikely(ts < cpu_buffer->write_stamp))
                  goto get_event;

            delta = diff;
            if (unlikely(test_time_stamp(delta))) {

                  commit = rb_add_time_stamp(cpu_buffer, &ts, &delta);
                  if (commit == -EBUSY)
                        goto out_fail;

                  if (commit == -EAGAIN)
                        goto again;

                  RB_WARN_ON(cpu_buffer, commit < 0);
            }
      }

 get_event:
      event = __rb_reserve_next(cpu_buffer, 0, length, &ts);
      if (unlikely(PTR_ERR(event) == -EAGAIN))
            goto again;

      if (!event)
            goto out_fail;

      if (!rb_event_is_commit(cpu_buffer, event))
            delta = 0;

      event->time_delta = delta;

      return event;

 out_fail:
      rb_end_commit(cpu_buffer);
      return NULL;
}

#ifdef CONFIG_TRACING

#define TRACE_RECURSIVE_DEPTH 16

static int trace_recursive_lock(void)
{
      current->trace_recursion++;

      if (likely(current->trace_recursion < TRACE_RECURSIVE_DEPTH))
            return 0;

      /* Disable all tracing before we do anything else */
      tracing_off_permanent();

      printk_once(KERN_WARNING "Tracing recursion: depth[%ld]:"
                "HC[%lu]:SC[%lu]:NMI[%lu]\n",
                current->trace_recursion,
                hardirq_count() >> HARDIRQ_SHIFT,
                softirq_count() >> SOFTIRQ_SHIFT,
                in_nmi());

      WARN_ON_ONCE(1);
      return -1;
}

static void trace_recursive_unlock(void)
{
      WARN_ON_ONCE(!current->trace_recursion);

      current->trace_recursion--;
}

#else

#define trace_recursive_lock()            (0)
#define trace_recursive_unlock()    do { } while (0)

#endif

static DEFINE_PER_CPU(int, rb_need_resched);

/**
 * ring_buffer_lock_reserve - reserve a part of the buffer
 * @buffer: the ring buffer to reserve from
 * @length: the length of the data to reserve (excluding event header)
 *
 * Returns a reseverd event on the ring buffer to copy directly to.
 * The user of this interface will need to get the body to write into
 * and can use the ring_buffer_event_data() interface.
 *
 * The length is the length of the data needed, not the event length
 * which also includes the event header.
 *
 * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
 * If NULL is returned, then nothing has been allocated or locked.
 */
struct ring_buffer_event *
ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      struct ring_buffer_event *event;
      int cpu, resched;

      if (ring_buffer_flags != RB_BUFFERS_ON)
            return NULL;

      if (atomic_read(&buffer->record_disabled))
            return NULL;

      /* If we are tracing schedule, we don't want to recurse */
      resched = ftrace_preempt_disable();

      if (trace_recursive_lock())
            goto out_nocheck;

      cpu = raw_smp_processor_id();

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            goto out;

      cpu_buffer = buffer->buffers[cpu];

      if (atomic_read(&cpu_buffer->record_disabled))
            goto out;

      if (length > BUF_MAX_DATA_SIZE)
            goto out;

      event = rb_reserve_next_event(cpu_buffer, length);
      if (!event)
            goto out;

      /*
       * Need to store resched state on this cpu.
       * Only the first needs to.
       */

      if (preempt_count() == 1)
            per_cpu(rb_need_resched, cpu) = resched;

      return event;

 out:
      trace_recursive_unlock();

 out_nocheck:
      ftrace_preempt_enable(resched);
      return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);

static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
                  struct ring_buffer_event *event)
{
      local_inc(&cpu_buffer->entries);

      /*
       * The event first in the commit queue updates the
       * time stamp.
       */
      if (rb_event_is_commit(cpu_buffer, event))
            cpu_buffer->write_stamp += event->time_delta;

      rb_end_commit(cpu_buffer);
}

/**
 * ring_buffer_unlock_commit - commit a reserved
 * @buffer: The buffer to commit to
 * @event: The event pointer to commit.
 *
 * This commits the data to the ring buffer, and releases any locks held.
 *
 * Must be paired with ring_buffer_lock_reserve.
 */
int ring_buffer_unlock_commit(struct ring_buffer *buffer,
                        struct ring_buffer_event *event)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      int cpu = raw_smp_processor_id();

      cpu_buffer = buffer->buffers[cpu];

      rb_commit(cpu_buffer, event);

      trace_recursive_unlock();

      /*
       * Only the last preempt count needs to restore preemption.
       */
      if (preempt_count() == 1)
            ftrace_preempt_enable(per_cpu(rb_need_resched, cpu));
      else
            preempt_enable_no_resched_notrace();

      return 0;
}
EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);

static inline void rb_event_discard(struct ring_buffer_event *event)
{
      /* array[0] holds the actual length for the discarded event */
      event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
      event->type_len = RINGBUF_TYPE_PADDING;
      /* time delta must be non zero */
      if (!event->time_delta)
            event->time_delta = 1;
}

/**
 * ring_buffer_event_discard - discard any event in the ring buffer
 * @event: the event to discard
 *
 * Sometimes a event that is in the ring buffer needs to be ignored.
 * This function lets the user discard an event in the ring buffer
 * and then that event will not be read later.
 *
 * Note, it is up to the user to be careful with this, and protect
 * against races. If the user discards an event that has been consumed
 * it is possible that it could corrupt the ring buffer.
 */
void ring_buffer_event_discard(struct ring_buffer_event *event)
{
      rb_event_discard(event);
}
EXPORT_SYMBOL_GPL(ring_buffer_event_discard);

/**
 * ring_buffer_commit_discard - discard an event that has not been committed
 * @buffer: the ring buffer
 * @event: non committed event to discard
 *
 * This is similar to ring_buffer_event_discard but must only be
 * performed on an event that has not been committed yet. The difference
 * is that this will also try to free the event from the ring buffer
 * if another event has not been added behind it.
 *
 * If another event has been added behind it, it will set the event
 * up as discarded, and perform the commit.
 *
 * If this function is called, do not call ring_buffer_unlock_commit on
 * the event.
 */
void ring_buffer_discard_commit(struct ring_buffer *buffer,
                        struct ring_buffer_event *event)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      int cpu;

      /* The event is discarded regardless */
      rb_event_discard(event);

      cpu = smp_processor_id();
      cpu_buffer = buffer->buffers[cpu];

      /*
       * This must only be called if the event has not been
       * committed yet. Thus we can assume that preemption
       * is still disabled.
       */
      RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));

      if (rb_try_to_discard(cpu_buffer, event))
            goto out;

      /*
       * The commit is still visible by the reader, so we
       * must increment entries.
       */
      local_inc(&cpu_buffer->entries);
 out:
      rb_end_commit(cpu_buffer);

      trace_recursive_unlock();

      /*
       * Only the last preempt count needs to restore preemption.
       */
      if (preempt_count() == 1)
            ftrace_preempt_enable(per_cpu(rb_need_resched, cpu));
      else
            preempt_enable_no_resched_notrace();

}
EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);

/**
 * ring_buffer_write - write data to the buffer without reserving
 * @buffer: The ring buffer to write to.
 * @length: The length of the data being written (excluding the event header)
 * @data: The data to write to the buffer.
 *
 * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
 * one function. If you already have the data to write to the buffer, it
 * may be easier to simply call this function.
 *
 * Note, like ring_buffer_lock_reserve, the length is the length of the data
 * and not the length of the event which would hold the header.
 */
int ring_buffer_write(struct ring_buffer *buffer,
                  unsigned long length,
                  void *data)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      struct ring_buffer_event *event;
      void *body;
      int ret = -EBUSY;
      int cpu, resched;

      if (ring_buffer_flags != RB_BUFFERS_ON)
            return -EBUSY;

      if (atomic_read(&buffer->record_disabled))
            return -EBUSY;

      resched = ftrace_preempt_disable();

      cpu = raw_smp_processor_id();

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            goto out;

      cpu_buffer = buffer->buffers[cpu];

      if (atomic_read(&cpu_buffer->record_disabled))
            goto out;

      if (length > BUF_MAX_DATA_SIZE)
            goto out;

      event = rb_reserve_next_event(cpu_buffer, length);
      if (!event)
            goto out;

      body = rb_event_data(event);

      memcpy(body, data, length);

      rb_commit(cpu_buffer, event);

      ret = 0;
 out:
      ftrace_preempt_enable(resched);

      return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_write);

static int rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
{
      struct buffer_page *reader = cpu_buffer->reader_page;
      struct buffer_page *head = cpu_buffer->head_page;
      struct buffer_page *commit = cpu_buffer->commit_page;

      return reader->read == rb_page_commit(reader) &&
            (commit == reader ||
             (commit == head &&
              head->read == rb_page_commit(commit)));
}

/**
 * ring_buffer_record_disable - stop all writes into the buffer
 * @buffer: The ring buffer to stop writes to.
 *
 * This prevents all writes to the buffer. Any attempt to write
 * to the buffer after this will fail and return NULL.
 *
 * The caller should call synchronize_sched() after this.
 */
void ring_buffer_record_disable(struct ring_buffer *buffer)
{
      atomic_inc(&buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_disable);

/**
 * ring_buffer_record_enable - enable writes to the buffer
 * @buffer: The ring buffer to enable writes
 *
 * Note, multiple disables will need the same number of enables
 * to truely enable the writing (much like preempt_disable).
 */
void ring_buffer_record_enable(struct ring_buffer *buffer)
{
      atomic_dec(&buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_enable);

/**
 * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
 * @buffer: The ring buffer to stop writes to.
 * @cpu: The CPU buffer to stop
 *
 * This prevents all writes to the buffer. Any attempt to write
 * to the buffer after this will fail and return NULL.
 *
 * The caller should call synchronize_sched() after this.
 */
void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
{
      struct ring_buffer_per_cpu *cpu_buffer;

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            return;

      cpu_buffer = buffer->buffers[cpu];
      atomic_inc(&cpu_buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);

/**
 * ring_buffer_record_enable_cpu - enable writes to the buffer
 * @buffer: The ring buffer to enable writes
 * @cpu: The CPU to enable.
 *
 * Note, multiple disables will need the same number of enables
 * to truely enable the writing (much like preempt_disable).
 */
void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
{
      struct ring_buffer_per_cpu *cpu_buffer;

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            return;

      cpu_buffer = buffer->buffers[cpu];
      atomic_dec(&cpu_buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);

/**
 * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
 * @buffer: The ring buffer
 * @cpu: The per CPU buffer to get the entries from.
 */
unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      unsigned long ret;

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            return 0;

      cpu_buffer = buffer->buffers[cpu];
      ret = (local_read(&cpu_buffer->entries) - cpu_buffer->overrun)
            - cpu_buffer->read;

      return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);

/**
 * ring_buffer_overrun_cpu - get the number of overruns in a cpu_buffer
 * @buffer: The ring buffer
 * @cpu: The per CPU buffer to get the number of overruns from
 */
unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      unsigned long ret;

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            return 0;

      cpu_buffer = buffer->buffers[cpu];
      ret = cpu_buffer->overrun;

      return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);

/**
 * ring_buffer_nmi_dropped_cpu - get the number of nmis that were dropped
 * @buffer: The ring buffer
 * @cpu: The per CPU buffer to get the number of overruns from
 */
unsigned long ring_buffer_nmi_dropped_cpu(struct ring_buffer *buffer, int cpu)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      unsigned long ret;

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            return 0;

      cpu_buffer = buffer->buffers[cpu];
      ret = cpu_buffer->nmi_dropped;

      return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_nmi_dropped_cpu);

/**
 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by commits
 * @buffer: The ring buffer
 * @cpu: The per CPU buffer to get the number of overruns from
 */
unsigned long
ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      unsigned long ret;

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            return 0;

      cpu_buffer = buffer->buffers[cpu];
      ret = cpu_buffer->commit_overrun;

      return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);

/**
 * ring_buffer_entries - get the number of entries in a buffer
 * @buffer: The ring buffer
 *
 * Returns the total number of entries in the ring buffer
 * (all CPU entries)
 */
unsigned long ring_buffer_entries(struct ring_buffer *buffer)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      unsigned long entries = 0;
      int cpu;

      /* if you care about this being correct, lock the buffer */
      for_each_buffer_cpu(buffer, cpu) {
            cpu_buffer = buffer->buffers[cpu];
            entries += (local_read(&cpu_buffer->entries) -
                      cpu_buffer->overrun) - cpu_buffer->read;
      }

      return entries;
}
EXPORT_SYMBOL_GPL(ring_buffer_entries);

/**
 * ring_buffer_overrun_cpu - get the number of overruns in buffer
 * @buffer: The ring buffer
 *
 * Returns the total number of overruns in the ring buffer
 * (all CPU entries)
 */
unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      unsigned long overruns = 0;
      int cpu;

      /* if you care about this being correct, lock the buffer */
      for_each_buffer_cpu(buffer, cpu) {
            cpu_buffer = buffer->buffers[cpu];
            overruns += cpu_buffer->overrun;
      }

      return overruns;
}
EXPORT_SYMBOL_GPL(ring_buffer_overruns);

static void rb_iter_reset(struct ring_buffer_iter *iter)
{
      struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;

      /* Iterator usage is expected to have record disabled */
      if (list_empty(&cpu_buffer->reader_page->list)) {
            iter->head_page = cpu_buffer->head_page;
            iter->head = cpu_buffer->head_page->read;
      } else {
            iter->head_page = cpu_buffer->reader_page;
            iter->head = cpu_buffer->reader_page->read;
      }
      if (iter->head)
            iter->read_stamp = cpu_buffer->read_stamp;
      else
            iter->read_stamp = iter->head_page->page->time_stamp;
}

/**
 * ring_buffer_iter_reset - reset an iterator
 * @iter: The iterator to reset
 *
 * Resets the iterator, so that it will start from the beginning
 * again.
 */
void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      unsigned long flags;

      if (!iter)
            return;

      cpu_buffer = iter->cpu_buffer;

      spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
      rb_iter_reset(iter);
      spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);

/**
 * ring_buffer_iter_empty - check if an iterator has no more to read
 * @iter: The iterator to check
 */
int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
{
      struct ring_buffer_per_cpu *cpu_buffer;

      cpu_buffer = iter->cpu_buffer;

      return iter->head_page == cpu_buffer->commit_page &&
            iter->head == rb_commit_index(cpu_buffer);
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);

static void
rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
                 struct ring_buffer_event *event)
{
      u64 delta;

      switch (event->type_len) {
      case RINGBUF_TYPE_PADDING:
            return;

      case RINGBUF_TYPE_TIME_EXTEND:
            delta = event->array[0];
            delta <<= TS_SHIFT;
            delta += event->time_delta;
            cpu_buffer->read_stamp += delta;
            return;

      case RINGBUF_TYPE_TIME_STAMP:
            /* FIXME: not implemented */
            return;

      case RINGBUF_TYPE_DATA:
            cpu_buffer->read_stamp += event->time_delta;
            return;

      default:
            BUG();
      }
      return;
}

static void
rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
                    struct ring_buffer_event *event)
{
      u64 delta;

      switch (event->type_len) {
      case RINGBUF_TYPE_PADDING:
            return;

      case RINGBUF_TYPE_TIME_EXTEND:
            delta = event->array[0];
            delta <<= TS_SHIFT;
            delta += event->time_delta;
            iter->read_stamp += delta;
            return;

      case RINGBUF_TYPE_TIME_STAMP:
            /* FIXME: not implemented */
            return;

      case RINGBUF_TYPE_DATA:
            iter->read_stamp += event->time_delta;
            return;

      default:
            BUG();
      }
      return;
}

static struct buffer_page *
rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
{
      struct buffer_page *reader = NULL;
      unsigned long flags;
      int nr_loops = 0;

      local_irq_save(flags);
      __raw_spin_lock(&cpu_buffer->lock);

 again:
      /*
       * This should normally only loop twice. But because the
       * start of the reader inserts an empty page, it causes
       * a case where we will loop three times. There should be no
       * reason to loop four times (that I know of).
       */
      if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
            reader = NULL;
            goto out;
      }

      reader = cpu_buffer->reader_page;

      /* If there's more to read, return this page */
      if (cpu_buffer->reader_page->read < rb_page_size(reader))
            goto out;

      /* Never should we have an index greater than the size */
      if (RB_WARN_ON(cpu_buffer,
                   cpu_buffer->reader_page->read > rb_page_size(reader)))
            goto out;

      /* check if we caught up to the tail */
      reader = NULL;
      if (cpu_buffer->commit_page == cpu_buffer->reader_page)
            goto out;

      /*
       * Splice the empty reader page into the list around the head.
       * Reset the reader page to size zero.
       */

      reader = cpu_buffer->head_page;
      cpu_buffer->reader_page->list.next = reader->list.next;
      cpu_buffer->reader_page->list.prev = reader->list.prev;

      local_set(&cpu_buffer->reader_page->write, 0);
      local_set(&cpu_buffer->reader_page->entries, 0);
      local_set(&cpu_buffer->reader_page->page->commit, 0);

      /* Make the reader page now replace the head */
      reader->list.prev->next = &cpu_buffer->reader_page->list;
      reader->list.next->prev = &cpu_buffer->reader_page->list;

      /*
       * If the tail is on the reader, then we must set the head
       * to the inserted page, otherwise we set it one before.
       */
      cpu_buffer->head_page = cpu_buffer->reader_page;

      if (cpu_buffer->commit_page != reader)
            rb_inc_page(cpu_buffer, &cpu_buffer->head_page);

      /* Finally update the reader page to the new head */
      cpu_buffer->reader_page = reader;
      rb_reset_reader_page(cpu_buffer);

      goto again;

 out:
      __raw_spin_unlock(&cpu_buffer->lock);
      local_irq_restore(flags);

      return reader;
}

static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
{
      struct ring_buffer_event *event;
      struct buffer_page *reader;
      unsigned length;

      reader = rb_get_reader_page(cpu_buffer);

      /* This function should not be called when buffer is empty */
      if (RB_WARN_ON(cpu_buffer, !reader))
            return;

      event = rb_reader_event(cpu_buffer);

      if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX
                  || rb_discarded_event(event))
            cpu_buffer->read++;

      rb_update_read_stamp(cpu_buffer, event);

      length = rb_event_length(event);
      cpu_buffer->reader_page->read += length;
}

static void rb_advance_iter(struct ring_buffer_iter *iter)
{
      struct ring_buffer *buffer;
      struct ring_buffer_per_cpu *cpu_buffer;
      struct ring_buffer_event *event;
      unsigned length;

      cpu_buffer = iter->cpu_buffer;
      buffer = cpu_buffer->buffer;

      /*
       * Check if we are at the end of the buffer.
       */
      if (iter->head >= rb_page_size(iter->head_page)) {
            /* discarded commits can make the page empty */
            if (iter->head_page == cpu_buffer->commit_page)
                  return;
            rb_inc_iter(iter);
            return;
      }

      event = rb_iter_head_event(iter);

      length = rb_event_length(event);

      /*
       * This should not be called to advance the header if we are
       * at the tail of the buffer.
       */
      if (RB_WARN_ON(cpu_buffer,
                   (iter->head_page == cpu_buffer->commit_page) &&
                   (iter->head + length > rb_commit_index(cpu_buffer))))
            return;

      rb_update_iter_read_stamp(iter, event);

      iter->head += length;

      /* check for end of page padding */
      if ((iter->head >= rb_page_size(iter->head_page)) &&
          (iter->head_page != cpu_buffer->commit_page))
            rb_advance_iter(iter);
}

static struct ring_buffer_event *
rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      struct ring_buffer_event *event;
      struct buffer_page *reader;
      int nr_loops = 0;

      cpu_buffer = buffer->buffers[cpu];

 again:
      /*
       * We repeat when a timestamp is encountered. It is possible
       * to get multiple timestamps from an interrupt entering just
       * as one timestamp is about to be written, or from discarded
       * commits. The most that we can have is the number on a single page.
       */
      if (RB_WARN_ON(cpu_buffer, ++nr_loops > RB_TIMESTAMPS_PER_PAGE))
            return NULL;

      reader = rb_get_reader_page(cpu_buffer);
      if (!reader)
            return NULL;

      event = rb_reader_event(cpu_buffer);

      switch (event->type_len) {
      case RINGBUF_TYPE_PADDING:
            if (rb_null_event(event))
                  RB_WARN_ON(cpu_buffer, 1);
            /*
             * Because the writer could be discarding every
             * event it creates (which would probably be bad)
             * if we were to go back to "again" then we may never
             * catch up, and will trigger the warn on, or lock
             * the box. Return the padding, and we will release
             * the current locks, and try again.
             */
            return event;

      case RINGBUF_TYPE_TIME_EXTEND:
            /* Internal data, OK to advance */
            rb_advance_reader(cpu_buffer);
            goto again;

      case RINGBUF_TYPE_TIME_STAMP:
            /* FIXME: not implemented */
            rb_advance_reader(cpu_buffer);
            goto again;

      case RINGBUF_TYPE_DATA:
            if (ts) {
                  *ts = cpu_buffer->read_stamp + event->time_delta;
                  ring_buffer_normalize_time_stamp(buffer,
                                           cpu_buffer->cpu, ts);
            }
            return event;

      default:
            BUG();
      }

      return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_peek);

static struct ring_buffer_event *
rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
{
      struct ring_buffer *buffer;
      struct ring_buffer_per_cpu *cpu_buffer;
      struct ring_buffer_event *event;
      int nr_loops = 0;

      if (ring_buffer_iter_empty(iter))
            return NULL;

      cpu_buffer = iter->cpu_buffer;
      buffer = cpu_buffer->buffer;

 again:
      /*
       * We repeat when a timestamp is encountered.
       * We can get multiple timestamps by nested interrupts or also
       * if filtering is on (discarding commits). Since discarding
       * commits can be frequent we can get a lot of timestamps.
       * But we limit them by not adding timestamps if they begin
       * at the start of a page.
       */
      if (RB_WARN_ON(cpu_buffer, ++nr_loops > RB_TIMESTAMPS_PER_PAGE))
            return NULL;

      if (rb_per_cpu_empty(cpu_buffer))
            return NULL;

      event = rb_iter_head_event(iter);

      switch (event->type_len) {
      case RINGBUF_TYPE_PADDING:
            if (rb_null_event(event)) {
                  rb_inc_iter(iter);
                  goto again;
            }
            rb_advance_iter(iter);
            return event;

      case RINGBUF_TYPE_TIME_EXTEND:
            /* Internal data, OK to advance */
            rb_advance_iter(iter);
            goto again;

      case RINGBUF_TYPE_TIME_STAMP:
            /* FIXME: not implemented */
            rb_advance_iter(iter);
            goto again;

      case RINGBUF_TYPE_DATA:
            if (ts) {
                  *ts = iter->read_stamp + event->time_delta;
                  ring_buffer_normalize_time_stamp(buffer,
                                           cpu_buffer->cpu, ts);
            }
            return event;

      default:
            BUG();
      }

      return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);

static inline int rb_ok_to_lock(void)
{
      /*
       * If an NMI die dumps out the content of the ring buffer
       * do not grab locks. We also permanently disable the ring
       * buffer too. A one time deal is all you get from reading
       * the ring buffer from an NMI.
       */
      if (likely(!in_nmi()))
            return 1;

      tracing_off_permanent();
      return 0;
}

/**
 * ring_buffer_peek - peek at the next event to be read
 * @buffer: The ring buffer to read
 * @cpu: The cpu to peak at
 * @ts: The timestamp counter of this event.
 *
 * This will return the event that will be read next, but does
 * not consume the data.
 */
struct ring_buffer_event *
ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
{
      struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
      struct ring_buffer_event *event;
      unsigned long flags;
      int dolock;

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            return NULL;

      dolock = rb_ok_to_lock();
 again:
      local_irq_save(flags);
      if (dolock)
            spin_lock(&cpu_buffer->reader_lock);
      event = rb_buffer_peek(buffer, cpu, ts);
      if (event && event->type_len == RINGBUF_TYPE_PADDING)
            rb_advance_reader(cpu_buffer);
      if (dolock)
            spin_unlock(&cpu_buffer->reader_lock);
      local_irq_restore(flags);

      if (event && event->type_len == RINGBUF_TYPE_PADDING) {
            cpu_relax();
            goto again;
      }

      return event;
}

/**
 * ring_buffer_iter_peek - peek at the next event to be read
 * @iter: The ring buffer iterator
 * @ts: The timestamp counter of this event.
 *
 * This will return the event that will be read next, but does
 * not increment the iterator.
 */
struct ring_buffer_event *
ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
{
      struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
      struct ring_buffer_event *event;
      unsigned long flags;

 again:
      spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
      event = rb_iter_peek(iter, ts);
      spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);

      if (event && event->type_len == RINGBUF_TYPE_PADDING) {
            cpu_relax();
            goto again;
      }

      return event;
}

/**
 * ring_buffer_consume - return an event and consume it
 * @buffer: The ring buffer to get the next event from
 *
 * Returns the next event in the ring buffer, and that event is consumed.
 * Meaning, that sequential reads will keep returning a different event,
 * and eventually empty the ring buffer if the producer is slower.
 */
struct ring_buffer_event *
ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      struct ring_buffer_event *event = NULL;
      unsigned long flags;
      int dolock;

      dolock = rb_ok_to_lock();

 again:
      /* might be called in atomic */
      preempt_disable();

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            goto out;

      cpu_buffer = buffer->buffers[cpu];
      local_irq_save(flags);
      if (dolock)
            spin_lock(&cpu_buffer->reader_lock);

      event = rb_buffer_peek(buffer, cpu, ts);
      if (event)
            rb_advance_reader(cpu_buffer);

      if (dolock)
            spin_unlock(&cpu_buffer->reader_lock);
      local_irq_restore(flags);

 out:
      preempt_enable();

      if (event && event->type_len == RINGBUF_TYPE_PADDING) {
            cpu_relax();
            goto again;
      }

      return event;
}
EXPORT_SYMBOL_GPL(ring_buffer_consume);

/**
 * ring_buffer_read_start - start a non consuming read of the buffer
 * @buffer: The ring buffer to read from
 * @cpu: The cpu buffer to iterate over
 *
 * This starts up an iteration through the buffer. It also disables
 * the recording to the buffer until the reading is finished.
 * This prevents the reading from being corrupted. This is not
 * a consuming read, so a producer is not expected.
 *
 * Must be paired with ring_buffer_finish.
 */
struct ring_buffer_iter *
ring_buffer_read_start(struct ring_buffer *buffer, int cpu)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      struct ring_buffer_iter *iter;
      unsigned long flags;

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            return NULL;

      iter = kmalloc(sizeof(*iter), GFP_KERNEL);
      if (!iter)
            return NULL;

      cpu_buffer = buffer->buffers[cpu];

      iter->cpu_buffer = cpu_buffer;

      atomic_inc(&cpu_buffer->record_disabled);
      synchronize_sched();

      spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
      __raw_spin_lock(&cpu_buffer->lock);
      rb_iter_reset(iter);
      __raw_spin_unlock(&cpu_buffer->lock);
      spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);

      return iter;
}
EXPORT_SYMBOL_GPL(ring_buffer_read_start);

/**
 * ring_buffer_finish - finish reading the iterator of the buffer
 * @iter: The iterator retrieved by ring_buffer_start
 *
 * This re-enables the recording to the buffer, and frees the
 * iterator.
 */
void
ring_buffer_read_finish(struct ring_buffer_iter *iter)
{
      struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;

      atomic_dec(&cpu_buffer->record_disabled);
      kfree(iter);
}
EXPORT_SYMBOL_GPL(ring_buffer_read_finish);

/**
 * ring_buffer_read - read the next item in the ring buffer by the iterator
 * @iter: The ring buffer iterator
 * @ts: The time stamp of the event read.
 *
 * This reads the next event in the ring buffer and increments the iterator.
 */
struct ring_buffer_event *
ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
{
      struct ring_buffer_event *event;
      struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
      unsigned long flags;

 again:
      spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
      event = rb_iter_peek(iter, ts);
      if (!event)
            goto out;

      rb_advance_iter(iter);
 out:
      spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);

      if (event && event->type_len == RINGBUF_TYPE_PADDING) {
            cpu_relax();
            goto again;
      }

      return event;
}
EXPORT_SYMBOL_GPL(ring_buffer_read);

/**
 * ring_buffer_size - return the size of the ring buffer (in bytes)
 * @buffer: The ring buffer.
 */
unsigned long ring_buffer_size(struct ring_buffer *buffer)
{
      return BUF_PAGE_SIZE * buffer->pages;
}
EXPORT_SYMBOL_GPL(ring_buffer_size);

static void
rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
{
      cpu_buffer->head_page
            = list_entry(cpu_buffer->pages.next, struct buffer_page, list);
      local_set(&cpu_buffer->head_page->write, 0);
      local_set(&cpu_buffer->head_page->entries, 0);
      local_set(&cpu_buffer->head_page->page->commit, 0);

      cpu_buffer->head_page->read = 0;

      cpu_buffer->tail_page = cpu_buffer->head_page;
      cpu_buffer->commit_page = cpu_buffer->head_page;

      INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
      local_set(&cpu_buffer->reader_page->write, 0);
      local_set(&cpu_buffer->reader_page->entries, 0);
      local_set(&cpu_buffer->reader_page->page->commit, 0);
      cpu_buffer->reader_page->read = 0;

      cpu_buffer->nmi_dropped = 0;
      cpu_buffer->commit_overrun = 0;
      cpu_buffer->overrun = 0;
      cpu_buffer->read = 0;
      local_set(&cpu_buffer->entries, 0);
      local_set(&cpu_buffer->committing, 0);
      local_set(&cpu_buffer->commits, 0);

      cpu_buffer->write_stamp = 0;
      cpu_buffer->read_stamp = 0;
}

/**
 * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
 * @buffer: The ring buffer to reset a per cpu buffer of
 * @cpu: The CPU buffer to be reset
 */
void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
{
      struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
      unsigned long flags;

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            return;

      atomic_inc(&cpu_buffer->record_disabled);

      spin_lock_irqsave(&cpu_buffer->reader_lock, flags);

      __raw_spin_lock(&cpu_buffer->lock);

      rb_reset_cpu(cpu_buffer);

      __raw_spin_unlock(&cpu_buffer->lock);

      spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);

      atomic_dec(&cpu_buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);

/**
 * ring_buffer_reset - reset a ring buffer
 * @buffer: The ring buffer to reset all cpu buffers
 */
void ring_buffer_reset(struct ring_buffer *buffer)
{
      int cpu;

      for_each_buffer_cpu(buffer, cpu)
            ring_buffer_reset_cpu(buffer, cpu);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset);

/**
 * rind_buffer_empty - is the ring buffer empty?
 * @buffer: The ring buffer to test
 */
int ring_buffer_empty(struct ring_buffer *buffer)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      unsigned long flags;
      int dolock;
      int cpu;
      int ret;

      dolock = rb_ok_to_lock();

      /* yes this is racy, but if you don't like the race, lock the buffer */
      for_each_buffer_cpu(buffer, cpu) {
            cpu_buffer = buffer->buffers[cpu];
            local_irq_save(flags);
            if (dolock)
                  spin_lock(&cpu_buffer->reader_lock);
            ret = rb_per_cpu_empty(cpu_buffer);
            if (dolock)
                  spin_unlock(&cpu_buffer->reader_lock);
            local_irq_restore(flags);

            if (!ret)
                  return 0;
      }

      return 1;
}
EXPORT_SYMBOL_GPL(ring_buffer_empty);

/**
 * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
 * @buffer: The ring buffer
 * @cpu: The CPU buffer to test
 */
int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
{
      struct ring_buffer_per_cpu *cpu_buffer;
      unsigned long flags;
      int dolock;
      int ret;

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            return 1;

      dolock = rb_ok_to_lock();

      cpu_buffer = buffer->buffers[cpu];
      local_irq_save(flags);
      if (dolock)
            spin_lock(&cpu_buffer->reader_lock);
      ret = rb_per_cpu_empty(cpu_buffer);
      if (dolock)
            spin_unlock(&cpu_buffer->reader_lock);
      local_irq_restore(flags);

      return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);

/**
 * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
 * @buffer_a: One buffer to swap with
 * @buffer_b: The other buffer to swap with
 *
 * This function is useful for tracers that want to take a "snapshot"
 * of a CPU buffer and has another back up buffer lying around.
 * it is expected that the tracer handles the cpu buffer not being
 * used at the moment.
 */
int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
                   struct ring_buffer *buffer_b, int cpu)
{
      struct ring_buffer_per_cpu *cpu_buffer_a;
      struct ring_buffer_per_cpu *cpu_buffer_b;
      int ret = -EINVAL;

      if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
          !cpumask_test_cpu(cpu, buffer_b->cpumask))
            goto out;

      /* At least make sure the two buffers are somewhat the same */
      if (buffer_a->pages != buffer_b->pages)
            goto out;

      ret = -EAGAIN;

      if (ring_buffer_flags != RB_BUFFERS_ON)
            goto out;

      if (atomic_read(&buffer_a->record_disabled))
            goto out;

      if (atomic_read(&buffer_b->record_disabled))
            goto out;

      cpu_buffer_a = buffer_a->buffers[cpu];
      cpu_buffer_b = buffer_b->buffers[cpu];

      if (atomic_read(&cpu_buffer_a->record_disabled))
            goto out;

      if (atomic_read(&cpu_buffer_b->record_disabled))
            goto out;

      /*
       * We can't do a synchronize_sched here because this
       * function can be called in atomic context.
       * Normally this will be called from the same CPU as cpu.
       * If not it's up to the caller to protect this.
       */
      atomic_inc(&cpu_buffer_a->record_disabled);
      atomic_inc(&cpu_buffer_b->record_disabled);

      buffer_a->buffers[cpu] = cpu_buffer_b;
      buffer_b->buffers[cpu] = cpu_buffer_a;

      cpu_buffer_b->buffer = buffer_a;
      cpu_buffer_a->buffer = buffer_b;

      atomic_dec(&cpu_buffer_a->record_disabled);
      atomic_dec(&cpu_buffer_b->record_disabled);

      ret = 0;
out:
      return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);

/**
 * ring_buffer_alloc_read_page - allocate a page to read from buffer
 * @buffer: the buffer to allocate for.
 *
 * This function is used in conjunction with ring_buffer_read_page.
 * When reading a full page from the ring buffer, these functions
 * can be used to speed up the process. The calling function should
 * allocate a few pages first with this function. Then when it
 * needs to get pages from the ring buffer, it passes the result
 * of this function into ring_buffer_read_page, which will swap
 * the page that was allocated, with the read page of the buffer.
 *
 * Returns:
 *  The page allocated, or NULL on error.
 */
void *ring_buffer_alloc_read_page(struct ring_buffer *buffer)
{
      struct buffer_data_page *bpage;
      unsigned long addr;

      addr = __get_free_page(GFP_KERNEL);
      if (!addr)
            return NULL;

      bpage = (void *)addr;

      rb_init_page(bpage);

      return bpage;
}
EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);

/**
 * ring_buffer_free_read_page - free an allocated read page
 * @buffer: the buffer the page was allocate for
 * @data: the page to free
 *
 * Free a page allocated from ring_buffer_alloc_read_page.
 */
void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
{
      free_page((unsigned long)data);
}
EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);

/**
 * ring_buffer_read_page - extract a page from the ring buffer
 * @buffer: buffer to extract from
 * @data_page: the page to use allocated from ring_buffer_alloc_read_page
 * @len: amount to extract
 * @cpu: the cpu of the buffer to extract
 * @full: should the extraction only happen when the page is full.
 *
 * This function will pull out a page from the ring buffer and consume it.
 * @data_page must be the address of the variable that was returned
 * from ring_buffer_alloc_read_page. This is because the page might be used
 * to swap with a page in the ring buffer.
 *
 * for example:
 *    rpage = ring_buffer_alloc_read_page(buffer);
 *    if (!rpage)
 *          return error;
 *    ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
 *    if (ret >= 0)
 *          process_page(rpage, ret);
 *
 * When @full is set, the function will not return true unless
 * the writer is off the reader page.
 *
 * Note: it is up to the calling functions to handle sleeps and wakeups.
 *  The ring buffer can be used anywhere in the kernel and can not
 *  blindly call wake_up. The layer that uses the ring buffer must be
 *  responsible for that.
 *
 * Returns:
 *  >=0 if data has been transferred, returns the offset of consumed data.
 *  <0 if no data has been transferred.
 */
int ring_buffer_read_page(struct ring_buffer *buffer,
                    void **data_page, size_t len, int cpu, int full)
{
      struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
      struct ring_buffer_event *event;
      struct buffer_data_page *bpage;
      struct buffer_page *reader;
      unsigned long flags;
      unsigned int commit;
      unsigned int read;
      u64 save_timestamp;
      int ret = -1;

      if (!cpumask_test_cpu(cpu, buffer->cpumask))
            goto out;

      /*
       * If len is not big enough to hold the page header, then
       * we can not copy anything.
       */
      if (len <= BUF_PAGE_HDR_SIZE)
            goto out;

      len -= BUF_PAGE_HDR_SIZE;

      if (!data_page)
            goto out;

      bpage = *data_page;
      if (!bpage)
            goto out;

      spin_lock_irqsave(&cpu_buffer->reader_lock, flags);

      reader = rb_get_reader_page(cpu_buffer);
      if (!reader)
            goto out_unlock;

      event = rb_reader_event(cpu_buffer);

      read = reader->read;
      commit = rb_page_commit(reader);

      /*
       * If this page has been partially read or
       * if len is not big enough to read the rest of the page or
       * a writer is still on the page, then
       * we must copy the data from the page to the buffer.
       * Otherwise, we can simply swap the page with the one passed in.
       */
      if (read || (len < (commit - read)) ||
          cpu_buffer->reader_page == cpu_buffer->commit_page) {
            struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
            unsigned int rpos = read;
            unsigned int pos = 0;
            unsigned int size;

            if (full)
                  goto out_unlock;

            if (len > (commit - read))
                  len = (commit - read);

            size = rb_event_length(event);

            if (len < size)
                  goto out_unlock;

            /* save the current timestamp, since the user will need it */
            save_timestamp = cpu_buffer->read_stamp;

            /* Need to copy one event at a time */
            do {
                  memcpy(bpage->data + pos, rpage->data + rpos, size);

                  len -= size;

                  rb_advance_reader(cpu_buffer);
                  rpos = reader->read;
                  pos += size;

                  event = rb_reader_event(cpu_buffer);
                  size = rb_event_length(event);
            } while (len > size);

            /* update bpage */
            local_set(&bpage->commit, pos);
            bpage->time_stamp = save_timestamp;

            /* we copied everything to the beginning */
            read = 0;
      } else {
            /* update the entry counter */
            cpu_buffer->read += local_read(&reader->entries);

            /* swap the pages */
            rb_init_page(bpage);
            bpage = reader->page;
            reader->page = *data_page;
            local_set(&reader->write, 0);
            local_set(&reader->entries, 0);
            reader->read = 0;
            *data_page = bpage;
      }
      ret = read;

 out_unlock:
      spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);

 out:
      return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_read_page);

#ifdef CONFIG_TRACING
static ssize_t
rb_simple_read(struct file *filp, char __user *ubuf,
             size_t cnt, loff_t *ppos)
{
      unsigned long *p = filp->private_data;
      char buf[64];
      int r;

      if (test_bit(RB_BUFFERS_DISABLED_BIT, p))
            r = sprintf(buf, "permanently disabled\n");
      else
            r = sprintf(buf, "%d\n", test_bit(RB_BUFFERS_ON_BIT, p));

      return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
}

static ssize_t
rb_simple_write(struct file *filp, const char __user *ubuf,
            size_t cnt, loff_t *ppos)
{
      unsigned long *p = filp->private_data;
      char buf[64];
      unsigned long val;
      int ret;

      if (cnt >= sizeof(buf))
            return -EINVAL;

      if (copy_from_user(&buf, ubuf, cnt))
            return -EFAULT;

      buf[cnt] = 0;

      ret = strict_strtoul(buf, 10, &val);
      if (ret < 0)
            return ret;

      if (val)
            set_bit(RB_BUFFERS_ON_BIT, p);
      else
            clear_bit(RB_BUFFERS_ON_BIT, p);

      (*ppos)++;

      return cnt;
}

static const struct file_operations rb_simple_fops = {
      .open       = tracing_open_generic,
      .read       = rb_simple_read,
      .write            = rb_simple_write,
};


static __init int rb_init_debugfs(void)
{
      struct dentry *d_tracer;

      d_tracer = tracing_init_dentry();

      trace_create_file("tracing_on", 0644, d_tracer,
                      &ring_buffer_flags, &rb_simple_fops);

      return 0;
}

fs_initcall(rb_init_debugfs);
#endif

#ifdef CONFIG_HOTPLUG_CPU
static int rb_cpu_notify(struct notifier_block *self,
                   unsigned long action, void *hcpu)
{
      struct ring_buffer *buffer =
            container_of(self, struct ring_buffer, cpu_notify);
      long cpu = (long)hcpu;

      switch (action) {
      case CPU_UP_PREPARE:
      case CPU_UP_PREPARE_FROZEN:
            if (cpumask_test_cpu(cpu, buffer->cpumask))
                  return NOTIFY_OK;

            buffer->buffers[cpu] =
                  rb_allocate_cpu_buffer(buffer, cpu);
            if (!buffer->buffers[cpu]) {
                  WARN(1, "failed to allocate ring buffer on CPU %ld\n",
                       cpu);
                  return NOTIFY_OK;
            }
            smp_wmb();
            cpumask_set_cpu(cpu, buffer->cpumask);
            break;
      case CPU_DOWN_PREPARE:
      case CPU_DOWN_PREPARE_FROZEN:
            /*
             * Do nothing.
             *  If we were to free the buffer, then the user would
             *  lose any trace that was in the buffer.
             */
            break;
      default:
            break;
      }
      return NOTIFY_OK;
}
#endif

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