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blktrace.c

/*
 * Copyright (C) 2006 Jens Axboe <axboe@kernel.dk>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */
#include <linux/kernel.h>
#include <linux/blkdev.h>
#include <linux/blktrace_api.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/mutex.h>
#include <linux/debugfs.h>
#include <linux/time.h>
#include <asm/uaccess.h>

static unsigned int blktrace_seq __read_mostly = 1;

/*
 * Send out a notify message.
 */
static void trace_note(struct blk_trace *bt, pid_t pid, int action,
                   const void *data, size_t len)
{
      struct blk_io_trace *t;

      t = relay_reserve(bt->rchan, sizeof(*t) + len);
      if (t) {
            const int cpu = smp_processor_id();

            t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
            t->time = ktime_to_ns(ktime_get());
            t->device = bt->dev;
            t->action = action;
            t->pid = pid;
            t->cpu = cpu;
            t->pdu_len = len;
            memcpy((void *) t + sizeof(*t), data, len);
      }
}

/*
 * Send out a notify for this process, if we haven't done so since a trace
 * started
 */
static void trace_note_tsk(struct blk_trace *bt, struct task_struct *tsk)
{
      tsk->btrace_seq = blktrace_seq;
      trace_note(bt, tsk->pid, BLK_TN_PROCESS, tsk->comm, sizeof(tsk->comm));
}

static void trace_note_time(struct blk_trace *bt)
{
      struct timespec now;
      unsigned long flags;
      u32 words[2];

      getnstimeofday(&now);
      words[0] = now.tv_sec;
      words[1] = now.tv_nsec;

      local_irq_save(flags);
      trace_note(bt, 0, BLK_TN_TIMESTAMP, words, sizeof(words));
      local_irq_restore(flags);
}

static int act_log_check(struct blk_trace *bt, u32 what, sector_t sector,
                   pid_t pid)
{
      if (((bt->act_mask << BLK_TC_SHIFT) & what) == 0)
            return 1;
      if (sector < bt->start_lba || sector > bt->end_lba)
            return 1;
      if (bt->pid && pid != bt->pid)
            return 1;

      return 0;
}

/*
 * Data direction bit lookup
 */
static u32 ddir_act[2] __read_mostly = { BLK_TC_ACT(BLK_TC_READ), BLK_TC_ACT(BLK_TC_WRITE) };

/*
 * Bio action bits of interest
 */
static u32 bio_act[9] __read_mostly = { 0, BLK_TC_ACT(BLK_TC_BARRIER), BLK_TC_ACT(BLK_TC_SYNC), 0, BLK_TC_ACT(BLK_TC_AHEAD), 0, 0, 0, BLK_TC_ACT(BLK_TC_META) };

/*
 * More could be added as needed, taking care to increment the decrementer
 * to get correct indexing
 */
#define trace_barrier_bit(rw) \
      (((rw) & (1 << BIO_RW_BARRIER)) >> (BIO_RW_BARRIER - 0))
#define trace_sync_bit(rw)    \
      (((rw) & (1 << BIO_RW_SYNC)) >> (BIO_RW_SYNC - 1))
#define trace_ahead_bit(rw)   \
      (((rw) & (1 << BIO_RW_AHEAD)) << (2 - BIO_RW_AHEAD))
#define trace_meta_bit(rw)    \
      (((rw) & (1 << BIO_RW_META)) >> (BIO_RW_META - 3))

/*
 * The worker for the various blk_add_trace*() types. Fills out a
 * blk_io_trace structure and places it in a per-cpu subbuffer.
 */
void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
                 int rw, u32 what, int error, int pdu_len, void *pdu_data)
{
      struct task_struct *tsk = current;
      struct blk_io_trace *t;
      unsigned long flags;
      unsigned long *sequence;
      pid_t pid;
      int cpu;

      if (unlikely(bt->trace_state != Blktrace_running))
            return;

      what |= ddir_act[rw & WRITE];
      what |= bio_act[trace_barrier_bit(rw)];
      what |= bio_act[trace_sync_bit(rw)];
      what |= bio_act[trace_ahead_bit(rw)];
      what |= bio_act[trace_meta_bit(rw)];

      pid = tsk->pid;
      if (unlikely(act_log_check(bt, what, sector, pid)))
            return;

      /*
       * A word about the locking here - we disable interrupts to reserve
       * some space in the relay per-cpu buffer, to prevent an irq
       * from coming in and stepping on our toes. Once reserved, it's
       * enough to get preemption disabled to prevent read of this data
       * before we are through filling it. get_cpu()/put_cpu() does this
       * for us
       */
      local_irq_save(flags);

      if (unlikely(tsk->btrace_seq != blktrace_seq))
            trace_note_tsk(bt, tsk);

      t = relay_reserve(bt->rchan, sizeof(*t) + pdu_len);
      if (t) {
            cpu = smp_processor_id();
            sequence = per_cpu_ptr(bt->sequence, cpu);

            t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
            t->sequence = ++(*sequence);
            t->time = ktime_to_ns(ktime_get());
            t->sector = sector;
            t->bytes = bytes;
            t->action = what;
            t->pid = pid;
            t->device = bt->dev;
            t->cpu = cpu;
            t->error = error;
            t->pdu_len = pdu_len;

            if (pdu_len)
                  memcpy((void *) t + sizeof(*t), pdu_data, pdu_len);
      }

      local_irq_restore(flags);
}

EXPORT_SYMBOL_GPL(__blk_add_trace);

static struct dentry *blk_tree_root;
static DEFINE_MUTEX(blk_tree_mutex);
static unsigned int root_users;

static inline void blk_remove_root(void)
{
      if (blk_tree_root) {
            debugfs_remove(blk_tree_root);
            blk_tree_root = NULL;
      }
}

static void blk_remove_tree(struct dentry *dir)
{
      mutex_lock(&blk_tree_mutex);
      debugfs_remove(dir);
      if (--root_users == 0)
            blk_remove_root();
      mutex_unlock(&blk_tree_mutex);
}

static struct dentry *blk_create_tree(const char *blk_name)
{
      struct dentry *dir = NULL;
      int created = 0;

      mutex_lock(&blk_tree_mutex);

      if (!blk_tree_root) {
            blk_tree_root = debugfs_create_dir("block", NULL);
            if (!blk_tree_root)
                  goto err;
            created = 1;
      }

      dir = debugfs_create_dir(blk_name, blk_tree_root);
      if (dir)
            root_users++;
      else {
            /* Delete root only if we created it */
            if (created)
                  blk_remove_root();
      }

err:
      mutex_unlock(&blk_tree_mutex);
      return dir;
}

static void blk_trace_cleanup(struct blk_trace *bt)
{
      relay_close(bt->rchan);
      debugfs_remove(bt->dropped_file);
      blk_remove_tree(bt->dir);
      free_percpu(bt->sequence);
      kfree(bt);
}

static int blk_trace_remove(struct request_queue *q)
{
      struct blk_trace *bt;

      bt = xchg(&q->blk_trace, NULL);
      if (!bt)
            return -EINVAL;

      if (bt->trace_state == Blktrace_setup ||
          bt->trace_state == Blktrace_stopped)
            blk_trace_cleanup(bt);

      return 0;
}

static int blk_dropped_open(struct inode *inode, struct file *filp)
{
      filp->private_data = inode->i_private;

      return 0;
}

static ssize_t blk_dropped_read(struct file *filp, char __user *buffer,
                        size_t count, loff_t *ppos)
{
      struct blk_trace *bt = filp->private_data;
      char buf[16];

      snprintf(buf, sizeof(buf), "%u\n", atomic_read(&bt->dropped));

      return simple_read_from_buffer(buffer, count, ppos, buf, strlen(buf));
}

static const struct file_operations blk_dropped_fops = {
      .owner =    THIS_MODULE,
      .open =           blk_dropped_open,
      .read =           blk_dropped_read,
};

/*
 * Keep track of how many times we encountered a full subbuffer, to aid
 * the user space app in telling how many lost events there were.
 */
static int blk_subbuf_start_callback(struct rchan_buf *buf, void *subbuf,
                             void *prev_subbuf, size_t prev_padding)
{
      struct blk_trace *bt;

      if (!relay_buf_full(buf))
            return 1;

      bt = buf->chan->private_data;
      atomic_inc(&bt->dropped);
      return 0;
}

static int blk_remove_buf_file_callback(struct dentry *dentry)
{
      debugfs_remove(dentry);
      return 0;
}

static struct dentry *blk_create_buf_file_callback(const char *filename,
                                       struct dentry *parent,
                                       int mode,
                                       struct rchan_buf *buf,
                                       int *is_global)
{
      return debugfs_create_file(filename, mode, parent, buf,
                              &relay_file_operations);
}

static struct rchan_callbacks blk_relay_callbacks = {
      .subbuf_start           = blk_subbuf_start_callback,
      .create_buf_file  = blk_create_buf_file_callback,
      .remove_buf_file  = blk_remove_buf_file_callback,
};

/*
 * Setup everything required to start tracing
 */
int do_blk_trace_setup(struct request_queue *q, struct block_device *bdev,
                  struct blk_user_trace_setup *buts)
{
      struct blk_trace *old_bt, *bt = NULL;
      struct dentry *dir = NULL;
      char b[BDEVNAME_SIZE];
      int ret, i;

      if (!buts->buf_size || !buts->buf_nr)
            return -EINVAL;

      strcpy(buts->name, bdevname(bdev, b));

      /*
       * some device names have larger paths - convert the slashes
       * to underscores for this to work as expected
       */
      for (i = 0; i < strlen(buts->name); i++)
            if (buts->name[i] == '/')
                  buts->name[i] = '_';

      ret = -ENOMEM;
      bt = kzalloc(sizeof(*bt), GFP_KERNEL);
      if (!bt)
            goto err;

      bt->sequence = alloc_percpu(unsigned long);
      if (!bt->sequence)
            goto err;

      ret = -ENOENT;
      dir = blk_create_tree(buts->name);
      if (!dir)
            goto err;

      bt->dir = dir;
      bt->dev = bdev->bd_dev;
      atomic_set(&bt->dropped, 0);

      ret = -EIO;
      bt->dropped_file = debugfs_create_file("dropped", 0444, dir, bt, &blk_dropped_fops);
      if (!bt->dropped_file)
            goto err;

      bt->rchan = relay_open("trace", dir, buts->buf_size,
                        buts->buf_nr, &blk_relay_callbacks, bt);
      if (!bt->rchan)
            goto err;

      bt->act_mask = buts->act_mask;
      if (!bt->act_mask)
            bt->act_mask = (u16) -1;

      bt->start_lba = buts->start_lba;
      bt->end_lba = buts->end_lba;
      if (!bt->end_lba)
            bt->end_lba = -1ULL;

      bt->pid = buts->pid;
      bt->trace_state = Blktrace_setup;

      ret = -EBUSY;
      old_bt = xchg(&q->blk_trace, bt);
      if (old_bt) {
            (void) xchg(&q->blk_trace, old_bt);
            goto err;
      }

      return 0;
err:
      if (dir)
            blk_remove_tree(dir);
      if (bt) {
            if (bt->dropped_file)
                  debugfs_remove(bt->dropped_file);
            free_percpu(bt->sequence);
            if (bt->rchan)
                  relay_close(bt->rchan);
            kfree(bt);
      }
      return ret;
}

static int blk_trace_setup(struct request_queue *q, struct block_device *bdev,
                     char __user *arg)
{
      struct blk_user_trace_setup buts;
      int ret;

      ret = copy_from_user(&buts, arg, sizeof(buts));
      if (ret)
            return -EFAULT;

      ret = do_blk_trace_setup(q, bdev, &buts);
      if (ret)
            return ret;

      if (copy_to_user(arg, &buts, sizeof(buts)))
            return -EFAULT;

      return 0;
}

static int blk_trace_startstop(struct request_queue *q, int start)
{
      struct blk_trace *bt;
      int ret;

      if ((bt = q->blk_trace) == NULL)
            return -EINVAL;

      /*
       * For starting a trace, we can transition from a setup or stopped
       * trace. For stopping a trace, the state must be running
       */
      ret = -EINVAL;
      if (start) {
            if (bt->trace_state == Blktrace_setup ||
                bt->trace_state == Blktrace_stopped) {
                  blktrace_seq++;
                  smp_mb();
                  bt->trace_state = Blktrace_running;

                  trace_note_time(bt);
                  ret = 0;
            }
      } else {
            if (bt->trace_state == Blktrace_running) {
                  bt->trace_state = Blktrace_stopped;
                  relay_flush(bt->rchan);
                  ret = 0;
            }
      }

      return ret;
}

/**
 * blk_trace_ioctl: - handle the ioctls associated with tracing
 * @bdev:   the block device
 * @cmd:    the ioctl cmd
 * @arg:    the argument data, if any
 *
 **/
int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
{
      struct request_queue *q;
      int ret, start = 0;

      q = bdev_get_queue(bdev);
      if (!q)
            return -ENXIO;

      mutex_lock(&bdev->bd_mutex);

      switch (cmd) {
      case BLKTRACESETUP:
            ret = blk_trace_setup(q, bdev, arg);
            break;
      case BLKTRACESTART:
            start = 1;
      case BLKTRACESTOP:
            ret = blk_trace_startstop(q, start);
            break;
      case BLKTRACETEARDOWN:
            ret = blk_trace_remove(q);
            break;
      default:
            ret = -ENOTTY;
            break;
      }

      mutex_unlock(&bdev->bd_mutex);
      return ret;
}

/**
 * blk_trace_shutdown: - stop and cleanup trace structures
 * @q:    the request queue associated with the device
 *
 **/
void blk_trace_shutdown(struct request_queue *q)
{
      if (q->blk_trace) {
            blk_trace_startstop(q, 0);
            blk_trace_remove(q);
      }
}

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