trace: judicious error checking of trace_seq results

[linux-2.6/libata-dev.git] / block / 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 <trace/block.h>
#include <linux/uaccess.h>
#include <../kernel/trace/trace_output.h>

static unsigned int blktrace_seq __read_mostly = 1;

static struct trace_array *blk_tr;
static int __read_mostly  blk_tracer_enabled;

/* Select an alternative, minimalistic output than the original one */
#define TRACE_BLK_OPT_CLASSIC   0x1

static struct tracer_opt blk_tracer_opts[] = {
        /* Default disable the minimalistic output */
        { TRACER_OPT(blk_classic, TRACE_BLK_OPT_CLASSIC) },
        { }
};

static struct tracer_flags blk_tracer_flags = {
        .val  = 0,
        .opts = blk_tracer_opts,
};

/* Global reference count of probes */
static DEFINE_MUTEX(blk_probe_mutex);
static atomic_t blk_probes_ref = ATOMIC_INIT(0);

static int blk_register_tracepoints(void);
static void blk_unregister_tracepoints(void);

/*
 * 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;

        if (!bt->rchan)
                return;

        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);
}

void __trace_note_message(struct blk_trace *bt, const char *fmt, ...)
{
        int n;
        va_list args;
        unsigned long flags;
        char *buf;

        if (blk_tr) {
                va_start(args, fmt);
                ftrace_vprintk(fmt, args);
                va_end(args);
                return;
        }

        if (!bt->msg_data)
                return;

        local_irq_save(flags);
        buf = per_cpu_ptr(bt->msg_data, smp_processor_id());
        va_start(args, fmt);
        n = vscnprintf(buf, BLK_TN_MAX_MSG, fmt, args);
        va_end(args);

        trace_note(bt, 0, BLK_TN_MESSAGE, buf, n);
        local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(__trace_note_message);

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) };

/* The ilog2() calls fall out because they're constant */
#define MASK_TC_BIT(rw, __name) ((rw & (1 << BIO_RW_ ## __name)) << \
          (ilog2(BLK_TC_ ## __name) + BLK_TC_SHIFT - BIO_RW_ ## __name))

/*
 * The worker for the various blk_add_trace*() types. Fills out a
 * blk_io_trace structure and places it in a per-cpu subbuffer.
 */
static 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 ring_buffer_event *event = NULL;
        struct blk_io_trace *t;
        unsigned long flags;
        unsigned long *sequence;
        pid_t pid;
        int cpu, pc = 0;

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

        what |= ddir_act[rw & WRITE];
        what |= MASK_TC_BIT(rw, BARRIER);
        what |= MASK_TC_BIT(rw, SYNC);
        what |= MASK_TC_BIT(rw, AHEAD);
        what |= MASK_TC_BIT(rw, META);
        what |= MASK_TC_BIT(rw, DISCARD);

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

        if (blk_tr) {
                struct trace_entry *ent;
                tracing_record_cmdline(current);

                event = ring_buffer_lock_reserve(blk_tr->buffer,
                                                 sizeof(*t) + pdu_len, &flags);
                if (!event)
                        return;

                ent = ring_buffer_event_data(event);
                t = (struct blk_io_trace *)ent;
                pc = preempt_count();
                tracing_generic_entry_update(ent, 0, pc);
                ent->type = TRACE_BLK;
                goto record_it;
        }

        /*
         * 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.
         */
        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) {
                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());
record_it:
                /*
                 * These two are not needed in ftrace as they are in the
                 * generic trace_entry, filled by tracing_generic_entry_update,
                 * but for the trace_event->bin() synthesizer benefit we do it
                 * here too.
                 */
                t->cpu = cpu;
                t->pid = pid;

                t->sector = sector;
                t->bytes = bytes;
                t->action = what;
                t->device = bt->dev;
                t->error = error;
                t->pdu_len = pdu_len;

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

                if (blk_tr) {
                        ring_buffer_unlock_commit(blk_tr->buffer, event, flags);
                        if (pid != 0 &&
                            !(blk_tracer_flags.val & TRACE_BLK_OPT_CLASSIC) &&
                            (trace_flags & TRACE_ITER_STACKTRACE) != 0)
                                __trace_stack(blk_tr, NULL, flags, 5, pc);
                        trace_wake_up();
                        return;
                }
        }

        local_irq_restore(flags);
}

static struct dentry *blk_tree_root;
static DEFINE_MUTEX(blk_tree_mutex);

static void blk_trace_cleanup(struct blk_trace *bt)
{
        debugfs_remove(bt->msg_file);
        debugfs_remove(bt->dropped_file);
        relay_close(bt->rchan);
        free_percpu(bt->sequence);
        free_percpu(bt->msg_data);
        kfree(bt);
        mutex_lock(&blk_probe_mutex);
        if (atomic_dec_and_test(&blk_probes_ref))
                blk_unregister_tracepoints();
        mutex_unlock(&blk_probe_mutex);
}

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;
}
EXPORT_SYMBOL_GPL(blk_trace_remove);

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,
};

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

        return 0;
}

static ssize_t blk_msg_write(struct file *filp, const char __user *buffer,
                                size_t count, loff_t *ppos)
{
        char *msg;
        struct blk_trace *bt;

        if (count > BLK_TN_MAX_MSG)
                return -EINVAL;

        msg = kmalloc(count, GFP_KERNEL);
        if (msg == NULL)
                return -ENOMEM;

        if (copy_from_user(msg, buffer, count)) {
                kfree(msg);
                return -EFAULT;
        }

        bt = filp->private_data;
        __trace_note_message(bt, "%s", msg);
        kfree(msg);

        return count;
}

static const struct file_operations blk_msg_fops = {
        .owner =        THIS_MODULE,
        .open =         blk_msg_open,
        .write =        blk_msg_write,
};

/*
 * 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)
{
        struct dentry *parent = dentry->d_parent;
        debugfs_remove(dentry);

        /*
        * this will fail for all but the last file, but that is ok. what we
        * care about is the top level buts->name directory going away, when
        * the last trace file is gone. Then we don't have to rmdir() that
        * manually on trace stop, so it nicely solves the issue with
        * force killing of running traces.
        */

        debugfs_remove(parent);
        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, char *name, dev_t dev,
                        struct blk_user_trace_setup *buts)
{
        struct blk_trace *old_bt, *bt = NULL;
        struct dentry *dir = NULL;
        int ret, i;

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

        strncpy(buts->name, name, BLKTRACE_BDEV_SIZE);
        buts->name[BLKTRACE_BDEV_SIZE - 1] = '\0';

        /*
         * 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;

        bt->msg_data = __alloc_percpu(BLK_TN_MAX_MSG);
        if (!bt->msg_data)
                goto err;

        ret = -ENOENT;

        if (!blk_tree_root) {
                blk_tree_root = debugfs_create_dir("block", NULL);
                if (!blk_tree_root)
                        return -ENOMEM;
        }

        dir = debugfs_create_dir(buts->name, blk_tree_root);

        if (!dir)
                goto err;

        bt->dir = dir;
        bt->dev = 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->msg_file = debugfs_create_file("msg", 0222, dir, bt, &blk_msg_fops);
        if (!bt->msg_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;

        mutex_lock(&blk_probe_mutex);
        if (atomic_add_return(1, &blk_probes_ref) == 1) {
                ret = blk_register_tracepoints();
                if (ret)
                        goto probe_err;
        }
        mutex_unlock(&blk_probe_mutex);

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

        return 0;
probe_err:
        atomic_dec(&blk_probes_ref);
        mutex_unlock(&blk_probe_mutex);
err:
        if (bt) {
                if (bt->msg_file)
                        debugfs_remove(bt->msg_file);
                if (bt->dropped_file)
                        debugfs_remove(bt->dropped_file);
                free_percpu(bt->sequence);
                free_percpu(bt->msg_data);
                if (bt->rchan)
                        relay_close(bt->rchan);
                kfree(bt);
        }
        return ret;
}

int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
                    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, name, dev, &buts);
        if (ret)
                return ret;

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

        return 0;
}
EXPORT_SYMBOL_GPL(blk_trace_setup);

int blk_trace_startstop(struct request_queue *q, int start)
{
        int ret;
        struct blk_trace *bt = q->blk_trace;

        if (bt == 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;
}
EXPORT_SYMBOL_GPL(blk_trace_startstop);

/**
 * 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;
        char b[BDEVNAME_SIZE];

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

        mutex_lock(&bdev->bd_mutex);

        switch (cmd) {
        case BLKTRACESETUP:
                bdevname(bdev, b);
                ret = blk_trace_setup(q, b, bdev->bd_dev, 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);
        }
}

/*
 * blktrace probes
 */

/**
 * blk_add_trace_rq - Add a trace for a request oriented action
 * @q:          queue the io is for
 * @rq:         the source request
 * @what:       the action
 *
 * Description:
 *     Records an action against a request. Will log the bio offset + size.
 *
 **/
static void blk_add_trace_rq(struct request_queue *q, struct request *rq,
                                    u32 what)
{
        struct blk_trace *bt = q->blk_trace;
        int rw = rq->cmd_flags & 0x03;

        if (likely(!bt))
                return;

        if (blk_discard_rq(rq))
                rw |= (1 << BIO_RW_DISCARD);

        if (blk_pc_request(rq)) {
                what |= BLK_TC_ACT(BLK_TC_PC);
                __blk_add_trace(bt, 0, rq->data_len, rw, what, rq->errors,
                                sizeof(rq->cmd), rq->cmd);
        } else  {
                what |= BLK_TC_ACT(BLK_TC_FS);
                __blk_add_trace(bt, rq->hard_sector, rq->hard_nr_sectors << 9,
                                rw, what, rq->errors, 0, NULL);
        }
}

static void blk_add_trace_rq_abort(struct request_queue *q, struct request *rq)
{
        blk_add_trace_rq(q, rq, BLK_TA_ABORT);
}

static void blk_add_trace_rq_insert(struct request_queue *q, struct request *rq)
{
        blk_add_trace_rq(q, rq, BLK_TA_INSERT);
}

static void blk_add_trace_rq_issue(struct request_queue *q, struct request *rq)
{
        blk_add_trace_rq(q, rq, BLK_TA_ISSUE);
}

static void blk_add_trace_rq_requeue(struct request_queue *q,
                                     struct request *rq)
{
        blk_add_trace_rq(q, rq, BLK_TA_REQUEUE);
}

static void blk_add_trace_rq_complete(struct request_queue *q,
                                      struct request *rq)
{
        blk_add_trace_rq(q, rq, BLK_TA_COMPLETE);
}

/**
 * blk_add_trace_bio - Add a trace for a bio oriented action
 * @q:          queue the io is for
 * @bio:        the source bio
 * @what:       the action
 *
 * Description:
 *     Records an action against a bio. Will log the bio offset + size.
 *
 **/
static void blk_add_trace_bio(struct request_queue *q, struct bio *bio,
                                     u32 what)
{
        struct blk_trace *bt = q->blk_trace;

        if (likely(!bt))
                return;

        __blk_add_trace(bt, bio->bi_sector, bio->bi_size, bio->bi_rw, what,
                        !bio_flagged(bio, BIO_UPTODATE), 0, NULL);
}

static void blk_add_trace_bio_bounce(struct request_queue *q, struct bio *bio)
{
        blk_add_trace_bio(q, bio, BLK_TA_BOUNCE);
}

static void blk_add_trace_bio_complete(struct request_queue *q, struct bio *bio)
{
        blk_add_trace_bio(q, bio, BLK_TA_COMPLETE);
}

static void blk_add_trace_bio_backmerge(struct request_queue *q,
                                        struct bio *bio)
{
        blk_add_trace_bio(q, bio, BLK_TA_BACKMERGE);
}

static void blk_add_trace_bio_frontmerge(struct request_queue *q,
                                         struct bio *bio)
{
        blk_add_trace_bio(q, bio, BLK_TA_FRONTMERGE);
}

static void blk_add_trace_bio_queue(struct request_queue *q, struct bio *bio)
{
        blk_add_trace_bio(q, bio, BLK_TA_QUEUE);
}

static void blk_add_trace_getrq(struct request_queue *q,
                                struct bio *bio, int rw)
{
        if (bio)
                blk_add_trace_bio(q, bio, BLK_TA_GETRQ);
        else {
                struct blk_trace *bt = q->blk_trace;

                if (bt)
                        __blk_add_trace(bt, 0, 0, rw, BLK_TA_GETRQ, 0, 0, NULL);
        }
}


static void blk_add_trace_sleeprq(struct request_queue *q,
                                  struct bio *bio, int rw)
{
        if (bio)
                blk_add_trace_bio(q, bio, BLK_TA_SLEEPRQ);
        else {
                struct blk_trace *bt = q->blk_trace;

                if (bt)
                        __blk_add_trace(bt, 0, 0, rw, BLK_TA_SLEEPRQ,
                                        0, 0, NULL);
        }
}

static void blk_add_trace_plug(struct request_queue *q)
{
        struct blk_trace *bt = q->blk_trace;

        if (bt)
                __blk_add_trace(bt, 0, 0, 0, BLK_TA_PLUG, 0, 0, NULL);
}

static void blk_add_trace_unplug_io(struct request_queue *q)
{
        struct blk_trace *bt = q->blk_trace;

        if (bt) {
                unsigned int pdu = q->rq.count[READ] + q->rq.count[WRITE];
                __be64 rpdu = cpu_to_be64(pdu);

                __blk_add_trace(bt, 0, 0, 0, BLK_TA_UNPLUG_IO, 0,
                                sizeof(rpdu), &rpdu);
        }
}

static void blk_add_trace_unplug_timer(struct request_queue *q)
{
        struct blk_trace *bt = q->blk_trace;

        if (bt) {
                unsigned int pdu = q->rq.count[READ] + q->rq.count[WRITE];
                __be64 rpdu = cpu_to_be64(pdu);

                __blk_add_trace(bt, 0, 0, 0, BLK_TA_UNPLUG_TIMER, 0,
                                sizeof(rpdu), &rpdu);
        }
}

static void blk_add_trace_split(struct request_queue *q, struct bio *bio,
                                unsigned int pdu)
{
        struct blk_trace *bt = q->blk_trace;

        if (bt) {
                __be64 rpdu = cpu_to_be64(pdu);

                __blk_add_trace(bt, bio->bi_sector, bio->bi_size, bio->bi_rw,
                                BLK_TA_SPLIT, !bio_flagged(bio, BIO_UPTODATE),
                                sizeof(rpdu), &rpdu);
        }
}

/**
 * blk_add_trace_remap - Add a trace for a remap operation
 * @q:          queue the io is for
 * @bio:        the source bio
 * @dev:        target device
 * @from:       source sector
 * @to:         target sector
 *
 * Description:
 *     Device mapper or raid target sometimes need to split a bio because
 *     it spans a stripe (or similar). Add a trace for that action.
 *
 **/
static void blk_add_trace_remap(struct request_queue *q, struct bio *bio,
                                       dev_t dev, sector_t from, sector_t to)
{
        struct blk_trace *bt = q->blk_trace;
        struct blk_io_trace_remap r;

        if (likely(!bt))
                return;

        r.device = cpu_to_be32(dev);
        r.device_from = cpu_to_be32(bio->bi_bdev->bd_dev);
        r.sector = cpu_to_be64(to);

        __blk_add_trace(bt, from, bio->bi_size, bio->bi_rw, BLK_TA_REMAP,
                        !bio_flagged(bio, BIO_UPTODATE), sizeof(r), &r);
}

/**
 * blk_add_driver_data - Add binary message with driver-specific data
 * @q:          queue the io is for
 * @rq:         io request
 * @data:       driver-specific data
 * @len:        length of driver-specific data
 *
 * Description:
 *     Some drivers might want to write driver-specific data per request.
 *
 **/
void blk_add_driver_data(struct request_queue *q,
                         struct request *rq,
                         void *data, size_t len)
{
        struct blk_trace *bt = q->blk_trace;

        if (likely(!bt))
                return;

        if (blk_pc_request(rq))
                __blk_add_trace(bt, 0, rq->data_len, 0, BLK_TA_DRV_DATA,
                                rq->errors, len, data);
        else
                __blk_add_trace(bt, rq->hard_sector, rq->hard_nr_sectors << 9,
                                0, BLK_TA_DRV_DATA, rq->errors, len, data);
}
EXPORT_SYMBOL_GPL(blk_add_driver_data);

static int blk_register_tracepoints(void)
{
        int ret;

        ret = register_trace_block_rq_abort(blk_add_trace_rq_abort);
        WARN_ON(ret);
        ret = register_trace_block_rq_insert(blk_add_trace_rq_insert);
        WARN_ON(ret);
        ret = register_trace_block_rq_issue(blk_add_trace_rq_issue);
        WARN_ON(ret);
        ret = register_trace_block_rq_requeue(blk_add_trace_rq_requeue);
        WARN_ON(ret);
        ret = register_trace_block_rq_complete(blk_add_trace_rq_complete);
        WARN_ON(ret);
        ret = register_trace_block_bio_bounce(blk_add_trace_bio_bounce);
        WARN_ON(ret);
        ret = register_trace_block_bio_complete(blk_add_trace_bio_complete);
        WARN_ON(ret);
        ret = register_trace_block_bio_backmerge(blk_add_trace_bio_backmerge);
        WARN_ON(ret);
        ret = register_trace_block_bio_frontmerge(blk_add_trace_bio_frontmerge);
        WARN_ON(ret);
        ret = register_trace_block_bio_queue(blk_add_trace_bio_queue);
        WARN_ON(ret);
        ret = register_trace_block_getrq(blk_add_trace_getrq);
        WARN_ON(ret);
        ret = register_trace_block_sleeprq(blk_add_trace_sleeprq);
        WARN_ON(ret);
        ret = register_trace_block_plug(blk_add_trace_plug);
        WARN_ON(ret);
        ret = register_trace_block_unplug_timer(blk_add_trace_unplug_timer);
        WARN_ON(ret);
        ret = register_trace_block_unplug_io(blk_add_trace_unplug_io);
        WARN_ON(ret);
        ret = register_trace_block_split(blk_add_trace_split);
        WARN_ON(ret);
        ret = register_trace_block_remap(blk_add_trace_remap);
        WARN_ON(ret);
        return 0;
}

static void blk_unregister_tracepoints(void)
{
        unregister_trace_block_remap(blk_add_trace_remap);
        unregister_trace_block_split(blk_add_trace_split);
        unregister_trace_block_unplug_io(blk_add_trace_unplug_io);
        unregister_trace_block_unplug_timer(blk_add_trace_unplug_timer);
        unregister_trace_block_plug(blk_add_trace_plug);
        unregister_trace_block_sleeprq(blk_add_trace_sleeprq);
        unregister_trace_block_getrq(blk_add_trace_getrq);
        unregister_trace_block_bio_queue(blk_add_trace_bio_queue);
        unregister_trace_block_bio_frontmerge(blk_add_trace_bio_frontmerge);
        unregister_trace_block_bio_backmerge(blk_add_trace_bio_backmerge);
        unregister_trace_block_bio_complete(blk_add_trace_bio_complete);
        unregister_trace_block_bio_bounce(blk_add_trace_bio_bounce);
        unregister_trace_block_rq_complete(blk_add_trace_rq_complete);
        unregister_trace_block_rq_requeue(blk_add_trace_rq_requeue);
        unregister_trace_block_rq_issue(blk_add_trace_rq_issue);
        unregister_trace_block_rq_insert(blk_add_trace_rq_insert);
        unregister_trace_block_rq_abort(blk_add_trace_rq_abort);

        tracepoint_synchronize_unregister();
}

/*
 * struct blk_io_tracer formatting routines
 */

static void fill_rwbs(char *rwbs, const struct blk_io_trace *t)
{
        int i = 0;

        if (t->action & BLK_TC_DISCARD)
                rwbs[i++] = 'D';
        else if (t->action & BLK_TC_WRITE)
                rwbs[i++] = 'W';
        else if (t->bytes)
                rwbs[i++] = 'R';
        else
                rwbs[i++] = 'N';

        if (t->action & BLK_TC_AHEAD)
                rwbs[i++] = 'A';
        if (t->action & BLK_TC_BARRIER)
                rwbs[i++] = 'B';
        if (t->action & BLK_TC_SYNC)
                rwbs[i++] = 'S';
        if (t->action & BLK_TC_META)
                rwbs[i++] = 'M';

        rwbs[i] = '\0';
}

static inline
const struct blk_io_trace *te_blk_io_trace(const struct trace_entry *ent)
{
        return (const struct blk_io_trace *)ent;
}

static inline const void *pdu_start(const struct trace_entry *ent)
{
        return te_blk_io_trace(ent) + 1;
}

static inline u32 t_sec(const struct trace_entry *ent)
{
        return te_blk_io_trace(ent)->bytes >> 9;
}

static inline unsigned long long t_sector(const struct trace_entry *ent)
{
        return te_blk_io_trace(ent)->sector;
}

static inline __u16 t_error(const struct trace_entry *ent)
{
        return te_blk_io_trace(ent)->sector;
}

static __u64 get_pdu_int(const struct trace_entry *ent)
{
        const __u64 *val = pdu_start(ent);
        return be64_to_cpu(*val);
}

static void get_pdu_remap(const struct trace_entry *ent,
                          struct blk_io_trace_remap *r)
{
        const struct blk_io_trace_remap *__r = pdu_start(ent);
        __u64 sector = __r->sector;

        r->device = be32_to_cpu(__r->device);
        r->device_from = be32_to_cpu(__r->device_from);
        r->sector = be64_to_cpu(sector);
}

static int blk_log_action_iter(struct trace_iterator *iter, const char *act)
{
        char rwbs[6];
        unsigned long long ts  = ns2usecs(iter->ts);
        unsigned long usec_rem = do_div(ts, USEC_PER_SEC);
        unsigned secs          = (unsigned long)ts;
        const struct trace_entry *ent = iter->ent;
        const struct blk_io_trace *t = (const struct blk_io_trace *)ent;

        fill_rwbs(rwbs, t);

        return trace_seq_printf(&iter->seq,
                                "%3d,%-3d %2d %5d.%06lu %5u %2s %3s ",
                                MAJOR(t->device), MINOR(t->device), iter->cpu,
                                secs, usec_rem, ent->pid, act, rwbs);
}

static int blk_log_action_seq(struct trace_seq *s, const struct blk_io_trace *t,
                              const char *act)
{
        char rwbs[6];
        fill_rwbs(rwbs, t);
        return trace_seq_printf(s, "%3d,%-3d %2s %3s ",
                                MAJOR(t->device), MINOR(t->device), act, rwbs);
}

static int blk_log_generic(struct trace_seq *s, const struct trace_entry *ent)
{
        const char *cmd = trace_find_cmdline(ent->pid);

        if (t_sec(ent))
                return trace_seq_printf(s, "%llu + %u [%s]\n",
                                        t_sector(ent), t_sec(ent), cmd);
        return trace_seq_printf(s, "[%s]\n", cmd);
}

static int blk_log_with_error(struct trace_seq *s,
                              const struct trace_entry *ent)
{
        if (t_sec(ent))
                return trace_seq_printf(s, "%llu + %u [%d]\n", t_sector(ent),
                                        t_sec(ent), t_error(ent));
        return trace_seq_printf(s, "%llu [%d]\n", t_sector(ent), t_error(ent));
}

static int blk_log_remap(struct trace_seq *s, const struct trace_entry *ent)
{
        struct blk_io_trace_remap r = { .device = 0, };

        get_pdu_remap(ent, &r);
        return trace_seq_printf(s, "%llu + %u <- (%d,%d) %llu\n",
                               t_sector(ent),
                               t_sec(ent), MAJOR(r.device), MINOR(r.device),
                               (unsigned long long)r.sector);
}

static int blk_log_plug(struct trace_seq *s, const struct trace_entry *ent)
{
        return trace_seq_printf(s, "[%s]\n", trace_find_cmdline(ent->pid));
}

static int blk_log_unplug(struct trace_seq *s, const struct trace_entry *ent)
{
        return trace_seq_printf(s, "[%s] %llu\n", trace_find_cmdline(ent->pid),
                                get_pdu_int(ent));
}

static int blk_log_split(struct trace_seq *s, const struct trace_entry *ent)
{
        return trace_seq_printf(s, "%llu / %llu [%s]\n", t_sector(ent),
                                get_pdu_int(ent), trace_find_cmdline(ent->pid));
}

/*
 * struct tracer operations
 */

static void blk_tracer_print_header(struct seq_file *m)
{
        if (!(blk_tracer_flags.val & TRACE_BLK_OPT_CLASSIC))
                return;
        seq_puts(m, "# DEV   CPU TIMESTAMP     PID ACT FLG\n"
                    "#  |     |     |           |   |   |\n");
}

static void blk_tracer_start(struct trace_array *tr)
{
        tracing_reset_online_cpus(tr);

        mutex_lock(&blk_probe_mutex);
        if (atomic_add_return(1, &blk_probes_ref) == 1)
                if (blk_register_tracepoints())
                        atomic_dec(&blk_probes_ref);
        mutex_unlock(&blk_probe_mutex);
        trace_flags &= ~TRACE_ITER_CONTEXT_INFO;
}

static int blk_tracer_init(struct trace_array *tr)
{
        blk_tr = tr;
        blk_tracer_start(tr);
        mutex_lock(&blk_probe_mutex);
        blk_tracer_enabled++;
        mutex_unlock(&blk_probe_mutex);
        return 0;
}

static void blk_tracer_stop(struct trace_array *tr)
{
        trace_flags |= TRACE_ITER_CONTEXT_INFO;
        mutex_lock(&blk_probe_mutex);
        if (atomic_dec_and_test(&blk_probes_ref))
                blk_unregister_tracepoints();
        mutex_unlock(&blk_probe_mutex);
}

static void blk_tracer_reset(struct trace_array *tr)
{
        if (!atomic_read(&blk_probes_ref))
                return;

        mutex_lock(&blk_probe_mutex);
        blk_tracer_enabled--;
        WARN_ON(blk_tracer_enabled < 0);
        mutex_unlock(&blk_probe_mutex);

        blk_tracer_stop(tr);
}

static struct {
        const char *act[2];
        int        (*print)(struct trace_seq *s, const struct trace_entry *ent);
} what2act[] __read_mostly = {
        [__BLK_TA_QUEUE]        = {{  "Q", "queue" },      blk_log_generic },
        [__BLK_TA_BACKMERGE]    = {{  "M", "backmerge" },  blk_log_generic },
        [__BLK_TA_FRONTMERGE]   = {{  "F", "frontmerge" }, blk_log_generic },
        [__BLK_TA_GETRQ]        = {{  "G", "getrq" },      blk_log_generic },
        [__BLK_TA_SLEEPRQ]      = {{  "S", "sleeprq" },    blk_log_generic },
        [__BLK_TA_REQUEUE]      = {{  "R", "requeue" },    blk_log_with_error },
        [__BLK_TA_ISSUE]        = {{  "D", "issue" },      blk_log_generic },
        [__BLK_TA_COMPLETE]     = {{  "C", "complete" },   blk_log_with_error },
        [__BLK_TA_PLUG]         = {{  "P", "plug" },       blk_log_plug },
        [__BLK_TA_UNPLUG_IO]    = {{  "U", "unplug_io" },  blk_log_unplug },
        [__BLK_TA_UNPLUG_TIMER] = {{ "UT", "unplug_timer" }, blk_log_unplug },
        [__BLK_TA_INSERT]       = {{  "I", "insert" },     blk_log_generic },
        [__BLK_TA_SPLIT]        = {{  "X", "split" },      blk_log_split },
        [__BLK_TA_BOUNCE]       = {{  "B", "bounce" },     blk_log_generic },
        [__BLK_TA_REMAP]        = {{  "A", "remap" },      blk_log_remap },
};

static int blk_trace_event_print(struct trace_iterator *iter, int flags)
{
        struct trace_seq *s = &iter->seq;
        const struct blk_io_trace *t = (struct blk_io_trace *)iter->ent;
        const u16 what = t->action & ((1 << BLK_TC_SHIFT) - 1);
        int ret;

        if (!trace_print_context(iter))
                return TRACE_TYPE_PARTIAL_LINE;

        if (unlikely(what == 0 || what > ARRAY_SIZE(what2act)))
                ret = trace_seq_printf(s, "Bad pc action %x\n", what);
        else {
                const bool long_act = !!(trace_flags & TRACE_ITER_VERBOSE);
                ret = blk_log_action_seq(s, t, what2act[what].act[long_act]);
                if (ret)
                        ret = what2act[what].print(s, iter->ent);
        }

        return ret ? TRACE_TYPE_HANDLED : TRACE_TYPE_PARTIAL_LINE;
}

static int blk_trace_synthesize_old_trace(struct trace_iterator *iter)
{
        struct trace_seq *s = &iter->seq;
        struct blk_io_trace *t = (struct blk_io_trace *)iter->ent;
        const int offset = offsetof(struct blk_io_trace, sector);
        struct blk_io_trace old = {
                .magic    = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION,
                .time     = ns2usecs(iter->ts),
        };

        if (!trace_seq_putmem(s, &old, offset))
                return 0;
        return trace_seq_putmem(s, &t->sector,
                                sizeof(old) - offset + t->pdu_len);
}

static int blk_trace_event_print_binary(struct trace_iterator *iter, int flags)
{
        return blk_trace_synthesize_old_trace(iter) ?
                        TRACE_TYPE_HANDLED : TRACE_TYPE_PARTIAL_LINE;
}

static enum print_line_t blk_tracer_print_line(struct trace_iterator *iter)
{
        const struct blk_io_trace *t;
        u16 what;
        int ret;

        if (!(blk_tracer_flags.val & TRACE_BLK_OPT_CLASSIC))
                return TRACE_TYPE_UNHANDLED;

        t = (const struct blk_io_trace *)iter->ent;
        what = t->action & ((1 << BLK_TC_SHIFT) - 1);

        if (unlikely(what == 0 || what > ARRAY_SIZE(what2act)))
                ret = trace_seq_printf(&iter->seq, "Bad pc action %x\n", what);
        else {
                const bool long_act = !!(trace_flags & TRACE_ITER_VERBOSE);
                ret = blk_log_action_iter(iter, what2act[what].act[long_act]);
                if (ret)
                        ret = what2act[what].print(&iter->seq, iter->ent);
        }

        return ret ? TRACE_TYPE_HANDLED : TRACE_TYPE_PARTIAL_LINE;
}

static struct tracer blk_tracer __read_mostly = {
        .name           = "blk",
        .init           = blk_tracer_init,
        .reset          = blk_tracer_reset,
        .start          = blk_tracer_start,
        .stop           = blk_tracer_stop,
        .print_header   = blk_tracer_print_header,
        .print_line     = blk_tracer_print_line,
        .flags          = &blk_tracer_flags,
};

static struct trace_event trace_blk_event = {
        .type           = TRACE_BLK,
        .trace          = blk_trace_event_print,
        .latency_trace  = blk_trace_event_print,
        .raw            = trace_nop_print,
        .hex            = trace_nop_print,
        .binary         = blk_trace_event_print_binary,
};

static int __init init_blk_tracer(void)
{
        if (!register_ftrace_event(&trace_blk_event)) {
                pr_warning("Warning: could not register block events\n");
                return 1;
        }

        if (register_tracer(&blk_tracer) != 0) {
                pr_warning("Warning: could not register the block tracer\n");
                unregister_ftrace_event(&trace_blk_event);
                return 1;
        }

        return 0;
}

device_initcall(init_blk_tracer);

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

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

        kfree(bt);
        return 0;
}

/*
 * Setup everything required to start tracing
 */
static int blk_trace_setup_queue(struct request_queue *q, dev_t dev)
{
        struct blk_trace *old_bt, *bt = NULL;
        int ret;

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

        bt->dev = dev;
        bt->act_mask = (u16)-1;
        bt->end_lba = -1ULL;
        bt->trace_state = Blktrace_running;

        old_bt = xchg(&q->blk_trace, bt);
        if (old_bt != NULL) {
                (void)xchg(&q->blk_trace, old_bt);
                kfree(bt);
                ret = -EBUSY;
        }
        return 0;
err:
        return ret;
}

/*
 * sysfs interface to enable and configure tracing
 */

static ssize_t sysfs_blk_trace_enable_show(struct device *dev,
                                           struct device_attribute *attr,
                                           char *buf)
{
        struct hd_struct *p = dev_to_part(dev);
        struct block_device *bdev;
        ssize_t ret = -ENXIO;

        lock_kernel();
        bdev = bdget(part_devt(p));
        if (bdev != NULL) {
                struct request_queue *q = bdev_get_queue(bdev);

                if (q != NULL) {
                        mutex_lock(&bdev->bd_mutex);
                        ret = sprintf(buf, "%u\n", !!q->blk_trace);
                        mutex_unlock(&bdev->bd_mutex);
                }

                bdput(bdev);
        }

        unlock_kernel();
        return ret;
}

static ssize_t sysfs_blk_trace_enable_store(struct device *dev,
                                            struct device_attribute *attr,
                                            const char *buf, size_t count)
{
        struct block_device *bdev;
        struct request_queue *q;
        struct hd_struct *p;
        int value;
        ssize_t ret = -ENXIO;

        if (count == 0 || sscanf(buf, "%d", &value) != 1)
                goto out;

        lock_kernel();
        p = dev_to_part(dev);
        bdev = bdget(part_devt(p));
        if (bdev == NULL)
                goto out_unlock_kernel;

        q = bdev_get_queue(bdev);
        if (q == NULL)
                goto out_bdput;

        mutex_lock(&bdev->bd_mutex);
        if (value)
                ret = blk_trace_setup_queue(q, bdev->bd_dev);
        else
                ret = blk_trace_remove_queue(q);
        mutex_unlock(&bdev->bd_mutex);

        if (ret == 0)
                ret = count;
out_bdput:
        bdput(bdev);
out_unlock_kernel:
        unlock_kernel();
out:
        return ret;
}

static ssize_t sysfs_blk_trace_attr_show(struct device *dev,
                                         struct device_attribute *attr,
                                         char *buf);
static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
                                          struct device_attribute *attr,
                                          const char *buf, size_t count);
#define BLK_TRACE_DEVICE_ATTR(_name) \
        DEVICE_ATTR(_name, S_IRUGO | S_IWUSR, \
                    sysfs_blk_trace_attr_show, \
                    sysfs_blk_trace_attr_store)

static DEVICE_ATTR(enable, S_IRUGO | S_IWUSR,
                   sysfs_blk_trace_enable_show, sysfs_blk_trace_enable_store);
static BLK_TRACE_DEVICE_ATTR(act_mask);
static BLK_TRACE_DEVICE_ATTR(pid);
static BLK_TRACE_DEVICE_ATTR(start_lba);
static BLK_TRACE_DEVICE_ATTR(end_lba);

static struct attribute *blk_trace_attrs[] = {
        &dev_attr_enable.attr,
        &dev_attr_act_mask.attr,
        &dev_attr_pid.attr,
        &dev_attr_start_lba.attr,
        &dev_attr_end_lba.attr,
        NULL
};

struct attribute_group blk_trace_attr_group = {
        .name  = "trace",
        .attrs = blk_trace_attrs,
};

static int blk_str2act_mask(const char *str)
{
        int mask = 0;
        char *copy = kstrdup(str, GFP_KERNEL), *s;

        if (copy == NULL)
                return -ENOMEM;

        s = strstrip(copy);

        while (1) {
                char *sep = strchr(s, ',');

                if (sep != NULL)
                        *sep = '\0';

                if (strcasecmp(s, "barrier") == 0)
                        mask |= BLK_TC_BARRIER;
                else if (strcasecmp(s, "complete") == 0)
                        mask |= BLK_TC_COMPLETE;
                else if (strcasecmp(s, "fs") == 0)
                        mask |= BLK_TC_FS;
                else if (strcasecmp(s, "issue") == 0)
                        mask |= BLK_TC_ISSUE;
                else if (strcasecmp(s, "pc") == 0)
                        mask |= BLK_TC_PC;
                else if (strcasecmp(s, "queue") == 0)
                        mask |= BLK_TC_QUEUE;
                else if (strcasecmp(s, "read") == 0)
                        mask |= BLK_TC_READ;
                else if (strcasecmp(s, "requeue") == 0)
                        mask |= BLK_TC_REQUEUE;
                else if (strcasecmp(s, "sync") == 0)
                        mask |= BLK_TC_SYNC;
                else if (strcasecmp(s, "write") == 0)
                        mask |= BLK_TC_WRITE;

                if (sep == NULL)
                        break;

                s = sep + 1;
        }
        kfree(copy);

        return mask;
}

static ssize_t sysfs_blk_trace_attr_show(struct device *dev,
                                         struct device_attribute *attr,
                                         char *buf)
{
        struct hd_struct *p = dev_to_part(dev);
        struct request_queue *q;
        struct block_device *bdev;
        ssize_t ret = -ENXIO;

        lock_kernel();
        bdev = bdget(part_devt(p));
        if (bdev == NULL)
                goto out_unlock_kernel;

        q = bdev_get_queue(bdev);
        if (q == NULL)
                goto out_bdput;
        mutex_lock(&bdev->bd_mutex);
        if (q->blk_trace == NULL)
                ret = sprintf(buf, "disabled\n");
        else if (attr == &dev_attr_act_mask)
                ret = sprintf(buf, "%#x\n", q->blk_trace->act_mask);
        else if (attr == &dev_attr_pid)
                ret = sprintf(buf, "%u\n", q->blk_trace->pid);
        else if (attr == &dev_attr_start_lba)
                ret = sprintf(buf, "%llu\n", q->blk_trace->start_lba);
        else if (attr == &dev_attr_end_lba)
                ret = sprintf(buf, "%llu\n", q->blk_trace->end_lba);
        mutex_unlock(&bdev->bd_mutex);
out_bdput:
        bdput(bdev);
out_unlock_kernel:
        unlock_kernel();
        return ret;
}

static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
                                          struct device_attribute *attr,
                                          const char *buf, size_t count)
{
        struct block_device *bdev;
        struct request_queue *q;
        struct hd_struct *p;
        u64 value;
        ssize_t ret = -ENXIO;

        if (count == 0)
                goto out;

        if (attr == &dev_attr_act_mask) {
                if (sscanf(buf, "%llx", &value) != 1) {
                        /* Assume it is a list of trace category names */
                        value = blk_str2act_mask(buf);
                        if (value < 0)
                                goto out;
                }
        } else if (sscanf(buf, "%llu", &value) != 1)
                goto out;

        lock_kernel();
        p = dev_to_part(dev);
        bdev = bdget(part_devt(p));
        if (bdev == NULL)
                goto out_unlock_kernel;

        q = bdev_get_queue(bdev);
        if (q == NULL)
                goto out_bdput;

        mutex_lock(&bdev->bd_mutex);
        ret = 0;
        if (q->blk_trace == NULL)
                ret = blk_trace_setup_queue(q, bdev->bd_dev);

        if (ret == 0) {
                if (attr == &dev_attr_act_mask)
                        q->blk_trace->act_mask = value;
                else if (attr == &dev_attr_pid)
                        q->blk_trace->pid = value;
                else if (attr == &dev_attr_start_lba)
                        q->blk_trace->start_lba = value;
                else if (attr == &dev_attr_end_lba)
                        q->blk_trace->end_lba = value;
                ret = count;
        }
        mutex_unlock(&bdev->bd_mutex);
out_bdput:
        bdput(bdev);
out_unlock_kernel:
        unlock_kernel();
out:
        return ret;
}