blktrace.c

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/*
 * Copyright (C) 2006 Jens Axboe <[email protected]>
 *
 * 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/slab.h>
#include <linux/debugfs.h>
#include <linux/export.h>
#include <linux/time.h>
#include <linux/uaccess.h>

#include <trace/events/block.h>

#include "trace_output.h"

#ifdef CONFIG_BLK_DEV_IO_TRACE

static unsigned int blktrace_seq __read_mostly = 1;

static struct trace_array *blk_tr;
static bool blk_tracer_enabled __read_mostly;

/* 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 atomic_t blk_probes_ref = ATOMIC_INIT(0);

static void 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;
    struct ring_buffer_event *event = NULL;
    struct ring_buffer *buffer = NULL;
    int pc = 0;
    int cpu = smp_processor_id();
    bool blk_tracer = blk_tracer_enabled;

    if (blk_tracer) {
        buffer = blk_tr->buffer;
        pc = preempt_count();
        event = trace_buffer_lock_reserve(buffer, TRACE_BLK,
                          sizeof(*t) + len,
                          0, pc);
        if (!event)
            return;
        t = ring_buffer_event_data(event);
        goto record_it;
    }

    if (!bt->rchan)
        return;

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

        if (blk_tracer)
            trace_buffer_unlock_commit(buffer, event, 0, pc);
    }
}

/*
 * 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 (unlikely(bt->trace_state != Blktrace_running &&
             !blk_tracer_enabled))
        return;

    /*
     * If the BLK_TC_NOTIFY action mask isn't set, don't send any note
     * message to the trace.
     */
    if (!(bt->act_mask & BLK_TC_NOTIFY))
        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 && (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 const u32 ddir_act[2] = { BLK_TC_ACT(BLK_TC_READ),
                 BLK_TC_ACT(BLK_TC_WRITE) };

#define BLK_TC_RAHEAD       BLK_TC_AHEAD

/* The ilog2() calls fall out because they're constant */
#define MASK_TC_BIT(rw, __name) ((rw & REQ_ ## __name) << \
      (ilog2(BLK_TC_ ## __name) + BLK_TC_SHIFT - __REQ_ ## __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 ring_buffer *buffer = NULL;
    struct blk_io_trace *t;
    unsigned long flags = 0;
    unsigned long *sequence;
    pid_t pid;
    int cpu, pc = 0;
    bool blk_tracer = blk_tracer_enabled;

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

    what |= ddir_act[rw & WRITE];
    what |= MASK_TC_BIT(rw, SYNC);
    what |= MASK_TC_BIT(rw, RAHEAD);
    what |= MASK_TC_BIT(rw, META);
    what |= MASK_TC_BIT(rw, DISCARD);
    what |= MASK_TC_BIT(rw, FLUSH);
    what |= MASK_TC_BIT(rw, FUA);

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

    if (blk_tracer) {
        tracing_record_cmdline(current);

        buffer = blk_tr->buffer;
        pc = preempt_count();
        event = trace_buffer_lock_reserve(buffer, TRACE_BLK,
                          sizeof(*t) + pdu_len,
                          0, pc);
        if (!event)
            return;
        t = ring_buffer_event_data(event);
        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_tracer) {
            trace_buffer_unlock_commit(buffer, event, 0, pc);
            return;
        }
    }

    local_irq_restore(flags);
}

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

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

static void blk_trace_cleanup(struct blk_trace *bt)
{
    blk_trace_free(bt);
    if (atomic_dec_and_test(&blk_probes_ref))
        blk_unregister_tracepoints();
}

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_running)
        blk_trace_cleanup(bt);

    return 0;
}
EXPORT_SYMBOL_GPL(blk_trace_remove);

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 =     simple_open,
    .read =     blk_dropped_read,
    .llseek =   default_llseek,
};

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 + 1, GFP_KERNEL);
    if (msg == NULL)
        return -ENOMEM;

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

    msg[count] = '\0';
    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 =     simple_open,
    .write =    blk_msg_write,
    .llseek =   noop_llseek,
};

/*
 * 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,
                           umode_t 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,
};

static void blk_trace_setup_lba(struct blk_trace *bt,
                struct block_device *bdev)
{
    struct hd_struct *part = NULL;

    if (bdev)
        part = bdev->bd_part;

    if (part) {
        bt->start_lba = part->start_sect;
        bt->end_lba = part->start_sect + part->nr_sects;
    } else {
        bt->start_lba = 0;
        bt->end_lba = -1ULL;
    }
}

/*
 * Setup everything required to start tracing
 */
int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
               struct block_device *bdev,
               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] = '_';

    bt = kzalloc(sizeof(*bt), GFP_KERNEL);
    if (!bt)
        return -ENOMEM;

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

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

    ret = -ENOENT;

    mutex_lock(&blk_tree_mutex);
    if (!blk_tree_root) {
        blk_tree_root = debugfs_create_dir("block", NULL);
        if (!blk_tree_root) {
            mutex_unlock(&blk_tree_mutex);
            goto err;
        }
    }
    mutex_unlock(&blk_tree_mutex);

    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;

    blk_trace_setup_lba(bt, bdev);

    /* overwrite with user settings */
    if (buts->start_lba)
        bt->start_lba = buts->start_lba;
    if (buts->end_lba)
        bt->end_lba = buts->end_lba;

    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;
    }

    if (atomic_inc_return(&blk_probes_ref) == 1)
        blk_register_tracepoints();

    return 0;
err:
    blk_trace_free(bt);
    return ret;
}

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

    if (copy_to_user(arg, &buts, sizeof(buts))) {
        blk_trace_remove(q);
        return -EFAULT;
    }
    return 0;
}
EXPORT_SYMBOL_GPL(blk_trace_setup);

#if defined(CONFIG_COMPAT) && defined(CONFIG_X86_64)
static int compat_blk_trace_setup(struct request_queue *q, char *name,
                  dev_t dev, struct block_device *bdev,
                  char __user *arg)
{
    struct blk_user_trace_setup buts;
    struct compat_blk_user_trace_setup cbuts;
    int ret;

    if (copy_from_user(&cbuts, arg, sizeof(cbuts)))
        return -EFAULT;

    buts = (struct blk_user_trace_setup) {
        .act_mask = cbuts.act_mask,
        .buf_size = cbuts.buf_size,
        .buf_nr = cbuts.buf_nr,
        .start_lba = cbuts.start_lba,
        .end_lba = cbuts.end_lba,
        .pid = cbuts.pid,
    };
    memcpy(&buts.name, &cbuts.name, 32);

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

    if (copy_to_user(arg, &buts.name, 32)) {
        blk_trace_remove(q);
        return -EFAULT;
    }

    return 0;
}
#endif

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);

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, bdev, arg);
        break;
#if defined(CONFIG_COMPAT) && defined(CONFIG_X86_64)
    case BLKTRACESETUP32:
        bdevname(bdev, b);
        ret = compat_blk_trace_setup(q, b, bdev->bd_dev, bdev, arg);
        break;
#endif
    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;
}

void blk_trace_shutdown(struct request_queue *q)
{
    if (q->blk_trace) {
        blk_trace_startstop(q, 0);
        blk_trace_remove(q);
    }
}

/*
 * blktrace probes
 */

static void blk_add_trace_rq(struct request_queue *q, struct request *rq,
                 u32 what)
{
    struct blk_trace *bt = q->blk_trace;

    if (likely(!bt))
        return;

    if (rq->cmd_type == REQ_TYPE_BLOCK_PC) {
        what |= BLK_TC_ACT(BLK_TC_PC);
        __blk_add_trace(bt, 0, blk_rq_bytes(rq), rq->cmd_flags,
                what, rq->errors, rq->cmd_len, rq->cmd);
    } else  {
        what |= BLK_TC_ACT(BLK_TC_FS);
        __blk_add_trace(bt, blk_rq_pos(rq), blk_rq_bytes(rq),
                rq->cmd_flags, what, rq->errors, 0, NULL);
    }
}

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

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

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

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

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

static void blk_add_trace_bio(struct request_queue *q, struct bio *bio,
                  u32 what, int error)
{
    struct blk_trace *bt = q->blk_trace;

    if (likely(!bt))
        return;

    if (!error && !bio_flagged(bio, BIO_UPTODATE))
        error = EIO;

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

static void blk_add_trace_bio_bounce(void *ignore,
                     struct request_queue *q, struct bio *bio)
{
    blk_add_trace_bio(q, bio, BLK_TA_BOUNCE, 0);
}

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

static void blk_add_trace_bio_backmerge(void *ignore,
                    struct request_queue *q,
                    struct bio *bio)
{
    blk_add_trace_bio(q, bio, BLK_TA_BACKMERGE, 0);
}

static void blk_add_trace_bio_frontmerge(void *ignore,
                     struct request_queue *q,
                     struct bio *bio)
{
    blk_add_trace_bio(q, bio, BLK_TA_FRONTMERGE, 0);
}

static void blk_add_trace_bio_queue(void *ignore,
                    struct request_queue *q, struct bio *bio)
{
    blk_add_trace_bio(q, bio, BLK_TA_QUEUE, 0);
}

static void blk_add_trace_getrq(void *ignore,
                struct request_queue *q,
                struct bio *bio, int rw)
{
    if (bio)
        blk_add_trace_bio(q, bio, BLK_TA_GETRQ, 0);
    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(void *ignore,
                  struct request_queue *q,
                  struct bio *bio, int rw)
{
    if (bio)
        blk_add_trace_bio(q, bio, BLK_TA_SLEEPRQ, 0);
    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(void *ignore, 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(void *ignore, struct request_queue *q,
                    unsigned int depth, bool explicit)
{
    struct blk_trace *bt = q->blk_trace;

    if (bt) {
        __be64 rpdu = cpu_to_be64(depth);
        u32 what;

        if (explicit)
            what = BLK_TA_UNPLUG_IO;
        else
            what = BLK_TA_UNPLUG_TIMER;

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

static void blk_add_trace_split(void *ignore,
                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);
    }
}

static void blk_add_trace_bio_remap(void *ignore,
                    struct request_queue *q, struct bio *bio,
                    dev_t dev, sector_t from)
{
    struct blk_trace *bt = q->blk_trace;
    struct blk_io_trace_remap r;

    if (likely(!bt))
        return;

    r.device_from = cpu_to_be32(dev);
    r.device_to   = cpu_to_be32(bio->bi_bdev->bd_dev);
    r.sector_from = cpu_to_be64(from);

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

static void blk_add_trace_rq_remap(void *ignore,
                   struct request_queue *q,
                   struct request *rq, dev_t dev,
                   sector_t from)
{
    struct blk_trace *bt = q->blk_trace;
    struct blk_io_trace_remap r;

    if (likely(!bt))
        return;

    r.device_from = cpu_to_be32(dev);
    r.device_to   = cpu_to_be32(disk_devt(rq->rq_disk));
    r.sector_from = cpu_to_be64(from);

    __blk_add_trace(bt, blk_rq_pos(rq), blk_rq_bytes(rq),
            rq_data_dir(rq), BLK_TA_REMAP, !!rq->errors,
            sizeof(r), &r);
}

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 (rq->cmd_type == REQ_TYPE_BLOCK_PC)
        __blk_add_trace(bt, 0, blk_rq_bytes(rq), 0,
                BLK_TA_DRV_DATA, rq->errors, len, data);
    else
        __blk_add_trace(bt, blk_rq_pos(rq), blk_rq_bytes(rq), 0,
                BLK_TA_DRV_DATA, rq->errors, len, data);
}
EXPORT_SYMBOL_GPL(blk_add_driver_data);

static void blk_register_tracepoints(void)
{
    int ret;

    ret = register_trace_block_rq_abort(blk_add_trace_rq_abort, NULL);
    WARN_ON(ret);
    ret = register_trace_block_rq_insert(blk_add_trace_rq_insert, NULL);
    WARN_ON(ret);
    ret = register_trace_block_rq_issue(blk_add_trace_rq_issue, NULL);
    WARN_ON(ret);
    ret = register_trace_block_rq_requeue(blk_add_trace_rq_requeue, NULL);
    WARN_ON(ret);
    ret = register_trace_block_rq_complete(blk_add_trace_rq_complete, NULL);
    WARN_ON(ret);
    ret = register_trace_block_bio_bounce(blk_add_trace_bio_bounce, NULL);
    WARN_ON(ret);
    ret = register_trace_block_bio_complete(blk_add_trace_bio_complete, NULL);
    WARN_ON(ret);
    ret = register_trace_block_bio_backmerge(blk_add_trace_bio_backmerge, NULL);
    WARN_ON(ret);
    ret = register_trace_block_bio_frontmerge(blk_add_trace_bio_frontmerge, NULL);
    WARN_ON(ret);
    ret = register_trace_block_bio_queue(blk_add_trace_bio_queue, NULL);
    WARN_ON(ret);
    ret = register_trace_block_getrq(blk_add_trace_getrq, NULL);
    WARN_ON(ret);
    ret = register_trace_block_sleeprq(blk_add_trace_sleeprq, NULL);
    WARN_ON(ret);
    ret = register_trace_block_plug(blk_add_trace_plug, NULL);
    WARN_ON(ret);
    ret = register_trace_block_unplug(blk_add_trace_unplug, NULL);
    WARN_ON(ret);
    ret = register_trace_block_split(blk_add_trace_split, NULL);
    WARN_ON(ret);
    ret = register_trace_block_bio_remap(blk_add_trace_bio_remap, NULL);
    WARN_ON(ret);
    ret = register_trace_block_rq_remap(blk_add_trace_rq_remap, NULL);
    WARN_ON(ret);
}

static void blk_unregister_tracepoints(void)
{
    unregister_trace_block_rq_remap(blk_add_trace_rq_remap, NULL);
    unregister_trace_block_bio_remap(blk_add_trace_bio_remap, NULL);
    unregister_trace_block_split(blk_add_trace_split, NULL);
    unregister_trace_block_unplug(blk_add_trace_unplug, NULL);
    unregister_trace_block_plug(blk_add_trace_plug, NULL);
    unregister_trace_block_sleeprq(blk_add_trace_sleeprq, NULL);
    unregister_trace_block_getrq(blk_add_trace_getrq, NULL);
    unregister_trace_block_bio_queue(blk_add_trace_bio_queue, NULL);
    unregister_trace_block_bio_frontmerge(blk_add_trace_bio_frontmerge, NULL);
    unregister_trace_block_bio_backmerge(blk_add_trace_bio_backmerge, NULL);
    unregister_trace_block_bio_complete(blk_add_trace_bio_complete, NULL);
    unregister_trace_block_bio_bounce(blk_add_trace_bio_bounce, NULL);
    unregister_trace_block_rq_complete(blk_add_trace_rq_complete, NULL);
    unregister_trace_block_rq_requeue(blk_add_trace_rq_requeue, NULL);
    unregister_trace_block_rq_issue(blk_add_trace_rq_issue, NULL);
    unregister_trace_block_rq_insert(blk_add_trace_rq_insert, NULL);
    unregister_trace_block_rq_abort(blk_add_trace_rq_abort, NULL);

    tracepoint_synchronize_unregister();
}

/*
 * struct blk_io_tracer formatting routines
 */

static void fill_rwbs(char *rwbs, const struct blk_io_trace *t)
{
    int i = 0;
    int tc = t->action >> BLK_TC_SHIFT;

    if (t->action == BLK_TN_MESSAGE) {
        rwbs[i++] = 'N';
        goto out;
    }

    if (tc & BLK_TC_FLUSH)
        rwbs[i++] = 'F';

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

    if (tc & BLK_TC_FUA)
        rwbs[i++] = 'F';
    if (tc & BLK_TC_AHEAD)
        rwbs[i++] = 'A';
    if (tc & BLK_TC_SYNC)
        rwbs[i++] = 'S';
    if (tc & BLK_TC_META)
        rwbs[i++] = 'M';
out:
    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_action(const struct trace_entry *ent)
{
    return te_blk_io_trace(ent)->action;
}

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

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)->error;
}

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_from = __r->sector_from;

    r->device_from = be32_to_cpu(__r->device_from);
    r->device_to   = be32_to_cpu(__r->device_to);
    r->sector_from = be64_to_cpu(sector_from);
}

typedef int (blk_log_action_t) (struct trace_iterator *iter, const char *act);

static int blk_log_action_classic(struct trace_iterator *iter, const char *act)
{
    char rwbs[RWBS_LEN];
    unsigned long long ts  = iter->ts;
    unsigned long nsec_rem = do_div(ts, NSEC_PER_SEC);
    unsigned secs          = (unsigned long)ts;
    const struct blk_io_trace *t = te_blk_io_trace(iter->ent);

    fill_rwbs(rwbs, t);

    return trace_seq_printf(&iter->seq,
                "%3d,%-3d %2d %5d.%09lu %5u %2s %3s ",
                MAJOR(t->device), MINOR(t->device), iter->cpu,
                secs, nsec_rem, iter->ent->pid, act, rwbs);
}

static int blk_log_action(struct trace_iterator *iter, const char *act)
{
    char rwbs[RWBS_LEN];
    const struct blk_io_trace *t = te_blk_io_trace(iter->ent);

    fill_rwbs(rwbs, t);
    return trace_seq_printf(&iter->seq, "%3d,%-3d %2s %3s ",
                MAJOR(t->device), MINOR(t->device), act, rwbs);
}

static int blk_log_dump_pdu(struct trace_seq *s, const struct trace_entry *ent)
{
    const unsigned char *pdu_buf;
    int pdu_len;
    int i, end, ret;

    pdu_buf = pdu_start(ent);
    pdu_len = te_blk_io_trace(ent)->pdu_len;

    if (!pdu_len)
        return 1;

    /* find the last zero that needs to be printed */
    for (end = pdu_len - 1; end >= 0; end--)
        if (pdu_buf[end])
            break;
    end++;

    if (!trace_seq_putc(s, '('))
        return 0;

    for (i = 0; i < pdu_len; i++) {

        ret = trace_seq_printf(s, "%s%02x",
                       i == 0 ? "" : " ", pdu_buf[i]);
        if (!ret)
            return ret;

        /*
         * stop when the rest is just zeroes and indicate so
         * with a ".." appended
         */
        if (i == end && end != pdu_len - 1)
            return trace_seq_puts(s, " ..) ");
    }

    return trace_seq_puts(s, ") ");
}

static int blk_log_generic(struct trace_seq *s, const struct trace_entry *ent)
{
    char cmd[TASK_COMM_LEN];

    trace_find_cmdline(ent->pid, cmd);

    if (t_action(ent) & BLK_TC_ACT(BLK_TC_PC)) {
        int ret;

        ret = trace_seq_printf(s, "%u ", t_bytes(ent));
        if (!ret)
            return 0;
        ret = blk_log_dump_pdu(s, ent);
        if (!ret)
            return 0;
        return trace_seq_printf(s, "[%s]\n", cmd);
    } else {
        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_action(ent) & BLK_TC_ACT(BLK_TC_PC)) {
        int ret;

        ret = blk_log_dump_pdu(s, ent);
        if (ret)
            return trace_seq_printf(s, "[%d]\n", t_error(ent));
        return 0;
    } else {
        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_from = 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_from), MINOR(r.device_from),
                (unsigned long long)r.sector_from);
}

static int blk_log_plug(struct trace_seq *s, const struct trace_entry *ent)
{
    char cmd[TASK_COMM_LEN];

    trace_find_cmdline(ent->pid, cmd);

    return trace_seq_printf(s, "[%s]\n", cmd);
}

static int blk_log_unplug(struct trace_seq *s, const struct trace_entry *ent)
{
    char cmd[TASK_COMM_LEN];

    trace_find_cmdline(ent->pid, cmd);

    return trace_seq_printf(s, "[%s] %llu\n", cmd, get_pdu_int(ent));
}

static int blk_log_split(struct trace_seq *s, const struct trace_entry *ent)
{
    char cmd[TASK_COMM_LEN];

    trace_find_cmdline(ent->pid, cmd);

    return trace_seq_printf(s, "%llu / %llu [%s]\n", t_sector(ent),
                get_pdu_int(ent), cmd);
}

static int blk_log_msg(struct trace_seq *s, const struct trace_entry *ent)
{
    int ret;
    const struct blk_io_trace *t = te_blk_io_trace(ent);

    ret = trace_seq_putmem(s, t + 1, t->pdu_len);
    if (ret)
        return trace_seq_putc(s, '\n');
    return ret;
}

/*
 * 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)
{
    blk_tracer_enabled = true;
}

static int blk_tracer_init(struct trace_array *tr)
{
    blk_tr = tr;
    blk_tracer_start(tr);
    return 0;
}

static void blk_tracer_stop(struct trace_array *tr)
{
    blk_tracer_enabled = false;
}

static void blk_tracer_reset(struct trace_array *tr)
{
    blk_tracer_stop(tr);
}

static const struct {
    const char *act[2];
    int    (*print)(struct trace_seq *s, const struct trace_entry *ent);
} what2act[] = {
    [__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 enum print_line_t print_one_line(struct trace_iterator *iter,
                    bool classic)
{
    struct trace_seq *s = &iter->seq;
    const struct blk_io_trace *t;
    u16 what;
    int ret;
    bool long_act;
    blk_log_action_t *log_action;

    t      = te_blk_io_trace(iter->ent);
    what       = t->action & ((1 << BLK_TC_SHIFT) - 1);
    long_act   = !!(trace_flags & TRACE_ITER_VERBOSE);
    log_action = classic ? &blk_log_action_classic : &blk_log_action;

    if (t->action == BLK_TN_MESSAGE) {
        ret = log_action(iter, long_act ? "message" : "m");
        if (ret)
            ret = blk_log_msg(s, iter->ent);
        goto out;
    }

    if (unlikely(what == 0 || what >= ARRAY_SIZE(what2act)))
        ret = trace_seq_printf(s, "Unknown action %x\n", what);
    else {
        ret = log_action(iter, what2act[what].act[long_act]);
        if (ret)
            ret = what2act[what].print(s, iter->ent);
    }
out:
    return ret ? TRACE_TYPE_HANDLED : TRACE_TYPE_PARTIAL_LINE;
}

static enum print_line_t blk_trace_event_print(struct trace_iterator *iter,
                           int flags, struct trace_event *event)
{
    return print_one_line(iter, false);
}

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     = 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 enum print_line_t
blk_trace_event_print_binary(struct trace_iterator *iter, int flags,
                 struct trace_event *event)
{
    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)
{
    if (!(blk_tracer_flags.val & TRACE_BLK_OPT_CLASSIC))
        return TRACE_TYPE_UNHANDLED;

    return print_one_line(iter, true);
}

static int blk_tracer_set_flag(u32 old_flags, u32 bit, int set)
{
    /* don't output context-info for blk_classic output */
    if (bit == TRACE_BLK_OPT_CLASSIC) {
        if (set)
            trace_flags &= ~TRACE_ITER_CONTEXT_INFO;
        else
            trace_flags |= TRACE_ITER_CONTEXT_INFO;
    }
    return 0;
}

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,
    .set_flag   = blk_tracer_set_flag,
};

static struct trace_event_functions trace_blk_event_funcs = {
    .trace      = blk_trace_event_print,
    .binary     = blk_trace_event_print_binary,
};

static struct trace_event trace_blk_event = {
    .type       = TRACE_BLK,
    .funcs      = &trace_blk_event_funcs,
};

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;

    if (atomic_dec_and_test(&blk_probes_ref))
        blk_unregister_tracepoints();

    blk_trace_free(bt);
    return 0;
}

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

    bt = kzalloc(sizeof(*bt), GFP_KERNEL);
    if (!bt)
        return -ENOMEM;

    bt->msg_data = __alloc_percpu(BLK_TN_MAX_MSG, __alignof__(char));
    if (!bt->msg_data)
        goto free_bt;

    bt->dev = bdev->bd_dev;
    bt->act_mask = (u16)-1;

    blk_trace_setup_lba(bt, bdev);

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

    if (atomic_inc_return(&blk_probes_ref) == 1)
        blk_register_tracepoints();
    return 0;

free_bt:
    blk_trace_free(bt);
    return ret;
}

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

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 BLK_TRACE_DEVICE_ATTR(enable);
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 const struct {
    int mask;
    const char *str;
} mask_maps[] = {
    { BLK_TC_READ,      "read"      },
    { BLK_TC_WRITE,     "write"     },
    { BLK_TC_FLUSH,     "flush"     },
    { BLK_TC_SYNC,      "sync"      },
    { BLK_TC_QUEUE,     "queue"     },
    { BLK_TC_REQUEUE,   "requeue"   },
    { BLK_TC_ISSUE,     "issue"     },
    { BLK_TC_COMPLETE,  "complete"  },
    { BLK_TC_FS,        "fs"        },
    { BLK_TC_PC,        "pc"        },
    { BLK_TC_AHEAD,     "ahead"     },
    { BLK_TC_META,      "meta"      },
    { BLK_TC_DISCARD,   "discard"   },
    { BLK_TC_DRV_DATA,  "drv_data"  },
    { BLK_TC_FUA,       "fua"       },
};

static int blk_trace_str2mask(const char *str)
{
    int i;
    int mask = 0;
    char *buf, *s, *token;

    buf = kstrdup(str, GFP_KERNEL);
    if (buf == NULL)
        return -ENOMEM;
    s = strstrip(buf);

    while (1) {
        token = strsep(&s, ",");
        if (token == NULL)
            break;

        if (*token == '\0')
            continue;

        for (i = 0; i < ARRAY_SIZE(mask_maps); i++) {
            if (strcasecmp(token, mask_maps[i].str) == 0) {
                mask |= mask_maps[i].mask;
                break;
            }
        }
        if (i == ARRAY_SIZE(mask_maps)) {
            mask = -EINVAL;
            break;
        }
    }
    kfree(buf);

    return mask;
}

static ssize_t blk_trace_mask2str(char *buf, int mask)
{
    int i;
    char *p = buf;

    for (i = 0; i < ARRAY_SIZE(mask_maps); i++) {
        if (mask & mask_maps[i].mask) {
            p += sprintf(p, "%s%s",
                    (p == buf) ? "" : ",", mask_maps[i].str);
        }
    }
    *p++ = '\n';

    return p - buf;
}

static struct request_queue *blk_trace_get_queue(struct block_device *bdev)
{
    if (bdev->bd_disk == NULL)
        return NULL;

    return bdev_get_queue(bdev);
}

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;

    bdev = bdget(part_devt(p));
    if (bdev == NULL)
        goto out;

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

    mutex_lock(&bdev->bd_mutex);

    if (attr == &dev_attr_enable) {
        ret = sprintf(buf, "%u\n", !!q->blk_trace);
        goto out_unlock_bdev;
    }

    if (q->blk_trace == NULL)
        ret = sprintf(buf, "disabled\n");
    else if (attr == &dev_attr_act_mask)
        ret = blk_trace_mask2str(buf, 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);

out_unlock_bdev:
    mutex_unlock(&bdev->bd_mutex);
out_bdput:
    bdput(bdev);
out:
    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 = -EINVAL;

    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 */
            ret = blk_trace_str2mask(buf);
            if (ret < 0)
                goto out;
            value = ret;
        }
    } else if (sscanf(buf, "%llu", &value) != 1)
        goto out;

    ret = -ENXIO;

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

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

    mutex_lock(&bdev->bd_mutex);

    if (attr == &dev_attr_enable) {
        if (value)
            ret = blk_trace_setup_queue(q, bdev);
        else
            ret = blk_trace_remove_queue(q);
        goto out_unlock_bdev;
    }

    ret = 0;
    if (q->blk_trace == NULL)
        ret = blk_trace_setup_queue(q, bdev);

    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;
    }

out_unlock_bdev:
    mutex_unlock(&bdev->bd_mutex);
out_bdput:
    bdput(bdev);
out:
    return ret ? ret : count;
}

int blk_trace_init_sysfs(struct device *dev)
{
    return sysfs_create_group(&dev->kobj, &blk_trace_attr_group);
}

void blk_trace_remove_sysfs(struct device *dev)
{
    sysfs_remove_group(&dev->kobj, &blk_trace_attr_group);
}

#endif /* CONFIG_BLK_DEV_IO_TRACE */

#ifdef CONFIG_EVENT_TRACING

void blk_dump_cmd(char *buf, struct request *rq)
{
    int i, end;
    int len = rq->cmd_len;
    unsigned char *cmd = rq->cmd;

    if (rq->cmd_type != REQ_TYPE_BLOCK_PC) {
        buf[0] = '\0';
        return;
    }

    for (end = len - 1; end >= 0; end--)
        if (cmd[end])
            break;
    end++;

    for (i = 0; i < len; i++) {
        buf += sprintf(buf, "%s%02x", i == 0 ? "" : " ", cmd[i]);
        if (i == end && end != len - 1) {
            sprintf(buf, " ..");
            break;
        }
    }
}

void blk_fill_rwbs(char *rwbs, u32 rw, int bytes)
{
    int i = 0;

    if (rw & REQ_FLUSH)
        rwbs[i++] = 'F';

    if (rw & WRITE)
        rwbs[i++] = 'W';
    else if (rw & REQ_DISCARD)
        rwbs[i++] = 'D';
    else if (bytes)
        rwbs[i++] = 'R';
    else
        rwbs[i++] = 'N';

    if (rw & REQ_FUA)
        rwbs[i++] = 'F';
    if (rw & REQ_RAHEAD)
        rwbs[i++] = 'A';
    if (rw & REQ_SYNC)
        rwbs[i++] = 'S';
    if (rw & REQ_META)
        rwbs[i++] = 'M';
    if (rw & REQ_SECURE)
        rwbs[i++] = 'E';

    rwbs[i] = '\0';
}

#endif /* CONFIG_EVENT_TRACING */