tracing/blktrace: move the tracing file to kernel/trace

Impact: cleanup

Move blktrace.c to kernel/trace, also move its config entry.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 1562 insertions, 0 deletions

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 25131a5d5e4f..4fee43c01942 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -302,6 +302,29 @@ config WORKQUEUE_TRACER
           For example it can help a developer to decide whether he should
           choose a per cpu workqueue instead of a singlethreaded one.
 
+config BLK_DEV_IO_TRACE
+	bool "Support for tracing block io actions"
+	depends on SYSFS
+	select RELAY
+	select DEBUG_FS
+	select TRACEPOINTS
+	select TRACING
+	select STACKTRACE
+	help
+	  Say Y here if you want to be able to trace the block layer actions
+	  on a given queue. Tracing allows you to see any traffic happening
+	  on a block device queue. For more information (and the userspace
+	  support tools needed), fetch the blktrace tools from:
+
+	  git://git.kernel.dk/blktrace.git
+
+	  Tracing also is possible using the ftrace interface, e.g.:
+
+	    echo 1 > /sys/block/sda/sda1/trace/enable
+	    echo blk > /sys/kernel/debug/tracing/current_tracer
+	    cat /sys/kernel/debug/tracing/trace_pipe
+
+	  If unsure, say N.
 
 config DYNAMIC_FTRACE
 	bool "enable/disable ftrace tracepoints dynamically"
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index f76d48f3527d..627090bc262d 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -37,5 +37,6 @@ obj-$(CONFIG_HW_BRANCH_TRACER) += trace_hw_branches.o
 obj-$(CONFIG_POWER_TRACER) += trace_power.o
 obj-$(CONFIG_KMEMTRACE) += kmemtrace.o
 obj-$(CONFIG_WORKQUEUE_TRACER) += trace_workqueue.o
+obj-$(CONFIG_BLK_DEV_IO_TRACE)	+= blktrace.o
 
 libftrace-y := ftrace.o
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
new file mode 100644
index 000000000000..3b91da064820
--- /dev/null
+++ b/kernel/trace/blktrace.c
@@ -0,0 +1,1538 @@
+/*
+ * 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 "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 = 0;
+	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) {
+		tracing_record_cmdline(current);
+
+		pc = preempt_count();
+		event = trace_buffer_lock_reserve(blk_tr, 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_tr) {
+			trace_buffer_unlock_commit(blk_tr, event, 0, pc);
+			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)
+{
+	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 enum print_line_t 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 enum print_line_t
+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,
+	.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;
+}