[patch 09/10] Move blktrace to instrumentation directory

[Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>]

[-- Attachment #1: move-blktrace-to-instrumentation.patch --]
[-- Type: text/plain, Size: 29434 bytes --]

This block IO tracing belongs to the instrumentation category.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Jens Axboe <jens.axboe@oracle.com>
---
 block/Makefile             |    1 
 block/blktrace.c           |  576 ---------------------------------------------
 instrumentation/Makefile   |    1 
 instrumentation/blktrace.c |  576 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 577 insertions(+), 577 deletions(-)

Index: linux-2.6-lttng.stable/block/Makefile
===================================================================
--- linux-2.6-lttng.stable.orig/block/Makefile	2007-10-29 09:51:05.000000000 -0400
+++ linux-2.6-lttng.stable/block/Makefile	2007-10-29 09:53:17.000000000 -0400
@@ -10,5 +10,4 @@ obj-$(CONFIG_IOSCHED_AS)	+= as-iosched.o
 obj-$(CONFIG_IOSCHED_DEADLINE)	+= deadline-iosched.o
 obj-$(CONFIG_IOSCHED_CFQ)	+= cfq-iosched.o
 
-obj-$(CONFIG_BLK_DEV_IO_TRACE)	+= blktrace.o
 obj-$(CONFIG_BLOCK_COMPAT)	+= compat_ioctl.o
Index: linux-2.6-lttng.stable/block/blktrace.c
===================================================================
--- linux-2.6-lttng.stable.orig/block/blktrace.c	2007-10-29 09:51:05.000000000 -0400
+++ /dev/null	1970-01-01 00:00:00.000000000 +0000
@@ -1,576 +0,0 @@
-/*
- * Copyright (C) 2006 Jens Axboe <axboe@kernel.dk>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
- *
- */
-#include <linux/kernel.h>
-#include <linux/blkdev.h>
-#include <linux/blktrace_api.h>
-#include <linux/percpu.h>
-#include <linux/init.h>
-#include <linux/mutex.h>
-#include <linux/debugfs.h>
-#include <linux/time.h>
-#include <asm/uaccess.h>
-
-static DEFINE_PER_CPU(unsigned long long, blk_trace_cpu_offset) = { 0, };
-static unsigned int blktrace_seq __read_mostly = 1;
-
-/*
- * Send out a notify message.
- */
-static void trace_note(struct blk_trace *bt, pid_t pid, int action,
-		       const void *data, size_t len)
-{
-	struct blk_io_trace *t;
-
-	t = relay_reserve(bt->rchan, sizeof(*t) + len);
-	if (t) {
-		const int cpu = smp_processor_id();
-
-		t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
-		t->time = cpu_clock(cpu) - per_cpu(blk_trace_cpu_offset, cpu);
-		t->device = bt->dev;
-		t->action = action;
-		t->pid = pid;
-		t->cpu = cpu;
-		t->pdu_len = len;
-		memcpy((void *) t + sizeof(*t), data, len);
-	}
-}
-
-/*
- * Send out a notify for this process, if we haven't done so since a trace
- * started
- */
-static void trace_note_tsk(struct blk_trace *bt, struct task_struct *tsk)
-{
-	tsk->btrace_seq = blktrace_seq;
-	trace_note(bt, tsk->pid, BLK_TN_PROCESS, tsk->comm, sizeof(tsk->comm));
-}
-
-static void trace_note_time(struct blk_trace *bt)
-{
-	struct timespec now;
-	unsigned long flags;
-	u32 words[2];
-
-	getnstimeofday(&now);
-	words[0] = now.tv_sec;
-	words[1] = now.tv_nsec;
-
-	local_irq_save(flags);
-	trace_note(bt, 0, BLK_TN_TIMESTAMP, words, sizeof(words));
-	local_irq_restore(flags);
-}
-
-static int act_log_check(struct blk_trace *bt, u32 what, sector_t sector,
-			 pid_t pid)
-{
-	if (((bt->act_mask << BLK_TC_SHIFT) & what) == 0)
-		return 1;
-	if (sector < bt->start_lba || sector > bt->end_lba)
-		return 1;
-	if (bt->pid && pid != bt->pid)
-		return 1;
-
-	return 0;
-}
-
-/*
- * Data direction bit lookup
- */
-static u32 ddir_act[2] __read_mostly = { BLK_TC_ACT(BLK_TC_READ), BLK_TC_ACT(BLK_TC_WRITE) };
-
-/*
- * Bio action bits of interest
- */
-static u32 bio_act[9] __read_mostly = { 0, BLK_TC_ACT(BLK_TC_BARRIER), BLK_TC_ACT(BLK_TC_SYNC), 0, BLK_TC_ACT(BLK_TC_AHEAD), 0, 0, 0, BLK_TC_ACT(BLK_TC_META) };
-
-/*
- * More could be added as needed, taking care to increment the decrementer
- * to get correct indexing
- */
-#define trace_barrier_bit(rw)	\
-	(((rw) & (1 << BIO_RW_BARRIER)) >> (BIO_RW_BARRIER - 0))
-#define trace_sync_bit(rw)	\
-	(((rw) & (1 << BIO_RW_SYNC)) >> (BIO_RW_SYNC - 1))
-#define trace_ahead_bit(rw)	\
-	(((rw) & (1 << BIO_RW_AHEAD)) << (2 - BIO_RW_AHEAD))
-#define trace_meta_bit(rw)	\
-	(((rw) & (1 << BIO_RW_META)) >> (BIO_RW_META - 3))
-
-/*
- * The worker for the various blk_add_trace*() types. Fills out a
- * blk_io_trace structure and places it in a per-cpu subbuffer.
- */
-void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
-		     int rw, u32 what, int error, int pdu_len, void *pdu_data)
-{
-	struct task_struct *tsk = current;
-	struct blk_io_trace *t;
-	unsigned long flags;
-	unsigned long *sequence;
-	pid_t pid;
-	int cpu;
-
-	if (unlikely(bt->trace_state != Blktrace_running))
-		return;
-
-	what |= ddir_act[rw & WRITE];
-	what |= bio_act[trace_barrier_bit(rw)];
-	what |= bio_act[trace_sync_bit(rw)];
-	what |= bio_act[trace_ahead_bit(rw)];
-	what |= bio_act[trace_meta_bit(rw)];
-
-	pid = tsk->pid;
-	if (unlikely(act_log_check(bt, what, sector, pid)))
-		return;
-
-	/*
-	 * A word about the locking here - we disable interrupts to reserve
-	 * some space in the relay per-cpu buffer, to prevent an irq
-	 * from coming in and stepping on our toes. Once reserved, it's
-	 * enough to get preemption disabled to prevent read of this data
-	 * before we are through filling it. get_cpu()/put_cpu() does this
-	 * for us
-	 */
-	local_irq_save(flags);
-
-	if (unlikely(tsk->btrace_seq != blktrace_seq))
-		trace_note_tsk(bt, tsk);
-
-	t = relay_reserve(bt->rchan, sizeof(*t) + pdu_len);
-	if (t) {
-		cpu = smp_processor_id();
-		sequence = per_cpu_ptr(bt->sequence, cpu);
-
-		t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
-		t->sequence = ++(*sequence);
-		t->time = cpu_clock(cpu) - per_cpu(blk_trace_cpu_offset, cpu);
-		t->sector = sector;
-		t->bytes = bytes;
-		t->action = what;
-		t->pid = pid;
-		t->device = bt->dev;
-		t->cpu = cpu;
-		t->error = error;
-		t->pdu_len = pdu_len;
-
-		if (pdu_len)
-			memcpy((void *) t + sizeof(*t), pdu_data, pdu_len);
-	}
-
-	local_irq_restore(flags);
-}
-
-EXPORT_SYMBOL_GPL(__blk_add_trace);
-
-static struct dentry *blk_tree_root;
-static struct mutex blk_tree_mutex;
-static unsigned int root_users;
-
-static inline void blk_remove_root(void)
-{
-	if (blk_tree_root) {
-		debugfs_remove(blk_tree_root);
-		blk_tree_root = NULL;
-	}
-}
-
-static void blk_remove_tree(struct dentry *dir)
-{
-	mutex_lock(&blk_tree_mutex);
-	debugfs_remove(dir);
-	if (--root_users == 0)
-		blk_remove_root();
-	mutex_unlock(&blk_tree_mutex);
-}
-
-static struct dentry *blk_create_tree(const char *blk_name)
-{
-	struct dentry *dir = NULL;
-
-	mutex_lock(&blk_tree_mutex);
-
-	if (!blk_tree_root) {
-		blk_tree_root = debugfs_create_dir("block", NULL);
-		if (!blk_tree_root)
-			goto err;
-	}
-
-	dir = debugfs_create_dir(blk_name, blk_tree_root);
-	if (dir)
-		root_users++;
-	else
-		blk_remove_root();
-
-err:
-	mutex_unlock(&blk_tree_mutex);
-	return dir;
-}
-
-static void blk_trace_cleanup(struct blk_trace *bt)
-{
-	relay_close(bt->rchan);
-	debugfs_remove(bt->dropped_file);
-	blk_remove_tree(bt->dir);
-	free_percpu(bt->sequence);
-	kfree(bt);
-}
-
-static int blk_trace_remove(struct request_queue *q)
-{
-	struct blk_trace *bt;
-
-	bt = xchg(&q->blk_trace, NULL);
-	if (!bt)
-		return -EINVAL;
-
-	if (bt->trace_state == Blktrace_setup ||
-	    bt->trace_state == Blktrace_stopped)
-		blk_trace_cleanup(bt);
-
-	return 0;
-}
-
-static int blk_dropped_open(struct inode *inode, struct file *filp)
-{
-	filp->private_data = inode->i_private;
-
-	return 0;
-}
-
-static ssize_t blk_dropped_read(struct file *filp, char __user *buffer,
-				size_t count, loff_t *ppos)
-{
-	struct blk_trace *bt = filp->private_data;
-	char buf[16];
-
-	snprintf(buf, sizeof(buf), "%u\n", atomic_read(&bt->dropped));
-
-	return simple_read_from_buffer(buffer, count, ppos, buf, strlen(buf));
-}
-
-static const struct file_operations blk_dropped_fops = {
-	.owner =	THIS_MODULE,
-	.open =		blk_dropped_open,
-	.read =		blk_dropped_read,
-};
-
-/*
- * Keep track of how many times we encountered a full subbuffer, to aid
- * the user space app in telling how many lost events there were.
- */
-static int blk_subbuf_start_callback(struct rchan_buf *buf, void *subbuf,
-				     void *prev_subbuf, size_t prev_padding)
-{
-	struct blk_trace *bt;
-
-	if (!relay_buf_full(buf))
-		return 1;
-
-	bt = buf->chan->private_data;
-	atomic_inc(&bt->dropped);
-	return 0;
-}
-
-static int blk_remove_buf_file_callback(struct dentry *dentry)
-{
-	debugfs_remove(dentry);
-	return 0;
-}
-
-static struct dentry *blk_create_buf_file_callback(const char *filename,
-						   struct dentry *parent,
-						   int mode,
-						   struct rchan_buf *buf,
-						   int *is_global)
-{
-	return debugfs_create_file(filename, mode, parent, buf,
-					&relay_file_operations);
-}
-
-static struct rchan_callbacks blk_relay_callbacks = {
-	.subbuf_start		= blk_subbuf_start_callback,
-	.create_buf_file	= blk_create_buf_file_callback,
-	.remove_buf_file	= blk_remove_buf_file_callback,
-};
-
-/*
- * Setup everything required to start tracing
- */
-int do_blk_trace_setup(struct request_queue *q, struct block_device *bdev,
-			struct blk_user_trace_setup *buts)
-{
-	struct blk_trace *old_bt, *bt = NULL;
-	struct dentry *dir = NULL;
-	char b[BDEVNAME_SIZE];
-	int ret, i;
-
-	if (!buts->buf_size || !buts->buf_nr)
-		return -EINVAL;
-
-	strcpy(buts->name, bdevname(bdev, b));
-
-	/*
-	 * some device names have larger paths - convert the slashes
-	 * to underscores for this to work as expected
-	 */
-	for (i = 0; i < strlen(buts->name); i++)
-		if (buts->name[i] == '/')
-			buts->name[i] = '_';
-
-	ret = -ENOMEM;
-	bt = kzalloc(sizeof(*bt), GFP_KERNEL);
-	if (!bt)
-		goto err;
-
-	bt->sequence = alloc_percpu(unsigned long);
-	if (!bt->sequence)
-		goto err;
-
-	ret = -ENOENT;
-	dir = blk_create_tree(buts->name);
-	if (!dir)
-		goto err;
-
-	bt->dir = dir;
-	bt->dev = bdev->bd_dev;
-	atomic_set(&bt->dropped, 0);
-
-	ret = -EIO;
-	bt->dropped_file = debugfs_create_file("dropped", 0444, dir, bt, &blk_dropped_fops);
-	if (!bt->dropped_file)
-		goto err;
-
-	bt->rchan = relay_open("trace", dir, buts->buf_size,
-				buts->buf_nr, &blk_relay_callbacks, bt);
-	if (!bt->rchan)
-		goto err;
-
-	bt->act_mask = buts->act_mask;
-	if (!bt->act_mask)
-		bt->act_mask = (u16) -1;
-
-	bt->start_lba = buts->start_lba;
-	bt->end_lba = buts->end_lba;
-	if (!bt->end_lba)
-		bt->end_lba = -1ULL;
-
-	bt->pid = buts->pid;
-	bt->trace_state = Blktrace_setup;
-
-	ret = -EBUSY;
-	old_bt = xchg(&q->blk_trace, bt);
-	if (old_bt) {
-		(void) xchg(&q->blk_trace, old_bt);
-		goto err;
-	}
-
-	return 0;
-err:
-	if (dir)
-		blk_remove_tree(dir);
-	if (bt) {
-		if (bt->dropped_file)
-			debugfs_remove(bt->dropped_file);
-		free_percpu(bt->sequence);
-		if (bt->rchan)
-			relay_close(bt->rchan);
-		kfree(bt);
-	}
-	return ret;
-}
-
-static int blk_trace_setup(struct request_queue *q, struct block_device *bdev,
-			   char __user *arg)
-{
-	struct blk_user_trace_setup buts;
-	int ret;
-
-	ret = copy_from_user(&buts, arg, sizeof(buts));
-	if (ret)
-		return -EFAULT;
-
-	ret = do_blk_trace_setup(q, bdev, &buts);
-	if (ret)
-		return ret;
-
-	if (copy_to_user(arg, &buts, sizeof(buts)))
-		return -EFAULT;
-
-	return 0;
-}
-
-static int blk_trace_startstop(struct request_queue *q, int start)
-{
-	struct blk_trace *bt;
-	int ret;
-
-	if ((bt = q->blk_trace) == NULL)
-		return -EINVAL;
-
-	/*
-	 * For starting a trace, we can transition from a setup or stopped
-	 * trace. For stopping a trace, the state must be running
-	 */
-	ret = -EINVAL;
-	if (start) {
-		if (bt->trace_state == Blktrace_setup ||
-		    bt->trace_state == Blktrace_stopped) {
-			blktrace_seq++;
-			smp_mb();
-			bt->trace_state = Blktrace_running;
-
-			trace_note_time(bt);
-			ret = 0;
-		}
-	} else {
-		if (bt->trace_state == Blktrace_running) {
-			bt->trace_state = Blktrace_stopped;
-			relay_flush(bt->rchan);
-			ret = 0;
-		}
-	}
-
-	return ret;
-}
-
-/**
- * blk_trace_ioctl: - handle the ioctls associated with tracing
- * @bdev:	the block device
- * @cmd: 	the ioctl cmd
- * @arg:	the argument data, if any
- *
- **/
-int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
-{
-	struct request_queue *q;
-	int ret, start = 0;
-
-	q = bdev_get_queue(bdev);
-	if (!q)
-		return -ENXIO;
-
-	mutex_lock(&bdev->bd_mutex);
-
-	switch (cmd) {
-	case BLKTRACESETUP:
-		ret = blk_trace_setup(q, bdev, arg);
-		break;
-	case BLKTRACESTART:
-		start = 1;
-	case BLKTRACESTOP:
-		ret = blk_trace_startstop(q, start);
-		break;
-	case BLKTRACETEARDOWN:
-		ret = blk_trace_remove(q);
-		break;
-	default:
-		ret = -ENOTTY;
-		break;
-	}
-
-	mutex_unlock(&bdev->bd_mutex);
-	return ret;
-}
-
-/**
- * blk_trace_shutdown: - stop and cleanup trace structures
- * @q:    the request queue associated with the device
- *
- **/
-void blk_trace_shutdown(struct request_queue *q)
-{
-	if (q->blk_trace) {
-		blk_trace_startstop(q, 0);
-		blk_trace_remove(q);
-	}
-}
-
-/*
- * Average offset over two calls to cpu_clock() with a gettimeofday()
- * in the middle
- */
-static void blk_check_time(unsigned long long *t, int this_cpu)
-{
-	unsigned long long a, b;
-	struct timeval tv;
-
-	a = cpu_clock(this_cpu);
-	do_gettimeofday(&tv);
-	b = cpu_clock(this_cpu);
-
-	*t = tv.tv_sec * 1000000000 + tv.tv_usec * 1000;
-	*t -= (a + b) / 2;
-}
-
-/*
- * calibrate our inter-CPU timings
- */
-static void blk_trace_check_cpu_time(void *data)
-{
-	unsigned long long *t;
-	int this_cpu = get_cpu();
-
-	t = &per_cpu(blk_trace_cpu_offset, this_cpu);
-
-	/*
-	 * Just call it twice, hopefully the second call will be cache hot
-	 * and a little more precise
-	 */
-	blk_check_time(t, this_cpu);
-	blk_check_time(t, this_cpu);
-
-	put_cpu();
-}
-
-static void blk_trace_set_ht_offsets(void)
-{
-#if defined(CONFIG_SCHED_SMT)
-	int cpu, i;
-
-	/*
-	 * now make sure HT siblings have the same time offset
-	 */
-	preempt_disable();
-	for_each_online_cpu(cpu) {
-		unsigned long long *cpu_off, *sibling_off;
-
-		for_each_cpu_mask(i, per_cpu(cpu_sibling_map, cpu)) {
-			if (i == cpu)
-				continue;
-
-			cpu_off = &per_cpu(blk_trace_cpu_offset, cpu);
-			sibling_off = &per_cpu(blk_trace_cpu_offset, i);
-			*sibling_off = *cpu_off;
-		}
-	}
-	preempt_enable();
-#endif
-}
-
-static __init int blk_trace_init(void)
-{
-	mutex_init(&blk_tree_mutex);
-	on_each_cpu(blk_trace_check_cpu_time, NULL, 1, 1);
-	blk_trace_set_ht_offsets();
-
-	return 0;
-}
-
-module_init(blk_trace_init);
-
Index: linux-2.6-lttng.stable/instrumentation/Makefile
===================================================================
--- linux-2.6-lttng.stable.orig/instrumentation/Makefile	2007-10-29 09:53:14.000000000 -0400
+++ linux-2.6-lttng.stable/instrumentation/Makefile	2007-10-29 09:53:24.000000000 -0400
@@ -10,3 +10,4 @@ obj-$(CONFIG_LOCKDEP) += lockdep.o
 ifeq ($(CONFIG_PROC_FS),y)
 obj-$(CONFIG_LOCKDEP) += lockdep_proc.o
 endif
+obj-$(CONFIG_BLK_DEV_IO_TRACE)	+= blktrace.o
Index: linux-2.6-lttng.stable/instrumentation/blktrace.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng.stable/instrumentation/blktrace.c	2007-10-29 09:53:17.000000000 -0400
@@ -0,0 +1,576 @@
+/*
+ * Copyright (C) 2006 Jens Axboe <axboe@kernel.dk>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/blkdev.h>
+#include <linux/blktrace_api.h>
+#include <linux/percpu.h>
+#include <linux/init.h>
+#include <linux/mutex.h>
+#include <linux/debugfs.h>
+#include <linux/time.h>
+#include <asm/uaccess.h>
+
+static DEFINE_PER_CPU(unsigned long long, blk_trace_cpu_offset) = { 0, };
+static unsigned int blktrace_seq __read_mostly = 1;
+
+/*
+ * Send out a notify message.
+ */
+static void trace_note(struct blk_trace *bt, pid_t pid, int action,
+		       const void *data, size_t len)
+{
+	struct blk_io_trace *t;
+
+	t = relay_reserve(bt->rchan, sizeof(*t) + len);
+	if (t) {
+		const int cpu = smp_processor_id();
+
+		t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
+		t->time = cpu_clock(cpu) - per_cpu(blk_trace_cpu_offset, cpu);
+		t->device = bt->dev;
+		t->action = action;
+		t->pid = pid;
+		t->cpu = cpu;
+		t->pdu_len = len;
+		memcpy((void *) t + sizeof(*t), data, len);
+	}
+}
+
+/*
+ * Send out a notify for this process, if we haven't done so since a trace
+ * started
+ */
+static void trace_note_tsk(struct blk_trace *bt, struct task_struct *tsk)
+{
+	tsk->btrace_seq = blktrace_seq;
+	trace_note(bt, tsk->pid, BLK_TN_PROCESS, tsk->comm, sizeof(tsk->comm));
+}
+
+static void trace_note_time(struct blk_trace *bt)
+{
+	struct timespec now;
+	unsigned long flags;
+	u32 words[2];
+
+	getnstimeofday(&now);
+	words[0] = now.tv_sec;
+	words[1] = now.tv_nsec;
+
+	local_irq_save(flags);
+	trace_note(bt, 0, BLK_TN_TIMESTAMP, words, sizeof(words));
+	local_irq_restore(flags);
+}
+
+static int act_log_check(struct blk_trace *bt, u32 what, sector_t sector,
+			 pid_t pid)
+{
+	if (((bt->act_mask << BLK_TC_SHIFT) & what) == 0)
+		return 1;
+	if (sector < bt->start_lba || sector > bt->end_lba)
+		return 1;
+	if (bt->pid && pid != bt->pid)
+		return 1;
+
+	return 0;
+}
+
+/*
+ * Data direction bit lookup
+ */
+static u32 ddir_act[2] __read_mostly = { BLK_TC_ACT(BLK_TC_READ), BLK_TC_ACT(BLK_TC_WRITE) };
+
+/*
+ * Bio action bits of interest
+ */
+static u32 bio_act[9] __read_mostly = { 0, BLK_TC_ACT(BLK_TC_BARRIER), BLK_TC_ACT(BLK_TC_SYNC), 0, BLK_TC_ACT(BLK_TC_AHEAD), 0, 0, 0, BLK_TC_ACT(BLK_TC_META) };
+
+/*
+ * More could be added as needed, taking care to increment the decrementer
+ * to get correct indexing
+ */
+#define trace_barrier_bit(rw)	\
+	(((rw) & (1 << BIO_RW_BARRIER)) >> (BIO_RW_BARRIER - 0))
+#define trace_sync_bit(rw)	\
+	(((rw) & (1 << BIO_RW_SYNC)) >> (BIO_RW_SYNC - 1))
+#define trace_ahead_bit(rw)	\
+	(((rw) & (1 << BIO_RW_AHEAD)) << (2 - BIO_RW_AHEAD))
+#define trace_meta_bit(rw)	\
+	(((rw) & (1 << BIO_RW_META)) >> (BIO_RW_META - 3))
+
+/*
+ * The worker for the various blk_add_trace*() types. Fills out a
+ * blk_io_trace structure and places it in a per-cpu subbuffer.
+ */
+void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
+		     int rw, u32 what, int error, int pdu_len, void *pdu_data)
+{
+	struct task_struct *tsk = current;
+	struct blk_io_trace *t;
+	unsigned long flags;
+	unsigned long *sequence;
+	pid_t pid;
+	int cpu;
+
+	if (unlikely(bt->trace_state != Blktrace_running))
+		return;
+
+	what |= ddir_act[rw & WRITE];
+	what |= bio_act[trace_barrier_bit(rw)];
+	what |= bio_act[trace_sync_bit(rw)];
+	what |= bio_act[trace_ahead_bit(rw)];
+	what |= bio_act[trace_meta_bit(rw)];
+
+	pid = tsk->pid;
+	if (unlikely(act_log_check(bt, what, sector, pid)))
+		return;
+
+	/*
+	 * A word about the locking here - we disable interrupts to reserve
+	 * some space in the relay per-cpu buffer, to prevent an irq
+	 * from coming in and stepping on our toes. Once reserved, it's
+	 * enough to get preemption disabled to prevent read of this data
+	 * before we are through filling it. get_cpu()/put_cpu() does this
+	 * for us
+	 */
+	local_irq_save(flags);
+
+	if (unlikely(tsk->btrace_seq != blktrace_seq))
+		trace_note_tsk(bt, tsk);
+
+	t = relay_reserve(bt->rchan, sizeof(*t) + pdu_len);
+	if (t) {
+		cpu = smp_processor_id();
+		sequence = per_cpu_ptr(bt->sequence, cpu);
+
+		t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
+		t->sequence = ++(*sequence);
+		t->time = cpu_clock(cpu) - per_cpu(blk_trace_cpu_offset, cpu);
+		t->sector = sector;
+		t->bytes = bytes;
+		t->action = what;
+		t->pid = pid;
+		t->device = bt->dev;
+		t->cpu = cpu;
+		t->error = error;
+		t->pdu_len = pdu_len;
+
+		if (pdu_len)
+			memcpy((void *) t + sizeof(*t), pdu_data, pdu_len);
+	}
+
+	local_irq_restore(flags);
+}
+
+EXPORT_SYMBOL_GPL(__blk_add_trace);
+
+static struct dentry *blk_tree_root;
+static struct mutex blk_tree_mutex;
+static unsigned int root_users;
+
+static inline void blk_remove_root(void)
+{
+	if (blk_tree_root) {
+		debugfs_remove(blk_tree_root);
+		blk_tree_root = NULL;
+	}
+}
+
+static void blk_remove_tree(struct dentry *dir)
+{
+	mutex_lock(&blk_tree_mutex);
+	debugfs_remove(dir);
+	if (--root_users == 0)
+		blk_remove_root();
+	mutex_unlock(&blk_tree_mutex);
+}
+
+static struct dentry *blk_create_tree(const char *blk_name)
+{
+	struct dentry *dir = NULL;
+
+	mutex_lock(&blk_tree_mutex);
+
+	if (!blk_tree_root) {
+		blk_tree_root = debugfs_create_dir("block", NULL);
+		if (!blk_tree_root)
+			goto err;
+	}
+
+	dir = debugfs_create_dir(blk_name, blk_tree_root);
+	if (dir)
+		root_users++;
+	else
+		blk_remove_root();
+
+err:
+	mutex_unlock(&blk_tree_mutex);
+	return dir;
+}
+
+static void blk_trace_cleanup(struct blk_trace *bt)
+{
+	relay_close(bt->rchan);
+	debugfs_remove(bt->dropped_file);
+	blk_remove_tree(bt->dir);
+	free_percpu(bt->sequence);
+	kfree(bt);
+}
+
+static int blk_trace_remove(struct request_queue *q)
+{
+	struct blk_trace *bt;
+
+	bt = xchg(&q->blk_trace, NULL);
+	if (!bt)
+		return -EINVAL;
+
+	if (bt->trace_state == Blktrace_setup ||
+	    bt->trace_state == Blktrace_stopped)
+		blk_trace_cleanup(bt);
+
+	return 0;
+}
+
+static int blk_dropped_open(struct inode *inode, struct file *filp)
+{
+	filp->private_data = inode->i_private;
+
+	return 0;
+}
+
+static ssize_t blk_dropped_read(struct file *filp, char __user *buffer,
+				size_t count, loff_t *ppos)
+{
+	struct blk_trace *bt = filp->private_data;
+	char buf[16];
+
+	snprintf(buf, sizeof(buf), "%u\n", atomic_read(&bt->dropped));
+
+	return simple_read_from_buffer(buffer, count, ppos, buf, strlen(buf));
+}
+
+static const struct file_operations blk_dropped_fops = {
+	.owner =	THIS_MODULE,
+	.open =		blk_dropped_open,
+	.read =		blk_dropped_read,
+};
+
+/*
+ * Keep track of how many times we encountered a full subbuffer, to aid
+ * the user space app in telling how many lost events there were.
+ */
+static int blk_subbuf_start_callback(struct rchan_buf *buf, void *subbuf,
+				     void *prev_subbuf, size_t prev_padding)
+{
+	struct blk_trace *bt;
+
+	if (!relay_buf_full(buf))
+		return 1;
+
+	bt = buf->chan->private_data;
+	atomic_inc(&bt->dropped);
+	return 0;
+}
+
+static int blk_remove_buf_file_callback(struct dentry *dentry)
+{
+	debugfs_remove(dentry);
+	return 0;
+}
+
+static struct dentry *blk_create_buf_file_callback(const char *filename,
+						   struct dentry *parent,
+						   int mode,
+						   struct rchan_buf *buf,
+						   int *is_global)
+{
+	return debugfs_create_file(filename, mode, parent, buf,
+					&relay_file_operations);
+}
+
+static struct rchan_callbacks blk_relay_callbacks = {
+	.subbuf_start		= blk_subbuf_start_callback,
+	.create_buf_file	= blk_create_buf_file_callback,
+	.remove_buf_file	= blk_remove_buf_file_callback,
+};
+
+/*
+ * Setup everything required to start tracing
+ */
+int do_blk_trace_setup(struct request_queue *q, struct block_device *bdev,
+			struct blk_user_trace_setup *buts)
+{
+	struct blk_trace *old_bt, *bt = NULL;
+	struct dentry *dir = NULL;
+	char b[BDEVNAME_SIZE];
+	int ret, i;
+
+	if (!buts->buf_size || !buts->buf_nr)
+		return -EINVAL;
+
+	strcpy(buts->name, bdevname(bdev, b));
+
+	/*
+	 * some device names have larger paths - convert the slashes
+	 * to underscores for this to work as expected
+	 */
+	for (i = 0; i < strlen(buts->name); i++)
+		if (buts->name[i] == '/')
+			buts->name[i] = '_';
+
+	ret = -ENOMEM;
+	bt = kzalloc(sizeof(*bt), GFP_KERNEL);
+	if (!bt)
+		goto err;
+
+	bt->sequence = alloc_percpu(unsigned long);
+	if (!bt->sequence)
+		goto err;
+
+	ret = -ENOENT;
+	dir = blk_create_tree(buts->name);
+	if (!dir)
+		goto err;
+
+	bt->dir = dir;
+	bt->dev = bdev->bd_dev;
+	atomic_set(&bt->dropped, 0);
+
+	ret = -EIO;
+	bt->dropped_file = debugfs_create_file("dropped", 0444, dir, bt, &blk_dropped_fops);
+	if (!bt->dropped_file)
+		goto err;
+
+	bt->rchan = relay_open("trace", dir, buts->buf_size,
+				buts->buf_nr, &blk_relay_callbacks, bt);
+	if (!bt->rchan)
+		goto err;
+
+	bt->act_mask = buts->act_mask;
+	if (!bt->act_mask)
+		bt->act_mask = (u16) -1;
+
+	bt->start_lba = buts->start_lba;
+	bt->end_lba = buts->end_lba;
+	if (!bt->end_lba)
+		bt->end_lba = -1ULL;
+
+	bt->pid = buts->pid;
+	bt->trace_state = Blktrace_setup;
+
+	ret = -EBUSY;
+	old_bt = xchg(&q->blk_trace, bt);
+	if (old_bt) {
+		(void) xchg(&q->blk_trace, old_bt);
+		goto err;
+	}
+
+	return 0;
+err:
+	if (dir)
+		blk_remove_tree(dir);
+	if (bt) {
+		if (bt->dropped_file)
+			debugfs_remove(bt->dropped_file);
+		free_percpu(bt->sequence);
+		if (bt->rchan)
+			relay_close(bt->rchan);
+		kfree(bt);
+	}
+	return ret;
+}
+
+static int blk_trace_setup(struct request_queue *q, struct block_device *bdev,
+			   char __user *arg)
+{
+	struct blk_user_trace_setup buts;
+	int ret;
+
+	ret = copy_from_user(&buts, arg, sizeof(buts));
+	if (ret)
+		return -EFAULT;
+
+	ret = do_blk_trace_setup(q, bdev, &buts);
+	if (ret)
+		return ret;
+
+	if (copy_to_user(arg, &buts, sizeof(buts)))
+		return -EFAULT;
+
+	return 0;
+}
+
+static int blk_trace_startstop(struct request_queue *q, int start)
+{
+	struct blk_trace *bt;
+	int ret;
+
+	if ((bt = q->blk_trace) == NULL)
+		return -EINVAL;
+
+	/*
+	 * For starting a trace, we can transition from a setup or stopped
+	 * trace. For stopping a trace, the state must be running
+	 */
+	ret = -EINVAL;
+	if (start) {
+		if (bt->trace_state == Blktrace_setup ||
+		    bt->trace_state == Blktrace_stopped) {
+			blktrace_seq++;
+			smp_mb();
+			bt->trace_state = Blktrace_running;
+
+			trace_note_time(bt);
+			ret = 0;
+		}
+	} else {
+		if (bt->trace_state == Blktrace_running) {
+			bt->trace_state = Blktrace_stopped;
+			relay_flush(bt->rchan);
+			ret = 0;
+		}
+	}
+
+	return ret;
+}
+
+/**
+ * blk_trace_ioctl: - handle the ioctls associated with tracing
+ * @bdev:	the block device
+ * @cmd: 	the ioctl cmd
+ * @arg:	the argument data, if any
+ *
+ **/
+int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
+{
+	struct request_queue *q;
+	int ret, start = 0;
+
+	q = bdev_get_queue(bdev);
+	if (!q)
+		return -ENXIO;
+
+	mutex_lock(&bdev->bd_mutex);
+
+	switch (cmd) {
+	case BLKTRACESETUP:
+		ret = blk_trace_setup(q, bdev, arg);
+		break;
+	case BLKTRACESTART:
+		start = 1;
+	case BLKTRACESTOP:
+		ret = blk_trace_startstop(q, start);
+		break;
+	case BLKTRACETEARDOWN:
+		ret = blk_trace_remove(q);
+		break;
+	default:
+		ret = -ENOTTY;
+		break;
+	}
+
+	mutex_unlock(&bdev->bd_mutex);
+	return ret;
+}
+
+/**
+ * blk_trace_shutdown: - stop and cleanup trace structures
+ * @q:    the request queue associated with the device
+ *
+ **/
+void blk_trace_shutdown(struct request_queue *q)
+{
+	if (q->blk_trace) {
+		blk_trace_startstop(q, 0);
+		blk_trace_remove(q);
+	}
+}
+
+/*
+ * Average offset over two calls to cpu_clock() with a gettimeofday()
+ * in the middle
+ */
+static void blk_check_time(unsigned long long *t, int this_cpu)
+{
+	unsigned long long a, b;
+	struct timeval tv;
+
+	a = cpu_clock(this_cpu);
+	do_gettimeofday(&tv);
+	b = cpu_clock(this_cpu);
+
+	*t = tv.tv_sec * 1000000000 + tv.tv_usec * 1000;
+	*t -= (a + b) / 2;
+}
+
+/*
+ * calibrate our inter-CPU timings
+ */
+static void blk_trace_check_cpu_time(void *data)
+{
+	unsigned long long *t;
+	int this_cpu = get_cpu();
+
+	t = &per_cpu(blk_trace_cpu_offset, this_cpu);
+
+	/*
+	 * Just call it twice, hopefully the second call will be cache hot
+	 * and a little more precise
+	 */
+	blk_check_time(t, this_cpu);
+	blk_check_time(t, this_cpu);
+
+	put_cpu();
+}
+
+static void blk_trace_set_ht_offsets(void)
+{
+#if defined(CONFIG_SCHED_SMT)
+	int cpu, i;
+
+	/*
+	 * now make sure HT siblings have the same time offset
+	 */
+	preempt_disable();
+	for_each_online_cpu(cpu) {
+		unsigned long long *cpu_off, *sibling_off;
+
+		for_each_cpu_mask(i, per_cpu(cpu_sibling_map, cpu)) {
+			if (i == cpu)
+				continue;
+
+			cpu_off = &per_cpu(blk_trace_cpu_offset, cpu);
+			sibling_off = &per_cpu(blk_trace_cpu_offset, i);
+			*sibling_off = *cpu_off;
+		}
+	}
+	preempt_enable();
+#endif
+}
+
+static __init int blk_trace_init(void)
+{
+	mutex_init(&blk_tree_mutex);
+	on_each_cpu(blk_trace_check_cpu_time, NULL, 1, 1);
+	blk_trace_set_ht_offsets();
+
+	return 0;
+}
+
+module_init(blk_trace_init);
+

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68