block: add block_{touch|dirty}_buffer tracepoint

The former is triggered from touch_buffer() and the latter
mark_buffer_dirty().

This is part of tracepoint additions to improve visiblity into
dirtying / writeback operations for io tracer and userland.

v2: Transformed writeback_dirty_buffer to block_dirty_buffer and made
    it share TP definition with block_touch_buffer.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/buffer.c

@@ -41,6 +41,7 @@
 #include <linux/bitops.h>
 #include <linux/mpage.h>
 #include <linux/bit_spinlock.h>
+#include <trace/events/block.h>
 
 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
 
@@ -55,6 +56,7 @@ EXPORT_SYMBOL(init_buffer);
 
 inline void touch_buffer(struct buffer_head *bh)
 {
+	trace_block_touch_buffer(bh);
 	mark_page_accessed(bh->b_page);
 }
 EXPORT_SYMBOL(touch_buffer);
@@ -1119,6 +1121,8 @@ void mark_buffer_dirty(struct buffer_head *bh)
 {
 	WARN_ON_ONCE(!buffer_uptodate(bh));
 
+	trace_block_dirty_buffer(bh);
+
 	/*
 	 * Very *carefully* optimize the it-is-already-dirty case.
 	 *

include/trace/events/block.h

@@ -6,10 +6,61 @@
 
 #include <linux/blktrace_api.h>
 #include <linux/blkdev.h>
+#include <linux/buffer_head.h>
 #include <linux/tracepoint.h>
 
 #define RWBS_LEN	8
 
+DECLARE_EVENT_CLASS(block_buffer,
+
+	TP_PROTO(struct buffer_head *bh),
+
+	TP_ARGS(bh),
+
+	TP_STRUCT__entry (
+		__field(  dev_t,	dev			)
+		__field(  sector_t,	sector			)
+		__field(  size_t,	size			)
+	),
+
+	TP_fast_assign(
+		__entry->dev		= bh->b_bdev->bd_dev;
+		__entry->sector		= bh->b_blocknr;
+		__entry->size		= bh->b_size;
+	),
+
+	TP_printk("%d,%d sector=%llu size=%zu",
+		MAJOR(__entry->dev), MINOR(__entry->dev),
+		(unsigned long long)__entry->sector, __entry->size
+	)
+);
+
+/**
+ * block_touch_buffer - mark a buffer accessed
+ * @bh: buffer_head being touched
+ *
+ * Called from touch_buffer().
+ */
+DEFINE_EVENT(block_buffer, block_touch_buffer,
+
+	TP_PROTO(struct buffer_head *bh),
+
+	TP_ARGS(bh)
+);
+
+/**
+ * block_dirty_buffer - mark a buffer dirty
+ * @bh: buffer_head being dirtied
+ *
+ * Called from mark_buffer_dirty().
+ */
+DEFINE_EVENT(block_buffer, block_dirty_buffer,
+
+	TP_PROTO(struct buffer_head *bh),
+
+	TP_ARGS(bh)
+);
+
 DECLARE_EVENT_CLASS(block_rq_with_error,
 
 	TP_PROTO(struct request_queue *q, struct request *rq),