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>

2 files changed, 55 insertions, 0 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index a8c2dfb68dcd..87ff335fbbe3 100644
--- a/fs/buffer.c
+++ b/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.
          *
diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index b408f518a819..9961726523d0 100644
--- a/include/trace/events/block.h
+++ b/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),