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Subject[PATCH 6/9] block: add block_touch_buffer tracepoint
Date
Add block_touch_buffer tracepoint which gets triggered on
touch_buffer().

Because touch_buffer() is defined as macro in linux/buffer_head.h,
this creates circular dependency between linux/buffer_head.h and
events/block.h. As event header needs buffer_head details only when
the tracepoints are actually created (CREATE_TRACE_POINTS is defined),
this can be easily solved by including buffer_head.h before setting
CREATE_TRACE_POINTS and including the event header to create
tracepoints.

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

Signed-off-by: Tejun Heo <tj@kernel.org>
---
block/blk-core.c | 1 +
include/linux/buffer_head.h | 7 ++++++-
include/trace/events/block.h | 25 +++++++++++++++++++++++++
3 files changed, 32 insertions(+), 1 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index dd45d6e..8f59db3 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -29,6 +29,7 @@
#include <linux/fault-inject.h>
#include <linux/list_sort.h>
#include <linux/delay.h>
+#include <linux/buffer_head.h>

#define CREATE_TRACE_POINTS
#include <trace/events/block.h>
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 458f497..245caed 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -13,6 +13,7 @@
#include <linux/pagemap.h>
#include <linux/wait.h>
#include <linux/atomic.h>
+#include <trace/events/block.h>

#ifdef CONFIG_BLOCK

@@ -126,7 +127,11 @@ BUFFER_FNS(Write_EIO, write_io_error)
BUFFER_FNS(Unwritten, unwritten)

#define bh_offset(bh) ((unsigned long)(bh)->b_data & ~PAGE_MASK)
-#define touch_buffer(bh) mark_page_accessed(bh->b_page)
+
+#define touch_buffer(bh) do { \
+ trace_block_touch_buffer(bh); \
+ mark_page_accessed(bh->b_page); \
+ } while (0)

/* If we *know* page->private refers to buffer_heads */
#define page_buffers(page) \
diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index 983f8a8..4fcc09d 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -6,10 +6,35 @@

#include <linux/blktrace_api.h>
#include <linux/blkdev.h>
+#include <linux/buffer_head.h>
#include <linux/tracepoint.h>

#define RWBS_LEN 8

+TRACE_EVENT(block_touch_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 get_bh sector=%llu size=%zu",
+ MAJOR(__entry->dev), MINOR(__entry->dev),
+ (unsigned long long)__entry->sector, __entry->size
+ )
+);
+
DECLARE_EVENT_CLASS(block_rq_with_error,

TP_PROTO(struct request_queue *q, struct request *rq),
--
1.7.3.1


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