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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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