block: Add nr_bios to block_rq_remap tracepoint

Adding the number of bios in a remapped request to 'block_rq_remap'
tracepoint.

Request remapper clones bios in a request to track the completion
status of each bio. So the number of bios can be useful information
for investigation.

Related discussions:
  http://www.redhat.com/archives/dm-devel/2013-August/msg00084.html
  http://www.redhat.com/archives/dm-devel/2013-September/msg00024.html

Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 15 insertions, 2 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2fdb4a451b49..0e6f765aa1f5 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -862,6 +862,17 @@ static inline unsigned int blk_rq_get_max_sectors(struct request *rq)
         return blk_queue_get_max_sectors(q, rq->cmd_flags);
 }
 
+static inline unsigned int blk_rq_count_bios(struct request *rq)
+{
+        unsigned int nr_bios = 0;
+        struct bio *bio;
+
+        __rq_for_each_bio(bio, rq)
+                nr_bios++;
+
+        return nr_bios;
+}
+
 /*
  * Request issue related functions.
  */
diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index 60ae7c3db912..4c2301d2ef1a 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -618,6 +618,7 @@ TRACE_EVENT(block_rq_remap,
                 __field( unsigned int,  nr_sector       )
                 __field( dev_t,         old_dev         )
                 __field( sector_t,      old_sector      )
+                __field( unsigned int,  nr_bios         )
                 __array( char,          rwbs,   RWBS_LEN)
         ),
 
@@ -627,15 +628,16 @@ TRACE_EVENT(block_rq_remap,
                 __entry->nr_sector      = blk_rq_sectors(rq);
                 __entry->old_dev        = dev;
                 __entry->old_sector     = from;
+                __entry->nr_bios        = blk_rq_count_bios(rq);
                 blk_fill_rwbs(__entry->rwbs, rq->cmd_flags, blk_rq_bytes(rq));
         ),
 
-        TP_printk("%d,%d %s %llu + %u <- (%d,%d) %llu",
+        TP_printk("%d,%d %s %llu + %u <- (%d,%d) %llu %u",
                   MAJOR(__entry->dev), MINOR(__entry->dev), __entry->rwbs,
                   (unsigned long long)__entry->sector,
                   __entry->nr_sector,
                   MAJOR(__entry->old_dev), MINOR(__entry->old_dev),
-                  (unsigned long long)__entry->old_sector)
+                  (unsigned long long)__entry->old_sector, __entry->nr_bios)
 );
 
 #endif /* _TRACE_BLOCK_H */