[RFC] tracing/events: block: also try to get dev_t via driver core for some events

[Steffen Maier]

Complements v2.6.31 commit 55782138e47d ("tracing/events: convert block
trace points to TRACE_EVENT()") for cases where rq->rq_disk == NULL:
  block_rq_requeue, block_rq_insert, block_rq_issue;
and for cases where bio == NULL:
  block_getrq, block_sleeprq.

NB: The NULL pointer check for q->kobj.parent is certainly racy and
I don't have enough experience if it's good enough for a trace event.

Since I don't know when above cases would occur,
I'm not sure this is worth it.

Signed-off-by: Steffen Maier <ma...@linux.ibm.com>
---
 include/trace/events/block.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index cffedc26e8a3..c476b7af404b 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -86,7 +86,9 @@ TRACE_EVENT(block_rq_requeue,
        ),
 
        TP_fast_assign(
-               __entry->dev       = rq->rq_disk ? disk_devt(rq->rq_disk) : 0;
+               __entry->dev       = rq->rq_disk ? disk_devt(rq->rq_disk) :
+               (q->kobj.parent ?
+                container_of(q->kobj.parent, struct device, kobj)->devt : 0);
                __entry->sector    = blk_rq_trace_sector(rq);
                __entry->nr_sector = blk_rq_trace_nr_sectors(rq);
 
@@ -162,7 +164,9 @@ DECLARE_EVENT_CLASS(block_rq,
        ),
 
        TP_fast_assign(
-               __entry->dev       = rq->rq_disk ? disk_devt(rq->rq_disk) : 0;
+               __entry->dev       = rq->rq_disk ? disk_devt(rq->rq_disk) :
+               (q->kobj.parent ?
+                container_of(q->kobj.parent, struct device, kobj)->devt : 0);
                __entry->sector    = blk_rq_trace_sector(rq);
                __entry->nr_sector = blk_rq_trace_nr_sectors(rq);
                __entry->bytes     = blk_rq_bytes(rq);
@@ -397,7 +401,9 @@ DECLARE_EVENT_CLASS(block_get_rq,
         ),
 
        TP_fast_assign(
-               __entry->dev            = bio ? bio_dev(bio) : 0;
+               __entry->dev            = bio ? bio_dev(bio) :
+               (q->kobj.parent ?
+                container_of(q->kobj.parent, struct device, kobj)->devt : 0);
                __entry->sector         = bio ? bio->bi_iter.bi_sector : 0;
                __entry->nr_sector      = bio ? bio_sectors(bio) : 0;
                blk_fill_rwbs(__entry->rwbs,
-- 
2.13.5