linux-kernel - Re: [RFC patch 1/5] trace event block fix unassigned field

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Date:	Wed, 5 Jan 2011 14:34:25 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	Li Zefan <lizf@...fujitsu.com>, Alan.Brunelle@...com
Subject: Re: [RFC patch 1/5] trace event block fix unassigned field

* Jeff Moyer (jmoyer@...hat.com) wrote:
> Mathieu Desnoyers <mathieu.desnoyers@...icios.com> writes:
> 
> > The "error" field in block_bio_complete is not assigned, leaving the memory area
> > uninitialized (keeping garbage data). Initialize it to 0.
> >
> > We should eventually remove this field when we find out if blktrace can live
> > without it.
> 
> Well, I'm fairly sure blkparse has the ability to print this field out,
> so we should probably just fill it in properly.  Something like the
> following untested patch should do.

I updated your patch slightly (documentation and build fix). It should be fine
now. Thanks!

Mathieu


trace event block fix unassigned field

The "error" field in block_bio_complete is not assigned, leaving the memory area
uninitialized (keeping garbage data). Pass an additional tracepoint argument to
this event to initialize this field.

From: Jeff Moyer <jmoyer@...hat.com>
Signed-off-by: Jeff Moyer <jmoyer@...hat.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: Frederic Weisbecker <fweisbec@...il.com>
CC: Ingo Molnar <mingo@...e.hu>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Jens Axboe <jens.axboe@...cle.com>
CC: Li Zefan <lizf@...fujitsu.com>
CC: Alan.Brunelle@...com
---
 drivers/md/dm.c              |    2 +-
 include/trace/events/block.h |    6 ++++--
 2 files changed, 5 insertions(+), 3 deletions(-)

Index: linux-2.6-lttng/include/trace/events/block.h
===================================================================
--- linux-2.6-lttng.orig/include/trace/events/block.h
+++ linux-2.6-lttng/include/trace/events/block.h
@@ -206,15 +206,16 @@ TRACE_EVENT(block_bio_bounce,
  * block_bio_complete - completed all work on the block operation
  * @q: queue holding the block operation
  * @bio: block operation completed
+ * @error: io error value
  *
  * This tracepoint indicates there is no further work to do on this
  * block IO operation @bio.
  */
 TRACE_EVENT(block_bio_complete,
 
-	TP_PROTO(struct request_queue *q, struct bio *bio),
+	TP_PROTO(struct request_queue *q, struct bio *bio, int error),
 
-	TP_ARGS(q, bio),
+	TP_ARGS(q, bio, error),
 
 	TP_STRUCT__entry(
 		__field( dev_t,		dev		)
@@ -228,6 +229,7 @@ TRACE_EVENT(block_bio_complete,
 		__entry->dev		= bio->bi_bdev->bd_dev;
 		__entry->sector		= bio->bi_sector;
 		__entry->nr_sector	= bio->bi_size >> 9;
+		__entry->error		= error;
 		blk_fill_rwbs(__entry->rwbs, bio->bi_rw, bio->bi_size);
 	),
 
Index: linux-2.6-lttng/drivers/md/dm.c
===================================================================
--- linux-2.6-lttng.orig/drivers/md/dm.c
+++ linux-2.6-lttng/drivers/md/dm.c
@@ -659,7 +659,7 @@ static void dec_pending(struct dm_io *io
 			free_io(md, io);
 
 			if (io_error != DM_ENDIO_REQUEUE) {
-				trace_block_bio_complete(md->queue, bio);
+				trace_block_bio_complete(md->queue, bio, io_error);
 
 				bio_endio(bio, io_error);
 			}


-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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