From: Jason Baron <jbaron@redhat.com>
Date: Mon, 26 Oct 2009 20:12:53 -0400
Subject: [block] blktrace: correctly record block to and from devs
Message-id: <20091026201253.GB2641@redhat.com>
Patchwork-id: 21235
O-Subject: Re: [PATCH RHEL5.5 1/2] correctly record block 'to' and 'from'
	devices (repost)
Bugzilla: 515551
RH-Acked-by: Jeff Moyer <jmoyer@redhat.com>
RH-Acked-by: Eric Sandeen <sandeen@redhat.com>

On Wed, Oct 21, 2009 at 04:32:18PM -0400, Jason Baron wrote:
>
> Record the correct 'to' and 'from' device number for block remap operation.
>

Jeff Moyer pointed out that the upstream blktrace userspace, places the
device 'from' field *before* the device 'to' field in the remap
structure. Thus, in order to make sure this fix also works with upstream
blktrace packages, we should match that ordering in the kernel.

Note that this also means that even if we do not apply the userspace
blktrace patch, we will get correct blktrace output for remap.

This patch replaces the previous kernel piece posted for this issue.
Resolves bz #515551.

thanks,

-Jason

Signed-off-by: Don Zickus <dzickus@redhat.com>

diff --git a/block/blktrace.c b/block/blktrace.c
index 13f17ec..f7dc5c6 100644
--- a/block/blktrace.c
+++ b/block/blktrace.c
@@ -802,7 +802,8 @@ void blk_add_trace_remap(struct request_queue *q, struct bio *bio,
 	if (likely(!bt))
 		return;
 
-	r.device = cpu_to_be32(dev);
+	r.device_from = cpu_to_be32(dev);
+	r.device_to = cpu_to_be32(bio->bi_bdev->bd_dev);
 	r.sector = cpu_to_be64(to);
 
 	__blk_add_trace(bt, from, bio->bi_size, bio->bi_rw, BLK_TA_REMAP,
diff --git a/include/linux/blktrace_api.h b/include/linux/blktrace_api.h
index c173e38..394dd22 100644
--- a/include/linux/blktrace_api.h
+++ b/include/linux/blktrace_api.h
@@ -95,8 +95,8 @@ struct blk_io_trace {
  * The remap event
  */
 struct blk_io_trace_remap {
-	__be32 device;
-	u32 __pad;
+	__be32 device_from;
+	u32 device_to;
 	__be64 sector;
 };