From 7aef2e780b13973ea60aed8c556107dabde6a495 Mon Sep 17 00:00:00 2001
From: Jianpeng Ma <majianpeng@gmail.com>
Date: Wed, 11 Sep 2013 13:21:07 -0600
Subject: [PATCH] block: trace all devices plug operation

In func blk_queue_bio, if list of plug is empty,it will call
blk_trace_plug.
If process deal with a single device,it't ok.But if process deal with
multi devices,it only trace the first device.
Using request_count to judge, it can soleve this problem.

In addition, i modify the comment.

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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