tree 5265a24ffeaea32e2cefacf83962764d6d661a36
parent 6e4664525b1db28f8c4e1130957f70a94c19213e
author Jianpeng Ma <majianpeng@gmail.com> 1378927267 -0600
committer Jens Axboe <axboe@kernel.dk> 1378927267 -0600

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>