From 01edede41e352e4879a89cdc5468f72ffc89b713 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan.kim@gmail.com>
Date: Tue, 8 Sep 2009 21:56:38 +0200
Subject: [PATCH] block: trace bio queueing trial only when it occurs
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If BIO is discarded or cross over end of device,
BIO queueing trial doesn't occur.

Actually the trace was called just before make_request at first:
[PATCH] Block queue IO tracing support (blktrace) as of 2006-03-23
      2056a782f8e7e65fd4bfd027506b4ce1c5e9ccd4

And then 2 patches added some checks between them:
[PATCH] md: check bio address after mapping through partitions
        5ddfe9691c91a244e8d1be597b6428fcefd58103,
[BLOCK] Don't allow empty barriers to be passed down to
queues that don't grok them
        51fd77bd9f512ab6cc9df0733ba1caaab89eb957

It breaks original goal.
Let's trace it only when it happens.

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
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