From e7e245000110a7794de8f925b9edc06a9c852f80 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Tue, 29 Oct 2013 12:11:47 -0600
Subject: [PATCH] blk-mq: don't disallow request merges for req->special being
 set

For blk-mq, if a driver has requested per-request payload data
to carry command structures, they are stuffed into req->special.
For an old style request based driver, req->special is used
for the same purpose but indicates that a per-driver request
structure has been prepared for the request already. So for the
old style driver, we do not merge such requests.

As most/all blk-mq drivers will use the payload feature, and
since we have no problem merging on these, make this check
dependent on whether it's a blk-mq enabled driver or not.

Reported-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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