From fb199746303a6bfd6121834ec9e810471185c530 Mon Sep 17 00:00:00 2001
From: Akinobu Mita <akinobu.mita@gmail.com>
Date: Mon, 21 Apr 2008 09:51:06 +0200
Subject: [PATCH] block: fix blk_register_queue() return value

blk_register_queue() returns -ENXIO when queue->request_fn is NULL.  But there
are some block drivers that call blk_register_queue() via add_disk() with
queue->request_fn == NULL.  (For example, brd, loop)

Although no one checks return value of blk_register_queue(), this patch makes
it return 0 instead of -ENXIO when queue->request_fn is NULL,

Also this patch adds warning when blk_register_queue() and
blk_unregister_queue() are called with queue == NULL rather than ignore
invalid usage silently.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
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