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>

1 files changed, 8 insertions, 2 deletions

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 54d0db116153..fc41d83be22b 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -276,9 +276,12 @@ int blk_register_queue(struct gendisk *disk)
 
         struct request_queue *q = disk->queue;
 
-        if (!q || !q->request_fn)
+        if (WARN_ON(!q))
                 return -ENXIO;
 
+        if (!q->request_fn)
+                return 0;
+
         ret = kobject_add(&q->kobj, kobject_get(&disk->dev.kobj),
                           "%s", "queue");
         if (ret < 0)
@@ -300,7 +303,10 @@ void blk_unregister_queue(struct gendisk *disk)
 {
         struct request_queue *q = disk->queue;
 
-        if (q && q->request_fn) {
+        if (WARN_ON(!q))
+                return;
+
+        if (q->request_fn) {
                 elv_unregister_queue(q);
 
                 kobject_uevent(&q->kobj, KOBJ_REMOVE);