block: kill QUEUE_ORDERED_BY_TAG

Nobody is making meaningful use of ORDERED_BY_TAG now and queue
draining for barrier requests will be removed soon which will render
the advantage of tag ordering moot.  Kill ORDERED_BY_TAG.  The
following users are affected.

* brd: converted to ORDERED_DRAIN.
* virtio_blk: ORDERED_TAG path was already marked deprecated.  Removed.
* xen-blkfront: ORDERED_TAG case dropped.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 0 insertions, 9 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 2aafafca2b13..79652809eee8 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -395,15 +395,6 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
                  * to implement write barrier support.
                  */
                 blk_queue_ordered(q, QUEUE_ORDERED_DRAIN_FLUSH);
-        } else if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER)) {
-                /*
-                 * If the BARRIER feature is supported the host expects us
-                 * to order request by tags.  This implies there is not
-                 * volatile write cache on the host, and that the host
-                 * never re-orders outstanding I/O.  This feature is not
-                 * useful for real life scenarious and deprecated.
-                 */
-                blk_queue_ordered(q, QUEUE_ORDERED_TAG);
         } else {
                 /*
                  * If the FLUSH feature is not supported we must assume that