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>

4 files changed, 5 insertions, 18 deletions

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 1c7f637..47a4127 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -482,7 +482,7 @@ static struct brd_device *brd_alloc(int i)
 	if (!brd->brd_queue)
 		goto out_free_dev;
 	blk_queue_make_request(brd->brd_queue, brd_make_request);
-	blk_queue_ordered(brd->brd_queue, QUEUE_ORDERED_TAG);
+	blk_queue_ordered(brd->brd_queue, QUEUE_ORDERED_DRAIN);
 	blk_queue_max_hw_sectors(brd->brd_queue, 1024);
 	blk_queue_bounce_limit(brd->brd_queue, BLK_BOUNCE_ANY);
 
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 2aafafc..7965280 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
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index ac1b682e..50ec6f83 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -424,8 +424,7 @@ static int xlvbd_barrier(struct blkfront_info *info)
 	const char *barrier;
 
 	switch (info->feature_barrier) {
-	case QUEUE_ORDERED_DRAIN:	barrier = "enabled (drain)"; break;
-	case QUEUE_ORDERED_TAG:		barrier = "enabled (tag)"; break;
+	case QUEUE_ORDERED_DRAIN:	barrier = "enabled"; break;
 	case QUEUE_ORDERED_NONE:	barrier = "disabled"; break;
 	default:			return -EINVAL;
 	}
@@ -1078,8 +1077,7 @@ static void blkfront_connect(struct blkfront_info *info)
 	 * we're dealing with a very old backend which writes
 	 * synchronously; draining will do what needs to get done.
 	 *
-	 * If there are barriers, then we can do full queued writes
-	 * with tagged barriers.
+	 * If there are barriers, then we use flush.
 	 *
 	 * If barriers are not supported, then there's no much we can
 	 * do, so just set ordering to NONE.
@@ -1087,7 +1085,7 @@ static void blkfront_connect(struct blkfront_info *info)
 	if (err)
 		info->feature_barrier = QUEUE_ORDERED_DRAIN;
 	else if (barrier)
-		info->feature_barrier = QUEUE_ORDERED_TAG;
+		info->feature_barrier = QUEUE_ORDERED_DRAIN_FLUSH;
 	else
 		info->feature_barrier = QUEUE_ORDERED_NONE;
 
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 2714bec..cdfc51a 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2151,9 +2151,7 @@ static int sd_revalidate_disk(struct gendisk *disk)
 
 	/*
 	 * We now have all cache related info, determine how we deal
-	 * with ordered requests.  Note that as the current SCSI
-	 * dispatch function can alter request order, we cannot use
-	 * QUEUE_ORDERED_TAG_* even when ordered tag is supported.
+	 * with ordered requests.
 	 */
 	if (sdkp->WCE)
 		ordered = sdkp->DPOFUA