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, 3 insertions, 5 deletions

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index ac1b682edecb..50ec6f834996 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;