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>

6 files changed, 13 insertions, 62 deletions

diff --git a/block/blk-barrier.c b/block/blk-barrier.c
index f0faefca032f..c807e9ca3a68 100644
--- a/block/blk-barrier.c
+++ b/block/blk-barrier.c
@@ -26,10 +26,7 @@ int blk_queue_ordered(struct request_queue *q, unsigned ordered)
         if (ordered != QUEUE_ORDERED_NONE &&
             ordered != QUEUE_ORDERED_DRAIN &&
             ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
-            ordered != QUEUE_ORDERED_DRAIN_FUA &&
-            ordered != QUEUE_ORDERED_TAG &&
-            ordered != QUEUE_ORDERED_TAG_FLUSH &&
-            ordered != QUEUE_ORDERED_TAG_FUA) {
+            ordered != QUEUE_ORDERED_DRAIN_FUA) {
                 printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
                 return -EINVAL;
         }
@@ -155,21 +152,9 @@ static inline bool start_ordered(struct request_queue *q, struct request **rqp)
          * For an empty barrier, there's no actual BAR request, which
          * in turn makes POSTFLUSH unnecessary.  Mask them off.
          */
-        if (!blk_rq_sectors(rq)) {
+        if (!blk_rq_sectors(rq))
                 q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
                                 QUEUE_ORDERED_DO_POSTFLUSH);
-                /*
-                 * Empty barrier on a write-through device w/ ordered
-                 * tag has no command to issue and without any command
-                 * to issue, ordering by tag can't be used.  Drain
-                 * instead.
-                 */
-                if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
-                    !(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
-                        q->ordered &= ~QUEUE_ORDERED_BY_TAG;
-                        q->ordered |= QUEUE_ORDERED_BY_DRAIN;
-                }
-        }
 
         /* stash away the original request */
         blk_dequeue_request(rq);
@@ -210,7 +195,7 @@ static inline bool start_ordered(struct request_queue *q, struct request **rqp)
         } else
                 skip |= QUEUE_ORDSEQ_PREFLUSH;
 
-        if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && queue_in_flight(q))
+        if (queue_in_flight(q))
                 rq = NULL;
         else
                 skip |= QUEUE_ORDSEQ_DRAIN;
@@ -257,16 +242,10 @@ bool blk_do_ordered(struct request_queue *q, struct request **rqp)
             rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
                 return true;
 
-        if (q->ordered & QUEUE_ORDERED_BY_TAG) {
-                /* Ordered by tag.  Blocking the next barrier is enough. */
-                if (is_barrier && rq != &q->bar_rq)
-                        *rqp = NULL;
-        } else {
-                /* Ordered by draining.  Wait for turn. */
-                WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
-                if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
-                        *rqp = NULL;
-        }
+        /* Ordered by draining.  Wait for turn. */
+        WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
+        if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
+                *rqp = NULL;
 
         return true;
 }
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 1c7f63792ff8..47a41272d26b 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 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
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;
 
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 2714becc2eaf..cdfc51ab9cf2 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
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 015375c7d031..7077bc0d6138 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -470,12 +470,7 @@ enum {
          * DRAIN        : ordering by draining is enough
          * DRAIN_FLUSH  : ordering by draining w/ pre and post flushes
          * DRAIN_FUA    : ordering by draining w/ pre flush and FUA write
-         * TAG          : ordering by tag is enough
-         * TAG_FLUSH    : ordering by tag w/ pre and post flushes
-         * TAG_FUA      : ordering by tag w/ pre flush and FUA write
          */
-        QUEUE_ORDERED_BY_DRAIN          = 0x01,
-        QUEUE_ORDERED_BY_TAG            = 0x02,
         QUEUE_ORDERED_DO_PREFLUSH       = 0x10,
         QUEUE_ORDERED_DO_BAR            = 0x20,
         QUEUE_ORDERED_DO_POSTFLUSH      = 0x40,
@@ -483,8 +478,7 @@ enum {
 
         QUEUE_ORDERED_NONE              = 0x00,
 
-        QUEUE_ORDERED_DRAIN             = QUEUE_ORDERED_BY_DRAIN |
-                                          QUEUE_ORDERED_DO_BAR,
+        QUEUE_ORDERED_DRAIN             = QUEUE_ORDERED_DO_BAR,
         QUEUE_ORDERED_DRAIN_FLUSH       = QUEUE_ORDERED_DRAIN |
                                           QUEUE_ORDERED_DO_PREFLUSH |
                                           QUEUE_ORDERED_DO_POSTFLUSH,
@@ -492,15 +486,6 @@ enum {
                                           QUEUE_ORDERED_DO_PREFLUSH |
                                           QUEUE_ORDERED_DO_FUA,
 
-        QUEUE_ORDERED_TAG               = QUEUE_ORDERED_BY_TAG |
-                                          QUEUE_ORDERED_DO_BAR,
-        QUEUE_ORDERED_TAG_FLUSH         = QUEUE_ORDERED_TAG |
-                                          QUEUE_ORDERED_DO_PREFLUSH |
-                                          QUEUE_ORDERED_DO_POSTFLUSH,
-        QUEUE_ORDERED_TAG_FUA           = QUEUE_ORDERED_TAG |
-                                          QUEUE_ORDERED_DO_PREFLUSH |
-                                          QUEUE_ORDERED_DO_FUA,
-
         /*
          * Ordered operation sequence
          */