block: make every barrier action optional

In all barrier sequences, the barrier write itself was always assumed
to be issued and thus didn't have corresponding control flag.  This
patch adds QUEUE_ORDERED_DO_BAR and unify action mask handling in
start_ordered() such that any barrier action can be skipped.

This patch doesn't introduce any visible behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

2 files changed, 29 insertions, 19 deletions

diff --git a/block/blk-barrier.c b/block/blk-barrier.c
index 43d479a1e664..1efabf829c53 100644
--- a/block/blk-barrier.c
+++ b/block/blk-barrier.c
@@ -158,19 +158,10 @@ static inline struct request *start_ordered(struct request_queue *q,
         q->ordered = q->next_ordered;
         q->ordseq |= QUEUE_ORDSEQ_STARTED;
 
-        /*
-         * Prep proxy barrier request.
-         */
+        /* stash away the original request */
         elv_dequeue_request(q, rq);
         q->orig_bar_rq = rq;
-        rq = &q->bar_rq;
-        blk_rq_init(q, rq);
-        if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
-                rq->cmd_flags |= REQ_RW;
-        if (q->ordered & QUEUE_ORDERED_DO_FUA)
-                rq->cmd_flags |= REQ_FUA;
-        init_request_from_bio(rq, q->orig_bar_rq->bio);
-        rq->end_io = bar_end_io;
+        rq = NULL;
 
         /*
          * Queue ordered sequence.  As we stack them at the head, we
@@ -181,12 +172,28 @@ static inline struct request *start_ordered(struct request_queue *q,
          * there will be no data written between the pre and post flush.
          * Hence a single flush will suffice.
          */
-        if ((q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) && !blk_empty_barrier(rq))
+        if ((q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) &&
+            !blk_empty_barrier(q->orig_bar_rq)) {
                 queue_flush(q, QUEUE_ORDERED_DO_POSTFLUSH);
-        else
+                rq = &q->post_flush_rq;
+        } else
                 q->ordseq |= QUEUE_ORDSEQ_POSTFLUSH;
 
-        elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
+        if (q->ordered & QUEUE_ORDERED_DO_BAR) {
+                rq = &q->bar_rq;
+
+                /* initialize proxy request and queue it */
+                blk_rq_init(q, rq);
+                if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
+                        rq->cmd_flags |= REQ_RW;
+                if (q->ordered & QUEUE_ORDERED_DO_FUA)
+                        rq->cmd_flags |= REQ_FUA;
+                init_request_from_bio(rq, q->orig_bar_rq->bio);
+                rq->end_io = bar_end_io;
+
+                elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
+        } else
+                q->ordseq |= QUEUE_ORDSEQ_BAR;
 
         if (q->ordered & QUEUE_ORDERED_DO_PREFLUSH) {
                 queue_flush(q, QUEUE_ORDERED_DO_PREFLUSH);
@@ -194,10 +201,10 @@ static inline struct request *start_ordered(struct request_queue *q,
         } else
                 q->ordseq |= QUEUE_ORDSEQ_PREFLUSH;
 
-        if ((q->ordered & QUEUE_ORDERED_BY_TAG) || q->in_flight == 0)
-                q->ordseq |= QUEUE_ORDSEQ_DRAIN;
-        else
+        if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && q->in_flight)
                 rq = NULL;
+        else
+                q->ordseq |= QUEUE_ORDSEQ_DRAIN;
 
         return rq;
 }
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 5c92b4432399..b044267009ed 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -526,12 +526,14 @@ enum {
         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,
         QUEUE_ORDERED_DO_FUA            = 0x80,
 
         QUEUE_ORDERED_NONE              = 0x00,
 
-        QUEUE_ORDERED_DRAIN             = QUEUE_ORDERED_BY_DRAIN,
+        QUEUE_ORDERED_DRAIN             = QUEUE_ORDERED_BY_DRAIN |
+                                          QUEUE_ORDERED_DO_BAR,
         QUEUE_ORDERED_DRAIN_FLUSH       = QUEUE_ORDERED_DRAIN |
                                           QUEUE_ORDERED_DO_PREFLUSH |
                                           QUEUE_ORDERED_DO_POSTFLUSH,
@@ -539,7 +541,8 @@ enum {
                                           QUEUE_ORDERED_DO_PREFLUSH |
                                           QUEUE_ORDERED_DO_FUA,
 
-        QUEUE_ORDERED_TAG               = QUEUE_ORDERED_BY_TAG,
+        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,