dm: convey that all flushes are processed as empty

Rename __clone_and_map_flush to __clone_and_map_empty_flush for added
clarity.

Simplify logic associated with REQ_FLUSH conditionals.

Introduce a BUG_ON() and add a few more helpful comments to the code
so that it is clear that all flushes are empty.

Cleanup __split_and_process_bio() so that an empty flush isn't processed
by a 'sector_count' focused while loop.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 15 insertions, 19 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index cd2f7e77b625..f934e9878436 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -621,16 +621,17 @@ static void dec_pending(struct dm_io *io, int error)
                 if (io_error == DM_ENDIO_REQUEUE)
                         return;
 
-                if (!(bio->bi_rw & REQ_FLUSH) || !bio->bi_size) {
-                        trace_block_bio_complete(md->queue, bio);
-                        bio_endio(bio, io_error);
-                } else {
+                if ((bio->bi_rw & REQ_FLUSH) && bio->bi_size) {
                         /*
                          * Preflush done for flush with data, reissue
                          * without REQ_FLUSH.
                          */
                         bio->bi_rw &= ~REQ_FLUSH;
                         queue_io(md, bio);
+                } else {
+                        /* done with normal IO or empty flush */
+                        trace_block_bio_complete(md->queue, bio);
+                        bio_endio(bio, io_error);
                 }
         }
 }
@@ -1132,16 +1133,15 @@ static void __issue_target_requests(struct clone_info *ci, struct dm_target *ti,
                 __issue_target_request(ci, ti, request_nr, len);
 }
 
-static int __clone_and_map_flush(struct clone_info *ci)
+static int __clone_and_map_empty_flush(struct clone_info *ci)
 {
         unsigned target_nr = 0;
         struct dm_target *ti;
 
+        BUG_ON(bio_has_data(ci->bio));
         while ((ti = dm_table_get_target(ci->map, target_nr++)))
                 __issue_target_requests(ci, ti, ti->num_flush_requests, 0);
 
-        ci->sector_count = 0;
-
         return 0;
 }
 
@@ -1282,7 +1282,6 @@ static int __clone_and_map(struct clone_info *ci)
  */
 static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
 {
-        bool is_flush = bio->bi_rw & REQ_FLUSH;
         struct clone_info ci;
         int error = 0;
 
@@ -1302,20 +1301,17 @@ static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
         ci.sector = bio->bi_sector;
         ci.idx = bio->bi_idx;
 
-        if (!is_flush) {
+        start_io_acct(ci.io);
+        if (bio->bi_rw & REQ_FLUSH) {
+                ci.bio = &ci.md->flush_bio;
+                ci.sector_count = 0;
+                error = __clone_and_map_empty_flush(&ci);
+                /* dec_pending submits any data associated with flush */
+        } else {
                 ci.bio = bio;
                 ci.sector_count = bio_sectors(bio);
-        } else {
-                ci.bio = &ci.md->flush_bio;
-                ci.sector_count = 1;
-        }
-
-        start_io_acct(ci.io);
-        while (ci.sector_count && !error) {
-                if (!is_flush)
+                while (ci.sector_count && !error)
                         error = __clone_and_map(&ci);
-                else
-                        error = __clone_and_map_flush(&ci);
         }
 
         /* drop the extra reference count */