block, drivers, fs: rename REQ_FLUSH to REQ_PREFLUSH

To avoid confusion between REQ_OP_FLUSH, which is handled by
request_fn drivers, and upper layers requesting the block layer
perform a flush sequence along with possibly a WRITE, this patch
renames REQ_FLUSH to REQ_PREFLUSH.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index 907df2b..9f5f460 100644
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -704,7 +704,7 @@
 	bio_list_init(&requeue);
 
 	while ((bio = bio_list_pop(writes))) {
-		if ((bio->bi_rw & REQ_FLUSH) ||
+		if ((bio->bi_rw & REQ_PREFLUSH) ||
 		    (bio_op(bio) == REQ_OP_DISCARD)) {
 			bio_list_add(&sync, bio);
 			continue;
@@ -1253,7 +1253,8 @@
 	 * We need to dec pending if this was a write.
 	 */
 	if (rw == WRITE) {
-		if (!(bio->bi_rw & REQ_FLUSH) && bio_op(bio) != REQ_OP_DISCARD)
+		if (!(bio->bi_rw & REQ_PREFLUSH) &&
+		    bio_op(bio) != REQ_OP_DISCARD)
 			dm_rh_dec(ms->rh, bio_record->write_region);
 		return error;
 	}