dm raid1: support discard

Enable discard support in the DM mirror target.
Also change an existing use of 'bvec' to 'addr' in the union.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-raid1.c

@@ -261,7 +261,7 @@ static int mirror_flush(struct dm_target *ti)
 	struct dm_io_request io_req = {
 		.bi_rw = WRITE_FLUSH,
 		.mem.type = DM_IO_KMEM,
-		.mem.ptr.bvec = NULL,
+		.mem.ptr.addr = NULL,
 		.client = ms->io_client,
 	};
 
@@ -637,6 +637,12 @@ static void do_write(struct mirror_set *ms, struct bio *bio)
 		.client = ms->io_client,
 	};
 
+	if (bio->bi_rw & REQ_DISCARD) {
+		io_req.bi_rw |= REQ_DISCARD;
+		io_req.mem.type = DM_IO_KMEM;
+		io_req.mem.ptr.addr = NULL;
+	}
+
 	for (i = 0, m = ms->mirror; i < ms->nr_mirrors; i++, m++)
 		map_region(dest++, m, bio);
 
@@ -670,7 +676,8 @@ static void do_writes(struct mirror_set *ms, struct bio_list *writes)
 	bio_list_init(&requeue);
 
 	while ((bio = bio_list_pop(writes))) {
-		if (bio->bi_rw & REQ_FLUSH) {
+		if ((bio->bi_rw & REQ_FLUSH) ||
+		    (bio->bi_rw & REQ_DISCARD)) {
 			bio_list_add(&sync, bio);
 			continue;
 		}
@@ -1076,6 +1083,7 @@ static int mirror_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	ti->private = ms;
 	ti->split_io = dm_rh_get_region_size(ms->rh);
 	ti->num_flush_requests = 1;
+	ti->num_discard_requests = 1;
 
 	ms->kmirrord_wq = create_singlethread_workqueue("kmirrord");
 	if (!ms->kmirrord_wq) {