dm error: add DAX support

Allow the error target to replace an existing DAX-enabled target.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-table.c

@@ -922,7 +922,8 @@ static int dm_table_determine_type(struct dm_table *t)
 	if (bio_based) {
 		/* We must use this table as bio-based */
 		t->type = DM_TYPE_BIO_BASED;
-		if (dm_table_supports_dax(t))
+		if (dm_table_supports_dax(t) ||
+		    (list_empty(devices) && live_md_type == DM_TYPE_DAX_BIO_BASED))
 			t->type = DM_TYPE_DAX_BIO_BASED;
 		return 0;
 	}

drivers/md/dm-target.c

@@ -148,9 +148,15 @@ static void io_err_release_clone_rq(struct request *clone)
 {
 }
 
+static long io_err_direct_access(struct dm_target *ti, sector_t sector,
+				 void __pmem **kaddr, pfn_t *pfn, long size)
+{
+	return -EIO;
+}
+
 static struct target_type error_target = {
 	.name = "error",
-	.version = {1, 4, 0},
+	.version = {1, 5, 0},
 	.features = DM_TARGET_WILDCARD,
 	.ctr  = io_err_ctr,
 	.dtr  = io_err_dtr,
@@ -158,6 +164,7 @@ static struct target_type error_target = {
 	.map_rq = io_err_map_rq,
 	.clone_and_map_rq = io_err_clone_and_map_rq,
 	.release_clone_rq = io_err_release_clone_rq,
+	.direct_access = io_err_direct_access,
 };
 
 int __init dm_target_init(void)