dm ioctl: allow change device target type to error

index f1b7586..1ee9e41 100644
@@ -1250,7 +1250,7 @@ static int populate_table(struct dm_table *table,
 
 static int table_load(struct dm_ioctl *param, size_t param_size)
 {
-	int r;
+	int r = 0;
 	struct hash_cell *hc;
 	struct dm_table *t, *old_map = NULL;
 	struct mapped_device *md;

@@ -1280,6 +1280,9 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
 		goto out;
 	}
 
+	if (dm_is_error_target(t))
+		goto error_target;
+
 	/* Protect md->type and md->queue against concurrent table loads. */
 	dm_lock_md_type(md);
 	if (dm_get_md_type(md) == DM_TYPE_NONE)

@@ -1303,6 +1306,7 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
 	}
 	dm_unlock_md_type(md);
 
+error_target:
 	/* stage inactive table */
 	down_write(&_hash_lock);
 	hc = dm_get_mdptr(md);

index f221812..27be46a 100644
@@ -184,6 +184,18 @@ static int alloc_targets(struct dm_table *t, unsigned int num)
 	return 0;
 }
 
+bool dm_is_error_target(struct dm_table *t)
+{
+	unsigned i;
+
+	for (i = 0; i < t->num_targets; i++) {
+		struct dm_target *tgt = t->targets + i;
+		if (strcmp(tgt->type->name, "error") == 0)
+			return true;
+	}
+	return false;
+}
+
 int dm_table_create(struct dm_table **result, fmode_t mode,
 		    unsigned num_targets, struct mapped_device *md)
 {

index 45b97da..c7bceeb 100644
@@ -69,6 +69,7 @@ unsigned dm_table_get_type(struct dm_table *t);
 struct target_type *dm_table_get_immutable_target_type(struct dm_table *t);
 bool dm_table_request_based(struct dm_table *t);
 bool dm_table_supports_discards(struct dm_table *t);
+bool dm_is_error_target(struct dm_table *t);
 int dm_table_alloc_md_mempools(struct dm_table *t);
 void dm_table_free_md_mempools(struct dm_table *t);
 struct dm_md_mempools *dm_table_get_md_mempools(struct dm_table *t);