elevator: allow name aliases

Since we now lookup elevator types with the appropriate multiqueue
capability, allow schedulers to register with an alias alongside
the real name. This is in preparation for allowing 'mq-deadline'
to register an alias of 'deadline' as well.
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/elevator.c

@@ -83,6 +83,16 @@ bool elv_bio_merge_ok(struct request *rq, struct bio *bio)
 }
 EXPORT_SYMBOL(elv_bio_merge_ok);
 
+static bool elevator_match(const struct elevator_type *e, const char *name)
+{
+	if (!strcmp(e->elevator_name, name))
+		return true;
+	if (e->elevator_alias && !strcmp(e->elevator_alias, name))
+		return true;
+
+	return false;
+}
+
 /*
  * Return scheduler with name 'name' and with matching 'mq capability
  */
@@ -91,7 +101,7 @@ static struct elevator_type *elevator_find(const char *name, bool mq)
 	struct elevator_type *e;
 
 	list_for_each_entry(e, &elv_list, list) {
-		if (!strcmp(e->elevator_name, name) && (mq == e->uses_mq))
+		if (elevator_match(e, name) && (mq == e->uses_mq))
 			return e;
 	}
 
@@ -922,9 +932,9 @@ int elv_register(struct elevator_type *e)
 	spin_unlock(&elv_list_lock);
 
 	/* print pretty message */
-	if (!strcmp(e->elevator_name, chosen_elevator) ||
+	if (elevator_match(e, chosen_elevator) ||
 			(!*chosen_elevator &&
-			 !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
+			 elevator_match(e, CONFIG_DEFAULT_IOSCHED)))
 				def = " (default)";
 
 	printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
@@ -1077,8 +1087,7 @@ static int __elevator_change(struct request_queue *q, const char *name)
 	if (!e)
 		return -EINVAL;
 
-	if (q->elevator &&
-	    !strcmp(elevator_name, q->elevator->type->elevator_name)) {
+	if (q->elevator && elevator_match(q->elevator->type, elevator_name)) {
 		elevator_put(e);
 		return 0;
 	}
@@ -1114,6 +1123,7 @@ ssize_t elv_iosched_show(struct request_queue *q, char *name)
 	struct elevator_queue *e = q->elevator;
 	struct elevator_type *elv = NULL;
 	struct elevator_type *__e;
+	bool uses_mq = q->mq_ops != NULL;
 	int len = 0;
 
 	if (!queue_is_rq_based(q))
@@ -1126,7 +1136,8 @@ ssize_t elv_iosched_show(struct request_queue *q, char *name)
 
 	spin_lock(&elv_list_lock);
 	list_for_each_entry(__e, &elv_list, list) {
-		if (elv && !strcmp(elv->elevator_name, __e->elevator_name)) {
+		if (elv && elevator_match(elv, __e->elevator_name) &&
+		    (__e->uses_mq == uses_mq)) {
 			len += sprintf(name+len, "[%s] ", elv->elevator_name);
 			continue;
 		}

include/linux/elevator.h

@@ -144,6 +144,7 @@ struct elevator_type
 	size_t icq_align;	/* ditto */
 	struct elv_fs_entry *elevator_attrs;
 	char elevator_name[ELV_NAME_MAX];
+	const char *elevator_alias;
 	struct module *elevator_owner;
 	bool uses_mq;
 #ifdef CONFIG_BLK_DEBUG_FS