On 10/25/2017 11:32 AM, Omar Sandoval wrote:

On Wed, Oct 25, 2017 at 12:04:46PM -0600, Jens Axboe wrote:

quoted

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.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 block/elevator.c         | 22 ++++++++++++++++------
 include/linux/elevator.h |  1 +
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/block/elevator.c b/block/elevator.c
index b70e69f795db..dc0432e12ecf 100644
--- a/block/elevator.c
+++ b/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;
 	}

@@ -1126,7 +1135,8 @@ 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 ^ (q->mq_ops != NULL))) {

Same thing here, (__e->uses_mq == (q->mq_ops != NULL)). Still confusing
but less so.

I'll just add a

bool uses_mq = q->mq_ops != NULL;

to make it clearer.

-- 
Jens Axboe