block: respect BLK_MQ_F_NO_SCHED

If one driver claims that it doesn't support io scheduler via
BLK_MQ_F_NO_SCHED, we should not allow to change and show the
availabe io schedulers.

This patch adds check to enhance this behaviour.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/block/elevator.c b/block/elevator.c
index dbeecf7be719..4d9084a14c10 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -1098,12 +1098,20 @@ int elevator_change(struct request_queue *q, const char *name)
 }
 EXPORT_SYMBOL(elevator_change);
 
+static inline bool elv_support_iosched(struct request_queue *q)
+{
+        if (q->mq_ops && q->tag_set && (q->tag_set->flags &
+                                BLK_MQ_F_NO_SCHED))
+                return false;
+        return true;
+}
+
 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
                           size_t count)
 {
         int ret;
 
-        if (!(q->mq_ops || q->request_fn))
+        if (!(q->mq_ops || q->request_fn) || !elv_support_iosched(q))
                 return count;
 
         ret = __elevator_change(q, name);
@@ -1135,7 +1143,7 @@ ssize_t elv_iosched_show(struct request_queue *q, char *name)
                         len += sprintf(name+len, "[%s] ", elv->elevator_name);
                         continue;
                 }
-                if (__e->uses_mq && q->mq_ops)
+                if (__e->uses_mq && q->mq_ops && elv_support_iosched(q))
                         len += sprintf(name+len, "%s ", __e->elevator_name);
                 else if (!__e->uses_mq && !q->mq_ops)
                         len += sprintf(name+len, "%s ", __e->elevator_name);