[PATCH 1/4] block: respect BLK_MQ_F_NO_SCHED

[Ming Lei]

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....@redhat.com>
---
 block/elevator.c | 12 ++++++++++--
 1 file 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);
-- 
2.9.3