blk-mq-sched: allow setting of default IO scheduler

Add Kconfig entries to manage what devices get assigned an MQ
scheduler, and add a blk-mq flag for drivers to opt out of scheduling.
The latter is useful for admin type queues that still allocate a blk-mq
queue and tag set, but aren't use for normal IO.

Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 26759798a0b3..d05061f27bb1 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -366,3 +366,23 @@ void blk_mq_sched_teardown(struct request_queue *q)
         queue_for_each_hw_ctx(q, hctx, i)
                 blk_mq_sched_free_tags(set, hctx, i);
 }
+
+int blk_mq_sched_init(struct request_queue *q)
+{
+        int ret;
+
+#if defined(CONFIG_DEFAULT_SQ_NONE)
+        if (q->nr_hw_queues == 1)
+                return 0;
+#endif
+#if defined(CONFIG_DEFAULT_MQ_NONE)
+        if (q->nr_hw_queues > 1)
+                return 0;
+#endif
+
+        mutex_lock(&q->sysfs_lock);
+        ret = elevator_init(q, NULL);
+        mutex_unlock(&q->sysfs_lock);
+
+        return ret;
+}