- * For blk-mq devices supporting IO scheduling, we default to using mq-deadline,
- * if available, for single queue devices. If deadline isn't available OR
- * deadline initialization fails OR we have multiple queues, default to "none".
+ * For single queue devices, default to using mq-deadline. If we have multiple
+ * queues or mq-deadline is not available, default to "none".
+ */
+static struct elevator_type *elevator_get_default(struct request_queue *q)
+{
+ if (q->nr_hw_queues != 1)
+ return NULL;
+
+ return elevator_get(q, "mq-deadline", false);
+}
+
+/*
+ * Get the first elevator providing the features required by the request queue.
+ * Default to "none" if no matching elevator is found.
+ */
+static struct elevator_type *elevator_get_by_features(struct request_queue *q)
+{
+ struct elevator_type *e;
+
+ spin_lock(&elv_list_lock);
+
+ list_for_each_entry(e, &elv_list, list) {
+ if (elv_support_features(e->elevator_features,
+ q->required_elevator_features))
+ break;
+ }
+
+ if (e && !try_module_get(e->elevator_owner))
+ e = NULL;
+
+ spin_unlock(&elv_list_lock);
+
+ return e;
+}
+
+/*
+ * For a device queue that has no required features, use the default elevator
+ * settings. Otherwise, use the first elevator available matching the required
+ * features. If no suitable elevator is find or if the chosen elevator
+ * initialization fails, fall back to the "none" elevator (no elevator).