1 files changed, 104 insertions, 0 deletions

diff --git a/drivers/block/noop-iosched.c b/drivers/block/noop-iosched.c
new file mode 100644
index 000000000000..888c477e02b3
--- /dev/null
+++ b/drivers/block/noop-iosched.c
@@ -0,0 +1,104 @@
+/*
+ * elevator noop
+ */
+#include <linux/blkdev.h>
+#include <linux/elevator.h>
+#include <linux/bio.h>
+#include <linux/module.h>
+#include <linux/init.h>
+
+/*
+ * See if we can find a request that this buffer can be coalesced with.
+ */
+static int elevator_noop_merge(request_queue_t *q, struct request **req,
+                               struct bio *bio)
+{
+        struct list_head *entry = &q->queue_head;
+        struct request *__rq;
+        int ret;
+
+        if ((ret = elv_try_last_merge(q, bio))) {
+                *req = q->last_merge;
+                return ret;
+        }
+
+        while ((entry = entry->prev) != &q->queue_head) {
+                __rq = list_entry_rq(entry);
+
+                if (__rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER))
+                        break;
+                else if (__rq->flags & REQ_STARTED)
+                        break;
+
+                if (!blk_fs_request(__rq))
+                        continue;
+
+                if ((ret = elv_try_merge(__rq, bio))) {
+                        *req = __rq;
+                        q->last_merge = __rq;
+                        return ret;
+                }
+        }
+
+        return ELEVATOR_NO_MERGE;
+}
+
+static void elevator_noop_merge_requests(request_queue_t *q, struct request *req,
+                                         struct request *next)
+{
+        list_del_init(&next->queuelist);
+}
+
+static void elevator_noop_add_request(request_queue_t *q, struct request *rq,
+                                      int where)
+{
+        if (where == ELEVATOR_INSERT_FRONT)
+                list_add(&rq->queuelist, &q->queue_head);
+        else
+                list_add_tail(&rq->queuelist, &q->queue_head);
+
+        /*
+         * new merges must not precede this barrier
+         */
+        if (rq->flags & REQ_HARDBARRIER)
+                q->last_merge = NULL;
+        else if (!q->last_merge)
+                q->last_merge = rq;
+}
+
+static struct request *elevator_noop_next_request(request_queue_t *q)
+{
+        if (!list_empty(&q->queue_head))
+                return list_entry_rq(q->queue_head.next);
+
+        return NULL;
+}
+
+static struct elevator_type elevator_noop = {
+        .ops = {
+                .elevator_merge_fn              = elevator_noop_merge,
+                .elevator_merge_req_fn          = elevator_noop_merge_requests,
+                .elevator_next_req_fn           = elevator_noop_next_request,
+                .elevator_add_req_fn            = elevator_noop_add_request,
+        },
+        .elevator_name = "noop",
+        .elevator_owner = THIS_MODULE,
+};
+
+static int __init noop_init(void)
+{
+        return elv_register(&elevator_noop);
+}
+
+static void __exit noop_exit(void)
+{
+        elv_unregister(&elevator_noop);
+}
+
+module_init(noop_init);
+module_exit(noop_exit);
+
+
+MODULE_AUTHOR("Jens Axboe");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("No-op IO scheduler");