From 5a7c47eefb31f6b4982add7473ef3e551b058ea4 Mon Sep 17 00:00:00 2001
From: Tejun Heo <htejun@gmail.com>
Date: Thu, 10 Nov 2005 18:21:30 +0100
Subject: [BLOCK] noop-iosched: reimplementation of request dispatching

The original implementation directly used dispatch queue.  As new
generic dispatch queue imposes stricter rules over ioscheds and
dispatch queue usage, this direct use becomes somewhat problematic.
This patch reimplements noop-iosched such that it complies to generic
iosched model better.  Request merging with q->last_merge and
rq->queuelist.prev/next work again now.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jens Axboe <axboe@suse.de
---
 block/noop-iosched.c | 85 ++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 79 insertions(+), 6 deletions(-)

(limited to 'block')

diff --git a/block/noop-iosched.c b/block/noop-iosched.c
index e54f006e7e603..f370e4a7fe6d7 100644
--- a/block/noop-iosched.c
+++ b/block/noop-iosched.c
@@ -7,21 +7,94 @@
 #include <linux/module.h>
 #include <linux/init.h>
 
-static void elevator_noop_add_request(request_queue_t *q, struct request *rq)
+struct noop_data {
+	struct list_head queue;
+};
+
+static void noop_merged_requests(request_queue_t *q, struct request *rq,
+				 struct request *next)
+{
+	list_del_init(&next->queuelist);
+}
+
+static int noop_dispatch(request_queue_t *q, int force)
+{
+	struct noop_data *nd = q->elevator->elevator_data;
+
+	if (!list_empty(&nd->queue)) {
+		struct request *rq;
+		rq = list_entry(nd->queue.next, struct request, queuelist);
+		list_del_init(&rq->queuelist);
+		elv_dispatch_sort(q, rq);
+		return 1;
+	}
+	return 0;
+}
+
+static void noop_add_request(request_queue_t *q, struct request *rq)
+{
+	struct noop_data *nd = q->elevator->elevator_data;
+
+	list_add_tail(&rq->queuelist, &nd->queue);
+}
+
+static int noop_queue_empty(request_queue_t *q)
 {
-	rq->flags |= REQ_NOMERGE;
-	elv_dispatch_add_tail(q, rq);
+	struct noop_data *nd = q->elevator->elevator_data;
+
+	return list_empty(&nd->queue);
+}
+
+static struct request *
+noop_former_request(request_queue_t *q, struct request *rq)
+{
+	struct noop_data *nd = q->elevator->elevator_data;
+
+	if (rq->queuelist.prev == &nd->queue)
+		return NULL;
+	return list_entry(rq->queuelist.prev, struct request, queuelist);
+}
+
+static struct request *
+noop_latter_request(request_queue_t *q, struct request *rq)
+{
+	struct noop_data *nd = q->elevator->elevator_data;
+
+	if (rq->queuelist.next == &nd->queue)
+		return NULL;
+	return list_entry(rq->queuelist.next, struct request, queuelist);
 }
 
-static int elevator_noop_dispatch(request_queue_t *q, int force)
+static int noop_init_queue(request_queue_t *q, elevator_t *e)
 {
+	struct noop_data *nd;
+
+	nd = kmalloc(sizeof(*nd), GFP_KERNEL);
+	if (!nd)
+		return -ENOMEM;
+	INIT_LIST_HEAD(&nd->queue);
+	e->elevator_data = nd;
 	return 0;
 }
 
+static void noop_exit_queue(elevator_t *e)
+{
+	struct noop_data *nd = e->elevator_data;
+
+	BUG_ON(!list_empty(&nd->queue));
+	kfree(nd);
+}
+
 static struct elevator_type elevator_noop = {
 	.ops = {
-		.elevator_dispatch_fn		= elevator_noop_dispatch,
-		.elevator_add_req_fn		= elevator_noop_add_request,
+		.elevator_merge_req_fn		= noop_merged_requests,
+		.elevator_dispatch_fn		= noop_dispatch,
+		.elevator_add_req_fn		= noop_add_request,
+		.elevator_queue_empty_fn	= noop_queue_empty,
+		.elevator_former_req_fn		= noop_former_request,
+		.elevator_latter_req_fn		= noop_latter_request,
+		.elevator_init_fn		= noop_init_queue,
+		.elevator_exit_fn		= noop_exit_queue,
 	},
 	.elevator_name = "noop",
 	.elevator_owner = THIS_MODULE,
-- 
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