Re: [PATCH scsi-misc-2.6 02/04] scsi: make scsi_queue_insert() use blk_requeue_request()

[Tejun Heo <htejun@gmail.com>]

02_scsi_REQ_SPECIAL_semantic_scsi_queue_insert.patch

	scsi_queue_insert() used to use blk_insert_request() for
	requeueing requests.  This behavior depends on the unobvious
	behavior of blk_insert_request() setting REQ_SPECIAL and
	REQ_SOFTBARRIER when requeueing.  This patch makes
	scsi_queue_insert() use blk_requeue_request() and explicitly
	set REQ_SOFTBARRIER.  As REQ_SPECIAL now means special
	requests, the flag is not set on requeue.

	Note that scsi_queue_insert() now calls scsi_run_queue()
	itself, and the prototype of the function is added right above
	scsi_queue_insert().  This is temporary, as later requeue path
	consolidation patchset removes scsi_queue_insert().  By adding
	temporary prototype, we can do away with unnecessary changes.

Signed-off-by: Tejun Heo <htejun@gmail.com>

 scsi_lib.c |   24 ++++++++++++++----------
 1 files changed, 14 insertions(+), 10 deletions(-)

Index: scsi-reqfn-export/drivers/scsi/scsi_lib.c
===================================================================
--- scsi-reqfn-export.orig/drivers/scsi/scsi_lib.c	2005-04-11 12:27:07.000000000 +0900
+++ scsi-reqfn-export/drivers/scsi/scsi_lib.c	2005-04-11 12:27:07.000000000 +0900
@@ -96,6 +96,8 @@ int scsi_insert_special_req(struct scsi_
 	return 0;
 }
 
+static void scsi_run_queue(struct request_queue *q);
+
 /*
  * Function:    scsi_queue_insert()
  *
@@ -119,6 +121,8 @@ int scsi_queue_insert(struct scsi_cmnd *
 {
 	struct Scsi_Host *host = cmd->device->host;
 	struct scsi_device *device = cmd->device;
+	struct request_queue *q = device->request_queue;
+	unsigned long flags;
 
 	SCSI_LOG_MLQUEUE(1,
 		 printk("Inserting command %p into mlqueue\n", cmd));
@@ -154,17 +158,17 @@ int scsi_queue_insert(struct scsi_cmnd *
 	scsi_device_unbusy(device);
 
 	/*
-	 * Insert this command at the head of the queue for it's device.
-	 * It will go before all other commands that are already in the queue.
-	 *
-	 * NOTE: there is magic here about the way the queue is plugged if
-	 * we have no outstanding commands.
-	 * 
-	 * Although this *doesn't* plug the queue, it does call the request
-	 * function.  The SCSI request function detects the blocked condition
-	 * and plugs the queue appropriately.
+	 * Requeue the command.  Turn on REQ_SOFTBARRIER to prevent
+	 * other requests from passing this request.
 	 */
-	blk_insert_request(device->request_queue, cmd->request, 1, cmd, 1);
+	cmd->request->flags |= REQ_SOFTBARRIER;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	blk_requeue_request(q, cmd->request);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	scsi_run_queue(q);
+
 	return 0;
 }