Re: [RFC][PATCH] limit state change to SDEV_BLOCK devices in scsi_internal_device_unblock

[Matthew Wilcox <matthew@wil.cx>]

On Mon, Apr 27, 2009 at 07:52:57PM -0400, Takahiro Yasui wrote:
> James Bottomley wrote:
> >> +	if (sdev->sdev_state != SDEV_BLOCK)
> > 
> > This isn't quite correct.  There are two blocked states in the model
> > currently:  SDEV_BLOCK and SDEV_CREATED_BLOCK ... you'd need to check
> > for both of them
> > 
> >> +		return 0;
> > 
> > Traditionally the return for an attempted invalid state transition is
> > -EINVAL.
> > 
> > I suppose for lower down, if you check the state, now we know we go 
> > 
> > SDEV_CREATED_BLOCK -> SDEV_CREATED
> > 
> > or
> > 
> > SDEV_BLOCK -> SDEV_RUNNING
> > 
> > so there's no need for the dual scsi_device_set_state.
> 
> Thank you for the comments. If I understand your comments correctly, 
> the state transition is better to be defined in scsi_device_set_state(),
> and both transitions, "SDEV_CREATED_BLOCK -> SDEV_CREATED" and
> "SDEV_BLOCK -> SDEV_RUNNING" need to be covered. I updated the patch
> so that the transition of "SDEV_OFFLINE -> SDEV_RUNNING" is prohibited.

I don't think that's what he meant.  I think he meant something more like:

scsi_internal_device_unblock(struct scsi_device *sdev)
{
	struct request_queue *q = sdev->request_queue;
-	int err;
	unsigned long flags;

	/*
	 * Try to transition the scsi device to SDEV_RUNNING
	 * and goose the device queue if successful.
	 */

+	if (sdev->sdev_state == SDEV_CREATED_BLOCK)
+		sdev->sdev_state = SDEV_CREATED;
+	else if (sdev->sdev_state == SDEV_BLOCK)
+		sdev->sdev_state = SDEV_RUNNING;
+	else
+		return -EINVAL;

-	err = scsi_device_set_state(sdev, SDEV_RUNNING);
-	if (err) {
-		err = scsi_device_set_state(sdev, SDEV_CREATED);
-
-		if (err)
-			return err;
-	}

	spin_lock_irqsave(q->queue_lock, flags);
	blk_start_queue(q);
	spin_unlock_irqrestore(q->queue_lock, flags);

	return 0;
}

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."