From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH v5 05/10] xen/blkfront: negotiate number of
 queues/rings to be used with backend
Date: Tue, 17 Nov 2015 09:20:32 -0500
Message-ID: <20151117142032.GE3003@char.us.oracle.com>
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To: Bob Liu <bob.liu@oracle.com>
Cc: jonathan.davies@citrix.com, felipe.franciosi@citrix.com, rafal.mielniczuk@citrix.com, linux-kernel@vger.kernel.org, xen-devel@lists.xen.org, axboe@fb.com, david.vrabel@citrix.com, avanzini.arianna@gmail.com, roger.pau@citrix.com
List-Id: xen-devel@lists.xenproject.org

On Tue, Nov 17, 2015 at 07:13:34AM +0800, Bob Liu wrote:
> 
> On 11/17/2015 05:27 AM, Konrad Rzeszutek Wilk wrote:
> >>  /* Common code used when first setting up, and when resuming. */
> >>  static int talk_to_blkback(struct xenbus_device *dev,
> >> @@ -1527,10 +1582,9 @@ static int talk_to_blkback(struct xenbus_device *dev,
> >>  {
> >>  	const char *message = NULL;
> >>  	struct xenbus_transaction xbt;
> >> -	int err, i;
> >> -	unsigned int max_page_order = 0;
> >> +	int err;
> >> +	unsigned int i, max_page_order = 0;
> >>  	unsigned int ring_page_order = 0;
> >> -	struct blkfront_ring_info *rinfo;
> > 
> > Why? You end up doing the 'struct blkfront_ring_info' decleration
> > in two of the loops below?
> 
> Oh, that's because Roger mentioned we would be tempted to declare rinfo only inside the for loop, to limit
> the scope.
> 
> >>  
> >>  	err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
> >>  			   "max-ring-page-order", "%u", &max_page_order);
> >> @@ -1542,7 +1596,8 @@ static int talk_to_blkback(struct xenbus_device *dev,
> >>  	}
> >>  
> >>  	for (i = 0; i < info->nr_rings; i++) {
> >> -		rinfo = &info->rinfo[i];
> >> +		struct blkfront_ring_info *rinfo = &info->rinfo[i];
> >> +
> > 
> > Here..
> > 
> >> @@ -1617,7 +1677,7 @@ again:
> >>  
> >>  	for (i = 0; i < info->nr_rings; i++) {
> >>  		int j;
> >> -		rinfo = &info->rinfo[i];
> >> +		struct blkfront_ring_info *rinfo = &info->rinfo[i];
> > 
> > And here?
> > 
> > It is not a big deal but I am curious of why add this change?
> > 
> >> @@ -1717,7 +1789,6 @@ static int blkfront_probe(struct xenbus_device *dev,
> >>  
> >>  	mutex_init(&info->mutex);
> >>  	spin_lock_init(&info->dev_lock);
> >> -	info->xbdev = dev;
> > 
> > That looks like a spurious change? Ah, I see that we do the same exact
> > operation earlier in the blkfront_probe.
> > 
> 
> The place of this line was changed because:
> 
> 1738         info->xbdev = dev;
> 
> 1739         /* Check if backend supports multiple queues. */
> 1740         err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
>                                          	^^^^
> 						We need xbdev to be set in advance.
>                                   
> 1741                            "multi-queue-max-queues", "%u", &backend_max_queues);
> 1742         if (err < 0)
> 1743                 backend_max_queues = 1;

Duh! Yes. Thanks.