linux-kernel - Re: [PATCH 5 of 5] virtio: expose added descriptors immediately

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Message-ID: <87ty5v1vqy.fsf@rustcorp.com.au>
Date:	Wed, 23 Nov 2011 11:49:01 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 5 of 5] virtio: expose added descriptors immediately

On Tue, 22 Nov 2011 08:29:08 +0200, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> On Tue, Nov 22, 2011 at 11:03:04AM +1030, Rusty Russell wrote:
> > -	/* If you haven't kicked in this long, you're probably doing something
> > -	 * wrong. */
> > -	WARN_ON(vq->num_added > vq->vring.num);
> > +	/* This is very unlikely, but theoretically possible.  Kick
> > +	 * just in case. */
> > +	if (unlikely(vq->num_added == 65535))
> 
> This is 0xffff but why use the decimal notation?

Interesting.  Why use hex?  Feels more like binary?

But I've changed it to "(1 << 16) - 1" to be clear.

> > +		virtqueue_kick(_vq);
> >  
> >  	pr_debug("Added buffer head %i to %p\n", head, vq);
> >  	END_USE(vq);
> 
> We also still need to reset vq->num_added, right?

virtqueue_kick does that for us.

Cheers,
Rusty.
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