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Date: Wed, 3 Dec 2014 10:27:36 +0100
From: Cornelia Huck <cornelia.huck@de.ibm.com>
Message-ID: <20141203102736.73576850.cornelia.huck@de.ibm.com>
In-Reply-To: <20141202190345.GA5185@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH RFC v5 07/19] virtio: allow virtio-1 queue
	layout
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: thuth@linux.vnet.ibm.com, rusty@rustcorp.com.au, qemu-devel@nongnu.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org

On Tue, 2 Dec 2014 21:03:45 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Tue, Dec 02, 2014 at 04:41:36PM +0100, Cornelia Huck wrote:
> >  void virtio_queue_set_num(VirtIODevice *vdev, int n, int num)
> >  {
> > +    /*
> > +     * For virtio-1 devices, the number of buffers may only be
> > +     * updated if the ring addresses have not yet been set up.
> 
> Where does it say that?

Hmpf, may have imagined that.

This means we either need to track whether used/avail have been
specified or calculated or move responsibility for re-calculation of
used/avail for the old layout into the callers.
> 
> > +     */
> > +    if (virtio_has_feature(vdev, VIRTIO_F_VERSION_1) &&
> > +        vdev->vq[n].vring.desc) {
> > +        error_report("tried to modify buffer num for virtio-1 device");
> > +        return;
> > +    }
> >      /* Don't allow guest to flip queue between existent and
> >       * nonexistent states, or to set it to an invalid size.
> >       */
>