Re: [Qemu-devel] [Qemu-block] [PATCH 1/2] dataplane: simplify indirect descriptor read

[Stefan Hajnoczi]

On Thu, Oct 29, 2015 at 11:28:05AM +0100, Igor Mammedov wrote:
> On Wed, 28 Oct 2015 17:48:02 +0200
> "Michael S. Tsirkin" <m...@redhat.com> wrote:
> > -        struct vring_desc *desc_ptr;
> > -        MemoryRegion *mr;
> > -
> >          /* Translate indirect descriptor */
> > -        desc_ptr = vring_map(&mr,
> > -                             indirect->addr + found * sizeof(desc),
> Is it correct to use 'found' as iterator here vs using desc.next
> as is done when translating direct descriptors?

That is how Linux drivers/vhost/vhost.c:get_indirect() does it.

QEMU hw/virtio/virtio.c honors desc.next.

The VIRTIO 1.0 specification says:

  The first indirect descriptor is located at start of the indirect
  descriptor table (index 0), additional indirect descriptors are
  chained by next field.

I think vhost and dataplane do not follow the specification here.
Fixing it is for a separate patch series.

Stefan

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