On Mon, Oct 07, 2013 at 04:32:17PM +0200, Cornelia Huck wrote:
> On Mon, 23 Sep 2013 13:39:30 +0300
> "Michael S. Tsirkin" <> wrote:
>
> > Resolves VIRTIO-23.
> >
> > Signed-off-by: Michael S. Tsirkin <>
> > ---
> > virtio-v1.0-wd01-part1-specification.txt | 23 ++++++++++++++++++++++-
> > 1 file changed, 22 insertions(+), 1 deletion(-)
> >
> > diff --git a/virtio-v1.0-wd01-part1-specification.txt b/virtio-v1.0-wd01-part1-specification.txt
> > index cafc34f..08cb857 100644
> > --- a/virtio-v1.0-wd01-part1-specification.txt
> > +++ b/virtio-v1.0-wd01-part1-specification.txt
> > @@ -1187,7 +1187,28 @@ Afterwards, CCW_CMD_SET_VQ is issued by the guest to inform the
> > host about the location used for its queue. The transmitted
> > structure is
> >
> > -struct vq_info_block {
> > +struct vq_info_block_legacy {
>
> That's not legacy, no?
>
> > + __u64 desc;
> > + __u64 avail;
> > + __u64 used;
> > + __u16 index;
> > + __u16 num;
> > + __u32 padding;
> > +} __attribute__ ((packed));
>
> Hm. This means the legacy and non-legacy cases transmit two
> incompatible structures with the same channel command. I'm not sure
> whether this is a good idea.
>
> The structures are different in length, and the host will fail if the
> structure transmitted is too short, but it is possible for the guest to
> transmit the longer structure to a legacy host and turn off the length
> check. Sure, that should not happen, but I'm not too fond of this
> structure.
>
> So we should either:
>
> - extend the old structure in a compatible way
> - use a new channel command for this purpose (and prepend the structure
> with a version field in case we want to change it again in the future)
This would burden 1.0 spec with legacy considerations.
IMO that's ugly.
Rusty sent a proposal where guest sets features
before configuring VQs.
If we vote this in, host can detect whether guest acked the VIRTIO_1
feature bit and handle the command appropriately.
> > +
> > +queue contains the guest address for Descriptor Table,
> > +Available Ring and Used Ring for virtqueue index respectively.
> > +The actual virtqueue size (number of allocated buffers) is
> > +transmitted in num.
> > +padding is a reserved field, and must be set to 0.
> > +
> > +2.3.3.2.1.1 Legacy Interface: A Note on Configuring a Virtqueue
> > +----------------------------------
> > +
> > +When configured through the legacy interface, transitional
> > +devices expect CCW_CMD_SET_VQ to transfer the following structure:
> > +
> > +struct vq_info_block_legacy {
> > __u64 queue;
> > __u32 align;
> > __u16 index;
