[Qemu-devel] Re: [PATCH] qemu/virtio-net: remove wrong s/g layout assumptions

[Anthony Liguori]

Michael S. Tsirkin wrote:
> virtio net currently assumes that the first s/g element it gets is
> always virtio net header. This is wrong.
> There should be no assumption on sg boundaries.  For example, the guest
> should be able to put the virtio_net_hdr in the front of the skbuf data
> if there is room.  Get rid of this assumption, properly consume space
> from iovec, always.
>   

Practically speaking, we ought to advertise a feature bit to let a 
kernel know that we are no longer broken.

Otherwise, there are a ton of old userspaces that will break with new 
guests.

--
Regards,

Anthony Liguori