Re: [Qemu-devel] [PATCH 0/7] virtio endian-ambivalent target fixes.

[Thomas Huth]

On Thu, 17 Oct 2013 14:23:35 +1030
Rusty Russell <address@hidden> wrote:

> This is a re-transmit of the core of the virtio endian code.  Since
> there seems to be some interest in ARM BE virtio, I've separated this from
> the direct problem I was solving: PowerPC LE.
> 
> Please apply!
> Rusty.
> 
> Rusty Russell (7):
>   virtio_get_byteswap: function for endian-ambivalent targets using
>     virtio.
>   virtio: allow byte swapping for vring and config access
>   hw/net/virtio-net: use virtio wrappers to access headers.
>   hw/net/virtio-balloon: use virtio wrappers to access page frame
>     numbers.
>   hw/block/virtio-blk: use virtio wrappers to access headers.
>   hw/scsi/virtio-scsi: use virtio wrappers to access headers.
>   hw/char/virtio-serial-bus: use virtio wrappers to access headers.

 Hi Rusty!

May I ask what's the current status of your virtio endian patches? We
likely need something similar when we enable Virtio v1.0 for S390
virtio-ccw since we then have to byteswap the virtio stuff there, too.
So I recently started to have a look at this... However, in your
patches, the byteswapping seems to be activated/disabled globally, with
the "virtio_byteswap" variable. But with Virtio v1.0, the guest can
decide on a per-device basis whether it wants to drive the device in
v1.0 mode (--> byteswap on S390) or in v0.9 legacy mode (--> no
byteswap), depending on whether it sets the VIRTIO_F_VERSION_1 feature
bit or not. I guess other architectures will have the same problem with
Virtio 1.0, too, when the guests are not running in little endian mode.
So I wonder whether it would it be feasible to change the code so that
the decision of byteswapping or not is done on a per-device basis
instead? What do you think?

 Regards,
  Thomas