Re: [Qemu-devel] [RFC PATCH 1/2] vhost: add VHOST_VRING_F_BYTESWAP flag

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Wed, 29 Oct 2014 09:42:09 +0100
Cédric Le Goater <clg@fr.ibm.com> wrote:

> When the guest and the host have a different endian order, the data 
> being accessed in the vring queues needs to be byteswapped.
> 
> This patch adds a VHOST_VRING_F_BYTESWAP flag to inform the vhost 
> kernel backend to byteswap vring data.
> 
> Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
> ---
>  hw/virtio/vhost.c           |   25 ++++++++++++++++++++++++-
>  include/hw/virtio/vhost.h   |    1 +
>  linux-headers/linux/vhost.h |    3 +++
>  3 files changed, 28 insertions(+), 1 deletion(-)

> +static bool vhost_virtqueue_needs_byteswap(VirtIODevice *vdev)
> +{
> +#ifdef TARGET_IS_BIENDIAN
> +#ifdef HOST_WORDS_BIGENDIAN
> +    return !virtio_is_big_endian(vdev);
> +#else
> +    return virtio_is_big_endian(vdev);
> +#endif
> +
> +#else
> +    return false;
> +#endif
> +}

*thinks aloud*

We call this function after features have been negotiated, so we should
be able to reuse this interface for virtio-1 by checking for
VIRTIO_F_VERSION_1, right?