On Mon, 3 Nov 2014 16:29:31 +0100 Cornelia Huck <cornelia.h...@de.ibm.com> wrote: > On Wed, 29 Oct 2014 09:42:09 +0100 > Cédric Le Goater <c...@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 <c...@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? > >
Yes. Moreover, we're not on a hot path, so we could simply ignore TARGET_IS_BIENDIAN and only have: static bool vhost_virtqueue_needs_byteswap(VirtIODevice *vdev) { #ifdef HOST_WORDS_BIGENDIAN return !virtio_is_big_endian(vdev); #else return virtio_is_big_endian(vdev); #endif } in which case, this would work right away with the changes brought by Conny's virtio-1 series: static inline bool virtio_device_is_legacy(VirtIODevice *vdev) { return !(vdev->guest_features[1] & (1 << (VIRTIO_F_VERSION_1 - 32))); } static inline bool virtio_is_big_endian(VirtIODevice *vdev) { if (virtio_device_is_legacy(vdev)) { assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN); return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG; } /* Devices conforming to VIRTIO 1.0 or later are always LE. */ return false; } Cheers. -- Greg