On Fri, Feb 20, 2015 at 11:14:47AM +0100, Greg Kurz wrote:
> Signed-off-by: Greg Kurz <gkurz@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/vhost/vhost.h | 20 ++++++++++++++------
> 1 file changed, 14 insertions(+), 6 deletions(-)
>
> Michael,
>
> The vhost_is_little_endian() helper adds unconditionnal overhead to fixed
> endian architectures: that is all architectures except arm and ppc64. This
> was addressed in QEMU with a TARGET_IS_BIENDIAN macro. Please give an
> advice about how to address this in the vhost code.
>
> Thanks.
I suggest creating a config option for this, default to off.
When disabled the flag won't be set so userspace
can discover it's availability.
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index ce2c68e..21e7d6a 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -176,34 +176,42 @@ static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit)
> return vq->acked_features & (1ULL << bit);
> }
>
> +static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq)
> +{
> + if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
> + return true;
> + else
> + return !vq->legacy_big_endian;
> +}
> +
> /* Memory accessors */
> static inline u16 vhost16_to_cpu(struct vhost_virtqueue *vq, __virtio16 val)
> {
> - return __virtio16_to_cpu(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
> + return __virtio16_to_cpu(vhost_is_little_endian(vq), val);
> }
>
> static inline __virtio16 cpu_to_vhost16(struct vhost_virtqueue *vq, u16 val)
> {
> - return __cpu_to_virtio16(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
> + return __cpu_to_virtio16(vhost_is_little_endian(vq), val);
> }
>
> static inline u32 vhost32_to_cpu(struct vhost_virtqueue *vq, __virtio32 val)
> {
> - return __virtio32_to_cpu(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
> + return __virtio32_to_cpu(vhost_is_little_endian(vq), val);
> }
>
> static inline __virtio32 cpu_to_vhost32(struct vhost_virtqueue *vq, u32 val)
> {
> - return __cpu_to_virtio32(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
> + return __cpu_to_virtio32(vhost_is_little_endian(vq), val);
> }
>
> static inline u64 vhost64_to_cpu(struct vhost_virtqueue *vq, __virtio64 val)
> {
> - return __virtio64_to_cpu(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
> + return __virtio64_to_cpu(vhost_is_little_endian(vq), val);
> }
>
> static inline __virtio64 cpu_to_vhost64(struct vhost_virtqueue *vq, u64 val)
> {
> - return __cpu_to_virtio64(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
> + return __cpu_to_virtio64(vhost_is_little_endian(vq), val);
> }
> #endif
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