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Re: [Qemu-devel] [PATCH v4 5/6] vhost: simplify vhost_needs_vring_endian
From: |
Laurent Vivier |
Subject: |
Re: [Qemu-devel] [PATCH v4 5/6] vhost: simplify vhost_needs_vring_endian() |
Date: |
Fri, 5 Feb 2016 14:02:14 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 |
On 05/02/2016 11:46, Greg Kurz wrote:
> After the call to virtio_vdev_has_feature(), we only care for legacy
> devices, so we don't need the extra check in virtio_is_big_endian().
>
> Also the device_endian field is always set (VIRTIO_DEVICE_ENDIAN_UNKNOWN
> may only happen on a virtio_load() path that cannot lead here), so we
> don't need the assert() either.
>
> This open codes the device_endian checking in vhost_needs_vring_endian().
> It also adds a comment to explain the logic, as recent reviews showed the
> cross-endian tweaks aren't that obvious.
>
> Signed-off-by: Greg Kurz <address@hidden>
Reviewed-by: Laurent Vivier <address@hidden>
> ---
> hw/virtio/vhost.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index bb17177f5e7e..9f8ac38ccf2d 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -749,6 +749,11 @@ static void vhost_log_stop(MemoryListener *listener,
> /* FIXME: implement */
> }
>
> +/* The vhost driver natively knows how to handle the vrings of non
> + * cross-endian legacy devices and modern devices. Only legacy devices
> + * exposed to a bi-endian guest may require the vhost driver to use a
> + * specific endianness.
> + */
> static inline bool vhost_needs_vring_endian(VirtIODevice *vdev)
> {
> if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
> @@ -756,9 +761,9 @@ static inline bool vhost_needs_vring_endian(VirtIODevice
> *vdev)
> }
> #ifdef TARGET_IS_BIENDIAN
> #ifdef HOST_WORDS_BIGENDIAN
> - return !virtio_is_big_endian(vdev);
> + return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_LITTLE;
> #else
> - return virtio_is_big_endian(vdev);
> + return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
> #endif
> #else
> return false;
>
>
- [Qemu-devel] [PATCH v4 0/6] virtio/vhost cross-endian cleanup, Greg Kurz, 2016/02/05
- [Qemu-devel] [PATCH v4 1/6] virtio-net: use the backend cross-endian capabilities, Greg Kurz, 2016/02/05
- [Qemu-devel] [PATCH v4 2/6] vhost-net: revert support of cross-endian vnet headers, Greg Kurz, 2016/02/05
- [Qemu-devel] [PATCH v4 3/6] virtio: move cross-endian helper to vhost, Greg Kurz, 2016/02/05
- [Qemu-devel] [PATCH v4 4/6] vhost: move virtio 1.0 check to cross-endian helper, Greg Kurz, 2016/02/05
- [Qemu-devel] [PATCH v4 5/6] vhost: simplify vhost_needs_vring_endian(), Greg Kurz, 2016/02/05
- [Qemu-devel] [PATCH v4 6/6] virtio: optimize virtio_access_is_big_endian() for little-endian targets, Greg Kurz, 2016/02/05
- Re: [Qemu-devel] [PATCH v4 0/6] virtio/vhost cross-endian cleanup, Laurent Vivier, 2016/02/05
- Re: [Qemu-devel] [PATCH v4 0/6] virtio/vhost cross-endian cleanup, Laurent Vivier, 2016/02/10