# Re: \[PATCH v6 7/8\] vhost: cross-endian support for legacy devices

- From: Cornelia Huck \<hidden\>
- Date: 2015-04-27 09:17:38 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2015/04/4479431
- Thread: https://ratatoskr.run/kvm/2015/04/4478259/t.md

```text
On Fri, 24 Apr 2015 14:27:24 +0200
Greg Kurz [ref] wrote:

> This patch brings cross-endian support to vhost when used to implement
> legacy virtio devices. Since it is a relatively rare situation, the
> feature availability is controlled by a kernel config option (not set
> by default).
> 
> The vq->is_le boolean field is added to cache the endianness to be
> used for ring accesses. It defaults to native endian, as expected
> by legacy virtio devices. When the ring gets active, we force little
> endian if the device is modern. When the ring is deactivated, we
> revert to the native endian default.
> 
> If cross-endian was compiled in, a vq->user_be boolean field is added
> so that userspace may request a specific endianness. This field is
> used to override the default when activating the ring of a legacy
> device. It has no effect on modern devices.
> 
> Signed-off-by: Greg Kurz <redacted>
> ---
> 
> Changes since v5:
> - fixed description in Kconfig
> - fixed error description in uapi header
> - dropped useless semi-colon in the vhost_vq_reset_user_be() stub
> 
>  drivers/vhost/Kconfig      |   15 ++++++++
>  drivers/vhost/vhost.c      |   85 +++++++++++++++++++++++++++++++++++++++++++-
>  drivers/vhost/vhost.h      |   11 +++++-
>  include/uapi/linux/vhost.h |   14 +++++++
>  4 files changed, 122 insertions(+), 3 deletions(-)
> 
Reviewed-by: Cornelia Huck <redacted>
```