Re: [RFC v2 2/3] libvhost-user: handle endianness as mandated by the spec

[Stefan Hajnoczi]

On Fri, Jul 17, 2020 at 11:29:28AM +0200, Marc Hartmayer wrote:
> Since virtio existed even before it got standardized, the virtio
> standard defines the following types of virtio devices:
> 
>  + legacy device (pre-virtio 1.0)
>  + non-legacy or VIRTIO 1.0 device
>  + transitional device (which can act both as legacy and non-legacy)
> 
> Virtio 1.0 defines the fields of the virtqueues as little endian,
> while legacy uses guest's native endian [1]. Currently libvhost-user
> does not handle virtio endianness at all, i.e. it works only if the
> native endianness matches with whatever is actually needed. That means
> things break spectacularly on big-endian targets. Let us handle virtio
> endianness for non-legacy as required by the virtio specification
> [1]. We will fence non-legacy virtio devices with the upcoming patch.
> 
> [1] 
> https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-210003
> 
> Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
> 
> ---
> Note: As we don't support legacy virtio devices there is dead code in
> libvhost-access.h that could be removed. But for the sake of
> completeness, I left it in the code.

Please remove the dead code. It is unlikely that legacy device support
will be required in the future and it will just confuse people reading
the code.

> ---
>  contrib/libvhost-user/libvhost-access.h |  61 ++++++++++++
>  contrib/libvhost-user/libvhost-user.c   | 119 ++++++++++++------------
>  2 files changed, 121 insertions(+), 59 deletions(-)
>  create mode 100644 contrib/libvhost-user/libvhost-access.h
> 
> diff --git a/contrib/libvhost-user/libvhost-access.h 
> b/contrib/libvhost-user/libvhost-access.h
> new file mode 100644
> index 000000000000..868ba3e7bfb8
> --- /dev/null
> +++ b/contrib/libvhost-user/libvhost-access.h
> @@ -0,0 +1,61 @@
> +#ifndef LIBVHOST_ACCESS_H

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