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

[Marc Hartmayer <mhartmay@linux.ibm.com>]

On Tue, Jul 21, 2020 at 01:48 PM +0100, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> 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.

Done.

>
>> ---
>>  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
>
> License/copyright header?

With the dead code removed there is no reason for having
libvhost-access.h so I’ve removed it.

-- 
Kind regards / Beste Grüße
   Marc Hartmayer

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