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

[Marc Hartmayer]

On Tue, Jul 21, 2020 at 06:44 PM +0200, Halil Pasic <pasic@linux.ibm.com> wrote:
> On Tue, 21 Jul 2020 09:40:10 -0400
> "Michael S. Tsirkin" <mst@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  
>> 
>> Who's "we" in this sentence? vhost user supports legacy generally ...
>
> In that sentence "we" is the library "libvhost-user". I would like
> to avoid s390x being an oddball regarding this. Marc's previous
> version made an attempt at correct endianness handling for legacy
> and non-legacy. That spawned a discussion on how we don't want
> legacy devices in this context. This series makes what seemed to be the
> consensus reached in that discussion explicit: namely that libvhost-user
> does not support legacy-virtio.

Hi Michael,

Polite ping - what’s your opinion? Thanks in advance.

[…snip]

-- 
Kind regards / Beste Grüße
   Marc Hartmayer

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