Re: [PATCH v2 00/15] virtio-gpio and various virtio cleanups

[Alex Bennée]

Stefan Hajnoczi <stefanha@redhat.com> writes:

> [[PGP Signed Part:Undecided]]
> On Tue, May 24, 2022 at 04:40:41PM +0100, Alex Bennée wrote:
>> Hi,
>> 
>> This series ostensibly adds virtio-user-gpio stubs to the build for
>> use with an external vhost-user daemon. We've been testing it with our
>> rust daemons from:
>> 
>>   https://github.com/rust-vmm/vhost-device
>> 
>> Getting the test enabled took some doing most likely because the need
>> for CONFIG support exercised additional paths in the code that were
>> not used for the simpler virtio-net tests. As a result the series has
>> a number of cleanup and documentation patches.
>> 
>> The final thing that needed fixing was the ensuring that
>> VHOST_USER_F_PROTOCOL_FEATURES didn't get squashed in the negotiation
>> process. This was the hardest thing to track down as we store the
>> feature bits in several places variously as:
>> 
>>   in VirtIODevice as:
>>     uint64_t guest_features;
>>     uint64_t host_features;
>>     uint64_t backend_features;
>
> None of these know about VHOST_USER_F_PROTOCOL_FEATURES and vhost-user's
> unfiltered feature bits should never be passed to VirtIODevice.
>
>> 
>>  in vhost_dev as:
>>     uint64_t features;
>>     uint64_t acked_features;
>>     uint64_t backend_features;
>
> I don't think these should know about VHOST_USER_F_PROTOCOL_FEATURES
> either. AFAIK vhost_dev deals with VIRTIO feature bits, not raw
> vhost-user GET_FEATURES.

So where does VHOST_USER_F_PROTOCOL_FEATURES get set before it's set
with the VHOST_USER_SET_FEATURES message? Currently it's fed via:

    uint64_t features = vhost_dev->acked_features;

in vhost_dev_set_features() which does apply a few extra bits
(VHOST_F_LOG_ALL/VIRTIO_F_IOMMU_PLATFORM). Maybe it should be adding
VHOST_USER_F_PROTOCOL_FEATURES here? How should it be signalled by the
vhost-user backend that this should be done? Overload the function?

>
> Stefan
>
> [[End of PGP Signed Part]]


-- 
Alex Bennée