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

[Stefan Hajnoczi]

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.

Stefan

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