Re: [PATCH v2 1/4] hw/virtio: incorporate backend features in features

[Michael S. Tsirkin]

On Thu, Jul 28, 2022 at 02:55:00PM +0100, Alex Bennée wrote:
> There are some extra bits used over a vhost-user connection which are
> hidden from the device itself. We need to set them here to ensure we
> enable things like the protocol extensions.
> 
> Currently net/vhost-user.c has it's own inscrutable way of persisting
> this data but it really should live in the core vhost_user code.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> Message-Id: <20220726192150.2435175-7-alex.bennee@linaro.org>

I went back and forth on this, but in the end I feel
it is safer to defer this one until after the release.

> ---
>  hw/virtio/vhost-user.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 75b8df21a4..1936a44e82 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -1460,7 +1460,14 @@ static int vhost_user_set_features(struct vhost_dev 
> *dev,
>       */
>      bool log_enabled = features & (0x1ULL << VHOST_F_LOG_ALL);
>  
> -    return vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES, features,
> +    /*
> +     * We need to include any extra backend only feature bits that
> +     * might be needed by our device. Currently this includes the
> +     * VHOST_USER_F_PROTOCOL_FEATURES bit for enabling protocol
> +     * features.
> +     */
> +    return vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES,
> +                              features | dev->backend_features,
>                                log_enabled);
>  }
>  
> -- 
> 2.30.2