Re: [PATCH v4 4/4] virtio: Convert feature properties to OnOffAuto

[Philippe Mathieu-Daudé]

On 8/1/25 07:17, Akihiko Odaki wrote:
> Some features are not always available with vhost. Legacy features are
> not available with vp_vdpa in particular. virtio devices used to disable
> them when not available even if the corresponding properties were
> explicitly set to "on".
>
> QEMU already has OnOffAuto type, which includes the "auto" value to let
> it automatically decide the effective value. Convert feature properties
> to OnOffAuto and set them "auto" by default to utilize it. This allows
> QEMU to report an error if they are set "on" and the corresponding
> features are not available.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>   include/hw/virtio/virtio.h | 38 +++++++++++++++++++++-----------------
>   hw/core/machine.c          |  4 +++-
>   hw/virtio/virtio-bus.c     | 14 ++++++++++++--
>   hw/virtio/virtio.c         |  4 +++-
>   4 files changed, 39 insertions(+), 21 deletions(-)


> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index c949af97668d..bff26b95dd74 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -36,7 +36,9 @@
>   #include "hw/virtio/virtio-iommu.h"
>   #include "audio/audio.h"
>   
> -GlobalProperty hw_compat_9_2[] = {};
> +GlobalProperty hw_compat_9_2[] = {
> +    { TYPE_VIRTIO_DEVICE, "x-force-features-auto", "on" },
> +};
>   const size_t hw_compat_9_2_len = G_N_ELEMENTS(hw_compat_9_2);


> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 85110bce3744..83f803fc703d 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -4013,11 +4013,13 @@ static void virtio_device_instance_finalize(Object *obj)
>   }
>   
>   static const Property virtio_properties[] = {
> -    DEFINE_VIRTIO_COMMON_FEATURES(VirtIODevice, host_features),
> +    DEFINE_VIRTIO_COMMON_FEATURES(VirtIODevice, requested_features),
>       DEFINE_PROP_BOOL("use-started", VirtIODevice, use_started, true),
>       DEFINE_PROP_BOOL("use-disabled-flag", VirtIODevice, use_disabled_flag, 
> true),
>       DEFINE_PROP_BOOL("x-disable-legacy-check", VirtIODevice,
>                        disable_legacy_check, false),
> +    DEFINE_PROP_BOOL("x-force-features-auto", VirtIODevice,
> +                     force_features_auto, false),

This doesn't seem an experiment, so can we not use the 'x-' prefix?

>   };