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

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 9/1/25 12:08, Akihiko Odaki wrote:
> On 2025/01/09 19:56, Philippe Mathieu-Daudé wrote:
>> 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?
> 
> I put x- prefix because it is only intended to be used for compatibility 
> purpose and users will not be interested in this.

I guess that's OK then.