Re: [PATCH RFC v2 08/13] qmp: update virtio features map to support extended features

[Paolo Abeni <pabeni@redhat.com>]

On 7/15/25 9:59 AM, Akihiko Odaki wrote:
> On 2025/07/11 22:02, Paolo Abeni wrote:
>> @@ -785,11 +821,12 @@ VirtioStatus *qmp_x_query_virtio_status(const char *path, Error **errp)
>>           status->vhost_dev->nvqs = hdev->nvqs;
>>           status->vhost_dev->vq_index = hdev->vq_index;
>>           status->vhost_dev->features =
>> -            qmp_decode_features(vdev->device_id, hdev->features);
>> +            qmp_decode_features(vdev->device_id, hdev->features_array);
>>           status->vhost_dev->acked_features =
>> -            qmp_decode_features(vdev->device_id, hdev->acked_features);
>> +            qmp_decode_features(vdev->device_id, hdev->acked_features_array);
>>           status->vhost_dev->backend_features =
>> -            qmp_decode_features(vdev->device_id, hdev->backend_features);
>> +            qmp_decode_features(vdev->device_id, hdev->backend_features_array);
>> +
>>           status->vhost_dev->protocol_features =
>>               qmp_decode_protocols(hdev->protocol_features);
>>           status->vhost_dev->max_queues = hdev->max_queues;
>> diff --git a/hw/virtio/virtio-qmp.h b/hw/virtio/virtio-qmp.h
>> index 245a446a56..e0a1e49035 100644
>> --- a/hw/virtio/virtio-qmp.h
>> +++ b/hw/virtio/virtio-qmp.h
>> @@ -18,6 +18,7 @@
>>   VirtIODevice *qmp_find_virtio_device(const char *path);
>>   VirtioDeviceStatus *qmp_decode_status(uint8_t bitmap);
>>   VhostDeviceProtocols *qmp_decode_protocols(uint64_t bitmap);
>> -VirtioDeviceFeatures *qmp_decode_features(uint16_t device_id, uint64_t bitmap);
>> +VirtioDeviceFeatures *qmp_decode_features(uint16_t device_id,
>> +                                          const uint64_t *bitmap);
>>   
>>   #endif
>> diff --git a/qapi/virtio.json b/qapi/virtio.json
>> index 73df718a26..f0442e144b 100644
>> --- a/qapi/virtio.json
>> +++ b/qapi/virtio.json
>> @@ -488,14 +488,18 @@
>>   #     unique features)
>>   #
>>   # @unknown-dev-features: Virtio device features bitmap that have not
>> -#     been decoded
>> +#     been decoded (lower 64 bit)
>> +#
>> +# @unknown-dev-features-dword2: Virtio device features bitmap that have not
>> +#     been decoded (bits 65-128)
>>   #
>>   # Since: 7.2
>>   ##
>>   { 'struct': 'VirtioDeviceFeatures',
>>     'data': { 'transports': [ 'str' ],
>>               '*dev-features': [ 'str' ],
>> -            '*unknown-dev-features': 'uint64' } }
>> +            '*unknown-dev-features': 'uint64',
>> +            '*unknown-dev-features-dword2': 'uint64' } }
> 
> Let's omit "dword" for consistency with unknown-dev-features, which is 
> also uint64 but don't have the keyword.

Ok. Can I infer that is actually legit to update a qapi struct
definition? It's not clear to me it such change violates any qemu
assumptions.

/P