Re: [PATCH] virtio: add num_vf callback to virtio_bus

[Yui Washizu <yui.washidu@gmail.com>]

On 3/9/2026 12:33 PM, Jason Wang wrote:
> On Mon, Mar 9, 2026 at 10:37 AM Yui Washizu <yui.washidu@gmail.com> wrote:
>> Recent QEMU versions added support for virtio SR-IOV emulation,
>> allowing virtio devices to expose SR-IOV VFs to the guest.
>> However, virtio_bus does not implement the num_vf callback of bus_type,
>> causing dev_num_vf() to return 0 for virtio devices even when
>> SR-IOV VFs are active.
>>
>> net/core/rtnetlink.c calls dev_num_vf(dev->dev.parent) to populate
>> IFLA_NUM_VF and IFLA_VFINFO_LIST
> Patch looks good but,
>
> If I understand correctly, ndo_get_vf_config is needed for
> IFLA_VFINFO_LIST but not implemeted in this patch?

Thank you for your comment.

I submitted this patch because I confirmed
that "ip link show" returns the correct VF IDs with this implementation.

In the current implementation,
I believe there is no information that would need to be referenced 
through IFLA_VFINFO_LIST.
Therefore, I did not include ndo_get_vf_config in this patch,
as it did not seem essential at this stage.

Would it be better to implement IFLA_VFINFO_LIST support together with this?

Regards,


>> in RTM_GETLINK responses.  For a
>> virtio-net device, dev.parent points to the virtio_device, whose bus
>> is virtio_bus.  Without num_vf, SR-IOV VF information is silently
>> omitted from tools that rely on rtnetlink, such as 'ip link show'.
>>
>> Add a num_vf callback that delegates to dev_num_vf(dev->parent),
>> which in turn reaches the underlying transport (pci_bus_type for
>> virtio-pci) where the actual VF count is tracked.  Non-PCI transports
>> are unaffected as dev_num_vf() returns 0 when no num_vf callback is
>> present.
>>
>> Signed-off-by: Yui Washizu <yui.washidu@gmail.com>
>> ---
>>   drivers/virtio/virtio.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
>> index 5bdc6b82b30b..299fa83be1d5 100644
>> --- a/drivers/virtio/virtio.c
>> +++ b/drivers/virtio/virtio.c
>> @@ -435,6 +435,14 @@ static void virtio_dev_shutdown(struct device *_d)
>>          dev->config->reset(dev);
>>   }
>>
>> +static int virtio_dev_num_vf(struct device *dev)
>> +{
>> +       struct virtio_device *vdev = dev_to_virtio(dev);
>> +
>> +       return dev_num_vf(vdev->dev.parent);
>> +}
>> +
>> +
>>   static const struct bus_type virtio_bus = {
>>          .name  = "virtio",
>>          .match = virtio_dev_match,
>> @@ -444,6 +452,7 @@ static const struct bus_type virtio_bus = {
>>          .remove = virtio_dev_remove,
>>          .irq_get_affinity = virtio_irq_get_affinity,
>>          .shutdown = virtio_dev_shutdown,
>> +       .num_vf = virtio_dev_num_vf,
>>   };
>>
>>   int __register_virtio_driver(struct virtio_driver *driver, struct module *owner)
>> --
>> 2.47.3
>>
> Thanks
>