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SubjectRe: [PATCH] virtio_pci: support enabling VFs
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On May 30, 2018, at 9:54 AM, Duyck, Alexander H  
<alexander.h.duyck@intel.com> wrote:

> On Wed, 2018-05-30 at 09:44 -0700, Rustad, Mark D wrote:
>> On May 30, 2018, at 9:22 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
>>
>>>> +static int virtio_pci_sriov_configure(struct pci_dev *pci_dev, int
>>>> num_vfs)
>>>> +{
>>>> + struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);
>>>> + struct virtio_device *vdev = &vp_dev->vdev;
>>>> + int (*sriov_configure)(struct pci_dev *pci_dev, int num_vfs);
>>>> +
>>>> + if (!(vdev->config->get_status(vdev) & VIRTIO_CONFIG_S_DRIVER_OK))
>>>> + return -EBUSY;
>>>> +
>>>> + if (!__virtio_test_bit(vdev, VIRTIO_F_SR_IOV))
>>>> + return -EINVAL;
>>>> +
>>>> + sriov_configure = pci_sriov_configure_simple;
>>>> + if (sriov_configure == NULL)
>>>> + return -ENOENT;
>>>
>>> BTW what is all this trickery in aid of?
>>
>> When SR-IOV support is not compiled into the kernel,
>> pci_sriov_configure_simple is #defined as NULL. This allows it to compile
>> in that case, even though there is utterly no way for it to be called in
>> that case. It is an alternative to #ifs in the code.
>
> Why even have the call though? I would wrap all of this in an #ifdef
> and strip it out since you couldn't support SR-IOV if it isn't present
> in the kernel anyway.

I am inclined to agree. In this case, the presence of #ifdefs I think would
be clearer. As written, someone will want to get rid of the pointer only to
create a build problem when SR-IOV is not configured.

--
Mark Rustad, Networking Division, Intel Corporation
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