Re: [PATCH] virtio_pci: support enabling VFs

["Rustad, Mark D" <mark.d.rustad@intel.com>]

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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