Re: [PATCH] virtio_pci: support enabling VFs

From: Rustad, Mark D
Date: Wed May 30 2018 - 13:12:11 EST


On May 30, 2018, at 9:54 AM, Duyck, Alexander H <alexander.h.duyck@xxxxxxxxx> 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@xxxxxxxxxx> 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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