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SubjectRe: [RFC PATCH V3] virtio_pci: Add SR-IOV support
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From: Mark Rustad <mark.d.rustad@intel.com>
Date: Sun, 25 Feb 2018 19:19:11 -0800

> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index 677924ae0350..ddd44a9d93ec 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -367,6 +367,54 @@ static void sriov_disable(struct pci_dev *dev)
> pci_iov_set_numvfs(dev, 0);
> }
>
> +/**
> + * pci_sriov_disable - standard helper to disable SR-IOV
> + * @dev:the PCI PF device whose VFs are to be disabled
> + */
> +int pci_sriov_disable(struct pci_dev *dev)
> +{
> + /*
> + * If vfs are assigned we cannot shut down SR-IOV without causing
> + * issues, so just leave the hardware available.
> + */
> + if (pci_vfs_assigned(dev)) {
> + pci_warn(&dev->dev,
> + "Cannot disable SR-IOV while VFs are assigned - VFs will not be deallocated\n");
> + return -EPERM;
> + }
> + pci_disable_sriov(dev);
> + return 0;
> +}
> +
> +static int pci_sriov_enable(struct pci_dev *dev, int num_vfs)
> +{
> + int rc;
> +
> + if (pci_num_vf(dev))
> + return -EINVAL;
> +
> + rc = pci_enable_sriov(dev, num_vfs);
> + if (rc) {
> + pci_warn(dev, "Failed to enable PCI sriov: %d\n", rc);
> + return rc;
> + }
> + dev_info(dev, "SR-IOV enabled with %d VFs\n", num_vfs);
> + return num_vfs;
> +}

I don't like these helpers on many different levels.

The pci_num_vf() test in pci_sriov_enable() is redundant, the pci_enable_sriov() code
path does that check and returns the same exact error code from sriov_enable().

Just call pci_enable_sriov() directly. The log message adds no value justifying
an entirely new (and confusingly named) helper. If the log message is useful, add
it to pci_enable_sriov().

Speaking of naming, is this stuff confusing or what? As a programmer
what am I supposed to think when I consider what may be the difference
between two interfaces, the only difference in naming is that two
words are transposed?

pci_enable_sriov()
pci_sriov_enable()

pci_disable_sriov()
pci_sriov_disable()

?!?!?!?!

As per pci_sriov_disable() explicitly, all it does different is check
for vf assignment and return failure.

If you want a little help that does that, name it appropriately.

pci_disable_sriov_if_unassigned()

So kill off pci_sriov_enable() helper completely, it is unnecessary,
and rename the disable helper so that it says something meaningful to
the reader.

Thanks.

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