Re: [PATCH v10 1/7] PCI: initialize and release SR-IOV capability

Yu Zhao
2009-03-10T01:18:42Z

On Sat, Mar 07, 2009 at 10:38:45AM +0800, Greg KH wrote:
> On Fri, Mar 06, 2009 at 01:08:10PM -0700, Matthew Wilcox wrote:
> > On Fri, Feb 20, 2009 at 02:54:42PM +0800, Yu Zhao wrote:
> > > + list_for_each_entry(pdev, &dev->bus->devices, bus_list)
> > > + if (pdev->sriov)
> > > + break;
> > > + if (list_empty(&dev->bus->devices) || !pdev->sriov)
> > > + pdev = NULL;
> > > + ctrl = 0;
> > > + if (!pdev && pci_ari_enabled(dev->bus))
> > > + ctrl |= PCI_SRIOV_CTRL_ARI;
> > > +
> >
> > I don't like this loop. At the end of a list_for_each_entry() loop,
> > pdev will not be pointing at a pci_device, it'll be pointing to some
> > offset from &dev->bus->devices. So checking pdev->sriov at this point
> > is really, really bad. I would prefer to see something like this:
> >
> > ctrl = 0;
> > list_for_each_entry(pdev, &dev->bus->devices, bus_list) {
> > if (pdev->sriov)
> > goto ari_enabled;
> > }
> >
> > if (pci_ari_enabled(dev->bus))
> > ctrl = PCI_SRIOV_CTRL_ARI;
> > ari_enabled:
> > pci_write_config_word(dev, pos + PCI_SRIOV_CTRL, ctrl);
>
> No, please use bus_for_each_dev() instead, or bus_find_device(), don't
> walk the bus list by hand. I'm kind of surprised that even builds. Hm,
> in looking at the 2.6.29-rc kernels, I notice it will not even build at
> all, you are now forced to use those functions, which is good.

The devices haven't been added at this time, so we can't use
bus_for_each_dev(). I guess that's why the `bus->devices' exists, and
actually pci_bus_add_devices() walks the bus list same way to retrieve
the devices and add them.

Thanks,
Yu