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

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Message-ID: <20090310011944.GB5063@yzhao-otc.sh.intel.com>
Date:	Tue, 10 Mar 2009 09:19:44 +0800
From:	Yu Zhao <yu.zhao@...el.com>
To:	Greg KH <greg@...ah.com>
Cc:	Matthew Wilcox <matthew@....cx>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Randy.Dunlap" <rdunlap@...otime.net>
Subject: Re: [PATCH v10 1/7] PCI: initialize and release SR-IOV capability

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
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