linux-kernel - Re: [PATCH 15/16 v6] PCI: document the SR-IOV sysfs entries

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Message-ID: <20081118150533.GB1251@kroah.com>
Date:	Tue, 18 Nov 2008 07:05:33 -0800
From:	Greg KH <greg@...ah.com>
To:	Yu Zhao <yu.zhao@...el.com>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"achiang@...com" <achiang@...com>,
	"grundler@...isc-linux.org" <grundler@...isc-linux.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"matthew@....cx" <matthew@....cx>,
	"randy.dunlap@...cle.com" <randy.dunlap@...cle.com>,
	"rdreier@...co.com" <rdreier@...co.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 15/16 v6] PCI: document the SR-IOV sysfs entries

On Mon, Nov 17, 2008 at 04:09:49PM +0800, Yu Zhao wrote:
> On Fri, Nov 14, 2008 at 08:55:38AM +0800, Greg KH wrote:
> > On Thu, Nov 13, 2008 at 02:50:24PM +0800, Yu Zhao wrote:
> > > On Fri, Nov 07, 2008 at 11:18:37AM +0800, Greg KH wrote:
> > > > On Fri, Nov 07, 2008 at 11:01:29AM +0800, Zhao, Yu wrote:
> > > > > Currently PCI subsystem has /sys/.../{vendor,device,...} bundled to the 
> > > > > main PCI device (I suppose this means the entries are created by 
> > > > > 'device_add')
> > > > >
> > > > > And after the PCI device is announced, 
> > > > > /sys/.../{config,resourceX,rom,vpd,iov,...} get created depending on if 
> > > > > these features are supported.
> > > > 
> > > > And that's a bug.  Let's not continue to make the same bug here as well.
> > > > 
> > > > > Making dynamic entries tie to the main PCI device would require PCI 
> > > > > subsystem to allocate different 'bus_type' for the devices, right?
> > > > 
> > > > No, it would just mean they need to be all added before the device is
> > > > fully registered with the driver core.
> > > 
> > > I looked into the PCI and driver core code again, but didn't figured out how
> > > to do it.
> > > 
> > > A 'pci_dev' is added by pci_bus_add_device() via device_add(), which creates
> > > sysfs entries according to 'dev_attrs' in the 'pci_bus_type'. If we want those
> > > dynamic entries to appear before the uevent is triggered, we have to bundle
> > > them into the 'dev_attrs'. Is this right way for the dynamic entries? Or I
> > > missed something?
> > 
> > Yes, that is correct.
> > 
> > Or you can add attributes before device_add() is called to the device,
> > which is probably much easier to do, right?
> > 
> > There are also "conditional" attributes, which get only displayed if
> > some kind of condition is met, I think you want to use those.
> 
> The problem is the sysfs directory of the PCI device is created by the
> kobject_add() in the device_add() as follows. And the static entries
> bundled with the 'pci_bus_type' are created by the bus_add_device().
> Between the kobject_add() and the kobject_uevent(), we don't have any
> other choice to add the dynamic entries.
> 
> In device_add():
> 
> 	error = kobject_add(&dev->kobj, dev->kobj.parent, "%s", dev->bus_id);
> 	...
> 	error = bus_add_device(dev);
> 	...
> 	kobject_uevent(&dev->kobj, KOBJ_ADD);
> 
> 
> So looks like the only way is to make the dynamic entries bundled with
> the 'pci_bus_type', which means they would become static no matter the
> device supports the entries (i.e. corresponding capabilities) or not.

No, this can work, other busses do this.  There are "conditional"
attributes that only get enabled if specific things happen, and you can
add attributes before device_add() is called.  See the scsi code for
examples of both of these options.

thanks,

greg k-h
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