linux-kernel - Re: [PATCH] pci: keep pci device resource name pointer right.

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Date:	Sat, 18 Apr 2009 22:37:18 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Greg KH <gregkh@...e.de>, Yinghai Lu <yinghai@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH] pci: keep pci device resource name pointer right.


* Kay Sievers <kay.sievers@...y.org> wrote:

> On Sat, 2009-04-18 at 22:00 +0200, Kay Sievers wrote:
> > On Sat, Apr 18, 2009 at 21:23, Greg KH <gregkh@...e.de> wrote:
> > > On Sat, Apr 18, 2009 at 12:19:21PM -0700, Yinghai Lu wrote:
> > >> Linus Torvalds wrote:
> > 
> > >> > Can we not make the rule be that the name should just be set before?
> > 
> > I guess, that's what they do already, otherwise they could not use dev_name().
> > 
> > >> pci_bus_add_device will call device_add.
> > >>
> > >> actually in device_add
> > >>
> > >>         /* first, register with generic layer. */
> > >>         error = kobject_add(&dev->kobj, dev->kobj.parent, "%s", dev_name(dev));
> > >>         if (error)
> > >>                 goto Error;
> > >>
> > >> will get one new name for that kobj, old name is freed.
> > >>
> > >> Will try to make kobject_add more smart to reuse the old one.
> > >
> > > I don't understand the problem here, how are you going to change the
> > > kobject core?  Is this just because you aren't getting a name for the
> > > resource?  If so, why would the driver core care about this?
> > 
> > Seems a bit odd what we do when registering a device.
> > 
> > Usually one sets the name with dev_set_name() which will name the
> > kobject. When one later registers the device, we reallocate the same
> > name, so the pointer changes. I guess the problem here is that the pci
> > code remembers the name pointer after it was set, but it will not be
> > the same after the device is live.
> > 
> > We should probably make device_add() pass a NULL as the name, and
> > kobject_add() in that case use the name that is properly set already.
> 
> Only to see if we are on the right track, does that fix the problem? If
> yes, we will fix it properly without the NULL hack deep in the kobject
> call.
> 
> Thanks,
> Kay
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index d230ff4..1969b20 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -890,8 +890,8 @@ int device_add(struct device *dev)
>  	if (parent)
>  		set_dev_node(dev, dev_to_node(parent));
>  
> -	/* first, register with generic layer. */
> -	error = kobject_add(&dev->kobj, dev->kobj.parent, "%s", dev_name(dev));
> +	/* we require the name to be set before, and pass NULL */
> +	error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);
>  	if (error)
>  		goto Error;
>  
> diff --git a/lib/kobject.c b/lib/kobject.c
> index a6dec32..48565d6 100644
> --- a/lib/kobject.c
> +++ b/lib/kobject.c
> @@ -218,6 +218,9 @@ int kobject_set_name_vargs(struct kobject *kobj, const char *fmt,
>  	const char *old_name = kobj->name;
>  	char *s;
>  
> +	if (kobj->name && !fmt)
> +		return 0;
> +
>  	kobj->name = kvasprintf(GFP_KERNEL, fmt, vargs);
>  	if (!kobj->name)
>  		return -ENOMEM;

This looks much cleaner to me - a NULL format string looks like a 
natural extension.

	Ingo
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