linux-kernel - Re: [PATCH 4/4] ACPI / PM: Expose lists of device power resources to user space

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Message-ID: <1463058.nlhMLeRgna@vostro.rjw.lan>
Date:	Wed, 23 Jan 2013 15:01:02 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Kristen C. Accardi" <kristen.c.accardi@...el.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [PATCH 4/4] ACPI / PM: Expose lists of device power resources to user space

On Tuesday, January 22, 2013 05:05:50 PM Greg Kroah-Hartman wrote:
> On Wed, Jan 23, 2013 at 01:28:40AM +0100, Rafael J. Wysocki wrote:
> > On Wednesday, January 23, 2013 01:17:47 AM Rafael J. Wysocki wrote:
> > > On Wednesday, January 23, 2013 01:08:54 AM Rafael J. Wysocki wrote:
> > > > On Tuesday, January 22, 2013 03:56:24 PM Greg Kroah-Hartman wrote:
> > > > > On Tue, Jan 22, 2013 at 03:28:23AM +0100, Rafael J. Wysocki wrote:
> > > 
> > > [...]
> > > 
> > > > > Oh, and same question about racing userspace, you will have problems
> > > > > here in that the symlinks will be showing up after the device is
> > > > > created.  Perhaps, to make the whole thing easier, you just change the
> > > > > acpi core code to hold off on the notification until you get all of
> > > > > these links and files set up and then tell userspace.  That's probably
> > > > > an easier fix.
> > > > 
> > > > I suppose so.
> > > > 
> > > > How can I do that?
> > > 
> > > Should I set dev->kobj.uevent_suppress before calling device_register() and
> > > then clear it and call the kobject_uevent(&dev->kobj, KOBJ_ADD) from the ACPI
> > > core after device_register() has returned and the files have been created?
> > 
> > I suppose along the lines of how firmware_class.c uses uevent_suppress?
> > 
> > Is there any safe mechanism for adding/removing sysfs attributes after
> > kobject_uevent(&dev->kobj, KOBJ_ADD) has been called for the given device?
> 
> Not really.  There is the KBOJ_CHANGE event that some subsystems use
> (hey look, ACPI already uses it), but that's usually used to tell
> userspace that the kobject has somehow "changed" status, just adding the
> initial files to it seems like a gratuitous "change", right?

Sure, that was a general question. :-)

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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