linux-kernel - Re: [PATCH] Introduce {sysfs,device}_create_file

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Date:	Wed, 12 May 2010 23:39:12 +0400
From:	Anton Vorontsov <cbouatmailru@...il.com>
To:	Greg KH <gregkh@...e.de>
Cc:	Kay Sievers <kay.sievers@...y.org>, Daniel Mack <daniel@...aq.de>,
	linux-kernel@...r.kernel.org,
	David Woodhouse <dwmw2@...radead.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	Len Brown <len.brown@...el.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Matt Reimer <mreimer@...p.net>,
	Evgeniy Polyakov <zbr@...emap.net>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] Introduce {sysfs,device}_create_file_mode

On Wed, May 12, 2010 at 12:19:55PM -0700, Greg KH wrote:
> On Wed, May 12, 2010 at 09:12:46PM +0200, Kay Sievers wrote:
> > On Wed, May 12, 2010 at 21:08, Anton Vorontsov <cbouatmailru@...il.com> wrote:
> > > On Wed, May 12, 2010 at 11:38:06AM -0700, Greg KH wrote:
> > >> On Wed, May 12, 2010 at 10:15:46PM +0400, Anton Vorontsov wrote:
> > >> > We need to create attributes with different modes across devices.
> > >> > We can do this by modifying attr.mode between device_create_file
> > >> > invocations, but that is racy in case of globally defined attrs.
> > >> >
> > >> > Luckily, there's sysfs_add_file_mode() function that seems to do
> > >> > exactly what we want, and if we use it, we don't need any locks
> > >> > to avoid races. Though, it isn't exposed via device-drivers core
> > >> > API.
> > >>
> > >> But you race the creation of the device notifying userspace, and then
> > >> the file being created, right?
> > >
> > > Yep, you've raised that question once, like 3 years ago. :-)
> > >
> > > http://lkml.org/lkml/2007/4/11/452
> > > http://lkml.org/lkml/2007/4/12/144
> > >
> > > In short: we can't use attr groups since the attributes creation
> > > is conditional. And we especially don't want to use the attr groups
> > > for attrs with different modes. But it's not a problem, because...
> > 
> > Groups have a filter callback for every member, to decide if the
> > attribute should be created or not.
> 
> Yeah, that's how we solved that issue a long time ago :)

But not loud enough for us to notice. ;-)

> Can you please switch to using attribute groups now, so that userspace
> doesn't have to handle 'change' events?

Yep.

Thanks,

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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