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

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Date:	Wed, 12 May 2010 21:12:46 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Anton Vorontsov <cbouatmailru@...il.com>
Cc:	Greg KH <gregkh@...e.de>, 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 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.

Kay
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