linux-kernel - Re: [PATCH 2/2] HID: roccat: using new sysfs_create_bin

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Date:	Sat, 13 Nov 2010 17:34:15 +0100
From:	Stefan Achatz <stefan_achatz@....de>
To:	Greg KH <gregkh@...e.de>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Eric Biederman <ebiederm@...stanetworks.com>,
	"Serge E. Hallyn" <serue@...ibm.com>, Tejun Heo <tj@...nel.org>,
	Jiri Kosina <jkosina@...e.cz>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Benjamin Thery <benjamin.thery@...l.net>
Subject: Re: [PATCH 2/2] HID: roccat: using new sysfs_create_bin_group() in
 kone driver

Am Samstag, den 13.11.2010, 06:39 -0800 schrieb Greg KH:
> On Fri, Nov 12, 2010 at 10:06:34PM -0800, Dmitry Torokhov wrote:
> > On Fri, Nov 12, 2010 at 04:52:32PM -0800, Greg KH wrote:
> > > On Fri, Nov 12, 2010 at 04:21:45PM -0800, Eric Biederman wrote:
> > > > On Fri, Nov 12, 2010 at 10:18 AM, Stefan Achatz <stefan_achatz@....de> wrote:
> > > > > hid-roccat-kone now uses new group functions for creating binary
> > > > > sysfs attributes.
> > > > 
> > > > Looking at this, I have a problem with the way this works.
> > > > You are still doing this the hard and racy way.
> > > > 
> > > > sysfs attributes that are only added when we initialize the hardware and
> > > > are only removed when we remove the driver should use the device layer
> > > > functions to create their attributes.
> > > > 
> > > > This achieves two things.  The code is easier to write because there
> > > > is less of it.
> > > > The notification to user space happens after the attributes appear so
> > > > that you don't
> > > > have strange hotplug races.
> > > > 
> > > > If there a chance you can look at implementing this in the simpler
> > > > race free way?
> > > 
> > > Good point, just attach this attribute group to the device and the
> > > driver core will automatically create the files for you.
> > > 
> > 
> > Attribute group in device structure is normally owned and managed by
> > subsystem core; without additional plumbing drivers should not be
> > touching it, at least not normally.
> > 
> > Plus we do not have binary attribute group in device structure [yet].
> 
> In thinking about it a bit more, why do you have so many binary
> attributes for this driver?  binary sysfs files are rare, so adding a
> binary attribute group pointer to the device or driver would just waste
> a lot of space that no one else uses.
> 
> What are these binary files for?  Who uses them?  I don't seem to be
> able to find them in the Documentation/ABI directory, or am I missing
> something here?

Documentation/ABI/testing/sysfs-driver-hid-roccat-kone

Stefan

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