linux-kernel - Re: [PATCH] sysfs: add devm_sysfs_create

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Message-ID: <20151107002407.GD28499@kroah.com>
Date:	Fri, 6 Nov 2015 16:24:07 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	htejun@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sysfs: add devm_sysfs_create_group() and friends

On Fri, Oct 30, 2015 at 08:13:11AM -0700, Dmitry Torokhov wrote:
> On Fri, Oct 30, 2015 at 07:40:37AM -0700, Greg Kroah-Hartman wrote:
> > On Fri, Oct 30, 2015 at 04:47:06AM -0700, Dmitry Torokhov wrote:
> > > Many drivers create additional driver-specific device attributes when
> > > binding to the device and providing managed version of sysfs_create_group()
> > > will simplify unbinding and error handling in probe path for such drivers.
> > 
> > But they really shouldn't, because if they do this, they have raced
> > userspace and tools don't know that the files are present.
> > 
> > I don't want to encourage drivers to do this at all, so I don't want to
> > make it easier for them to do things incorrectly.
> 
> The solution is not to forbid drivers from establishing attributes but
> rather notify userspace when device is fully bound to the driver. Then
> userspace that actually cares about these attributes will listen to
> proper events.
> 
> We can either do KOBJ_BOUND/KOBJ_UNBOUND or reuse
> KOBJ_ONLINE/KOBJ_OFFLINE. I'd prefer the former (adding new events).

bound/unbound makes a bit more sense, maybe that would work, haven't
thought that much about it.  Given that no one in the "real world" seem
to notice the race condition, that means that people aren't really using
tools like libudev to read sysfs attributes, so maybe no one even cares
about the contents of them :)

> > Yes, I know that input does this for its devices, but I still think it
> > is wrong and should be changed.  Let's not let this problem spread to
> > other subsystems please.
> 
> Like HID, chargers, hwmon, wireless drivers, leds, backlights, platform
> drivers and so on? Where are platform devices supposed to create their
> attributes? There are more than 300 drivers that add new groups and 581
> instance of device_create_file().

Platform drivers are the main problem right now, I don't know what to do
about them.  I hate those things :(

> Let's be realistic here and see that additional attributes are not going
> anywhere and adding devm interface just helps getting error handling
> right.

But the files are already removed from the system when the device is
removed, so with the exception of the odd error path on probe, this
isn't doing much.  Does it save much code when used?

thanks,

greg k-h
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