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

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Message-ID: <20151030151311.GA20183@dtor-pixel>
Date:	Fri, 30 Oct 2015 08:13:11 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 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).

> 
> 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().

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

Thanks.

-- 
Dmitry
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