From: Greg KH <gregkh@linuxfoundation.org>
To: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Colin Cross <ccross@android.com>,
Richard Purdie <richard.purdie@linuxfoundation.org>,
lkml <linux-kernel@vger.kernel.org>,
Bryan Wu <bryan.wu@canonical.com>
Subject: Re: sysfs permissions on dynamic attributes (led delay_on and delay_off)
Date: Sat, 21 Jul 2012 09:15:23 -0700 [thread overview]
Message-ID: <20120721161523.GB22896@kroah.com> (raw)
In-Reply-To: <20120721160855.GB7565@khazad-dum.debian.net>
On Sat, Jul 21, 2012 at 01:08:55PM -0300, Henrique de Moraes Holschuh wrote:
> On Sat, 21 Jul 2012, Colin Cross wrote:
> > The delay_on and delay_off files could easily override the values from
> > the trigger.
> >
> > Sending a KOBJ_CHANGE uevent is not a great solution, it's still
> > horribly racy in userspace. This script would never work reliably:
> > echo timer > trigger
> > echo 1000 > delay_on
> > echo 1000 > delay_off
> > echo 255 > brightness
>
> Yes, and the proper fix is to instead use a fully async userspace based on
> uevent callbacks. Nasty as all hell. Or the quick fix, which is to wait
> for the system to settle after every sysfs operation that could create new
> sysfs nodes.
>
> You could make sure that (1) no sysfs operation will return control to
> userspace until it is complete, so you'd have all new sysfs nodes available
> at the time the first echo returns [I believe it already works like that],
Yes it does, what's the problem here?
> and (2) either enhance sysfs to create nodes with the desired ownership and
> permissions
>From the kernel, you can also do this today, if you know it's "safe" for
users to read/write them.
greg k-h
next prev parent reply other threads:[~2012-07-21 16:15 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-21 0:46 sysfs permissions on dynamic attributes (led delay_on and delay_off) Colin Cross
2012-07-21 4:08 ` Greg KH
2012-07-21 5:14 ` Colin Cross
2012-07-21 15:07 ` Greg KH
2012-07-21 7:33 ` Richard Purdie
2012-07-21 8:26 ` Colin Cross
2012-07-21 11:21 ` Richard Purdie
2012-07-21 14:31 ` Henrique de Moraes Holschuh
2012-07-21 15:42 ` Colin Cross
2012-07-21 16:08 ` Henrique de Moraes Holschuh
2012-07-21 16:15 ` Greg KH [this message]
2012-07-21 16:23 ` Colin Cross
2012-07-21 16:13 ` Greg KH
2012-07-21 16:22 ` Colin Cross
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