linux-kernel - Race free attributes in sysfs

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Message-ID: <46502A8B.70803@drzeus.cx>
Date:	Sun, 20 May 2007 13:01:31 +0200
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	Greg KH <greg@...ah.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Race free attributes in sysfs

Hi Greg,

I'm reworking the sysfs stuff in the MMC layer to be a bit more flexible, but
there is one thing that has me baffled; how do you add attributes to an object
in a race free manner when you have a dynamic set of attributes.

I've looked at other parts of the kernel and they all use:

1. Add object.
2. Add attributes.

To me, it seems like there's a window between 1 and 2 where the object is in
/sys but doesn't have the proper attributes. Life for user space gets very
annoying if it has to add artificial delays to avoid this window.

So how do I do this properly? Something like this would, from my point of view,
be the sane method:

1. Add hidden object.
2. Add attributes.
3. Show object.

Rgds
-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org
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