Subject: Re: No more "device" symlinks for classes
From: Kay Sievers <kay.sievers@vrfy.org>
To: Pierre Ossman <drzeus-list@drzeus.cx>
Cc: Greg KH <greg@kroah.com>, LKML <linux-kernel@vger.kernel.org>
In-Reply-To: <45A9797F.9000806@drzeus.cx>
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	 <1168732961.14924.39.camel@pim.off.vrfy.org>  <45A9797F.9000806@drzeus.cx>
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Date: Sun, 14 Jan 2007 01:35:51 +0100
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On Sun, 2007-01-14 at 01:29 +0100, Pierre Ossman wrote:
> Kay Sievers wrote:
> >
> > The plan is to have a single unified tree at /sys/devices, where all
> > device-directories live below their parents, and /sys/class contains
> > only symlinks pointing into this single tree, just like /sys/bus.
> >
> > People want to stack class-devices, but this leads to a /sys/devices
> > tree and several small trees spread around in /sys/class. These trees
> > need to be connected by "device"-links and the "class:"-links, which
> > just doesn't make much sense if you can have one single tree with the
> > same information.
> >
> > In the unified tree, the "device"-link will always just point to the
> > parent device, that's why there is a config option to disable these
> > links and test current software not to depend on it.
> >
> I'm not sure I completely follow. Should an application look at the
> symlink (e.g. /sys/class/fooclass/foodev -> /sys/devices/...) and follow
> that one level up? If so, then this sounds a bit complicated. Especially
> from shell scripts.

We would have one single tree at /sys/devices, and always flat
classification without hierarchy at /sys/class and /sys/bus. If you
enter the device-tree by starting at /sys/class, you get the full path
to the device by reading the link, and get all the device's
dependencies(parents) in the devpath of the device,

I can't see any problem stripping the last element of a path with a
shell script. It's all implemented in current udev and HAL for quite
some time and it's pretty easy.

Kay

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