linux-kernel - Re: Documentation for sysfs, hotplug, and firmware loading.

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Message-ID: <20070720095401.68e9ce03@gondolin.boeblingen.de.ibm.com>
Date:	Fri, 20 Jul 2007 09:54:01 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Greg KH <greg@...ah.com>
Cc:	Rob Landley <rob@...dley.net>, Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org, Michael-Luke Jones <mlj28@....ac.uk>,
	Krzysztof Halasa <khc@...waw.pl>,
	Rod Whitby <rod@...tby.id.au>,
	Russell King <rmk@....linux.org.uk>, david@...g.hm
Subject: Re: Documentation for sysfs, hotplug, and firmware loading.

On Fri, 20 Jul 2007 00:00:01 -0700,
Greg KH <greg@...ah.com> wrote:

> > I don't insist on it, mknod insists on it.  You cannot mknod a dev node 
> > without specifying block or char.
> > 
> > You're saying that sysfs should provide major and minor numbers without 
> > anywhere specifying "char" or "block", meaning the major and minor numbers 
> > cannot be _used_.  I am insisting on getting the third piece of information 
> > without which "major" and "minor" are useless.
> > 
> > I asked very specifically about this at OLS, several times.  What you're 
> > telling me now seems to contradict what you told me then.
> 
> Here's the rule:
> 	If the SUBSYSTEM is "block", it's a block device.  Otherwise
> 	it's a char device.

That's actually quite confusing to the casual reader, since:

> But also realize that the majority of events you will get have nothing
> to do with device nodes.  I think you are forgetting this fact.

So the rule should be:
	If the SUBSYSTEM is "block" (implying major/minor are provided),
	it's a block device.
	If the SUBSYSTEM is not "block", and major/minor are provided,
	it's a char device.
	If major/minor are not provided, the event/device is not
	relevant to device node creation.
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