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Date: Fri, 10 Feb 2006 09:52:39 -0500
From: "Theodore Ts'o" <tytso@mit.edu>
To: Joerg Schilling <schilling@fokus.fraunhofer.de>
Cc: peter.read@gmail.com, mj@ucw.cz, matthias.andree@gmx.de,
       linux-kernel@vger.kernel.org, jim@why.dont.jablowme.net,
       jengelh@linux01.gwdg.de
Subject: Re: CD writing in future Linux (stirring up a hornets' nest)
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On Fri, Feb 10, 2006 at 03:32:28PM +0100, Joerg Schilling wrote:
> > Chapter and verse, please?  
> >
> > Can you please list the POSIX standard, section, and line number which
> > states that a particular device must always have the same st_rdev
> > across reboots, and hot plugs/unplugs?
> 
> A particular file on the system must not change st_dev while the system
> is running.
> 
> http://www.opengroup.org/onlinepubs/009695399/basedefs/sys/stat.h.html

1)  File != device.

2)  st_dev != st_rdev

3) The reference you specified says nothing about st_dev (or st_rdev)
being invariant while the system is runnning.  Line number, please?

4) POSIX/SUS is very careful not to define what dev_t.  Use of mknod to
create block/chracter devices, and depending on any properties of
dev_t is likely to get you into trouble.

5) The st_rdev of a particular file, like /dev/hda *does* remain
invariant.  The device which it points to may change, but that's a
different matter --- and POSIX/SUS is very deliberately silent on your
subject.

THEREFORE, your claim that Linux's behaviour violates POSIX/SUS is
demonstrably false.  Quod erat demonstratum.

						- Ted
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