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Date: Thu, 17 May 2001 00:11:55 +0200
From: Ingo Oeser <ingo.oeser@informatik.tu-chemnitz.de>
To: "H. Peter Anvin" <hpa@transmeta.com>
Cc: Richard Gooch <rgooch@ras.ucalgary.ca>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Linus Torvalds <torvalds@transmeta.com>,
        Neil Brown <neilb@cse.unsw.edu.au>,
        Jeff Garzik <jgarzik@mandrakesoft.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        viro@math.psu.edu
Subject: Re: LANANA: To Pending Device Number Registrants
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In-Reply-To: <3B02F2EC.F189923@transmeta.com>; from hpa@transmeta.com on Wed, May 16, 2001 at 02:36:44PM -0700
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On Wed, May 16, 2001 at 02:36:44PM -0700, H. Peter Anvin wrote:
> > But all devices which export a CD-ROM interface will do so. So the
> > device node that is associated with the CD-ROM driver will export
> > CD-ROM semantics, and the trailing name will be "/cd".
> > 
> > Other interfaces a device exports, such as a CD-RW, appear as a
> > different device node ("generic" for SCSI, because we have no CD-RW
> > classification at this point).
> > 
> > My scheme works already, and works reliably. Nothing had to be done to
> > support the CD-ROM interface to CD-RW and DVD devices.
> > 
> 
> It's still completely braindamaged: (a) these interfaces aren't
> disjoint.  They refer to the same device, and will interfere with each
> other; (b) it is highly undesirable to tie the naming to the interfaces
> in this way.  It further restricts the namespaces you can export, for one
> thing.

We do this already with ide-scsi. A device is visible as /dev/hda
and /dev/sda at the same time. Or think IDE-CDRW: /dev/hda,
/dev/sr0 and /dev/sg0.

All at the same time.

It is perfectly normal to export different interfaces for the
same device. This is basically, what subfunctions on PCI do: Same
device with different interfaces. 

Just that we do it through a driver with ide and through the
hardware with a multi function PCI card.

Applications don't care about devices. They care about entities
that have capabilities and programming interfaces. What they
_really_ are and if this is only emulated is not important.

Sorry, I don't see your point here :-(


Regards

Ingo Oeser
-- 
10.+11.03.2001 - 3. Chemnitzer LinuxTag <http://www.tu-chemnitz.de/linux/tag>
         <<<<<<<<<<<<     been there and had much fun   >>>>>>>>>>>>