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Date:      Fri, 24 Jan 2003 15:29:36 -0800
From:      Marcel Moolenaar <marcel@xcllnt.net>
To:        phk@FreeBSD.ORG
Cc:        arch@FreeBSD.ORG
Subject:   Re: GEOM and CDROM media (was: CFR: Volume labels in FFS)
Message-ID:  <20030124232936.GB47190@dhcp01.pn.xcllnt.net>
In-Reply-To: <4614.1043447912@critter.freebsd.dk>
References:  <20030124222718.GN53114@roark.gnf.org> <4614.1043447912@critter.freebsd.dk>

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On Fri, Jan 24, 2003 at 11:38:32PM +0100, phk@FreeBSD.ORG wrote:
> In message <20030124222718.GN53114@roark.gnf.org>, Gordon Tetlow writes:
> 
> >I can also forsee being able to hook into devd to do some automounting magic
> >for things like zip disks and cdroms (obviously not with FFS, but cd9660
> >support would be a good thing to have once GEOM recognizes cdroms).
> 
> I am currently experimenting with code for removable devices which
> will poll the drive if there is a media in it (too many drives/interfaces
> are too stupid to tell us) and this can and could be include CDROMS
> as well.
> 
> The question in my mind is how to handle complex CDROM formats:

What about an intermediate layer that splits the physical media into
logical media based on the format. Example given below (forgive me
the unethical device naming -- it's for illustration purposes):

>    1: Data track
>    2: Data track
>    3: Music "You can build a mainframe from the things you find at home"
>    4: Music "I'm a mainframe baby"
>    5: Data track
>    6: Data track, multi-session with track 5.

/dev/cd0/data/track1
/dev/cd0/data/track2
/dev/cd0/data/track3
/dev/cd0/data/track4, multi-session with track 3
/dev/cd0/audio/track1
/dev/cd0/audio/track2

The track numbers are logical so you can treat /dev/cd0/audio as
a logical audio-only CD and /dev/cd0/data as a logical data-only
CD. Whether you want to have GEOM deal with audio tracks or
just present a logical audio CD depends on how loud you scream
if someone would write GEOM_MP3 :-)

You could treat the DVD VOBs in the same way I guess...

I guess the point I'm getting at is that GEOM stacks objects to
abstract the physical representation by presenting logical
entities. An abstraction layer based on the format seems to
fit in...

Just some random thoughts...

-- 
 Marcel Moolenaar	  USPA: A-39004		 marcel@xcllnt.net

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