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Re: [Qemu-devel] Audio cd's in guest OS

From: Jim C. Brown
Subject: Re: [Qemu-devel] Audio cd's in guest OS
Date: Sat, 5 Nov 2005 09:55:27 -0500
User-agent: Mutt/

On Sat, Nov 05, 2005 at 12:35:12PM +0100, Oliver Gerlich wrote:
> > Thanks - I should have known that someone had made a file system for
> > this. However I still think it would be great to be able to pass the
> > actual /dev/cdrom on to the guest OS, but I must admit that I have not
> > grasped the complexity yet on doing this, so I am going to do some
> > Qemu code reading before continuing - I am not even sure if it can be
> > done in VMWare although I  seam to remember that Windows as a host OS
> > running VMWare allows the guest access to a audio cdrom.
> > 

That is interesting. I wonder how they did it.

> Not sure how VMware does that; but actually I didn't even succeed
> accessing /dev/cdrom on the host when an audio cd is inserted:
> dd if=/dev/hdc of=/dev/null bs=2352 count=1
> dd: reading `/dev/hdc': Input/output error
> 0+0 records in
> 0+0 records out
> 0 bytes transferred in 0.077570 seconds (0 bytes/sec)
> I used a blocksize of 2352 because I've read that's the size for audio
> cds... It didn't work with bs=1 either.

It is the sector size. But audio cds are stored in a different format than
digital cds (the ones that contain filesystems on them such as ISO9660).
It is even possible to have both formats on a single cd-rom (so it works to hold
music for an audio cd player as well as music videos that can be played on a

dd only supports accessing the digital side of things. I don't recall how hard
it is to access raw audio, but I wouldn't be suprised if one needed low level
controller commands (like it's needed to burn cd-r(w)s or dvd-r(w)s).

> So maybe Qemu would have to access the cd drive on a lower level than
> via /dev/cdrom?


A quick&easy hack might be to have an -audio-cdrom option, that takes a 
full of *.wav's and generates an emulated audio cd for the guest. (Might have
to make it a monitor option as well, to allow swapping of audio and digital

Then to use real audio cdroms from the host, just mount them via CDFS.

May not be worth the effort.

> Just my 2 cents,
> Oliver Gerlich

Infinite complexity begets infinite beauty.
Infinite precision begets infinite perfection.

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