Re: [Xen-users] Using CD drives with Xen 3.0.3 on CentOS 4.4

[Nico Kadel-Garcia <nkadel@xxxxxxxxx>]

M.A. Williamson wrote:
> > I'd like to be able to use a CD drive on the Dom0 to be accessible on 
> > the DomU systems. I do see some notes involving cdrom drives in the 
> > Xen 3.1 Enterprise notes, and in the VT notes, but not for systems 
> > without that on-board virtualization feature. And the syntax of the 
> > cdrom command options are documented nowhere in 3.0.3.
> You can export the CD-ROM drive to the guest by using the file: 
> directive, as you would for other disks. This will work for iso files 
> and for /dev/cdrom
> e.g. something like
>
> disk = [ 'file:/dev/cdrom,hdd,r', <your entries for other disks go 
> here> ]
Hmm. That seems only fully workable for already mounted drives, but I'll 
check it out.
I am amused and confused by the use of  
'file:/var/lib/xen/images/file.img,hda,w ' as opposed to 
'file:/var/lib/xen/images/file.img,hda1,w'  and the fascinating 
partition adventures involved. It could also use some documentation. 
Having to deduce that sort of thing from scratch is asking for pain and 
work out the tradeoffs for yourself is asking for pain.
> will give the domain access to the contents of the real physical 
> CD-ROM drive. Note that you'll want to have the CD-ROM you want to use 
> in the drive when the domain boots, otherwise it'll confuse the 
> guest's probing of disk size. Using an ISO file is probably more 
> straightfoward and convenient. If you want to change ISO file you 
> should be able to use xm block-detach and xm block-attach to add a new 
> ISO to the guest. If you change the CD-ROM in an exported physical 
> drive, I'd suggest doing xm block-detach, then changing the CD, then 
> xm block-attach, so that the guest knows something has changed.
ISO files are great, but wind up taking space on your Dom0 to build. And 
creating them from DVD's becomes even more burdensome, and *burning* 
CD's or DVD's from the guest domain would be even more awkward.
> Note that the Xen paravirtualised block drive doesn't provide full 
> CD-ROM emulation: you should be able to mount the filesystem, but you 
> won't be able to treat it entirely like a CD drive because some of the 
> special operations will not be supported (eject springs to mind, but 
> there are other CD-ROM specific operations).
Yeah, that's why I hadn't even considered the file: approach. I may have 
to use it after all.
> Hopefully the above method will be sufficient from your needs. I run 
> my development machine on CentOS 4.4 (albeit running xen-unstable 
> built from source for my purposes) so can try to replicate and resolve 
> any specific problems you run into.
> Hope that helps some. You're quite right that this sort of thing 
> should be documented more thoroughly. Since the next release of RHEL 
> will include Xen, hopefully CentOS (5) integration will be an 
> improvement - sorry you had problems with the existing packages.
Thanks. How are you downloading the unstable source?

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