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'm afraid you're not going to be able to burn and optical disks from 
> either paravirt or HVM domains for the time being :-(
Drat. I was looking at using a DomU to run rsnapshot for network 
snapshot access, and do DVD burning from those, rather than having to do 
it on Dom0.
> You *could* add a second IDE controller card to your system, export 
> that to a guest via the PCI passthrough and then use that to drive a 
> CD writer, but this would be rather heavyweight and imply trust of the 
> guest OS.
Hmm. All the drives are SATA, it's only the CD/DVD drive that is IDE. 
Adding in another ATA card is begging for pain, especially physically 
routing the cables to the CD drive in the 1U servers I'm working with.  
That seems unwise.
> When USB virtualisation is working (it may already work in HVM) it 
> should be possible to pass a USB burner through to the guest, and that 
> would enable this kind of use.
I'm already using an external USB storage device, via the 
"file:/dev/sdc1,sdc1,w' syntax, which seems workable for external USB 
drives.
> > > 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.
> Afraid so, sorry :-( For many uses (e.g. just grabbing some files from 
> the disk), it should work OK. But you can't just boot off a CD-ROM in 
> a PV domain, nor can you place CD music, etc.
Yeah. that needs to be made clear. The Xen configuration files simply 
accept it and seem to ignore it. Putting in useful error messages would 
help.
> > Thanks. How are you downloading the unstable source?
> I get mine using mercurial:
> hg clone http://xenbits.xensource.com/xen-unstable.hg
Hmm. I'm not familiar with that source control system. (Ghods know I've 
worked with CVS, Perforce, Subversion, and some unspeakable homebrews!) 
Is there any reason to prefer it to the others, such as Subvresion which 
also supports branching properly?
> I'd generally recommend using a release version for production 
> systems, 3.0.4 being the latest and (hopefull) greatest. 
> http://xenbits2.xensource.com/xen-3.0.4-testing.hg should contain 
> 3.0.4 + bugfixes that are being tested to be rolled up into the next 
> 3.0.4.x update.
> There will be tarballs of 3.0.4 linked off one of the Xen homepages, 
> once they have been updated. Building your own Xen is reasonably 
> straightforward once you know your way around the components, and 
> there should be various HOWTOs hanging around.
> Hope that helps. If you still have problems with the CD-ROM we can try 
> and find a workaround for you.
It did help. I'd be happy to write up such notes and adventures for the 
FAQ's or installation notes, but I'm seeing significant divergence 
between packages such as RedHat's with the virtmanager tool on top of 
it, and the bare Xen tools. Weirdness such as the failure of the RHEL 
4.x SRPM published by Xensource  to be able to build the documentation 
put me off it for a while. Other oddness such as using non-getopt based 
command line arguments have also slowed me down. Examples include 
arguments using "create" instead of "--create", and alternating the use 
of "DomU", and "guest", or of "migrate" and "relocate" in both 
configuration files nad actual command line arguments, or the "xm 
migrate" command having its flags at the end, just waste my time having 
to look up and remember all the different argument structures.
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