Re: [Xen-devel] CDROM access

[Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>]

XenoLinux accesses CDROMs through a "Virtual Block Device".  The size of the 
disk is set by dom0 when it first probes its VBDs on boot.  If at that time, 
there is not a CDROM in the drive, then the size will have been initialised to 
zero.  Putting a CDROM in later does not (currently) make XenoLinux reprobe to 
update the VBD size, therefore it *still* thinks the size is zero.  That's 
probably why you can't mount the disk.

The XenoLinux VBD driver (and the underlying interface to block devices 
provided by Xen) currently don't support all the commands you'd usually use 
with a CD-ROM.  So things like multisession CD support and things that, for 
instance, operate (or lock) the drive tray won't work.

Reading normal data CDs, as you want to do should be fine though.  To make 
sure the size of the device is registered with Dom0 as being the correct size, 
boot with the CD in the drive (you may have to change your boot order in the 
BIOS if it's a bootable CD!).  Note that after boot you *can* change CDs 
whenever you want, it's just that XenoLinux won't see the device size change.

Also note that the system won't stop you ejecting CDs at any time, since the 
drive tray isn't locked (AFAIK) - so be sure the CD isn't in use before you 
hit the button!

At some stage, the CD-ROM functionality will hopefully be expanded to be a 
little more "normal" from the pov of domains.

Cheers,

Mark



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