Unable to attach a cdrom device to guest domain

Issue

It is impossible to block attach a cdrom device to a PV guest domain if the dom0 is running RHEL 5.6.

• Install RHEL 5.6 with Xen Hypervisor.
• Install a PV guest domain named "domu" using virt-manager (could be RHEL 5.6 or RHEL 5.5)
• Put a CD/DVD into DVD/CD drive
• Try following command,

# virsh attach-disk domu /dev/cdrom xvde

or 

# xm block-attach domu /dev/cdrom /dev/xvde

Although The attach-disk or block-attach command returns without error. The device /dev/xvde isn't created in guest domain.