Device_numberSourceDisks are attached to particular bus types:
A specification for a device number. There are more valid specifications than valid device numbers because of hardware and/or protocol limits.
A valid device number
make spec validates a given device number specification spec and returns a device number
of_string hvm name returns the interface which best matches the name by applying the policy: first check if it is a disk_number, else fall back to a linux_device for backwards compatability
to_linux_device i returns a possible linux string representation of interface i
of_linux_device x returns the interface corresponding to string x
to_xenstore_key i returns the xenstore key from interface i
of_xenstore_key key returns an interface from a xenstore key
to_disk_number i returns the corresponding non-negative disk number
of_disk_number hvm n returns the interface corresponding to disk number n which depends on whether the guest is hvm or not.