+(**
+ {2 Structures used to describe machines, disks, partitions and filesystems}
+
+ {3 Machine/device model}
+
+ The "machine/device model" that we currently understand looks
+ like this:
+
+{v
+machines
+ |
+ \--- host partitions / disk image files
+ ||
+ guest block devices
+ |
+ +--> guest partitions (eg. using MBR)
+ | |
+ \-(1)->+--- filesystems (eg. ext3)
+ |
+ \--- PVs for LVM
+ |||
+ VGs and LVs
+v}
+
+ (1) Filesystems and PVs may also appear directly on guest
+ block devices.
+
+ Partition schemes (eg. MBR) and filesystems register themselves
+ with this main module and they are queried first to get an idea
+ of the physical devices, partitions and filesystems potentially
+ available to the guest.
+
+ Volume management schemes (eg. LVM2) register themselves here
+ and are called later with "spare" physical devices and partitions
+ to see if they contain LVM data. If this results in additional
+ logical volumes then these are checked for filesystems.
+
+ Swap space is considered to be a dumb filesystem for the purposes
+ of this discussion.
+*)
+