The disk extent module implements a low level disk manager that safely space-multiplexes disks.
An new extent can be created from scratch using the mkdev command. Alternatively, a new extent can be created by allocating a new object. E.g., extent:=NEW(Extent.T).init("rz3a",32768,0) creates a new extent on the rz3a device spanning 32KB. This is done to obtain the very first extent object that spans an entire device. It is also possible to create child extents, one that is contained within extent, by passing the name of the partent extent to the init routine. E.g., childextent:=NEW(Extent.T).init("extent_rz3a",16384,0) creates a new extent on the extent_rz3a device spanning 16KB.
One can read and write to the disk via the read/write interface inherited from the Disk.T device object.
An extent can be shared between nontrusting parties. The object acts as a capability. To reserve a portion of a larger extent in order to hand it out to a third party, use the allocate method. Using this interface alone, multiple nontrusting parties can share a device, knowing that none of them can read or write each others' data.
Both size and offset values used by the read/write/init routines are in bytes.