The cowloop-driver is a copy-on-write loop driver (block device) which can be used on top of any other block driver. It shields the lower driver from any write access. Instead, it diverts all write-accesses to an arbitrary regular file, called the cowfile. When a modified block is read again later on, the cowloop-driver obtains the block from the cowfile, while non-modified blocks are obtained from the original read-only device. This mechanism allows block-devices to be used in a read-write fashion without modifying the underlying block-device itself.
