Hello !
just want to inform that here is a cool new loopback driver variant at: http://www.atconsultancy.nl/cowloop/
"The cowloop driver is a copy-on-write loop driver (block device) to be used on top of any other block driver. The cowloop driver
shields the lower driver from any write accesses. Instead, it diverts all write-accesses to an arbitrary regular file."
regards
Roland
ps:
I`m not directly involved in development - i just came across that site some time ago and thought it was worth being mentioned here.
(didn`t find a reference in the ML archive)