I feel strongly that -C and -a are mutually exclusive options, as are -U and -d.
-a maps a file as a device node - lofi's main job, it does not modify the file in any way (an upper layer filesystem or application may). -C/-U actually transforms a file in a destructive manner by doing a copy/modify/rename. The compress could take a long time and take a non trivial amount of cpu/memory and diskspace. So much that a progress indication would be good, however such a progress indication would be incompatible with the current output of -a since it is explicitly listed as being scriptable. -- Darren J Moffat
