[Users] mount ploop image from read-only fs

[Roman Haefeli]

Hi all

At the university I work, we plan to switch all containers from simfs to
ploop images on the long run. Despite the many advantages of using
ploop, there is one major drawback that keeps us from switching
production already now: We can't mount ploop images from read-only
snapshots. In case of a recovery of a single file, we have to copy the
ploop image from the read-only snapshot to some read-write storage in
order to be able to mount it and extract the file. For CTs with huge
ploop-images this is a big hurdle. 

Wouldn't it be possible to add a some flag to the 'ploop' utility to
allow mounting ploop images from read-only storage (by bypassing some
checks or skipping to set the dirty flag or whatever is necessary)?

Cheers,
Roman