libarchive and MAC labels

[priit at cc.ttu.ee]

I've created a patch for libarchive that allows storing and restoring MAC 
labels from/to a multilabel filesystem using bsdtar. Now before going 
anywhere with this I had a few questions:

- how much general interest is there in such a feature? Would this be a 
welcome addition to libarchive, either "upstream" or as integrated in the 
system source tree. I would be especially interested in the opinion of 
people who have already been involved with the MAC development.

- right now the labels are stored silently, similar to ACL-s and extended 
attributes. They are not extracted by default, only when the '-p' option 
is specified (default as root). This seems consistent, however it would 
also be possible to add a switch so that the labels wouldn't be archived 
unless explicitly requested.

- the labels are stored in text representation, as converted by 
mac_to_text(). This could potentially cause some future breakage, if the 
text representation ever changes. Also, restoring a label partially 
(let's say a biba+MLS label with only biba enabled) does not work. Any 
thoughts on that?

Thanks,
Priit.