semanage: allow '-m' to add new entries

[ensc]

It would be nice when semanage's -m operation would get a --force flag or so which would imply -a when entry does not exist.

Atm, it is very difficult to bring a system into a known state because every semanage invocation must be expressed by two commands; e.g.

semanage login -a -s unconfined_u -r s0-s0:c0.c1023 wheel || \
semanage login -m -s unconfined_u -r s0-s0:c0.c1023 wheel

because it might be unclear whether a mapping has been already defined.

Having an operation which translates to modify-or-add-when-not-existing would simplify things significantly. Tt would allow so use semanage -i transactions in more situations too.

[stephensmalley]

I'd be willing to take a patch that either introduces such a --force flag or that simply makes this the default behavior for -m (unless someone sees a problem with that), Patches to [email protected].