Limited support for pkg/unshare on FreeBSD

[dfr]

This does not really 'unshare' anything but does implement the setsid,
setpgrp and ctty options as well as the pipe-based signalling protocol
with the parent process which made it slightly easier to port buildah's
chroot isolation mechanism.

Signed-off-by: Doug Rabson dfr@rabson.org

[rhatdan]

@nalind @giuseppe PTAL

[giuseppe]

LGTM

[nalind]

OOMScoreAdj is in the non-Linux version of the Cmd struct, but it seems to be ignored. Should it be there?

[dfr]

OOMScoreAdj is in the non-Linux version of the Cmd struct, but it seems to be ignored. Should it be there?

I will remove it - as you can see its not implemented here and I'm not sure if there is a direct equivalent

[nalind]

The FreeBSD implementation could probably stand to drop the _Containers-unshare environment variable, which the Linux implementation uses for passing flags for unshare() down to the child process, but which doesn't appear to serve a purpose in the FreeBSD version.

Go ahead and move bailOnError from unshare_linux.go to unshare.go to avoid having to duplicate it in unshare_freebsd.go.

[dfr]

I've updated the branch with the suggested changes, please take a look.

[rhatdan]

LGTM