it relies on non-portable flock(2) semantics. Not only is flock(2) not
portable, but on some OSes that do have it, it is implemented in terms
of fcntl(2) locks, which are per-process rather than per-descriptor.
after similar calls related to struct pwd in libutil/pw_util.c:
- gr_equal()
Perform a deep comparison of two struct grp's. It does a thorough, yet
unoptimized comparison of all the members regardless of order.
- gr_make()
Create a string (see group(5)) from a struct grp.
- gr_dup()
Duplicate a struct grp. Returns a value that is a single contiguous
block of memory.
- gr_scan()
Create a struct grp from a string (as produced by gr_make()).
MFC after: 3 weeks
