I tried to make a call to flock(), which is documented in patch B
(although not in the internet docs). The compiler seems never to have
heard of LOCK_EX or LOCK_UN. Inspection of fcntl.h reveals that they
are not there. An oversight?
So I guess I can do the same thing with fcntl(filedes, FSETLK, F_WRLCK),
but do I need to set anything in the flock structure? I want to lock
the whole file, so I guess I need to set flock.l_whence to SEEK_SET,
flock.l_start to 0, and flock.l_len to 0. Is this right?