Why do we always seem to disagree? :-)

Yes, all bets are off in the case of a kernel/filesystem bug. But I am unconvinced that it is better to make it manual. I prefer the simpler code on general principles. But I would also isolate the calls into an atomic interface so that if something did go wrong I could fix more easily. Besides which, then I am in a better position to move to fcntl or some other kind of locking if I need it at some point.

BTW I already did isolate locking somewhere else. And now you cannot complain that nobody has posted examples where the return code of flock is checked. :-)

UPDATE
Thanks tye for pointing out that one not was not wanted. That noted not was not for naught. :-)