Linux 3.15 and newer support a vastly superior API for file locking, in which locks are owned by open file descriptions instead of by processes.  This is how everyone seems to expect POSIX locks to work, but now they can finally work that way.

Please add some interface to these locks to fcntl.lockf.  One option would be to use them by default and to fall back to standard POSIX locks if they're not available.  I don't know whether this would break existing code.

See http://man7.org/linux/man-pages/man2/fcntl.2.html for details.