illumos gate

Our flock(3C) support does not presently support locking files on remote file systems like NFS (see F_REMOTELOCK, and comments in fs_frlock()). In the event that one tries to lock an NFS-backed file, flock() presently fails with EINVAL. This is probably not quite right; e.g., in the manual page:

       EINVAL
                           The operation argument does not contain one of
                           LOCK_SH, LOCK_EX, or LOCK_UN; or the operation
                           argument contains LOCK_UN and LOCK_NB; or the
                           operation argument contains any bits other than
                           those set by LOCK_SH, LOCK_EX, LOCK_NB, and
                           LOCK_UN.
...
       EOPNOTSUPP
                           The locking of files of the type indicated by
                           the fildes argument is not supported.

The latter seems more appropriate here.

As an aside, a brief survey of the documentation of other platforms shows:

• FreeBSD and OpenBSD appear to use EOPNOTSUPP for this condition
• Mac OS X appears to use ENOTSUP
• Linux does not appear to document the possibility of a failure of this kind, but explicitly says EINVAL is for an invalid operation argument

It does not seem that flock() has been standardised.