logior for LOCK_NB and EWOULDBLOCK error, and note flock doesn't work
over NFS.
Unlock the file.
@end defvar
@defvar LOCK_NB
-Don't block when locking. May be specified by bitwise OR'ing
-it to one of the other operations.
+Don't block when locking. This is combined with one of the other
+operations using @code{logior} (@pxref{Bitwise Operations}). If
+@code{flock} would block an @code{EWOULDBLOCK} error is thrown
+(@pxref{Conventions}).
@end defvar
The return value is not specified. @var{file} may be an open
file descriptor or an open file descriptor port.
+
+Note that @code{flock} does not lock files across NFS.
@end deffn
@deffn {Scheme Procedure} select reads writes excepts [secs [usecs]]