sys_flock — 
     flock system call.
 
| long sys_flock ( | unsigned int fd, | 
| unsigned int cmd ); | 
   Apply a FL_FLOCK style lock to an open file descriptor.
   The cmd can be one of
   
   LOCK_SH -- a shared lock.
   
   LOCK_EX -- an exclusive lock.
   
   LOCK_UN -- remove an existing lock.
   
   LOCK_MAND -- a `mandatory' flock.  This exists to emulate Windows Share Modes.
   
   LOCK_MAND can be combined with LOCK_READ or LOCK_WRITE to allow other
   processes read and write access respectively.