lockf - apply, test or remove a POSIX lock on an open file
int lockf(int fd, int cmd, off_t
Apply, test or remove a POSIX lock on an open file. The file is specified by
fd. This call is just an interface for fcntl(2). Valid
operations are given below:
- Set an exclusive lock to the file. Only one process may hold an exclusive
lock for a given file at a given time. If the file is already locked it
blocks until the previous lock is released.
- Same as F_LOCK but never blocks and return error instead if the
file is already locked.
- Unlock the file.
- Test the lock: return 0 if fd is unlocked or locked by this
process; return -1, set errno to EACCES, if another process
holds the lock.
On success, zero is returned. On error, -1 is returned, and errno is set
- The file is locked and the LOCK_NB flag was selected, or operation
is prohibited because the file has been memory-mapped by another
- fd is not an open file descriptor.
- Specified lock operation would cause a deadlock.
- An invalid operation was specified in fd.
- Too many segment locks open, lock table is full.
fcntl(2), flock(2). There are also locks.txt and
mandatory.txt in /usr/src/linux/Documentation.