LOCKF

LOCKF

NAME SYNOPSIS DESCRIPTION RETURN VALUE ERRORS CONFORMING TO SEE ALSO

NAME

lockf - apply, test or remove a POSIX lock on an open file

SYNOPSIS

#include

int lockf(int fd, int cmd, off_t len);

DESCRIPTION

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:

F_LOCK

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.

F_TLOCK

Same as F_LOCK but never blocks and return error instead if the file is already locked.

F_ULOCK

Unlock the file.

F_TEST

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.

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

EAGAIN

The file is locked and the LOCK_NB flag was selected, or operation is prohibited because the file has been memory-mapped by another process.

EBADF

fd is not an open file descriptor.

EDEADLK

Specified lock operation would cause a deadlock.

EINVAL

An invalid operation was specified in fd.

ENOLCK

Too many segment locks open, lock table is full.

CONFORMING TO

SYSV

SEE ALSO

fcntl(2), flock(2) There are also locks.txt and mandatory.txt in /usr/src/linux/Documentation.