XXX
XXX WARNING: old character encoding and/or character set
XXX
LOCKF(3) Linux Programmer's Manual LOCKF(3)
NAME
lockf - apply, test or remove a POSIX lock on an open file
SYNOPSIS
#include<sys/file.h>
intlockf(int fd,int cmd,off_t len);
DESCRIPTION
Apply, test or remove a POSIX lock on a section of an open file. The
file is specified by fd, a file descriptor open for writing, the action
by cmd, and the section consists of byte positions pos..pos+len-1 if
len is positive, and pos-len..pos-1 if len is negative, where pos is
the current file position, and if len is zero, the section extends from
the current file position to infinity, encompassing the present and
future end-of-file positions. In all cases, the section may extend
past current end-of-file.
On Linux, this call is just an interface for fcntl(2). (In general,
the relation between lockf and fcntl is unspecified.)
Valid operations are given below:
F_LOCK Set an exclusive lock on the specified section of the file. If
(part of) this section is already locked, the call blocks until
the previous lock is released. If this section overlaps an ear-
lier locked section, both are merged. File locks are released
as soon as the process holding the locks closes some file
descriptor for the file. A child process does not inherit these
locks.
F_TLOCK
Same as F_LOCK but the call never blocks and returns an error
instead if the file is already locked.
F_ULOCK
Unlock the indicated section of the file. This may cause a
locked section to be split into two locked sections.
F_TEST Test the lock: return 0 if the specified section is unlocked or
locked by this process; return -1, set errno to EACCES, if
another process holds a lock.
RETURNVALUE
On success, zero is returned. On error, -1 is returned, and errno is
set appropriately.
ERRORS
EAGAIN The file is locked and F_TLOCK or F_TEST was specified, or the
operation is prohibited because the file has been memory-mapped
by another process.
EBADF fd is not an open file descriptor.
EDEADLK
The command was T_LOCK and this lock operation would cause a
deadlock.
EINVAL An invalid operation was specified in fd.
ENOLCK Too many segment locks open, lock table is full.
CONFORMINGTO
SYSV, POSIX 1003.1-2001
SEEALSO
fcntl(2), flock(2)
There are also locks.txt and mandatory.txt in /usr/src/linux/Documenta-
tion.
Linux 2.0 2002-04-22 LOCKF(3)
Take our 
