Name
lockf — apply, test or remove a POSIX lock on an open file
Synopsis
#include <unistd.h>
int
lockf( |
int fd, |
| int cmd, | |
off_t len); |
![[Note]](../stylesheet/note.png) |
Note | ||
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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, lockf() is just an
interface on top of fcntl(2) locking. Many
other systems implement lockf()
in this way, but note that POSIX.1-2001 leaves the
relationship between lockf()
and fcntl(2) locks unspecified.
A portable application should probably avoid mixing calls to
these interfaces.
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 earlier 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_LOCKbut 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
errnoto EAGAIN (EACCES on some other systems), if another process holds a lock.
RETURN VALUE
On success, zero is returned. On error, −1 is
returned, and errno is set
appropriately.
ERRORS
- EACCES or EAGAIN
-
The file is locked and
F_TLOCKorF_TESTwas specified, or the operation is prohibited because the file has been memory-mapped by another process. - EBADF
-
fdis not an open file descriptor; orcmdisF_LOCKorF_TLOCKandfdis not a writable file descriptor. - EDEADLK
-
The command was
F_LOCKand 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.
SEE ALSO
locks.txt and
mandatory-locking.txt in the
Linux kernel source directory Documentation/filesystems (on older
kernels, these files are directly under the Documentation directory, and mandatory-locking.txt is
called mandatory.txt)
COLOPHON
This page is part of release 3.52 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man−pages/.
|
Copyright 1997 Nicolás Lichtmaier <nickdebian.org> Created Thu Aug 7 00:44:00 ART 1997 %%%LICENSE_START(GPLv2+_DOC_FULL) This is free documentation; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU General Public License's references to "object code" and "executables" are to be interpreted as the output of any document formatting or typesetting system, including intermediate and printed output. This manual is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this manual; if not, see <http://www.gnu.org/licenses/>. %%%LICENSE_END Added section stuff, aeb, 2002-04-22. Corrected include file, drepper, 2003-06-15. |