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Diffstat (limited to 'man/man3/lockf.3')
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diff --git a/man/man3/lockf.3 b/man/man3/lockf.3 new file mode 100644 index 000000000..7267587c4 --- /dev/null +++ b/man/man3/lockf.3 @@ -0,0 +1,179 @@ +'\" t +.\" Copyright 1997 Nicolás Lichtmaier <nick@debian.org> +.\" Created Thu Aug 7 00:44:00 ART 1997 +.\" +.\" SPDX-License-Identifier: GPL-2.0-or-later +.\" +.\" Added section stuff, aeb, 2002-04-22. +.\" Corrected include file, drepper, 2003-06-15. +.\" +.TH lockf 3 (date) "Linux man-pages (unreleased)" +.SH NAME +lockf \- apply, test or remove a POSIX lock on an open file +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <unistd.h> +.P +.BI "int lockf(int " fd ", int " op ", off_t " len ); +.fi +.P +.RS -4 +Feature Test Macro Requirements for glibc (see +.BR feature_test_macros (7)): +.RE +.P +.BR lockf (): +.nf + _XOPEN_SOURCE >= 500 +.\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED + || /* glibc >= 2.19: */ _DEFAULT_SOURCE + || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE +.fi +.SH DESCRIPTION +Apply, test, or remove a POSIX lock on a section of an open file. +The file is specified by +.IR fd , +a file descriptor open for writing, the action by +.IR op , +and the section consists of byte positions +.IR pos .. pos + len \-1 +if +.I len +is positive, and +.IR pos \- len .. pos \-1 +if +.I len +is negative, where +.I pos +is the current file position, and if +.I 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. +.P +On Linux, +.BR lockf () +is just an interface on top of +.BR fcntl (2) +locking. +Many other systems implement +.BR lockf () +in this way, but note that POSIX.1 leaves the relationship between +.BR lockf () +and +.BR fcntl (2) +locks unspecified. +A portable application should probably avoid mixing calls +to these interfaces. +.P +Valid operations are given below: +.TP +.B 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. +.TP +.B F_TLOCK +Same as +.B F_LOCK +but the call never blocks and returns an error instead if the file is +already locked. +.TP +.B F_ULOCK +Unlock the indicated section of the file. +This may cause a locked section to be split into two locked sections. +.TP +.B F_TEST +Test the lock: return 0 if the specified section +is unlocked or locked by this process; return \-1, set +.I errno +to +.B EAGAIN +.RB ( EACCES +on some other systems), +if another process holds a lock. +.SH RETURN VALUE +On success, zero is returned. +On error, \-1 is returned, and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.BR EACCES " or " EAGAIN +The file is locked and +.B F_TLOCK +or +.B F_TEST +was specified, or the operation is prohibited because the file has +been memory-mapped by another process. +.TP +.B EBADF +.I fd +is not an open file descriptor; or +.I op +is +.B F_LOCK +or +.B F_TLOCK +and +.I fd +is not a writable file descriptor. +.TP +.B EDEADLK +.I op +was +.B F_LOCK +and this lock operation would cause a deadlock. +.TP +.B EINTR +While waiting to acquire a lock, the call was interrupted by +delivery of a signal caught by a handler; see +.BR signal (7). +.TP +.B EINVAL +An invalid operation was specified in +.IR op . +.TP +.B ENOLCK +Too many segment locks open, lock table is full. +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR lockf () +T} Thread safety MT-Safe +.TE +.SH STANDARDS +POSIX.1-2008. +.SH HISTORY +POSIX.1-2001, SVr4. +.SH SEE ALSO +.BR fcntl (2), +.BR flock (2) +.P +.I locks.txt +and +.I mandatory\-locking.txt +in the Linux kernel source directory +.I Documentation/filesystems +(on older kernels, these files are directly under the +.I Documentation +directory, and +.I mandatory\-locking.txt +is called +.IR mandatory.txt ) |