Return to flock.2 CVS log

Up to [CSRG BSD Unix] / 43BSDReno / lib / libc / sys

Annotation of 43BSDReno/lib/libc/sys/flock.2, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1983 The Regents of the University of California.
        !             2: .\" All rights reserved.
        !             3: .\"
        !             4: .\" Redistribution and use in source and binary forms are permitted provided
        !             5: .\" that: (1) source distributions retain this entire copyright notice and
        !             6: .\" comment, and (2) distributions including binaries display the following
        !             7: .\" acknowledgement:  ``This product includes software developed by the
        !             8: .\" University of California, Berkeley and its contributors'' in the
        !             9: .\" documentation or other materials provided with the distribution and in
        !            10: .\" all advertising materials mentioning features or use of this software.
        !            11: .\" Neither the name of the University nor the names of its contributors may
        !            12: .\" be used to endorse or promote products derived from this software without
        !            13: .\" specific prior written permission.
        !            14: .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
        !            15: .\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
        !            16: .\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            17: .\"
        !            18: .\"    @(#)flock.2     6.6 (Berkeley) 6/23/90
        !            19: .\"
        !            20: .TH FLOCK 2 "June 23, 1990"
        !            21: .UC 5
        !            22: .SH NAME
        !            23: flock \- apply or remove an advisory lock on an open file
        !            24: .SH SYNOPSIS
        !            25: .nf
        !            26: .ft B
        !            27: #include <sys/file.h>
        !            28: .PP
        !            29: .ft B
        !            30: .DT
        !            31: #define        LOCK_SH 1       /* shared lock */
        !            32: #define        LOCK_EX 2       /* exclusive lock */
        !            33: #define        LOCK_NB 4       /* don't block when locking */
        !            34: #define        LOCK_UN 8       /* unlock */
        !            35: .PP
        !            36: .ft B
        !            37: flock(fd, operation)
        !            38: int fd, operation;
        !            39: .fi
        !            40: .SH DESCRIPTION
        !            41: .I Flock
        !            42: applies or removes an
        !            43: .I advisory
        !            44: lock on the file associated with the file descriptor
        !            45: .IR fd .
        !            46: A lock is applied by specifying an
        !            47: .I operation
        !            48: parameter that is the inclusive or of
        !            49: LOCK_SH or LOCK_EX and, possibly, LOCK_NB.  To unlock
        !            50: an existing lock
        !            51: .I operation
        !            52: should be LOCK_UN.
        !            53: .PP
        !            54: Advisory locks allow cooperating processes to perform
        !            55: consistent operations on files, but do not guarantee
        !            56: consistency (i.e., processes may still access files
        !            57: without using advisory locks possibly resulting in
        !            58: inconsistencies).
        !            59: .PP
        !            60: The locking mechanism allows two types of locks:
        !            61: .I shared
        !            62: locks and
        !            63: .I exclusive
        !            64: locks.
        !            65: At any time multiple shared locks may be applied to a file,
        !            66: but at no time are multiple exclusive, or both shared and exclusive,
        !            67: locks allowed simultaneously on a file.  
        !            68: .PP
        !            69: A shared lock may be
        !            70: .I upgraded
        !            71: to an exclusive lock, and vice versa, simply by specifying
        !            72: the appropriate lock type; this results in the previous
        !            73: lock being released and the new lock applied (possibly
        !            74: after other processes have gained and released the lock).
        !            75: .PP
        !            76: Requesting a lock on an object that is already locked
        !            77: normally causes the caller to be blocked until the lock may be
        !            78: acquired.  If LOCK_NB is included in
        !            79: .IR operation ,
        !            80: then this will not happen; instead the call will fail and
        !            81: the error EWOULDBLOCK will be returned.
        !            82: .SH NOTES
        !            83: Locks are on files, not file descriptors.  That is, file descriptors
        !            84: duplicated through
        !            85: .IR dup (2)
        !            86: or
        !            87: .IR fork (2)
        !            88: do not result in multiple instances of a lock, but rather multiple
        !            89: references to a single lock.  If a process holding a lock on a file
        !            90: forks and the child explicitly unlocks the file, the parent will
        !            91: lose its lock.
        !            92: .PP
        !            93: Processes blocked awaiting a lock may be awakened by signals.
        !            94: .SH "RETURN VALUE
        !            95: Zero is returned if the operation was successful;
        !            96: on an error a \-1 is returned and an error code is left in
        !            97: the global location \fIerrno\fP.
        !            98: .SH "ERRORS
        !            99: The \fIflock\fP call fails if:
        !           100: .TP 20
        !           101: [EWOULDBLOCK]
        !           102: The file is locked and the LOCK_NB option was specified.
        !           103: .TP 20
        !           104: [EBADF]
        !           105: The argument \fIfd\fP is an invalid descriptor.
        !           106: .TP 20
        !           107: [EINVAL]
        !           108: The argument \fIfd\fP refers to an object other than a file.
        !           109: .SH "SEE ALSO"
        !           110: open(2), close(2), dup(2), execve(2), fork(2)

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.