2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
155 lines
4.5 KiB
Groff
155 lines
4.5 KiB
Groff
.\" $NetBSD: flock.2,v 1.21 2009/10/29 01:52:01 wiz Exp $
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.\"
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.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)flock.2 8.2 (Berkeley) 12/11/93
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.\"
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.Dd October 26, 2009
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.Dt FLOCK 2
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.Os
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.Sh NAME
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.Nm flock
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.Nd "apply or remove an advisory lock on an open file"
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In fcntl.h
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.Fd #define LOCK_SH 1 /* shared lock */
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.Fd #define LOCK_EX 2 /* exclusive lock */
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.Fd #define LOCK_NB 4 /* don't block when locking */
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.Fd #define LOCK_UN 8 /* unlock */
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.Ft int
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.Fn flock "int fd" "int operation"
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.Sh DESCRIPTION
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.Fn flock
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applies or removes an
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.Em advisory
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lock on the file associated with the file descriptor
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.Fa fd .
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A lock is applied by specifying an
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.Fa operation
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parameter that is one of
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.Dv LOCK_SH
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or
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.Dv LOCK_EX
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with the optional addition of
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.Dv LOCK_NB .
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To unlock
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an existing lock
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.Dv operation
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should be
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.Dv LOCK_UN .
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.Pp
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Advisory locks allow cooperating processes to perform
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consistent operations on files, but do not guarantee
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consistency (i.e., processes may still access files
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without using advisory locks possibly resulting in
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inconsistencies).
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.Pp
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The locking mechanism allows two types of locks:
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.Em shared
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locks and
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.Em exclusive
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locks.
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At any time multiple shared locks may be applied to a file,
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but at no time are multiple exclusive, or both shared and exclusive,
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locks allowed simultaneously on a file.
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.Pp
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A shared lock may be
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.Em upgraded
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to an exclusive lock, and vice versa, simply by specifying
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the appropriate lock type; this results in the previous
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lock being released and the new lock applied (possibly
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after other processes have gained and released the lock).
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.Pp
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Requesting a lock on an object that is already locked
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normally causes the caller to be blocked until the lock may be
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acquired.
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If
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.Dv LOCK_NB
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is included in
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.Fa operation ,
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then this will not happen; instead the call will fail and
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the error
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.Er EAGAIN
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will be returned.
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.Sh NOTES
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Locks are on files, not file descriptors.
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That is, file descriptors duplicated through
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.Xr dup 2
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or
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.Xr fork 2
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do not result in multiple instances of a lock, but rather multiple
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references to a single lock.
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If a process holding a lock on a file
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forks and the child explicitly unlocks the file, the parent will
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lose its lock.
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.Pp
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Processes blocked awaiting a lock may be awakened by signals.
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.Sh RETURN VALUES
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Zero is returned if the operation was successful;
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on an error a \-1 is returned and an error code is left in
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the global location
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.Va errno .
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.Sh ERRORS
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The
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.Fn flock
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call fails if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The file is locked and the
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.Dv LOCK_NB
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option was specified.
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.It Bq Er EBADF
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The argument
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.Fa fd
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is an invalid descriptor.
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.It Bq Er EINVAL
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The argument
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.Fa operation
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does not include exactly one of
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.Dv LOCK_EX ,
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.Dv LOCK_SH ,
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or
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.Dv LOCK_UN .
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.It Bq Er EOPNOTSUPP
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The argument
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.Fa fd
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refers to an object other than a file.
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.El
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.Sh SEE ALSO
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.Xr close 2 ,
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.Xr dup 2 ,
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.Xr execve 2 ,
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.Xr fork 2 ,
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.Xr open 2
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.Sh HISTORY
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The
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.Fn flock
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function call appeared in
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.Bx 4.2 .
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