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
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Groff
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Groff
.\" $NetBSD: lockf.3,v 1.10 2008/04/30 13:10:50 martin Exp $
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.\"
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.\" Copyright (c) 1997 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Klaus Klein and S.P. Zeidler.
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd December 19, 1997
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.Dt LOCKF 3
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.Os
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.Sh NAME
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.Nm lockf
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.Nd record locking on files
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft int
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.Fn lockf "int filedes" "int function" "off_t size"
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.Sh DESCRIPTION
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The
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.Fn lockf
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function allows sections of a file to be locked with advisory-mode locks.
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Calls to
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.Fn lockf
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from other processes which attempt to lock the locked file section will
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either return an error value or block until the section becomes unlocked.
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All the locks for a process are removed when the process terminates.
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.Pp
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The argument
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.Fa filedes
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is an open file descriptor.
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The file descriptor must have been opened either for write-only
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.Dv ( O_WRONLY )
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or read/write
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.Dv ( O_RDWR )
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operation.
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.Pp
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The
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.Fa function
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argument is a control value which specifies the action to be taken.
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The permissible values for
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.Fa function
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are as follows:
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.Bl -tag -width F_ULOCKXX -compact -offset indent
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.It Sy Function
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.Sy Description
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.It Dv F_ULOCK
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unlock locked sections
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.It Dv F_LOCK
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lock a section for exclusive use
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.It Dv F_TLOCK
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test and lock a section for exclusive use
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.It Dv F_TEST
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test a section for locks by other processes
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.El
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.Pp
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.Dv F_ULOCK
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removes locks from a section of the file;
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.Dv F_LOCK
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and
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.Dv F_TLOCK
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both lock a section of a file if the section is available;
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.Dv F_TEST
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detects if a lock by another process is present on the specified section.
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.Pp
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The
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.Fa size
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argument is the number of contiguous bytes to be locked or
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unlocked.
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The section to be locked or unlocked starts at the current
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offset in the file and extends forward for a positive size or backward
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for a negative size (the preceding bytes up to but not including the
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current offset).
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However, it is not permitted to lock a section that
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starts or extends before the beginning of the file.
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If
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.Fa size
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is 0, the section from the current offset through the largest possible
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file offset is locked (that is, from the current offset through the
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present or any future end-of-file).
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.Pp
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The sections locked with
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.Dv F_LOCK
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or
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.Dv F_TLOCK
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may, in whole or in part, contain or be contained by a previously
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locked section for the same process.
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When this occurs, or if adjacent
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locked sections would occur, the sections are combined into a single
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locked section.
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If the request would cause the number of locks to
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exceed a system-imposed limit, the request will fail.
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.Pp
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.Dv F_LOCK
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and
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.Dv F_TLOCK
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requests differ only by the action taken if the section is not
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available.
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.Dv F_LOCK
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blocks the calling process until the section is available.
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.Dv F_TLOCK
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makes the function fail if the section is already locked by another
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process.
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.Pp
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File locks are released on first close by the locking process of any
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file descriptor for the file.
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.Pp
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.Dv F_ULOCK
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requests release (wholly or in part) one or more locked sections
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controlled by the process.
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Locked sections will be unlocked starting
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at the current file offset through
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.Fa size
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bytes or to the end of file if size is 0.
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When all of a locked section
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is not released (that is, when the beginning or end of the area to be
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unlocked falls within a locked section), the remaining portions of
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that section are still locked by the process.
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Releasing the center
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portion of a locked section will cause the remaining locked beginning
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and end portions to become two separate locked sections.
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If the
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request would cause the number of locks in the system to exceed a
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system-imposed limit, the request will fail.
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.Pp
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An
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.Dv F_ULOCK
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request in which size is non-zero and the offset of the last byte of
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the requested section is the maximum value for an object of type
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off_t, when the process has an existing lock in which size is 0 and
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which includes the last byte of the requested section, will be treated
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as a request to unlock from the start of the requested section with a
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size equal to 0.
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Otherwise an
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.Dv F_ULOCK
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request will attempt to unlock only the requested section.
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.Pp
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A potential for deadlock occurs if a process controlling a locked
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region is put to sleep by attempting to lock the locked region of
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another process.
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This implementation detects that sleeping until a
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locked region is unlocked would cause a deadlock and fails with an
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.Er EDEADLK
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error.
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.Pp
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.Fn lockf ,
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.Xr fcntl 2
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and
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.Xr flock 2
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locks may be safely used concurrently.
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.Pp
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Blocking on a section is interrupted by any signal.
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.Sh RETURN VALUES
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If successful, the
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.Fn lockf
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function returns 0.
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Otherwise, it returns \-1, sets
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.Va errno
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to indicate an error, and existing locks are not changed.
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.Sh ERRORS
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.Fn lockf
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The argument
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.Fa function
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is
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.Dv F_TLOCK
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or
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.Dv F_TEST
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and the section is already locked by another process.
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.It Bq Er EBADF
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The argument
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.Fa filedes
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is not a valid open file descriptor.
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.Pp
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The argument
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.Fa function
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is
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.Dv F_LOCK
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or
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.Dv F_TLOCK ,
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and
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.Fa filedes
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is not a valid file descriptor open for writing.
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.It Bq Er EDEADLK
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The argument
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.Fa function
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is
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.Dv F_LOCK
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and a deadlock is detected.
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.It Bq Er EINTR
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The argument
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.Fa function
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is F_LOCK
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and
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.Fn lockf
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was interrupted by the delivery of a signal.
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.It Bq Er EINVAL
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The argument
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.Fa function
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is not one of
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.Dv F_ULOCK ,
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.Dv F_LOCK ,
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.Dv F_TLOCK
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or
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.Dv F_TEST .
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.Pp
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The argument
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.Fa filedes
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refers to a file that does not support locking.
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.It Bq Er ENOLCK
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The argument
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.Fa function
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is
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.Dv F_ULOCK ,
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.Dv F_LOCK
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or
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.Dv F_TLOCK ,
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and satisfying the lock or unlock request would result in the number
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of locked regions in the system exceeding a system-imposed limit.
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.El
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.Sh SEE ALSO
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.Xr fcntl 2 ,
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.Xr flock 2
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.Sh STANDARDS
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The
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.Fn lockf
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function conforms to
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.St -xpg4.2 .
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