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The problem with fcntl(2) locks is that they are not inherited by child processes. This breaks pidfile(3), where the common idiom is to open and lock the PID file before daemonizing.
102 lines
2.7 KiB
Groff
102 lines
2.7 KiB
Groff
.\"-
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.\" Copyright (c) 2007 Dag-Erling Coïdan Smørgrav
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.\" 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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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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.\" $FreeBSD$
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.\"
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.Dd June 6, 2009
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.Dt FLOPEN 3
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.Os
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.Sh NAME
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.Nm flopen
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.Nd "Reliably open and lock a file"
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.Sh LIBRARY
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.Lb libutil
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.Sh SYNOPSIS
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.In sys/fcntl.h
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.In libutil.h
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.Ft int
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.Fn flopen "const char *path" "int flags"
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.Ft int
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.Fn flopen "const char *path" "int flags" "mode_t mode"
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.Sh DESCRIPTION
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The
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.Fn flopen
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function opens or creates a file and acquires an exclusive lock on it.
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It is essentially equivalent with calling
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.Fn open
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with the same parameters followed by
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.Fn flock
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with an
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.Va operation
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argument of
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.Dv LOCK_EX ,
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except that
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.Fn flopen
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will attempt to detect and handle races that may occur between opening
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/ creating the file and locking it.
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Thus, it is well suited for opening lock files, PID files, spool
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files, mailboxes and other kinds of files which are used for
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synchronization between processes.
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.Pp
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If
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.Va flags
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includes
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.Dv O_NONBLOCK
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and the file is already locked,
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.Fn flopen
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will fail and set
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.Va errno
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to
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.Dv EWOULDBLOCK .
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.Pp
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As with
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.Fn open ,
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the additional
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.Va mode
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argument is required if
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.Va flags
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includes
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.Dv O_CREAT .
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.Sh RETURN VALUES
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If successful,
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.Fn flopen
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returns a valid file descriptor.
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Otherwise, it returns -1, and sets
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.Va errno
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as described in
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.Xr flock 2
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and
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.Xr open 2 .
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.Sh SEE ALSO
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.Xr errno 2 ,
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.Xr flock 2 ,
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.Xr open 2
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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function and this manual page were written by
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.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org .
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