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freebsd-dev/lib/libutil/flopen.3

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I'm tired of seeing this done incorrectly and non-portably, so add a flopen(3) function which reliably opens and locks a file. MFC after: 3 weeks
2007-05-10 14:43:31 +00:00
.\"-
.\" Copyright (c) 2007 Dag-Erling Co<43>dan Sm<53>rgrav
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
Revert (once again, and hopefully for the last time) to flock(2) locks. 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.
2009-06-06 18:47:03 +00:00
.Dd June 6, 2009
I'm tired of seeing this done incorrectly and non-portably, so add a flopen(3) function which reliably opens and locks a file. MFC after: 3 weeks
2007-05-10 14:43:31 +00:00
.Dt FLOPEN 3
.Os
.Sh NAME
.Nm flopen
.Nd "Reliably open and lock a file"
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In sys/fcntl.h
.In libutil.h
.Ft int
.Fn flopen "const char *path" "int flags"
.Ft int
.Fn flopen "const char *path" "int flags" "mode_t mode"
.Sh DESCRIPTION
The
.Fn flopen
function opens or creates a file and acquires an exclusive lock on it.
It is essentially equivalent with calling
.Fn open
Revert (once again, and hopefully for the last time) to flock(2) locks. 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.
2009-06-06 18:47:03 +00:00
with the same parameters followed by
.Fn flock
with an
.Va operation
argument of
.Dv LOCK_EX ,
I'm tired of seeing this done incorrectly and non-portably, so add a flopen(3) function which reliably opens and locks a file. MFC after: 3 weeks
2007-05-10 14:43:31 +00:00
except that
.Fn flopen
will attempt to detect and handle races that may occur between opening
/ creating the file and locking it.
Thus, it is well suited for opening lock files, PID files, spool
files, mailboxes and other kinds of files which are used for
synchronization between processes.
.Pp
DTRT when O_NONBLOCK is specified. MFC after: 3 weeks
2007-05-10 14:52:57 +00:00
If
.Va flags
includes
.Dv O_NONBLOCK
and the file is already locked,
.Fn flopen
will fail and set
.Va errno
to
.Dv EWOULDBLOCK .
.Pp
I'm tired of seeing this done incorrectly and non-portably, so add a flopen(3) function which reliably opens and locks a file. MFC after: 3 weeks
2007-05-10 14:43:31 +00:00
As with
Fix typo. Submitted by: Bård Skaflestad <bardsk@math.ntnu.no>
2007-05-10 18:15:30 +00:00
.Fn open ,
I'm tired of seeing this done incorrectly and non-portably, so add a flopen(3) function which reliably opens and locks a file. MFC after: 3 weeks
2007-05-10 14:43:31 +00:00
the additional
.Va mode
argument is required if
.Va flags
includes
.Dv O_CREAT .
DTRT when O_NONBLOCK is specified. MFC after: 3 weeks
2007-05-10 14:52:57 +00:00
.Sh RETURN VALUES
If successful,
.Fn flopen
returns a valid file descriptor.
Otherwise, it returns -1, and sets
.Va errno
as described in
Revert (once again, and hopefully for the last time) to flock(2) locks. 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.
2009-06-06 18:47:03 +00:00
.Xr flock 2
DTRT when O_NONBLOCK is specified. MFC after: 3 weeks
2007-05-10 14:52:57 +00:00
and
.Xr open 2 .
I'm tired of seeing this done incorrectly and non-portably, so add a flopen(3) function which reliably opens and locks a file. MFC after: 3 weeks
2007-05-10 14:43:31 +00:00
.Sh SEE ALSO
DTRT when O_NONBLOCK is specified. MFC after: 3 weeks
2007-05-10 14:52:57 +00:00
.Xr errno 2 ,
Revert (once again, and hopefully for the last time) to flock(2) locks. 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.
2009-06-06 18:47:03 +00:00
.Xr flock 2 ,
I'm tired of seeing this done incorrectly and non-portably, so add a flopen(3) function which reliably opens and locks a file. MFC after: 3 weeks
2007-05-10 14:43:31 +00:00
.Xr open 2
.Sh AUTHORS
.An -nosplit
The
.Nm
function and this manual page were written by
.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org .
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