freebsd-nq/lib/libutil/flopen.3

.\"-
.\" 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.
.\"
.\" $FreeBSD$
.\"
.Dd May 10, 2007
.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
with the same parameters followed by
.Fn flock
with an
.Va operation
argument of
.Dv LOCK_EX ,
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
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
As with
.Fn open ,
the additional
.Va mode
argument is required if
.Va flags
includes
.Dv O_CREAT .
.Sh RETURN VALUES
If successful,
.Fn flopen
returns a valid file descriptor.
Otherwise, it returns -1, and sets
.Va errno
as described in
.Xr flock 2
and
.Xr open 2 .
.Sh SEE ALSO
.Xr errno 2 ,
.Xr flock 2 ,
.Xr open 2
.Sh HISTORY
The
.Fn flopen
function first appeared in
.Fx 6.3 .
.Sh AUTHORS
.An -nosplit
The
.Nm
function and this manual page were written by
.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org .