.\"-
.\" Copyright (c) 2007 Dag-Erling Coïdan Smørgrav
.\" All rights reserved.
.\"
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.\" $FreeBSD: src/lib/libutil/flopen.3,v 1.7 2008/10/20 18:02:16 des Exp $
.\"
.Dd December 27, 2008
.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 an
.Fn fcntl
.Dv F_SETLK
or
.Dv F_SETLKW
operation with lock type
.Dv F_WRLCK ,
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
.Er 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 fcntl 2
and
.Xr open 2 .
.Sh SEE ALSO
.Xr errno 2 ,
.Xr fcntl 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 .