.\"	$NetBSD: fdatasync.2,v 1.16.56.1 2020/04/22 18:18:26 martin Exp $
.\"
.\" Copyright (c) 1998 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Klaus Klein.
.\"
.\" 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
.\"
.Dd October 25, 2003
.Dt FDATASYNC 2
.Os
.Sh NAME
.Nm fdatasync
.Nd synchronize the data of a file
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn fdatasync "int fd"
.Sh DESCRIPTION
The
.Fn fdatasync
function forces all modified data associated with the file descriptor
.Fa fd
to be flushed to stable storage.
.Pp
The functionality is as described for
.Xr fsync 2 ,
with the exception that file status information need not be synchronized,
which may result in a performance gain, compared to
.Xr fsync 2 .
This behaviour is commonly known as
.Bf -symbolic
synchronized I/O data integrity completion.
.Ef
.Sh RETURN VALUES
A value of 0 is returned on success.
Otherwise, a value \-1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn fdatasync
function will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument is not a valid file descriptor.
.It Bq Er EINVAL
This implementation does not support synchronized I/O for this file.
.It Bq Er ENOSYS
The
.Fn fdatasync
function is not supported by this implementation.
.El
.Pp
In the event that any of the I/O operations to be performed fail,
.Fn fdatasync
returns the error conditions defined for
.Xr read 2
and
.Xr write 2 ,
and outstanding I/O operations are not guaranteed to have been completed.
.Sh SEE ALSO
.Xr fsync 2 ,
.Xr open 2 ,
.Xr read 2 ,
.Xr write 2
.Sh STANDARDS
The
.Fn fdatasync
function conforms to
.St -p1003.1-2008 .