.\"	$NetBSD: posix_fadvise.2,v 1.6 2016/12/19 06:45:29 abhinav Exp $
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.\" Copyright (c)2006,2009 YAMAMOTO Takashi,
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.\" ------------------------------------------------------------
.Dd February 4, 2013
.Dt POSIX_FADVISE 2
.Os
.Sh NAME
.Nm posix_fadvise
.Nd hint at the future access pattern of a file
.\" ------------------------------------------------------------
.Sh LIBRARY
.Lb libc
.\" ------------------------------------------------------------
.Sh SYNOPSIS
.In fcntl.h
.Ft int
.Fn posix_fadvise "int fd" "off_t offset" "off_t size" "int hint"
.\" ------------------------------------------------------------
.Sh DESCRIPTION
.Fn posix_fadvise
hints at the application's access pattern to the file and range
given by
the file descriptor,
.Fa fd ,
and
.Fa offset
and
.Fa size .
If
.Fa size
is zero, it means to the end of file.
.Pp
.Fa hint
should be one of the following:
.Pp
.Bl -tag -offset indent -width POSIX_FADV_SEQUENTIAL -compact
.It POSIX_FADV_NORMAL
No hint.
(default)
.It POSIX_FADV_RANDOM
Random access.
.It POSIX_FADV_SEQUENTIAL
Sequential access.
(from lower offset to higher offset.)
.It POSIX_FADV_WILLNEED
Will be accessed.
.It POSIX_FADV_DONTNEED
Will not be accessed.
.It POSIX_FADV_NOREUSE
Will be accessed just once.
.El
.Pp
Calling
.Fn posix_fadvise
doesn't alter the semantics of the operations,
it is only a matter of performance.
.\" ------------------------------------------------------------
.Sh RETURN VALUES
On success,
.Fn posix_fadvise
returns 0.
Otherwise, it returns an error number.
.\" ------------------------------------------------------------
.Sh SEE ALSO
.Xr errno 2 ,
.Xr madvise 2
.\" ------------------------------------------------------------
.Sh BUGS
For
.Dv POSIX_FADV_NORMAL ,
.Dv POSIX_FADV_RANDOM ,
and
.Dv POSIX_FADV_SEQUENTIAL ,
the current implementation ignores
.Fa offset
and
.Fa size ,
and applies the hint to the whole file.