minix/lib/libc/sys/posix_fadvise.2

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.\" $NetBSD: posix_fadvise.2,v 1.5 2013/02/04 20:03:11 wiz Exp $
.\"
.\" Copyright (c)2006,2009 YAMAMOTO Takashi,
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
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.\" 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
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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 followings.
.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.