2004-11-03 13:51:07 +00:00
|
|
|
.\" Hey Emacs! This file is -*- nroff -*- source.
|
|
|
|
.\"
|
|
|
|
.\" Copyright 2003 Abhijit Menon-Sen <ams@wiw.org>
|
|
|
|
.\" Permission is granted to make and distribute verbatim copies of this
|
|
|
|
.\" manual provided the copyright notice and this permission notice are
|
|
|
|
.\" preserved on all copies.
|
|
|
|
.\"
|
|
|
|
.\" Permission is granted to copy and distribute modified versions of this
|
|
|
|
.\" manual under the conditions for verbatim copying, provided that the
|
|
|
|
.\" entire resulting derived work is distributed under the terms of a
|
|
|
|
.\" permission notice identical to this one.
|
2007-04-12 22:42:49 +00:00
|
|
|
.\"
|
2004-11-03 13:51:07 +00:00
|
|
|
.\" Since the Linux kernel and libraries are constantly changing, this
|
|
|
|
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
|
|
|
.\" responsibility for errors or omissions, or for damages resulting from
|
|
|
|
.\" the use of the information contained herein. The author(s) may not
|
|
|
|
.\" have taken the same level of care in the production of this manual,
|
|
|
|
.\" which is licensed free of charge, as they might when working
|
|
|
|
.\" professionally.
|
2007-04-12 22:42:49 +00:00
|
|
|
.\"
|
2004-11-03 13:51:07 +00:00
|
|
|
.\" Formatted or processed versions of this manual, if unaccompanied by
|
|
|
|
.\" the source, must acknowledge the copyright and authors of this work.
|
|
|
|
.\"
|
2005-04-11 15:04:27 +00:00
|
|
|
.\" 2005-04-08 mtk, noted kernel version and added BUGS
|
|
|
|
.\"
|
2007-05-30 05:36:26 +00:00
|
|
|
.TH POSIX_FADVISE 2 2003-02-14 "Linux" "Linux Programmer's Manual"
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH NAME
|
|
|
|
posix_fadvise \- predeclare an access pattern for file data
|
|
|
|
.SH SYNOPSIS
|
|
|
|
.nf
|
2006-03-01 03:29:07 +00:00
|
|
|
.B #define _XOPEN_SOURCE 600
|
2004-11-03 13:51:07 +00:00
|
|
|
.B #include <fcntl.h>
|
|
|
|
.sp
|
|
|
|
.BI "int posix_fadvise(int " fd ", off_t " offset ", off_t " len ", int " advice ");"
|
|
|
|
.fi
|
|
|
|
.SH DESCRIPTION
|
2007-05-12 09:06:04 +00:00
|
|
|
Programs can use
|
|
|
|
.BR posix_fadvise ()
|
|
|
|
to announce an intention to access
|
2004-11-03 13:51:07 +00:00
|
|
|
file data in a specific pattern in the future, thus allowing the kernel
|
2007-06-08 09:56:56 +00:00
|
|
|
to perform appropriate optimizations.
|
2004-11-03 13:51:07 +00:00
|
|
|
|
|
|
|
The \fIadvice\fP applies to a (not necessarily existent) region starting
|
|
|
|
at \fIoffset\fP and extending for \fIlen\fP bytes (or until the end of
|
2007-04-12 22:42:49 +00:00
|
|
|
the file if \fIlen\fP is 0) within the file referred to by \fIfd\fP.
|
|
|
|
The advice is not binding; it merely constitutes an expectation on behalf of
|
2004-11-03 13:51:07 +00:00
|
|
|
the application.
|
|
|
|
|
|
|
|
Permissible values for \fIadvice\fP include:
|
|
|
|
.TP
|
|
|
|
.B POSIX_FADV_NORMAL
|
|
|
|
Indicates that the application has no advice to give about its access
|
2007-04-12 22:42:49 +00:00
|
|
|
pattern for the specified data.
|
|
|
|
If no advice is given for an open file,
|
2004-11-03 13:51:07 +00:00
|
|
|
this is the default assumption.
|
|
|
|
.TP
|
|
|
|
.B POSIX_FADV_SEQUENTIAL
|
|
|
|
The application expects to access the specified data sequentially (with
|
|
|
|
lower offsets read before higher ones).
|
|
|
|
.TP
|
|
|
|
.B POSIX_FADV_RANDOM
|
|
|
|
The specified data will be accessed in random order.
|
|
|
|
.TP
|
|
|
|
.B POSIX_FADV_NOREUSE
|
|
|
|
The specified data will be accessed only once.
|
|
|
|
.TP
|
|
|
|
.B POSIX_FADV_WILLNEED
|
|
|
|
The specified data will be accessed in the near future.
|
|
|
|
.TP
|
|
|
|
.B POSIX_FADV_DONTNEED
|
|
|
|
The specified data will not be accessed in the near future.
|
|
|
|
.SH "RETURN VALUE"
|
2007-04-12 22:42:49 +00:00
|
|
|
On success, zero is returned.
|
2007-03-11 07:08:35 +00:00
|
|
|
On error, an error number is returned.
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH ERRORS
|
|
|
|
.TP
|
|
|
|
.B EBADF
|
|
|
|
The \fIfd\fP argument was not a valid file descriptor.
|
|
|
|
.TP
|
|
|
|
.B EINVAL
|
|
|
|
An invalid value was specified for \fIadvice\fP.
|
|
|
|
.TP
|
|
|
|
.B ESPIPE
|
2007-06-22 17:16:20 +00:00
|
|
|
The specified file descriptor refers to a pipe or FIFO.
|
|
|
|
(Linux actually
|
|
|
|
returns
|
|
|
|
.B EINVAL
|
|
|
|
in this case.)
|
2007-05-18 16:06:42 +00:00
|
|
|
.SH VERSIONS
|
2005-10-19 06:54:38 +00:00
|
|
|
.BR posix_fadvise ()
|
2005-04-11 15:04:27 +00:00
|
|
|
appeared in kernel 2.5.60.
|
2007-06-05 06:54:26 +00:00
|
|
|
Glibc support has been provided since version 2.2.
|
2005-04-11 15:04:27 +00:00
|
|
|
.\" Actually as fadvise64() -- MTK
|
2007-05-18 16:06:42 +00:00
|
|
|
.SH "CONFORMING TO"
|
|
|
|
POSIX.1-2001.
|
|
|
|
Note that the type of the
|
|
|
|
.I len
|
|
|
|
parameter was changed from
|
|
|
|
.I size_t
|
|
|
|
to
|
|
|
|
.I off_t
|
|
|
|
in POSIX.1-2003 TC1.
|
|
|
|
.SH NOTES
|
2004-11-03 13:51:07 +00:00
|
|
|
Under Linux, \fBPOSIX_FADV_NORMAL\fP sets the readahead window to the
|
|
|
|
default size for the backing device; \fBPOSIX_FADV_SEQUENTIAL\fP doubles
|
|
|
|
this size, and \fBPOSIX_FADV_RANDOM\fP disables file readahead entirely.
|
2005-07-05 13:50:51 +00:00
|
|
|
These changes affect the entire file, not just the specified region
|
2004-11-03 13:51:07 +00:00
|
|
|
(but other open file handles to the same file are unaffected).
|
|
|
|
|
2006-09-26 12:41:08 +00:00
|
|
|
\fBPOSIX_FADV_WILLNEED\fP initiates a
|
2007-04-12 22:42:49 +00:00
|
|
|
non-blocking read of the specified region into the page cache.
|
|
|
|
The amount of data read may be decreased by the kernel depending
|
|
|
|
on virtual memory load.
|
|
|
|
(A few megabytes will usually be fully satisfied,
|
2006-09-26 12:41:08 +00:00
|
|
|
and more is rarely useful.)
|
|
|
|
|
2007-04-12 22:42:49 +00:00
|
|
|
In kernels before 2.6.18, \fBPOSIX_FADV_NOREUSE\fP had the
|
2006-09-26 12:41:08 +00:00
|
|
|
same semantics as \fBPOSIX_FADV_WILLNEED\fP.
|
|
|
|
This was probably a bug; since kernel 2.6.18, this flag is a no-op.
|
2004-11-03 13:51:07 +00:00
|
|
|
|
|
|
|
\fBPOSIX_FADV_DONTNEED\fP attempts to free cached pages associated with
|
2007-04-12 22:42:49 +00:00
|
|
|
the specified region.
|
|
|
|
This is useful, for example, while streaming large
|
|
|
|
files.
|
|
|
|
A program may periodically request the kernel to free cached data
|
2004-11-03 13:51:07 +00:00
|
|
|
that has already been used, so that more useful cached pages are not
|
|
|
|
discarded instead.
|
|
|
|
|
|
|
|
Pages that have not yet been written out will be unaffected, so if the
|
|
|
|
application wishes to guarantee that pages will be released, it should
|
2007-05-12 09:06:04 +00:00
|
|
|
call
|
|
|
|
.BR fsync (2)
|
|
|
|
or
|
|
|
|
.BR fdatasync (2)
|
|
|
|
first.
|
2005-04-11 15:04:27 +00:00
|
|
|
.SH BUGS
|
2007-04-12 22:42:49 +00:00
|
|
|
In kernels before 2.6.6, if
|
2005-04-11 15:04:27 +00:00
|
|
|
.I len
|
|
|
|
was specified as 0, then this was interpreted literally as "zero bytes",
|
|
|
|
rather than as meaning "all bytes through to the end of the file".
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH "SEE ALSO"
|
2006-05-29 05:47:49 +00:00
|
|
|
.BR readahead (2),
|
2007-12-10 15:03:27 +00:00
|
|
|
.BR posix_fallocate (3),
|
2008-04-28 18:27:36 +00:00
|
|
|
.BR posix_madvise (3),
|
|
|
|
.\" FIXME . Write a posix_fadvise(3) page.
|
2007-01-28 20:00:24 +00:00
|
|
|
.BR feature_test_macros (7)
|