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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
.TH "POSIX_MADVISE" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" posix_madvise
.SH NAME
posix_madvise \- memory advisory information and alignment control
(\fBADVANCED REALTIME\fP)
.SH SYNOPSIS
.LP
\fB#include <sys/mman.h>
.br
.sp
int posix_madvise(void *\fP\fIaddr\fP\fB, size_t\fP \fIlen\fP\fB,
int\fP \fIadvice\fP\fB); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIposix_madvise\fP() function need only be supported if either
the Memory Mapped Files or the Shared Memory Objects options
are supported.
.LP
The \fIposix_madvise\fP() function shall advise the implementation
on the expected behavior of the application with respect to
the data in the memory starting at address \fIaddr\fP, and continuing
for \fIlen\fP bytes. The implementation may use this
information to optimize handling of the specified data. The \fIposix_madvise\fP()
function shall have no effect on the semantics
of access to memory in the specified range, although it may affect
the performance of access.
.LP
The implementation may require that \fIaddr\fP be a multiple of the
page size, which is the value returned by \fIsysconf\fP() when the
name value _SC_PAGESIZE is used.
.LP
The advice to be applied to the memory range is specified by the \fIadvice\fP
parameter and may be one of the following
values:
.TP 7
POSIX_MADV_NORMAL
.sp
Specifies that the application has no advice to give on its behavior
with respect to the specified range. It is the default
characteristic if no advice is given for a range of memory.
.TP 7
POSIX_MADV_SEQUENTIAL
.sp
Specifies that the application expects to access the specified range
sequentially from lower addresses to higher addresses.
.TP 7
POSIX_MADV_RANDOM
.sp
Specifies that the application expects to access the specified range
in a random order.
.TP 7
POSIX_MADV_WILLNEED
.sp
Specifies that the application expects to access the specified range
in the near future.
.TP 7
POSIX_MADV_DONTNEED
.sp
Specifies that the application expects that it will not access the
specified range in the near future.
.sp
.LP
These values are defined in the \fI<sys/mman.h>\fP header.
.SH RETURN VALUE
.LP
Upon successful completion, \fIposix_madvise\fP() shall return zero;
otherwise, an error number shall be returned to indicate
the error.
.SH ERRORS
.LP
The \fIposix_madvise\fP() function shall fail if:
.TP 7
.B EINVAL
The value of \fIadvice\fP is invalid.
.TP 7
.B ENOMEM
Addresses in the range starting at \fIaddr\fP and continuing for \fIlen\fP
bytes are partly or completely outside the range
allowed for the address space of the calling process.
.sp
.LP
The \fIposix_madvise\fP() function may fail if:
.TP 7
.B EINVAL
The value of \fIaddr\fP is not a multiple of the value returned by
\fIsysconf\fP()
when the name value _SC_PAGESIZE is used.
.TP 7
.B EINVAL
The value of \fIlen\fP is zero.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
The \fIposix_madvise\fP() function is part of the Advisory Information
option and need not be provided on all
implementations.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fImmap\fP() , \fIposix_fadvise\fP() , \fIsysconf\fP() , the Base
Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<sys/mman.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
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