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Add docs for readahead vfs module.

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Jeremy.
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Jeremy Allison 2007-04-06 21:11:48 +00:00 committed by Gerald W. Carter
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<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE refentry PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
<refentry id="vfs_readahead.8">
<refmeta>
<refentrytitle>vfs_readahead</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>vfs_readahead</refname>
<refpurpose>pre-load the kernel buffer cache</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>vfs objects = readahead</command>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>DESCRIPTION</title>
<para>This VFS module is part of the
<citerefentry><refentrytitle>samba</refentrytitle>
<manvolnum>7</manvolnum></citerefentry> suite.</para>
<para>This <command>vfs_readahead</command> VFS module detects
read requests at multiples of a given offset (hex 0x80000 by
default) and then tells the kernel via either the readahead
system call (on Linux) or the posix_fadvise system call to
pre-fetch this data into the buffer cache.</para>
<para>This module is useful for Windows Vista clients reading
data using the Windows Explorer program, which asynchronously
does multiple file read requests at offset boundaries of 0x80000
bytes.</para>
<para>The offset multiple used is given by the readahead:offset
option, which defaults to 0x80000.</para>
<para>The size of the disk read operations performed
by <command>vfs_readahead</command> is determined by the
readahead:length option. By default this is set to the
same value as the readahead:offset option and if not
set explicitly will use the current value of
readahead:offset.</para>
<para>This module is stackable.</para>
</refsect1>
<refsect1>
<title>OPTIONS</title>
<variablelist>
<varlistentry>
<term>readahead:offset = BYTES</term>
<listitem>
<para>The offset multiple that causes readahead to be
requested of the kernel buffer cache.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>readahead:length = BYTES</term>
<listitem>
<para>The number of bytes requested to be
read into the kernel buffer cache on each
readahead call.</para>
</listitem>
</varlistentry>
<para>The following suffixes may be applied to BYTES:</para>
<itemizedlist>
<listitem><para><command>K</command> - BYTES is a number of kilobytes</para></listitem>
<listitem><para><command>M</command> - BYTES is a number of megabytes</para></listitem>
<listitem><para><command>G</command> - BYTES is a number of gigabytes</para></listitem>
</itemizedlist>
</variablelist>
</refsect1>
<refsect1>
<title>EXAMPLES</title>
<programlisting>
<smbconfsection name="[hypothetical]"/>
<smbconfoption name="vfs objects">readahead</smbconfoption>
<smbconfoption name="readahead:length">1M</smbconfoption>
</programlisting>
</refsect1>
<refsect1>
<title>VERSION</title>
<para>This man page is correct for version 3.0.25 of the Samba suite.
</para>
</refsect1>
<refsect1>
<title>AUTHOR</title>
<para>The original Samba software and related utilities
were created by Andrew Tridgell. Samba is now developed
by the Samba Team as an Open Source project similar
to the way the Linux kernel is developed.</para>
</refsect1>
</refentry>