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Add docs for aio_linux vfs module.

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Autobuild-User: Jeremy Allison <jra@samba.org>
Autobuild-Date: Wed Apr 18 07:20:19 CEST 2012 on sn-devel-104
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Jeremy Allison 2012-04-17 20:20:28 -07:00
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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_aio_linux.8">
<refmeta>
<refentrytitle>vfs_aio_linux</refentrytitle>
<manvolnum>8</manvolnum>
<refmiscinfo class="source">Samba</refmiscinfo>
<refmiscinfo class="manual">System Administration tools</refmiscinfo>
<refmiscinfo class="version">3.6</refmiscinfo>
</refmeta>
<refnamediv>
<refname>vfs_aio_linux</refname>
<refpurpose>implement async I/O in Samba vfs using Linux kernel aio calls</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>vfs objects = aio_linux</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>The <command>aio_linux</command> VFS module enables asynchronous
I/O for Samba on Linux kernels that have the kernel AIO calls available
without using the Posix AIO interface. Posix AIO can suffer from severe
limitations. For example, on some Linux versions the
real-time signals that it uses are broken under heavy load.
Other systems only allow AIO when special kernel modules are
loaded or only allow a certain system-wide amount of async
requests being scheduled. Systems based on glibc (most Linux
systems) only allow a single outstanding request per file
descriptor which essentially makes Posix AIO useless on systems
using the glibc implementation.</para>
<para>To work around all these limitations, the aio_linux module
was written. It uses the Linux kernel AIO interface instead of the
internal Posix AIO interface to allow read and write calls
to be processed asynchronously. A queue size of 128 events
is used by default. To change this limit set the "aio num events"
parameter below.
</para>
<para>
Note that the smb.conf parameters <command>aio read size</command>
and <command>aio write size</command> must also be set appropriately
for this module to be active.
</para>
<para>This module MUST be listed last in any module stack as
the Samba VFS pread/pwrite interface is not thread-safe. This
module makes direct pread and pwrite system calls and does
NOT call the Samba VFS pread and pwrite interfaces.</para>
</refsect1>
<refsect1>
<title>EXAMPLES</title>
<para>Straight forward use:</para>
<programlisting>
<smbconfsection name="[cooldata]"/>
<smbconfoption name="path">/data/ice</smbconfoption>
<smbconfoption name="aio read size">1024</smbconfoption>
<smbconfoption name="aio write size">1024</smbconfoption>
<smbconfoption name="vfs objects">aio_linux</smbconfoption>
</programlisting>
</refsect1>
<refsect1>
<title>OPTIONS</title>
<variablelist>
<varlistentry>
<term>aio_linux:aio num events = INTEGER</term>
<listitem>
<para>Set the maximum size of the event queue
that is used to limit outstanding IO requests.
</para>
<para>By default this is set to 128.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>VERSION</title>
<para>This man page is correct for version 3.6.6 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>