diff options
Diffstat (limited to 'man/sd_readahead.xml')
| -rw-r--r-- | man/sd_readahead.xml | 178 |
1 files changed, 178 insertions, 0 deletions
diff --git a/man/sd_readahead.xml b/man/sd_readahead.xml new file mode 100644 index 0000000000..a1fc6f178f --- /dev/null +++ b/man/sd_readahead.xml @@ -0,0 +1,178 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<!-- + This file is part of systemd. + + Copyright 2010 Lennart Poettering + + systemd is free software; you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 2.1 of the License, or + (at your option) any later version. + + systemd is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with systemd; If not, see <http://www.gnu.org/licenses/>. +--> + +<refentry id="sd_notify"> + + <refentryinfo> + <title>sd_readahead</title> + <productname>systemd</productname> + + <authorgroup> + <author> + <contrib>Developer</contrib> + <firstname>Lennart</firstname> + <surname>Poettering</surname> + <email>lennart@poettering.net</email> + </author> + </authorgroup> + </refentryinfo> + + <refmeta> + <refentrytitle>sd_readahead</refentrytitle> + <manvolnum>3</manvolnum> + </refmeta> + + <refnamediv> + <refname>sd_readahead</refname> + <refpurpose>Control ongoing disk boot-time read-ahead operations</refpurpose> + </refnamediv> + + <refsynopsisdiv> + <funcsynopsis> + <funcsynopsisinfo>#include "sd-readahead.h"</funcsynopsisinfo> + + <funcprototype> + <funcdef>int <function>sd_readahead</function></funcdef> + <paramdef>const char *<parameter>action</parameter></paramdef> + </funcprototype> + </funcsynopsis> + </refsynopsisdiv> + + <refsect1> + <title>Description</title> + <para><function>sd_readahead()</function> may be + called by programs involved with early boot-up to + control ongoing boot-time disk read-ahead operations. It may be + used to terminate read-ahead operations in case an + uncommon disk access pattern is to be expected and + hence read-ahead replay or collection is unlikely to + have the desired speed-up effect on the current or + future boot-ups.</para> + + <para>The <parameter>action</parameter> should be one + of the following strings:</para> + + <variablelist> + <varlistentry> + <term>cancel</term> + + <listitem><para>Terminates read-ahead + data collection, and drops all + read-ahead data collected during this + boot-up.</para></listitem> + </varlistentry> + + <varlistentry> + <term>done</term> + + <listitem><para>Terminates read-ahead + data collection, but keeps all + read-ahead data collected during this + boot-up around for use during + subsequent boot-ups.</para></listitem> + </varlistentry> + + <varlistentry> + <term>noreplay</term> + + <listitem><para>Terminates read-ahead + replay.</para></listitem> + </varlistentry> + + </variablelist> + + </refsect1> + + <refsect1> + <title>Return Value</title> + + <para>On failure, these calls return a negative + errno-style error code. It is generally recommended to + ignore the return value of this call.</para> + </refsect1> + + <refsect1> + <title>Notes</title> + + <para>This function is provided by the reference + implementation of APIs for controlling boot-time + read-ahead and distributed with the systemd + package. The algorithm it implements is simple, and + can easily be reimplemented in daemons if it is + important to support this interface without using the + reference implementation.</para> + + <para>Internally, this function creates a file in + <filename>/run/systemd/readahead/</filename> which is + then used as flag file to notify the read-ahead + subsystem.</para> + + <para>For details about the algorithm check the + liberally licensed reference implementation sources: + <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/readahead/sd-readahead.c"/> + and <ulink + url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-readahead.h"/></para> + + <para><function>sd_readahead()</function> is + implemented in the reference implementation's drop-in + <filename>sd-readahead.c</filename> and + <filename>sd-readahead.h</filename> files. It is + recommended that applications consuming this API copy + the implementation into their source tree. For more + details about the reference implementation see + <citerefentry><refentrytitle>sd-readahead</refentrytitle><manvolnum>3</manvolnum></citerefentry></para> + + <para>If -DDISABLE_SYSTEMD is set during compilation + this function will always return 0 and otherwise + become a NOP.</para> + </refsect1> + + <refsect1> + <title>Examples</title> + + <example> + <title>Cancelling all read-ahead operations</title> + + <para>During boots where SELinux has to + relabel the file system hierarchy, it will + create a large amount of disk accesses that + are not necessary during normal boots. Hence + it is a good idea to disable both read-ahead replay and read-ahead collection. + </para> + + <programlisting>sd_readahead("cancel"); +sd_readahead("noreplay");</programlisting> + </example> + + </refsect1> + + <refsect1> + <title>See Also</title> + <para> + <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd-readahead</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry> + </para> + </refsect1> + +</refentry> |