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<!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_preopen.8">

<refmeta>
	<refentrytitle>vfs_preopen</refentrytitle>
	<manvolnum>8</manvolnum>
	<refmiscinfo class="source">Samba</refmiscinfo>
	<refmiscinfo class="manual">System Administration tools</refmiscinfo>
	<refmiscinfo class="version">&doc.version;</refmiscinfo>
</refmeta>

<refnamediv>
	<refname>vfs_preopen</refname>
	<refpurpose>Hide read latencies for applications reading numbered files</refpurpose>
</refnamediv>

<refsynopsisdiv>
	<cmdsynopsis>
		<command>vfs objects = preopen</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 module assists applications that want to read numbered
	files in sequence with very strict latency requirements. One area
	where this happens in video streaming applications that want to read
	one file per frame.</para>

	<para>When you use this module, a number of helper processes is
	started that speculatively open files and read a number of bytes to
	prime the file system cache, so that later on when the real
	application's request comes along, no disk access is necessary.</para>

	<para>This module is stackable.</para>

</refsect1>


<refsect1>
	<title>OPTIONS</title>

	<variablelist>

		<varlistentry>
		<term>preopen:posix-basic-regex = BOOL (default: no)</term>
		<listitem>
		<para>
		<command>preopen:posix-basic-regex = yes</command> changes
		the meaning of the <command>preopen:names</command> option.
		Further details are described there.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>preopen:names = /pattern1/pattern2/</term>
		<listitem>
		<para>
		preopen:names specifies the file name pattern(s) which should
		trigger the preopen helpers to do their work. We assume that
		the files are numbered incrementally. So if your file names
		are numbered FRAME00000.frm FRAME00001.frm and so on you would
		list them as <command>preopen:names=/FRAME*.frm/</command>.
		The default algorithm uses the first (at least 3) digits it finds
		in order to calculate the name of the next frames.
		</para>

		<para><command>preopen:posix-basic-regex = yes</command> changes
		the meaning of the <command>preopen:names</command> option.
		It means 'POSIX Basic Regular Expression' strings are used
		as patterns. The key is each pattern requires exactly one
		'subexpression' starting with '\(' and ending with '\)' in
		order to specify the position of the digits representing
		the incrementing frame numbers. Given a file names like
		Movie7599Frame0v1234.txt, Movie7599Frame1v1234.txt, Movie7599Frame2v1234.txt
		up to Movie7599Frame9v1234.txt you can use <command>preopen:names = /.*Frame\([0-9]\).*\.txt/</command>
		in order to match just a single digits, this might not be a real world example,
		but it shows the flexiblity that is possible here.
		</para>

		</listitem>
		</varlistentry>

		<varlistentry>
		<term>preopen:num_bytes = BYTES</term>
		<listitem>
		<para>
		Specifies the number of bytes the helpers should speculatively
		read, defaults to 1.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>preopen:helpers = NUM-PROCS</term>
		<listitem>
		<para>
		Number of forked helper processes, defaults to 1.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>preopen:queuelen = NUM-FILES</term>
		<listitem>
		<para>
		Number of files that should be speculatively opened. Defaults
		to the 10 subsequent files.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>preopen:nomatch_log_level = LOGLEVEL</term>
		<listitem>
		<para>
		In order to debug or audit the usage of the preopen logic
		you can use this option to specify at what log level details
		about filenames not matching any pattern from '<command>preopen:names</command>'
		are logged.
		</para>
		<para>
		Defaults to the log level 5.
		See also <citerefentry><refentrytitle>smb.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
		in the '<smbconfoption name="log level"/>' section
		for special handling of the 'preopen' debug class.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>preopen:match_log_level = LOGLEVEL</term>
		<listitem>
		<para>
		In order to debug or audit the usage of the preopen logic
		you can use this option to specify at what log level details
		about filenames actually matching a pattern from '<command>preopen:names</command>'
		are logged.
		</para>
		<para>
		See also '<command>preopen:founddigits_log_level</command>' and '<command>preopen:push_log_level</command>'.
		</para>
		<para>
		Defaults to the log level 5.
		See also <citerefentry><refentrytitle>smb.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
		in the '<smbconfoption name="log level"/>' section
		for special handling of the 'preopen' debug class.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>preopen:nodigits_log_level = LOGLEVEL</term>
		<listitem>
		<para>
		In order to debug or audit problems with the preopen configuration
		you can use this option to specify at what log level details
		about filenames actually matching a pattern from '<command>preopen:names</command>',
		but at the same time don't contain the expected digits, are logged.
		This is typically something the administrator wants to notice and
		adjust the configuration in order to define more precisely where to
		find the digits in the filename.
		</para>
		<para>
		Defaults to the log level 1.
		See also <citerefentry><refentrytitle>smb.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
		in the '<smbconfoption name="log level"/>' section
		for special handling of the 'preopen' debug class.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>preopen:founddigits_log_level = LOGLEVEL</term>
		<listitem>
		<para>
		In order to debug or audit the usage of the preopen logic
		you can use this option to specify at what log level details
		about filenames actually matching a pattern from '<command>preopen:names</command>',
		and at the same time having valid expected digits, are logged. This means enough information is available
		in order to queue preopens.
		</para>
		<para>
		Defaults to the log level 3.
		See also <citerefentry><refentrytitle>smb.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
		in the '<smbconfoption name="log level"/>' section
		for special handling of the 'preopen' debug class.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>preopen:reset_log_level = LOGLEVEL</term>
		<listitem>
		<para>
		If a matching filename belongs to a different pattern from '<command>preopen:names</command>',
		a different parent directory or differs in a significant way from the last filename
		that was found before, the module needs to reset it's internal queue state.
		This means that no more preopens will be pushed to helper processes belonging to the
		former queue state. In order to debug or audit such queue resets you can use this option to specify at what
		log level details are logged.
		</para>
		<para>
		Defaults to the log level 5.
		See also <citerefentry><refentrytitle>smb.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
		in the '<smbconfoption name="log level"/>' section
		for special handling of the 'preopen' debug class.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>preopen:push_log_level = LOGLEVEL</term>
		<listitem>
		<para>
		In order to debug or audit the usage of the preopen logic
		you can use this option to specify at what log level details
		about filenames actually pushed to preopen helper processes are logged.
		This means they will actually be preopened soon.
		</para>
		<para>
		Defaults to the log level 3.
		See also <citerefentry><refentrytitle>smb.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
		in the '<smbconfoption name="log level"/>' section
		for special handling of the 'preopen' debug class.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>preopen:queue_log_level = LOGLEVEL</term>
		<listitem>
		<para>
		In order to debug details about internal queue processing
		you can use this option to specify at what log level the details are logged.
		</para>
		<para>
		Defaults to the log level 10.
		See also <citerefentry><refentrytitle>smb.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
		in the '<smbconfoption name="log level"/>' section
		for special handling of the 'preopen' debug class.
		</para>
		</listitem>
		</varlistentry>

	</variablelist>
</refsect1>

<refsect1>
	<title>VERSION</title>
	<para>This man page is part of version &doc.version; 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>

	<para>The PREOPEN VFS module was created with contributions from
	Volker Lendecke and the developers at IBM.
	</para>
</refsect1>

</refentry>