samba-mirror/docs-xml/manpages/vfs_fileid.8.xml

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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_fileid.8">

<refmeta>
	<refentrytitle>vfs_fileid</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_fileid</refname>
	<refpurpose>Generates file_id structs with unique device id values for
	cluster setups. It also adds ways to deliberately break lock coherency for specific inodes</refpurpose>
</refnamediv>

<refsynopsisdiv>
	<cmdsynopsis>
		<command>vfs objects = fileid</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>Samba uses file_id structs to uniquely identify files
	for locking purpose. By default the file_id contains the device
	and inode number returned by the <command>stat()</command> system call.
	As the file_id is a unique identifier of a file, it must be the same
	on all nodes in a cluster setup. This module overloads the
	<command>SMB_VFS_FILE_ID_CREATE()</command> operation and
	generates the device number based on the configured algorithm
	(see the "fileid:algorithm" option).
	</para>

	<para>When using the fsname or fsid algorithm a
	<command>stat()</command> and <command>statfs()</command> call is
	required for all mounted file systems to generate the file_id. If e.g.
	an NFS file system is unresponsive such a call might block and the smbd
	process will become unresponsive. Use the "fileid:fstype deny",
	"fileid:fstype allow", "fileid:mntdir deny", or "fileid:mntdir allow"
	options to ignore potentially unresponsive file systems.
	</para>
</refsect1>


<refsect1>
	<title>OPTIONS</title>

	<variablelist>

		<varlistentry>
		<term>fileid:algorithm = ALGORITHM</term>
		<listitem>
		<para>Available algorithms are <command>fsname</command>,
		<command>fsid</command>, <command>next_module</command>. The default value is
		<command>fsname</command>. As well as the following legacy
		algorithms: <command>fsname_nodirs</command>, <command>fsname_norootdir</command>,
		<command>fsname_norootdir_ext</command> and <command>hostname</command>.
		</para>

		<para>The <command>fsname</command> algorithm generates
		device id by hashing the kernel device name.
		</para>

		<para>The <command>fsid</command> algorithm generates
		the device id from the <command>f_fsid</command> returned
		from the <command>statfs()</command> syscall.
		</para>

		<para>The <command>next_module</command> algorithm lets the next vfs module
		in the module chain generate the id. This is mainly used in combination
		with the various 'nolock' features the fileid module provides.
		</para>

		<para>The legacy <command>hostname</command> algorithm generates unique
		devid by hashing the hostname and low level device id.
		It also implies <command>fileid:nolock_all_inodes=yes</command>.
		This can be used to deliberately break lock coherency in a cluster
		and with <command>fileid:nolock_max_slots</command> also between local processes
		within a node. NOTE: Do not use this without knowing what you are doing!
		It breaks SMB semantics and it can lead to data corruption!
		This implies <command>fileid:nolock_all_inodes=yes</command>.
		</para>

		<para>The legacy <command>fsname_nodirs</command> algorithm is an alias
		for using the <command>fsname</command> algorithm together with
		<command>fileid:nolock_all_dirs=yes</command>.
		NOTE: Do not use this without knowing what you are doing!
		It breaks SMB semantics!
		See <command>fileid:nolock_paths</command> for a more fine grained
		approach.
		</para>

		<para>The legacy <command>fsname_norootdir</command> algorithm is an alias
		for using the <command>fsname</command> algorithm together with
		<command>fileid:nolock_paths= <quote>.</quote> </command>. It means
		this can be used to deliberately break lock coherency
		in a cluster for the root directory of a share.
		</para>

		<para>The legacy <command>fsname_norootdir_ext</command> algorithm is an alias
		for using the <command>fsname</command> algorithm together with
		<command>fileid:nolock_paths= <quote>.</quote></command> and
		<command>fileid:nolock_max_slots = 18446744073709551615</command>.
		It means this can be used to deliberately break lock coherency
		completely for the root directory of a share. Even local processes
		are no longer lock coherent.
		</para>

		</listitem>
		</varlistentry>

		<varlistentry>
		<term>fileid:mapping = ALGORITHM</term>
		<listitem>
		<para>This option is the legacy version of the
		<command>fileid:algorithm</command> option, which was used in earlier
		versions of fileid mapping feature in custom Samba 3.0 versions.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>fileid:fstype deny = LIST</term>
		<listitem>
		<para>List of file system types to be ignored for file_id
		generation.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>fileid:fstype allow = LIST</term>
		<listitem>
		<para>List of file system types to be allowed for file_id
		generation. If this option is set, file system types not listed
		here are ignored.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>fileid:mntdir deny = LIST</term>
		<listitem>
		<para>List of file system mount points to be ignored for
		file_id	generation.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>fileid:mntdir allow = LIST</term>
		<listitem>
		<para>List of file system mount points to be allowed for file_id
		generation. If this option is set, file system mount points
		not listed here are ignored.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>fileid:nolock_max_slots = NUMBER(1-18446744073709551615)</term>
		<listitem>
		<para>This option alters the behavior of the <command>nolock</command> algorithm
		in a way that it also breaks the lock coherency between individual processes
		on the same host. The default is to have just 1 concurrent slot available per host.
		By increasing the number of slots you can specify how many concurrent processes
		can work on a given inode without contention, the number should typically be larger
		than the number of logical cpus, maybe 2 times num_cpus.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>fileid:nolock_all_dirs = BOOL</term>
		<listitem>
		<para>This option triggers the use of the fileid nolock behavior
		for all directory inodes, which can be used to deliberately break
		the lock coherency for all directories.
		NOTE: Do not use this without knowing what you are doing!
		It breaks SMB semantics!
		See <command>fileid:nolock_paths</command> for a more fine grained
		approach.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>fileid:nolock_all_inodes = BOOL</term>
		<listitem>
		<para>This option triggers the use of the fileid nolock algorithm
		for all directoriy inode, which can be used to deliberately break
		the lock coherency for all directories.
		NOTE: Do not use this without knowing what you are doing!
		It breaks SMB semantics and it can lead to data corruption!
		See <command>fileid:nolock_paths</command> for a more fine grained
		approach.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>fileid:nolock_paths = LIST</term>
		<listitem>
		<para>This option specifies a path list referring to files and/or directories,
		which should use fileid nolock algorithm in order to deliberately break
		the lock coherency for them. The specified paths can be relative to
		the share root directory or absolute. The names are case sensitive unix pathnames!
		Note all paths are only evaluated at tree connect time, when the share is being connected, from there on
		only the related device and inode numbers from the stat() syscall are compared.
		Non existing paths will generate a log level 0 message.
		NOTE: This option should be used with care as it breaks SMB semantics!
		But it may help in situation where a specific (commonly read-only) inode is highly contended.
		</para>
		</listitem>
		</varlistentry>

		<varlistentry>
		<term>fileid:nolockinode = NUMBER</term>
		<listitem>
		<para>This legacy option triggers use of the fileid nolock behavior
		for the configured inode, while ignoring and device id. This can be used to deliberately break
		lock coherency for the corresponding file or directory in a
		cluster. Using the <command>fileid:nolock_paths</command> option is much more flexible and simpler to use.
		</para>
		</listitem>
		</varlistentry>
	</variablelist>
</refsect1>

<refsect1>
	<title>EXAMPLES</title>

	<para>Usage of the <command>fileid</command> module with the
	<command>fsid</command> algorithm:</para>

<programlisting>
        <smbconfsection name="[global]"/>
	<smbconfoption name="vfs objects">fileid</smbconfoption>
	<smbconfoption name="fileid:algorithm">fsid</smbconfoption>
</programlisting>

	<para>Usage of the <command>fileid</command> module in order
	avoid load on heavily contended (most likely read-only) inodes.</para>

<programlisting>
        <smbconfsection name="[global]"/>
	<smbconfoption name="vfs objects">fileid</smbconfoption>
	<smbconfoption name="fileid:algorithm">next_module</smbconfoption>
	<smbconfoption name="fileid:nolock_paths">. ContendedFolder1 /path/to/contended.exe</smbconfoption>
	<smbconfoption name="fileid:nolock_max_slots">256</smbconfoption>
</programlisting>

</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>

</refsect1>

</refentry>