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diff --git a/docs-xml/Samba-Developers-Guide/modules.xml b/docs-xml/Samba-Developers-Guide/modules.xml new file mode 100644 index 0000000..24f326c --- /dev/null +++ b/docs-xml/Samba-Developers-Guide/modules.xml @@ -0,0 +1,176 @@ +<?xml version="1.0" encoding="iso-8859-1"?> +<!DOCTYPE chapter PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc"> +<chapter id="modules"> +<chapterinfo> + <author> + <firstname>Jelmer</firstname><surname>Vernooij</surname> + <affiliation> + <orgname>Samba Team</orgname> + <address><email>jelmer@samba.org</email></address> + </affiliation> + </author> + <pubdate> 19 March 2003 </pubdate> +</chapterinfo> + +<title>Modules</title> + +<sect1> +<title>Advantages</title> + +<para> +The new modules system has the following advantages: +</para> + +<simplelist> +<member>Transparent loading of static and shared modules (no need +for a subsystem to know about modules)</member> +<member>Simple selection between shared and static modules at configure time</member> +<member>"preload modules" option for increasing performance for stable modules</member> +<member>No nasty #define stuff anymore</member> +<member>All backends are available as plugin now (including pdb_ldap and pdb_tdb)</member> +</simplelist> +</sect1> + +<sect1> +<title>Loading modules</title> + +<para> +Some subsystems in samba use different backends. These backends can be +either statically linked in to samba or available as a plugin. A subsystem +should have a function that allows a module to register itself. For example, +the passdb subsystem has: +</para> + +<para><programlisting> +NTSTATUS smb_register_passdb(int version, const char *name, pdb_init_function init); +</programlisting></para> + +<para> +This function will be called by the initialisation function of the module to +register itself. +</para> + +<sect2> +<title>Static modules</title> + +<para> +The modules system compiles a list of initialisation functions for the +static modules of each subsystem. This is a define. For example, +it is here currently (from <filename>include/config.h</filename>): +</para> + +<para><programlisting> +/* Static init functions */ +#define static_init_pdb { pdb_mysql_init(); pdb_ldap_init(); pdb_smbpasswd_init(); pdb_tdbsam_init(); pdb_guest_init();} +</programlisting></para> + +<para> +These functions should be called before the subsystem is used. That +should be done when the subsystem is initialised or first used. +</para> + +</sect2> + +<sect2> +<title>Shared modules</title> + +<para> +If a subsystem needs a certain backend, it should check if it has +already been registered. If the backend hasn't been registered already, +the subsystem should call smb_probe_module(char *subsystem, char *backend). +This function tries to load the correct module from a certain path +($LIBDIR/subsystem/backend.so). If the first character in 'backend' +is a slash, smb_probe_module() tries to load the module from the +absolute path specified in 'backend'. +</para> + +<para>After smb_probe_module() has been executed, the subsystem +should check again if the module has been registered. +</para> + +</sect2> +</sect1> + +<sect1> +<title>Writing modules</title> + +<para> +Each module has an initialisation function. For modules that are +included with samba this name is '<replaceable>subsystem</replaceable>_<replaceable>backend</replaceable>_init'. For external modules (that will never be built-in, but only available as a module) this name is always 'init_module'. (In the case of modules included with samba, the configure system will add a #define subsystem_backend_init() init_module()). +The prototype for these functions is: +</para> + +<para><programlisting> +NTSTATUS init_module(TALLOC_CTX *); +</programlisting></para> + +<para>This function should call one or more +registration functions. The function should return NT_STATUS_OK on success and +NT_STATUS_UNSUCCESSFUL or a more useful nt error code on failure.</para> + +<para>For example, pdb_ldap_init() contains: </para> + +<para><programlisting> +NTSTATUS pdb_ldap_init(TALLOC_CTX *) +{ +smb_register_passdb(PASSDB_INTERFACE_VERSION, "ldapsam", pdb_init_ldapsam); +smb_register_passdb(PASSDB_INTERFACE_VERSION, "ldapsam_nua", pdb_init_ldapsam_nua); + return NT_STATUS_OK; +} +</programlisting></para> + +<para> +The TALLOC_CTX pointer passed as a parameter must be a long-lived context, +that will stay around for as long as the program that loads the module +exists. It allows the caller to taloc_free any long lived data the +module choses to place on this context on program exit (giving a cleaner +valgrind trace). It should be used by modules in place of talloc_autofree_context(), +use of which makes programs thread-unsafe. Modules that don't care about +free on exist should use the NULL talloc context. +</para> + +<sect2> +<title>Static/Shared selection in configure.in</title> + +<para> +Some macros in configure.in generate the various defines and substs that +are necessary for the system to work correct. All modules that should +be built by default have to be added to the variable 'default_modules'. +For example, if ldap is found, pdb_ldap is added to this variable. +</para> + +<para> +On the bottom of configure.in, SMB_MODULE() should be called +for each module and SMB_SUBSYSTEM() for each subsystem. +</para> + +<para>Syntax:</para> + +<para><programlisting> +SMB_MODULE(<replaceable>subsystem</replaceable>_<replaceable>backend</replaceable>, <replaceable>object files</replaceable>, <replaceable>plugin name</replaceable>, <replaceable>subsystem name</replaceable>, <replaceable>static_action</replaceable>, <replaceable>shared_action</replaceable>) +SMB_SUBSYSTEM(<replaceable>subsystem</replaceable>,<replaceable>depfile</replaceable>) +</programlisting></para> + +<para>The depfile for a certain subsystem is the file that calls the +initialisation functions for the statically built in modules.</para> + +<para> +<replaceable>@SUBSYSTEM_MODULES@</replaceable> in Makefile.in will +be replaced with the names of the plugins to build. +</para> + +<para>You must make sure all .c files that contain defines that can +be changed by ./configure are rebuilt in the 'modules_clean' make target. +Practically, this means all c files that contain <command>static_init_subsystem;</command> calls need to be rebuilt. +</para> + +<note> +<para> +There currently also is a configure.in command called SMB_MODULE_PROVIVES(). +This is used for modules that register multiple things. It should not +be used as probing will most likely disappear in the future.</para> +</note> + +</sect2> +</sect1> +</chapter> |