JelmerVernooij Samba Team

jelmer@samba.org

19 March 2003 The new modules system has the following advantages: Transparent loading of static and shared modules (no need for a subsystem to know about modules) Simple selection between shared and static modules at configure time "preload modules" option for increasing performance for stable modules No nasty #define stuff anymore All backends are available as plugin now (including pdb_ldap and pdb_tdb) 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: BOOL smb_register_passdb(const char *name, pdb_init_function init, int version); This function will be called by the initialisation function of the module to register itself. 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 include/config.h): /* Static init functions */ #define static_init_pdb { pdb_mysql_init(); pdb_ldap_init(); pdb_smbpasswd_init(); pdb_tdbsam_init(); pdb_guest_init();} These functions should be called before the subsystem is used. That should be done when the subsystem is initialised or first used. 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'. After smb_probe_module() has been executed, the subsystem should check again if the module has been registered. Each module has an initialisation function. For modules that are included with samba this name is 'subsystem_backend_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: int init_module(void); This function should call one or more registration functions. The function should return non-zero on success and zero on failure. For example, pdb_ldap_init() contains: int pdb_ldap_init(void) { smb_register_passdb("ldapsam", pdb_init_ldapsam, PASSDB_INTERFACE_VERSION); smb_register_passdb("ldapsam_nua", pdb_init_ldapsam_nua, PASSDB_INTERFACE_VERSION); return TRUE; } 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. On the bottom of configure.in, SMB_MODULE() should be called for each module and SMB_SUBSYSTEM() for each subsystem. Syntax: SMB_MODULE(subsystem_backend, object files, plugin name, subsystem name, static_action, shared_action) SMB_SUBSYSTEM(subsystem) Also, make sure to add the correct directives to Makefile.in. @SUBSYSTEM_STATIC@ will be replaced with a list of objects files of the modules that need to be linked in statically. @SUBSYSTEM_MODULES@ will be replaced with the names of the plugins to build. You must make sure all .c files that contain defines that can be changed by ./configure are rebuilded in the 'modules_clean' make target. Practically, this means all c files that contain static_init_subsystem; calls need to be rebuilded.