Chapter 8. Modules

+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: +

+NTSTATUS smb_register_passdb(int version, const char *name, pdb_init_function init);
+

+This function will be called by the initialisation function of the module to +register itself. +

Static modules

+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. +

Shared modules

+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. +

Writing modules

+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: +

+NTSTATUS init_module(void);
+

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.

For example, pdb_ldap_init() contains:

+NTSTATUS pdb_ldap_init(void)
+{
+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;
+}
+

Static/Shared selection in configure.in

+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,depfile)
+

The depfile for a certain subsystem is the file that calls the +initialisation functions for the statically built in modules.

+@SUBSYSTEM_MODULES@ in Makefile.in 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. +

Note

+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.

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