lib: add hook infrastructure

Please refer to lib/hook.h for a description/documentation.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

lib/Makefile.am

@@ -33,6 +33,7 @@ libfrr_la_SOURCES = \
 	strlcpy.c \
 	strlcat.c \
 	module.c \
+	hook.c \
 	# end
 
 BUILT_SOURCES = route_types.h gitversion.h command_parse.h command_lex.h
@@ -57,6 +58,7 @@ pkginclude_HEADERS = \
 	spf_backoff.h \
 	srcdest_table.h \
 	module.h \
+	hook.h \
 	libfrr.h \
 	# end
 

lib/hook.c

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2016  David Lamparter, for NetDEF, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include "memory.h"
+#include "hook.h"
+
+DEFINE_MTYPE_STATIC(LIB, HOOK_ENTRY, "Hook entry")
+
+void _hook_register(struct hook *hook, void *funcptr, void *arg, bool has_arg,
+		    struct frrmod_runtime *module, const char *funcname)
+{
+	struct hookent *he = XCALLOC(MTYPE_HOOK_ENTRY, sizeof(*he));
+	he->hookfn = funcptr;
+	he->hookarg = arg;
+	he->has_arg = has_arg;
+	he->module = module;
+	he->fnname = funcname;
+
+	he->next = hook->entries;
+	hook->entries = he;
+}
+
+void _hook_unregister(struct hook *hook, void *funcptr,
+		      void *arg, bool has_arg)
+{
+	struct hookent *he, **prev;
+
+	for (prev = &hook->entries; (he = *prev) != NULL; prev = &he->next)
+		if (he->hookfn == funcptr && he->hookarg == arg
+				&& he->has_arg == has_arg)
+		{
+			*prev = he->next;
+			XFREE(MTYPE_HOOK_ENTRY, he);
+			break;
+		}
+}
+

lib/hook.h

@@ -0,0 +1,187 @@
+/*
+ * Copyright (c) 2016  David Lamparter, for NetDEF, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef _FRR_HOOK_H
+#define _FRR_HOOK_H
+
+#include <stdbool.h>
+
+#include "module.h"
+#include "memory.h"
+
+/* type-safe subscribable hook points
+ *
+ * where "type-safe" applies to the function pointers used for subscriptions
+ *
+ * overall usage:
+ * - to create a hook:
+ *
+ *   mydaemon.h:
+ *     #include "hook.h"
+ *     DECLARE_HOOK (some_update_event, (struct eventinfo *info), (info))
+ *
+ *   mydaemon.c:
+ *     DEFINE_HOOK (some_update_event, (struct eventinfo *info), (info))
+ *     ...
+ *     hook_call (some_update_event, info)
+ *
+ * Note:  the second and third macro args must be the hook function's
+ * parameter list, with the same names for each parameter.  The second
+ * macro arg is with types (used for defining things), the third arg is
+ * just the names (used for passing along parameters).
+ *
+ * Do not use parameter names starting with "hook", these can collide with
+ * names used by the hook code itself.
+ *
+ * The return value is always "int" for now;  hook_call will sum up the
+ * return values from each registered user.  Default is 0.
+ *
+ * There are no pre-defined semantics for the value, in most cases it is
+ * ignored.  For success/failure indication, 0 should be success, and
+ * handlers should make sure to only return 0 or 1 (not -1 or other values).
+ *
+ *
+ * - to use a hook / create a handler:
+ *
+ *     #include "mydaemon.h"
+ *     int event_handler (struct eventinfo *info) { ... }
+ *     hook_register (some_update_event, event_handler);
+ *
+ *   or, if you need an argument to be passed along (addonptr will be added
+ *   as first argument when calling the handler):
+ *
+ *     #include "mydaemon.h"
+ *     int event_handler (void *addonptr, struct eventinfo *info) { ... }
+ *     hook_register_arg (some_update_event, event_handler, addonptr);
+ *
+ *   (addonptr isn't typesafe, but that should be manageable.)
+ */
+
+/* TODO:
+ * - hook_unregister_all_module()
+ * - introspection / CLI / debug
+ * - testcases ;)
+ *
+ * For loadable modules, the idea is that hooks could be automatically
+ * unregistered when a module is unloaded.
+ *
+ * It's also possible to add a constructor (MTYPE style) to DEFINE_HOOK,
+ * which would make it possible for the CLI to show all hooks and all
+ * registered handlers.
+ */
+
+struct hookent {
+	struct hookent *next;
+	void *hookfn;		/* actually a function pointer */
+	void *hookarg;
+	bool has_arg;
+	struct frrmod_runtime *module;
+	const char *fnname;
+};
+
+struct hook {
+	const char *name;
+	struct hookent *entries;
+};
+
+/* subscribe/add callback function to a hook
+ *
+ * always use hook_register(), which uses the static inline helper from
+ * DECLARE_HOOK in order to get type safety
+ */
+extern void _hook_register(struct hook *hook, void *funcptr, void *arg,
+			   bool has_arg, struct frrmod_runtime *module,
+			   const char *funcname);
+#define hook_register(hookname, func) \
+	_hook_register(&_hook_ ## hookname, \
+			_hook_typecheck_ ## hookname (func), \
+			NULL, false, THIS_MODULE, #func)
+#define hook_register_arg(hookname, func, arg) \
+	_hook_register(&_hook_ ## hookname, \
+			_hook_typecheck_arg_ ## hookname (func), \
+			arg, true, THIS_MODULE, #func)
+
+extern void _hook_unregister(struct hook *hook, void *funcptr, void *arg,
+			     bool has_arg);
+#define hook_unregister(hookname, func) \
+	_hook_unregister(&_hook_ ## hookname, \
+			_hook_typecheck_ ## hookname (func), NULL, false)
+#define hook_unregister_arg(hookname, func, arg) \
+	_hook_unregister(&_hook_ ## hookname, \
+			_hook_typecheck_arg_ ## hookname (func), arg, true)
+
+/* invoke hooks
+ * this is private (static) to the file that has the DEFINE_HOOK statement
+ */
+#define hook_call(hookname, ...) \
+	hook_call_ ## hookname (__VA_ARGS__)
+
+/* helpers to add the void * arg */
+#define HOOK_ADDDEF(...) (void *hookarg , ## __VA_ARGS__)
+#define HOOK_ADDARG(...) (hookarg , ## __VA_ARGS__)
+
+/* use in header file - declares the hook and its arguments
+ * usage:  DECLARE_HOOK(my_hook, (int arg1, struct foo *arg2), (arg1, arg2))
+ * as above, "passlist" must use the same order and same names as "arglist"
+ *
+ * theoretically passlist is not neccessary, but let's keep things simple and
+ * use exact same args on DECLARE and DEFINE.
+ */
+#define DECLARE_HOOK(hookname, arglist, passlist) \
+	extern struct hook _hook_ ## hookname; \
+	__attribute__((unused)) \
+	static void *_hook_typecheck_ ## hookname ( \
+			int (*funcptr) arglist) { \
+		return (void *)funcptr; } \
+	__attribute__((unused)) \
+	static void *_hook_typecheck_arg_ ## hookname ( \
+			int (*funcptr) HOOK_ADDDEF arglist) { \
+		return (void *)funcptr; }
+
+/* use in source file - contains hook-related definitions.
+ */
+#define DEFINE_HOOK(hookname, arglist, passlist) \
+	struct hook _hook_ ## hookname = { \
+		.name = #hookname, \
+		.entries = NULL, \
+	}; \
+	static int hook_call_ ## hookname arglist { \
+		int hooksum = 0; \
+		struct hookent *he = _hook_ ## hookname .entries; \
+		void *hookarg; \
+		union { \
+			void *voidptr; \
+			int (*fptr) arglist; \
+			int (*farg) HOOK_ADDDEF arglist; \
+		} hookp; \
+		for (; he; he = he->next) { \
+			hookarg = he->hookarg; \
+			hookp.voidptr = he->hookfn; \
+			if (!he->has_arg) \
+				hooksum += hookp.fptr passlist; \
+			else \
+				hooksum += hookp.farg HOOK_ADDARG passlist; \
+		} \
+		return hooksum; \
+	}
+
+#endif /* _FRR_HOOK_H */

lib/libfrr.c

@@ -30,6 +30,8 @@
 #include "log_int.h"
 #include "module.h"
 
+DEFINE_HOOK(frr_late_init, (struct thread_master *tm), (tm))
+
 const char frr_sysconfdir[] = SYSCONFDIR;
 const char frr_vtydir[] = DAEMON_VTY_DIR;
 
@@ -311,9 +313,9 @@ int frr_getopt(int argc, char * const argv[], int *longindex)
 	return opt;
 }
 
+static struct thread_master *master;
 struct thread_master *frr_init(void)
 {
-	struct thread_master *master;
 	struct option_chain *oc;
 	struct frrmod_runtime *module;
 	char moderr[256];
@@ -354,6 +356,8 @@ struct thread_master *frr_init(void)
 
 void frr_config_fork(void)
 {
+	hook_call(frr_late_init, master);
+
 	if (di->instance) {
 		snprintf(config_default, sizeof(config_default), "%s/%s-%d.conf",
 				frr_sysconfdir, di->name, di->instance);

lib/libfrr.h

@@ -27,6 +27,7 @@
 #include "log.h"
 #include "getopt.h"
 #include "module.h"
+#include "hook.h"
 
 #define FRR_NO_PRIVSEP		(1 << 0)
 #define FRR_NO_TCPVTY		(1 << 1)
@@ -95,6 +96,7 @@ extern void frr_help_exit(int status);
 
 extern struct thread_master *frr_init(void);
 
+DECLARE_HOOK(frr_late_init, (struct thread_master *tm), (tm))
 extern void frr_config_fork(void);
 
 extern void frr_vty_serv(void);

zebra/rtread_getmsg.c

@@ -31,6 +31,10 @@
 #include "zebra/rib.h"
 #include "zebra/zserv.h"
 
+/* Thank you, Solaris, for polluting application symbol namespace. */
+#undef hook_register
+#undef hook_unregister
+
 #include <sys/stream.h>
 #include <sys/tihdr.h>