lib: add hook infrastructure

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

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

1 files changed, 187 insertions, 0 deletions

diff --git a/lib/hook.h b/lib/hook.h
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+++ b/lib/hook.h
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+/*
+ * 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 */