[mirror_frr.git] / lib / hook.h

// SPDX-License-Identifier: ISC
/*
 * Copyright (c) 2016  David Lamparter, for NetDEF, Inc.
 */

#ifndef _FRR_HOOK_H
#define _FRR_HOOK_H

#include <stdbool.h>

#include "module.h"
#include "memory.h"

#ifdef __cplusplus
extern "C" {
#endif

/* 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.)
 *
 * Hooks also support a "priority" value for ordering registered calls
 * relative to each other.  The priority is a signed integer where lower
 * values are called earlier.  There is also "Koohs", which is hooks with
 * reverse priority ordering (for cleanup/deinit hooks, so you can use the
 * same priority value).
 *
 * Recommended priority value ranges are:
 *
 *  -999 ...     0 ...  999 - main executable / daemon, or library
 * -1999 ... -1000          - modules registering calls that should run before
 *                            the daemon's bits
 *            1000 ... 1999 - modules calls that should run after daemon's
 *
 * Note: the default value is 1000, based on the following 2 expectations:
 * - most hook_register() usage will be in loadable modules
 * - usage of hook_register() in the daemon itself may need relative ordering
 *   to itself, making an explicit value the expected case
 *
 * The priority value is passed as extra argument on hook_register_prio() /
 * hook_register_arg_prio().  Whether a hook runs in reverse is determined
 * solely by the code defining / calling the hook.  (DECLARE_KOOH is actually
 * the same thing as DECLARE_HOOK, it's just there to make it obvious.)
 */

/* 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 : 1;
	bool ent_on_heap : 1;
	bool ent_used : 1;
	int priority;
	struct frrmod_runtime *module;
	const char *fnname;
};

struct hook {
	const char *name;
	struct hookent *entries;
	bool reverse;
};

#define HOOK_DEFAULT_PRIORITY 1000

/* 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, struct hookent *stackent,
			   void *funcptr, void *arg, bool has_arg,
			   struct frrmod_runtime *module,
			   const char *funcname, int priority);

/* most hook_register calls are not in a loop or similar and can use a
 * statically allocated "struct hookent" from the data segment
 */
#define _hook_reg_svar(hook, funcptr, arg, has_arg, module, funcname, prio)    \
	do {                                                                   \
		static struct hookent stack_hookent = {};                      \
		_hook_register(hook, &stack_hookent, funcptr, arg, has_arg,    \
			       module, funcname, prio);                        \
	} while (0)

#define hook_register(hookname, func)                                          \
	_hook_reg_svar(&_hook_##hookname, _hook_typecheck_##hookname(func),    \
		       NULL, false, THIS_MODULE, #func, HOOK_DEFAULT_PRIORITY)
#define hook_register_arg(hookname, func, arg)                                 \
	_hook_reg_svar(&_hook_##hookname,                                      \
		       _hook_typecheck_arg_##hookname(func), arg, true,        \
		       THIS_MODULE, #func, HOOK_DEFAULT_PRIORITY)
#define hook_register_prio(hookname, prio, func)                               \
	_hook_reg_svar(&_hook_##hookname, _hook_typecheck_##hookname(func),    \
		       NULL, false, THIS_MODULE, #func, prio)
#define hook_register_arg_prio(hookname, prio, func, arg)                      \
	_hook_reg_svar(&_hook_##hookname,                                      \
		       _hook_typecheck_arg_##hookname(func), arg, true,        \
		       THIS_MODULE, #func, prio)

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__)

/* and another helper to convert () into (void) to get a proper prototype */
#define _SKIP_10(x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, ret, ...) ret
#define _MAKE_VOID(...) _SKIP_10(, ##__VA_ARGS__, , , , , , , , , , void)

#define HOOK_VOIDIFY(...) (_MAKE_VOID(__VA_ARGS__) __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 necessary, 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 inline void *                           \
		_hook_typecheck_##hookname(int(*funcptr) HOOK_VOIDIFY arglist) \
	{                                                                      \
		return (void *)funcptr;                                        \
	}                                                                      \
	__attribute__((unused)) static inline void                             \
		*_hook_typecheck_arg_##hookname(int(*funcptr)                  \
							HOOK_ADDDEF arglist)   \
	{                                                                      \
		return (void *)funcptr;                                        \
	}                                                                      \
	MACRO_REQUIRE_SEMICOLON() /* end */

#define DECLARE_KOOH(hookname, arglist, passlist)                              \
	DECLARE_HOOK(hookname, arglist, passlist)

/* use in source file - contains hook-related definitions.
 */
#define DEFINE_HOOK_INT(hookname, arglist, passlist, rev)                      \
	struct hook _hook_##hookname = {                                       \
		.name = #hookname, .entries = NULL, .reverse = rev,            \
	};                                                                     \
	static int hook_call_##hookname HOOK_VOIDIFY arglist                   \
	{                                                                      \
		int hooksum = 0;                                               \
		struct hookent *he = _hook_##hookname.entries;                 \
		void *hookarg;                                                 \
		union {                                                        \
			void *voidptr;                                         \
			int(*fptr) HOOK_VOIDIFY 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;                                                \
	}                                                                      \
	MACRO_REQUIRE_SEMICOLON() /* end */

#define DEFINE_HOOK(hookname, arglist, passlist)                               \
	DEFINE_HOOK_INT(hookname, arglist, passlist, false)
#define DEFINE_KOOH(hookname, arglist, passlist)                               \
	DEFINE_HOOK_INT(hookname, arglist, passlist, true)

#ifdef __cplusplus
}
#endif

#endif /* _FRR_HOOK_H */
Commit	Line	Data
acddc0ed	1	// SPDX-License-Identifier: ISC
a5b38c5b DL	2	/*
a5b38c5b DL	3	* Copyright (c) 2016 David Lamparter, for NetDEF, Inc.
a5b38c5b DL	4	*/
	5
	6	#ifndef _FRR_HOOK_H
	7	#define _FRR_HOOK_H
	8
	9	#include <stdbool.h>
	10
	11	#include "module.h"
	12	#include "memory.h"
	13
5e244469 RW	14	#ifdef __cplusplus
	15	extern "C" {
	16	#endif
	17
a5b38c5b DL	18	/* type-safe subscribable hook points
	19	*
	20	* where "type-safe" applies to the function pointers used for subscriptions
	21	*
	22	* overall usage:
	23	* - to create a hook:
	24	*
	25	* mydaemon.h:
	26	* #include "hook.h"
8451921b	27	* DECLARE_HOOK (some_update_event, (struct eventinfo *info), (info));
a5b38c5b DL	28	*
a5b38c5b DL	29	* mydaemon.c:
8451921b	30	* DEFINE_HOOK (some_update_event, (struct eventinfo *info), (info));
a5b38c5b DL	31	* ...
	32	* hook_call (some_update_event, info)
	33	*
	34	* Note: the second and third macro args must be the hook function's
	35	* parameter list, with the same names for each parameter. The second
	36	* macro arg is with types (used for defining things), the third arg is
	37	* just the names (used for passing along parameters).
	38	*
	39	* Do not use parameter names starting with "hook", these can collide with
	40	* names used by the hook code itself.
	41	*
	42	* The return value is always "int" for now; hook_call will sum up the
	43	* return values from each registered user. Default is 0.
	44	*
	45	* There are no pre-defined semantics for the value, in most cases it is
	46	* ignored. For success/failure indication, 0 should be success, and
	47	* handlers should make sure to only return 0 or 1 (not -1 or other values).
	48	*
	49	*
	50	* - to use a hook / create a handler:
	51	*
	52	* #include "mydaemon.h"
	53	* int event_handler (struct eventinfo *info) { ... }
	54	* hook_register (some_update_event, event_handler);
	55	*
	56	* or, if you need an argument to be passed along (addonptr will be added
	57	* as first argument when calling the handler):
	58	*
	59	* #include "mydaemon.h"
	60	* int event_handler (void addonptr, struct eventinfo info) { ... }
	61	* hook_register_arg (some_update_event, event_handler, addonptr);
	62	*
	63	* (addonptr isn't typesafe, but that should be manageable.)
08c4c73b DL	64	*
	65	* Hooks also support a "priority" value for ordering registered calls
	66	* relative to each other. The priority is a signed integer where lower
	67	* values are called earlier. There is also "Koohs", which is hooks with
	68	* reverse priority ordering (for cleanup/deinit hooks, so you can use the
	69	* same priority value).
	70	*
	71	* Recommended priority value ranges are:
	72	*
	73	* -999 ... 0 ... 999 - main executable / daemon, or library
	74	* -1999 ... -1000 - modules registering calls that should run before
	75	* the daemon's bits
	76	* 1000 ... 1999 - modules calls that should run after daemon's
	77	*
	78	* Note: the default value is 1000, based on the following 2 expectations:
	79	* - most hook_register() usage will be in loadable modules
	80	* - usage of hook_register() in the daemon itself may need relative ordering
	81	* to itself, making an explicit value the expected case
	82	*
	83	* The priority value is passed as extra argument on hook_register_prio() /
	84	* hook_register_arg_prio(). Whether a hook runs in reverse is determined
	85	* solely by the code defining / calling the hook. (DECLARE_KOOH is actually
	86	* the same thing as DECLARE_HOOK, it's just there to make it obvious.)
a5b38c5b DL	87	*/
	88
	89	/* TODO:
	90	* - hook_unregister_all_module()
	91	* - introspection / CLI / debug
	92	* - testcases ;)
	93	*
	94	* For loadable modules, the idea is that hooks could be automatically
	95	* unregistered when a module is unloaded.
	96	*
	97	* It's also possible to add a constructor (MTYPE style) to DEFINE_HOOK,
	98	* which would make it possible for the CLI to show all hooks and all
	99	* registered handlers.
	100	*/
	101
	102	struct hookent {
	103	struct hookent *next;
d62a17ae	104	void hookfn; / actually a function pointer */
a5b38c5b	105	void *hookarg;
8d0a2918 DL	106	bool has_arg : 1;
	107	bool ent_on_heap : 1;
	108	bool ent_used : 1;
08c4c73b	109	int priority;
a5b38c5b DL	110	struct frrmod_runtime *module;
	111	const char *fnname;
	112	};
	113
	114	struct hook {
	115	const char *name;
	116	struct hookent *entries;
08c4c73b	117	bool reverse;
a5b38c5b DL	118	};
a5b38c5b DL	119
08c4c73b DL	120	#define HOOK_DEFAULT_PRIORITY 1000
08c4c73b DL	121
a5b38c5b DL	122	/* subscribe/add callback function to a hook
	123	*
	124	* always use hook_register(), which uses the static inline helper from
	125	* DECLARE_HOOK in order to get type safety
	126	*/
8d0a2918 DL	127	extern void _hook_register(struct hook hook, struct hookent stackent,
	128	void funcptr, void arg, bool has_arg,
	129	struct frrmod_runtime *module,
08c4c73b	130	const char *funcname, int priority);
8d0a2918 DL	131
	132	/* most hook_register calls are not in a loop or similar and can use a
	133	* statically allocated "struct hookent" from the data segment
	134	*/
	135	#define _hook_reg_svar(hook, funcptr, arg, has_arg, module, funcname, prio) \
	136	do { \
e01a788c	137	static struct hookent stack_hookent = {}; \
8d0a2918 DL	138	_hook_register(hook, &stack_hookent, funcptr, arg, has_arg, \
	139	module, funcname, prio); \
	140	} while (0)
	141
d62a17ae	142	#define hook_register(hookname, func) \
8d0a2918	143	_hook_reg_svar(&_hook_##hookname, _hook_typecheck_##hookname(func), \
08c4c73b	144	NULL, false, THIS_MODULE, #func, HOOK_DEFAULT_PRIORITY)
d62a17ae	145	#define hook_register_arg(hookname, func, arg) \
8d0a2918	146	_hook_reg_svar(&_hook_##hookname, \
d62a17ae	147	_hook_typecheck_arg_##hookname(func), arg, true, \
08c4c73b DL	148	THIS_MODULE, #func, HOOK_DEFAULT_PRIORITY)
08c4c73b DL	149	#define hook_register_prio(hookname, prio, func) \
8d0a2918	150	_hook_reg_svar(&_hook_##hookname, _hook_typecheck_##hookname(func), \
08c4c73b DL	151	NULL, false, THIS_MODULE, #func, prio)
08c4c73b DL	152	#define hook_register_arg_prio(hookname, prio, func, arg) \
8d0a2918	153	_hook_reg_svar(&_hook_##hookname, \
996c9314 LB	154	_hook_typecheck_arg_##hookname(func), arg, true, \
996c9314 LB	155	THIS_MODULE, #func, prio)
a5b38c5b DL	156
	157	extern void _hook_unregister(struct hook hook, void funcptr, void *arg,
	158	bool has_arg);
d62a17ae	159	#define hook_unregister(hookname, func) \
	160	_hook_unregister(&_hook_##hookname, _hook_typecheck_##hookname(func), \
	161	NULL, false)
	162	#define hook_unregister_arg(hookname, func, arg) \
	163	_hook_unregister(&_hook_##hookname, \
	164	_hook_typecheck_arg_##hookname(func), arg, true)
a5b38c5b DL	165
	166	/* invoke hooks
	167	* this is private (static) to the file that has the DEFINE_HOOK statement
	168	*/
d62a17ae	169	#define hook_call(hookname, ...) hook_call_##hookname(__VA_ARGS__)
a5b38c5b DL	170
	171	/* helpers to add the void * arg */
	172	#define HOOK_ADDDEF(...) (void *hookarg , ## __VA_ARGS__)
	173	#define HOOK_ADDARG(...) (hookarg , ## __VA_ARGS__)
	174
14040553 DL	175	/* and another helper to convert () into (void) to get a proper prototype */
	176	#define _SKIP_10(x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, ret, ...) ret
	177	#define _MAKE_VOID(...) _SKIP_10(, ##__VA_ARGS__, , , , , , , , , , void)
	178
	179	#define HOOK_VOIDIFY(...) (_MAKE_VOID(__VA_ARGS__) __VA_ARGS__)
	180
a5b38c5b	181	/* use in header file - declares the hook and its arguments
8451921b	182	* usage: DECLARE_HOOK(my_hook, (int arg1, struct foo *arg2), (arg1, arg2));
a5b38c5b DL	183	* as above, "passlist" must use the same order and same names as "arglist"
a5b38c5b DL	184	*
214d8a60	185	* theoretically passlist is not necessary, but let's keep things simple and
a5b38c5b DL	186	* use exact same args on DECLARE and DEFINE.
a5b38c5b DL	187	*/
d62a17ae	188	#define DECLARE_HOOK(hookname, arglist, passlist) \
d62a17ae	189	extern struct hook _hook_##hookname; \
14040553 DL	190	__attribute__((unused)) static inline void * \
14040553 DL	191	_hook_typecheck_##hookname(int(*funcptr) HOOK_VOIDIFY arglist) \
d62a17ae	192	{ \
	193	return (void *)funcptr; \
	194	} \
14040553 DL	195	__attribute__((unused)) static inline void \
	196	_hook_typecheck_arg_##hookname(int(funcptr) \
	197	HOOK_ADDDEF arglist) \
d62a17ae	198	{ \
d62a17ae	199	return (void *)funcptr; \
8451921b DL	200	} \
	201	MACRO_REQUIRE_SEMICOLON() /* end */
	202
996c9314	203	#define DECLARE_KOOH(hookname, arglist, passlist) \
08c4c73b	204	DECLARE_HOOK(hookname, arglist, passlist)
a5b38c5b DL	205
	206	/* use in source file - contains hook-related definitions.
	207	*/
08c4c73b	208	#define DEFINE_HOOK_INT(hookname, arglist, passlist, rev) \
d62a17ae	209	struct hook _hook_##hookname = { \
08c4c73b	210	.name = #hookname, .entries = NULL, .reverse = rev, \
d62a17ae	211	}; \
14040553	212	static int hook_call_##hookname HOOK_VOIDIFY arglist \
d62a17ae	213	{ \
	214	int hooksum = 0; \
	215	struct hookent *he = _hook_##hookname.entries; \
	216	void *hookarg; \
	217	union { \
	218	void *voidptr; \
14040553	219	int(*fptr) HOOK_VOIDIFY arglist; \
d62a17ae	220	int(*farg) HOOK_ADDDEF arglist; \
	221	} hookp; \
	222	for (; he; he = he->next) { \
	223	hookarg = he->hookarg; \
	224	hookp.voidptr = he->hookfn; \
	225	if (!he->has_arg) \
	226	hooksum += hookp.fptr passlist; \
	227	else \
	228	hooksum += hookp.farg HOOK_ADDARG passlist; \
	229	} \
	230	return hooksum; \
8451921b DL	231	} \
8451921b DL	232	MACRO_REQUIRE_SEMICOLON() /* end */
a5b38c5b	233
996c9314	234	#define DEFINE_HOOK(hookname, arglist, passlist) \
08c4c73b	235	DEFINE_HOOK_INT(hookname, arglist, passlist, false)
996c9314	236	#define DEFINE_KOOH(hookname, arglist, passlist) \
08c4c73b DL	237	DEFINE_HOOK_INT(hookname, arglist, passlist, true)
08c4c73b DL	238
5e244469 RW	239	#ifdef __cplusplus
	240	}
	241	#endif
	242
a5b38c5b	243	#endif /* _FRR_HOOK_H */