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// 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)
#define hook_have_hooks(hookname) (_hook_##hookname.entries != NULL)
/* 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 */
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