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