lib/hook.h

   1 /*
   2  * Copyright (c) 2016  David Lamparter, for NetDEF, Inc.
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice shall be included in
  12  * all copies or substantial portions of the Software.
  13  *
  14  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  15  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  17  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  18  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  19  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  20  * DEALINGS IN THE SOFTWARE.
  21  */
  22
  23 #ifndef _FRR_HOOK_H
  24 #define _FRR_HOOK_H
  25
  26 #include <stdbool.h>
  27
  28 #include "module.h"
  29 #include "memory.h"
  30
  31 /* type-safe subscribable hook points
  32  *
  33  * where "type-safe" applies to the function pointers used for subscriptions
  34  *
  35  * overall usage:
  36  * - to create a hook:
  37  *
  38  *   mydaemon.h:
  39  *     #include "hook.h"
  40  *     DECLARE_HOOK (some_update_event, (struct eventinfo *info), (info))
  41  *
  42  *   mydaemon.c:
  43  *     DEFINE_HOOK (some_update_event, (struct eventinfo *info), (info))
  44  *     ...
  45  *     hook_call (some_update_event, info)
  46  *
  47  * Note:  the second and third macro args must be the hook function's
  48  * parameter list, with the same names for each parameter.  The second
  49  * macro arg is with types (used for defining things), the third arg is
  50  * just the names (used for passing along parameters).
  51  *
  52  * Do not use parameter names starting with "hook", these can collide with
  53  * names used by the hook code itself.
  54  *
  55  * The return value is always "int" for now;  hook_call will sum up the
  56  * return values from each registered user.  Default is 0.
  57  *
  58  * There are no pre-defined semantics for the value, in most cases it is
  59  * ignored.  For success/failure indication, 0 should be success, and
  60  * handlers should make sure to only return 0 or 1 (not -1 or other values).
  61  *
  62  *
  63  * - to use a hook / create a handler:
  64  *
  65  *     #include "mydaemon.h"
  66  *     int event_handler (struct eventinfo *info) { ... }
  67  *     hook_register (some_update_event, event_handler);
  68  *
  69  *   or, if you need an argument to be passed along (addonptr will be added
  70  *   as first argument when calling the handler):
  71  *
  72  *     #include "mydaemon.h"
  73  *     int event_handler (void *addonptr, struct eventinfo *info) { ... }
  74  *     hook_register_arg (some_update_event, event_handler, addonptr);
  75  *
  76  *   (addonptr isn't typesafe, but that should be manageable.)
  77  */
  78
  79 /* TODO:
  80  * - hook_unregister_all_module()
  81  * - introspection / CLI / debug
  82  * - testcases ;)
  83  *
  84  * For loadable modules, the idea is that hooks could be automatically
  85  * unregistered when a module is unloaded.
  86  *
  87  * It's also possible to add a constructor (MTYPE style) to DEFINE_HOOK,
  88  * which would make it possible for the CLI to show all hooks and all
  89  * registered handlers.
  90  */
  91
  92 struct hookent {
  93         struct hookent *next;
  94         void *hookfn;           /* actually a function pointer */
  95         void *hookarg;
  96         bool has_arg;
  97         struct frrmod_runtime *module;
  98         const char *fnname;
  99 };
 100
 101 struct hook {
 102         const char *name;
 103         struct hookent *entries;
 104 };
 105
 106 /* subscribe/add callback function to a hook
 107  *
 108  * always use hook_register(), which uses the static inline helper from
 109  * DECLARE_HOOK in order to get type safety
 110  */
 111 extern void _hook_register(struct hook *hook, void *funcptr, void *arg,
 112                            bool has_arg, struct frrmod_runtime *module,
 113                            const char *funcname);
 114 #define hook_register(hookname, func) \
 115         _hook_register(&_hook_ ## hookname, \
 116                         _hook_typecheck_ ## hookname (func), \
 117                         NULL, false, THIS_MODULE, #func)
 118 #define hook_register_arg(hookname, func, arg) \
 119         _hook_register(&_hook_ ## hookname, \
 120                         _hook_typecheck_arg_ ## hookname (func), \
 121                         arg, true, THIS_MODULE, #func)
 122
 123 extern void _hook_unregister(struct hook *hook, void *funcptr, void *arg,
 124                              bool has_arg);
 125 #define hook_unregister(hookname, func) \
 126         _hook_unregister(&_hook_ ## hookname, \
 127                         _hook_typecheck_ ## hookname (func), NULL, false)
 128 #define hook_unregister_arg(hookname, func, arg) \
 129         _hook_unregister(&_hook_ ## hookname, \
 130                         _hook_typecheck_arg_ ## hookname (func), arg, true)
 131
 132 /* invoke hooks
 133  * this is private (static) to the file that has the DEFINE_HOOK statement
 134  */
 135 #define hook_call(hookname, ...) \
 136         hook_call_ ## hookname (__VA_ARGS__)
 137
 138 /* helpers to add the void * arg */
 139 #define HOOK_ADDDEF(...) (void *hookarg , ## __VA_ARGS__)
 140 #define HOOK_ADDARG(...) (hookarg , ## __VA_ARGS__)
 141
 142 /* use in header file - declares the hook and its arguments
 143  * usage:  DECLARE_HOOK(my_hook, (int arg1, struct foo *arg2), (arg1, arg2))
 144  * as above, "passlist" must use the same order and same names as "arglist"
 145  *
 146  * theoretically passlist is not neccessary, but let's keep things simple and
 147  * use exact same args on DECLARE and DEFINE.
 148  */
 149 #define DECLARE_HOOK(hookname, arglist, passlist) \
 150         extern struct hook _hook_ ## hookname; \
 151         __attribute__((unused)) \
 152         static void *_hook_typecheck_ ## hookname ( \
 153                         int (*funcptr) arglist) { \
 154                 return (void *)funcptr; } \
 155         __attribute__((unused)) \
 156         static void *_hook_typecheck_arg_ ## hookname ( \
 157                         int (*funcptr) HOOK_ADDDEF arglist) { \
 158                 return (void *)funcptr; }
 159
 160 /* use in source file - contains hook-related definitions.
 161  */
 162 #define DEFINE_HOOK(hookname, arglist, passlist) \
 163         struct hook _hook_ ## hookname = { \
 164                 .name = #hookname, \
 165                 .entries = NULL, \
 166         }; \
 167         static int hook_call_ ## hookname arglist { \
 168                 int hooksum = 0; \
 169                 struct hookent *he = _hook_ ## hookname .entries; \
 170                 void *hookarg; \
 171                 union { \
 172                         void *voidptr; \
 173                         int (*fptr) arglist; \
 174                         int (*farg) HOOK_ADDDEF arglist; \
 175                 } hookp; \
 176                 for (; he; he = he->next) { \
 177                         hookarg = he->hookarg; \
 178                         hookp.voidptr = he->hookfn; \
 179                         if (!he->has_arg) \
 180                                 hooksum += hookp.fptr passlist; \
 181                         else \
 182                                 hooksum += hookp.farg HOOK_ADDARG passlist; \
 183                 } \
 184                 return hooksum; \
 185         }
 186
 187 #endif /* _FRR_HOOK_H */