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  * Hooks also support a "priority" value for ordering registered calls
  79  * relative to each other.  The priority is a signed integer where lower
  80  * values are called earlier.  There is also "Koohs", which is hooks with
  81  * reverse priority ordering (for cleanup/deinit hooks, so you can use the
  82  * same priority value).
  83  *
  84  * Recommended priority value ranges are:
  85  *
  86  *  -999 ...     0 ...  999 - main executable / daemon, or library
  87  * -1999 ... -1000          - modules registering calls that should run before
  88  *                            the daemon's bits
  89  *            1000 ... 1999 - modules calls that should run after daemon's
  90  *
  91  * Note: the default value is 1000, based on the following 2 expectations:
  92  * - most hook_register() usage will be in loadable modules
  93  * - usage of hook_register() in the daemon itself may need relative ordering
  94  *   to itself, making an explicit value the expected case
  95  *
  96  * The priority value is passed as extra argument on hook_register_prio() /
  97  * hook_register_arg_prio().  Whether a hook runs in reverse is determined
  98  * solely by the code defining / calling the hook.  (DECLARE_KOOH is actually
  99  * the same thing as DECLARE_HOOK, it's just there to make it obvious.)
 100  */
 101
 102 /* TODO:
 103  * - hook_unregister_all_module()
 104  * - introspection / CLI / debug
 105  * - testcases ;)
 106  *
 107  * For loadable modules, the idea is that hooks could be automatically
 108  * unregistered when a module is unloaded.
 109  *
 110  * It's also possible to add a constructor (MTYPE style) to DEFINE_HOOK,
 111  * which would make it possible for the CLI to show all hooks and all
 112  * registered handlers.
 113  */
 114
 115 struct hookent {
 116         struct hookent *next;
 117         void *hookfn; /* actually a function pointer */
 118         void *hookarg;
 119         bool has_arg;
 120         int priority;
 121         struct frrmod_runtime *module;
 122         const char *fnname;
 123 };
 124
 125 struct hook {
 126         const char *name;
 127         struct hookent *entries;
 128         bool reverse;
 129 };
 130
 131 #define HOOK_DEFAULT_PRIORITY 1000
 132
 133 /* subscribe/add callback function to a hook
 134  *
 135  * always use hook_register(), which uses the static inline helper from
 136  * DECLARE_HOOK in order to get type safety
 137  */
 138 extern void _hook_register(struct hook *hook, void *funcptr, void *arg,
 139                            bool has_arg, struct frrmod_runtime *module,
 140                            const char *funcname, int priority);
 141 #define hook_register(hookname, func)                                          \
 142         _hook_register(&_hook_##hookname, _hook_typecheck_##hookname(func),    \
 143                        NULL, false, THIS_MODULE, #func, HOOK_DEFAULT_PRIORITY)
 144 #define hook_register_arg(hookname, func, arg)                                 \
 145         _hook_register(&_hook_##hookname,                                      \
 146                        _hook_typecheck_arg_##hookname(func), arg, true,        \
 147                        THIS_MODULE, #func, HOOK_DEFAULT_PRIORITY)
 148 #define hook_register_prio(hookname, prio, func)                               \
 149         _hook_register(&_hook_##hookname, _hook_typecheck_##hookname(func),    \
 150                        NULL, false, THIS_MODULE, #func, prio)
 151 #define hook_register_arg_prio(hookname, prio, func, arg)                      \
 152         _hook_register(&_hook_##hookname,                                      \
 153                        _hook_typecheck_arg_##hookname(func), arg, true,        \
 154                        THIS_MODULE, #func, prio)
 155
 156 extern void _hook_unregister(struct hook *hook, void *funcptr, void *arg,
 157                              bool has_arg);
 158 #define hook_unregister(hookname, func)                                        \
 159         _hook_unregister(&_hook_##hookname, _hook_typecheck_##hookname(func),  \
 160                          NULL, false)
 161 #define hook_unregister_arg(hookname, func, arg)                               \
 162         _hook_unregister(&_hook_##hookname,                                    \
 163                          _hook_typecheck_arg_##hookname(func), arg, true)
 164
 165 /* invoke hooks
 166  * this is private (static) to the file that has the DEFINE_HOOK statement
 167  */
 168 #define hook_call(hookname, ...) hook_call_##hookname(__VA_ARGS__)
 169
 170 /* helpers to add the void * arg */
 171 #define HOOK_ADDDEF(...) (void *hookarg , ## __VA_ARGS__)
 172 #define HOOK_ADDARG(...) (hookarg , ## __VA_ARGS__)
 173
 174 /* use in header file - declares the hook and its arguments
 175  * usage:  DECLARE_HOOK(my_hook, (int arg1, struct foo *arg2), (arg1, arg2))
 176  * as above, "passlist" must use the same order and same names as "arglist"
 177  *
 178  * theoretically passlist is not neccessary, but let's keep things simple and
 179  * use exact same args on DECLARE and DEFINE.
 180  */
 181 #define DECLARE_HOOK(hookname, arglist, passlist)                              \
 182         extern struct hook _hook_##hookname;                                   \
 183         __attribute__((unused)) static void *_hook_typecheck_##hookname(       \
 184                 int(*funcptr) arglist)                                         \
 185         {                                                                      \
 186                 return (void *)funcptr;                                        \
 187         }                                                                      \
 188         __attribute__((unused)) static void *_hook_typecheck_arg_##hookname(   \
 189                 int(*funcptr) HOOK_ADDDEF arglist)                             \
 190         {                                                                      \
 191                 return (void *)funcptr;                                        \
 192         }
 193 #define DECLARE_KOOH(hookname, arglist, passlist)                              \
 194         DECLARE_HOOK(hookname, arglist, passlist)
 195
 196 /* use in source file - contains hook-related definitions.
 197  */
 198 #define DEFINE_HOOK_INT(hookname, arglist, passlist, rev)                      \
 199         struct hook _hook_##hookname = {                                       \
 200                 .name = #hookname, .entries = NULL, .reverse = rev,            \
 201         };                                                                     \
 202         static int hook_call_##hookname arglist                                \
 203         {                                                                      \
 204                 int hooksum = 0;                                               \
 205                 struct hookent *he = _hook_##hookname.entries;                 \
 206                 void *hookarg;                                                 \
 207                 union {                                                        \
 208                         void *voidptr;                                         \
 209                         int(*fptr) arglist;                                    \
 210                         int(*farg) HOOK_ADDDEF arglist;                        \
 211                 } hookp;                                                       \
 212                 for (; he; he = he->next) {                                    \
 213                         hookarg = he->hookarg;                                 \
 214                         hookp.voidptr = he->hookfn;                            \
 215                         if (!he->has_arg)                                      \
 216                                 hooksum += hookp.fptr passlist;                \
 217                         else                                                   \
 218                                 hooksum += hookp.farg HOOK_ADDARG passlist;    \
 219                 }                                                              \
 220                 return hooksum;                                                \
 221         }
 222
 223 #define DEFINE_HOOK(hookname, arglist, passlist)                               \
 224         DEFINE_HOOK_INT(hookname, arglist, passlist, false)
 225 #define DEFINE_KOOH(hookname, arglist, passlist)                               \
 226         DEFINE_HOOK_INT(hookname, arglist, passlist, true)
 227
 228 #endif /* _FRR_HOOK_H */