lib/hook.h

   1 /*
   2  * Copyright (c) 2016  David Lamparter, for NetDEF, Inc.
   3  *
   4  * Permission to use, copy, modify, and distribute this software for any
   5  * purpose with or without fee is hereby granted, provided that the above
   6  * copyright notice and this permission notice appear in all copies.
   7  *
   8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15  */
  16
  17 #ifndef _FRR_HOOK_H
  18 #define _FRR_HOOK_H
  19
  20 #include <stdbool.h>
  21
  22 #include "module.h"
  23 #include "memory.h"
  24
  25 #ifdef __cplusplus
  26 extern "C" {
  27 #endif
  28
  29 /* type-safe subscribable hook points
  30  *
  31  * where "type-safe" applies to the function pointers used for subscriptions
  32  *
  33  * overall usage:
  34  * - to create a hook:
  35  *
  36  *   mydaemon.h:
  37  *     #include "hook.h"
  38  *     DECLARE_HOOK (some_update_event, (struct eventinfo *info), (info))
  39  *
  40  *   mydaemon.c:
  41  *     DEFINE_HOOK (some_update_event, (struct eventinfo *info), (info))
  42  *     ...
  43  *     hook_call (some_update_event, info)
  44  *
  45  * Note:  the second and third macro args must be the hook function's
  46  * parameter list, with the same names for each parameter.  The second
  47  * macro arg is with types (used for defining things), the third arg is
  48  * just the names (used for passing along parameters).
  49  *
  50  * Do not use parameter names starting with "hook", these can collide with
  51  * names used by the hook code itself.
  52  *
  53  * The return value is always "int" for now;  hook_call will sum up the
  54  * return values from each registered user.  Default is 0.
  55  *
  56  * There are no pre-defined semantics for the value, in most cases it is
  57  * ignored.  For success/failure indication, 0 should be success, and
  58  * handlers should make sure to only return 0 or 1 (not -1 or other values).
  59  *
  60  *
  61  * - to use a hook / create a handler:
  62  *
  63  *     #include "mydaemon.h"
  64  *     int event_handler (struct eventinfo *info) { ... }
  65  *     hook_register (some_update_event, event_handler);
  66  *
  67  *   or, if you need an argument to be passed along (addonptr will be added
  68  *   as first argument when calling the handler):
  69  *
  70  *     #include "mydaemon.h"
  71  *     int event_handler (void *addonptr, struct eventinfo *info) { ... }
  72  *     hook_register_arg (some_update_event, event_handler, addonptr);
  73  *
  74  *   (addonptr isn't typesafe, but that should be manageable.)
  75  *
  76  * Hooks also support a "priority" value for ordering registered calls
  77  * relative to each other.  The priority is a signed integer where lower
  78  * values are called earlier.  There is also "Koohs", which is hooks with
  79  * reverse priority ordering (for cleanup/deinit hooks, so you can use the
  80  * same priority value).
  81  *
  82  * Recommended priority value ranges are:
  83  *
  84  *  -999 ...     0 ...  999 - main executable / daemon, or library
  85  * -1999 ... -1000          - modules registering calls that should run before
  86  *                            the daemon's bits
  87  *            1000 ... 1999 - modules calls that should run after daemon's
  88  *
  89  * Note: the default value is 1000, based on the following 2 expectations:
  90  * - most hook_register() usage will be in loadable modules
  91  * - usage of hook_register() in the daemon itself may need relative ordering
  92  *   to itself, making an explicit value the expected case
  93  *
  94  * The priority value is passed as extra argument on hook_register_prio() /
  95  * hook_register_arg_prio().  Whether a hook runs in reverse is determined
  96  * solely by the code defining / calling the hook.  (DECLARE_KOOH is actually
  97  * the same thing as DECLARE_HOOK, it's just there to make it obvious.)
  98  */
  99
 100 /* TODO:
 101  * - hook_unregister_all_module()
 102  * - introspection / CLI / debug
 103  * - testcases ;)
 104  *
 105  * For loadable modules, the idea is that hooks could be automatically
 106  * unregistered when a module is unloaded.
 107  *
 108  * It's also possible to add a constructor (MTYPE style) to DEFINE_HOOK,
 109  * which would make it possible for the CLI to show all hooks and all
 110  * registered handlers.
 111  */
 112
 113 struct hookent {
 114         struct hookent *next;
 115         void *hookfn; /* actually a function pointer */
 116         void *hookarg;
 117         bool has_arg;
 118         int priority;
 119         struct frrmod_runtime *module;
 120         const char *fnname;
 121 };
 122
 123 struct hook {
 124         const char *name;
 125         struct hookent *entries;
 126         bool reverse;
 127 };
 128
 129 #define HOOK_DEFAULT_PRIORITY 1000
 130
 131 /* subscribe/add callback function to a hook
 132  *
 133  * always use hook_register(), which uses the static inline helper from
 134  * DECLARE_HOOK in order to get type safety
 135  */
 136 extern void _hook_register(struct hook *hook, void *funcptr, void *arg,
 137                            bool has_arg, struct frrmod_runtime *module,
 138                            const char *funcname, int priority);
 139 #define hook_register(hookname, func)                                          \
 140         _hook_register(&_hook_##hookname, _hook_typecheck_##hookname(func),    \
 141                        NULL, false, THIS_MODULE, #func, HOOK_DEFAULT_PRIORITY)
 142 #define hook_register_arg(hookname, func, arg)                                 \
 143         _hook_register(&_hook_##hookname,                                      \
 144                        _hook_typecheck_arg_##hookname(func), arg, true,        \
 145                        THIS_MODULE, #func, HOOK_DEFAULT_PRIORITY)
 146 #define hook_register_prio(hookname, prio, func)                               \
 147         _hook_register(&_hook_##hookname, _hook_typecheck_##hookname(func),    \
 148                        NULL, false, THIS_MODULE, #func, prio)
 149 #define hook_register_arg_prio(hookname, prio, func, arg)                      \
 150         _hook_register(&_hook_##hookname,                                      \
 151                        _hook_typecheck_arg_##hookname(func), arg, true,        \
 152                        THIS_MODULE, #func, prio)
 153
 154 extern void _hook_unregister(struct hook *hook, void *funcptr, void *arg,
 155                              bool has_arg);
 156 #define hook_unregister(hookname, func)                                        \
 157         _hook_unregister(&_hook_##hookname, _hook_typecheck_##hookname(func),  \
 158                          NULL, false)
 159 #define hook_unregister_arg(hookname, func, arg)                               \
 160         _hook_unregister(&_hook_##hookname,                                    \
 161                          _hook_typecheck_arg_##hookname(func), arg, true)
 162
 163 /* invoke hooks
 164  * this is private (static) to the file that has the DEFINE_HOOK statement
 165  */
 166 #define hook_call(hookname, ...) hook_call_##hookname(__VA_ARGS__)
 167
 168 /* helpers to add the void * arg */
 169 #define HOOK_ADDDEF(...) (void *hookarg , ## __VA_ARGS__)
 170 #define HOOK_ADDARG(...) (hookarg , ## __VA_ARGS__)
 171
 172 /* use in header file - declares the hook and its arguments
 173  * usage:  DECLARE_HOOK(my_hook, (int arg1, struct foo *arg2), (arg1, arg2))
 174  * as above, "passlist" must use the same order and same names as "arglist"
 175  *
 176  * theoretically passlist is not neccessary, but let's keep things simple and
 177  * use exact same args on DECLARE and DEFINE.
 178  */
 179 #define DECLARE_HOOK(hookname, arglist, passlist)                              \
 180         extern struct hook _hook_##hookname;                                   \
 181         __attribute__((unused)) static void *_hook_typecheck_##hookname(       \
 182                 int(*funcptr) arglist)                                         \
 183         {                                                                      \
 184                 return (void *)funcptr;                                        \
 185         }                                                                      \
 186         __attribute__((unused)) static void *_hook_typecheck_arg_##hookname(   \
 187                 int(*funcptr) HOOK_ADDDEF arglist)                             \
 188         {                                                                      \
 189                 return (void *)funcptr;                                        \
 190         }
 191 #define DECLARE_KOOH(hookname, arglist, passlist)                              \
 192         DECLARE_HOOK(hookname, arglist, passlist)
 193
 194 /* use in source file - contains hook-related definitions.
 195  */
 196 #define DEFINE_HOOK_INT(hookname, arglist, passlist, rev)                      \
 197         struct hook _hook_##hookname = {                                       \
 198                 .name = #hookname, .entries = NULL, .reverse = rev,            \
 199         };                                                                     \
 200         static int hook_call_##hookname arglist                                \
 201         {                                                                      \
 202                 int hooksum = 0;                                               \
 203                 struct hookent *he = _hook_##hookname.entries;                 \
 204                 void *hookarg;                                                 \
 205                 union {                                                        \
 206                         void *voidptr;                                         \
 207                         int(*fptr) arglist;                                    \
 208                         int(*farg) HOOK_ADDDEF arglist;                        \
 209                 } hookp;                                                       \
 210                 for (; he; he = he->next) {                                    \
 211                         hookarg = he->hookarg;                                 \
 212                         hookp.voidptr = he->hookfn;                            \
 213                         if (!he->has_arg)                                      \
 214                                 hooksum += hookp.fptr passlist;                \
 215                         else                                                   \
 216                                 hooksum += hookp.farg HOOK_ADDARG passlist;    \
 217                 }                                                              \
 218                 return hooksum;                                                \
 219         }
 220
 221 #define DEFINE_HOOK(hookname, arglist, passlist)                               \
 222         DEFINE_HOOK_INT(hookname, arglist, passlist, false)
 223 #define DEFINE_KOOH(hookname, arglist, passlist)                               \
 224         DEFINE_HOOK_INT(hookname, arglist, passlist, true)
 225
 226 #ifdef __cplusplus
 227 }
 228 #endif
 229
 230 #endif /* _FRR_HOOK_H */