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