src/side.c

   1 // SPDX-License-Identifier: MIT
   2 /*
   3  * Copyright 2022 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   4  */
   5
   6 #include <side/trace.h>
   7 #include <string.h>
   8
   9 #include "tracer.h"
  10 #include "rcu.h"
  11 #include "list.h"
  12
  13 /* Top 8 bits reserved for kernel tracer use. */
  14 #define SIDE_EVENT_ENABLED_KERNEL_MASK                  0xFF000000
  15 #define SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK       0x80000000
  16
  17 /* Allow 2^24 tracer callbacks to be registered on an event. */
  18 #define SIDE_EVENT_ENABLED_USER_MASK                    0x00FFFFFF
  19
  20 struct side_events_register_handle {
  21         struct side_list_node node;
  22         struct side_event_description **events;
  23         uint32_t nr_events;
  24 };
  25
  26 struct side_tracer_handle {
  27         struct side_list_node node;
  28         void (*cb)(enum side_tracer_notification notif,
  29                 struct side_event_description **events, uint32_t nr_events, void *priv);
  30         void *priv;
  31 };
  32
  33 static struct side_rcu_gp_state rcu_gp;
  34
  35 /*
  36  * Lazy initialization for early use within library constructors.
  37  */
  38 static bool initialized;
  39 /*
  40  * Do not register/unregister any more events after destructor.
  41  */
  42 static bool finalized;
  43
  44 static pthread_mutex_t side_lock = PTHREAD_MUTEX_INITIALIZER;
  45
  46 static DEFINE_SIDE_LIST_HEAD(side_events_list);
  47 static DEFINE_SIDE_LIST_HEAD(side_tracer_list);
  48
  49 /*
  50  * The empty callback has a NULL function callback pointer, which stops
  51  * iteration on the array of callbacks immediately.
  52  */
  53 const struct side_callback side_empty_callback;
  54
  55 void side_init(void) __attribute__((constructor));
  56 void side_exit(void) __attribute__((destructor));
  57
  58 void side_call(const struct side_event_description *desc, const struct side_arg_vec_description *sav_desc)
  59 {
  60         const struct side_callback *side_cb;
  61         unsigned int rcu_period;
  62         uint32_t enabled;
  63
  64         if (side_unlikely(finalized))
  65                 return;
  66         if (side_unlikely(!initialized))
  67                 side_init();
  68         if (side_unlikely(desc->flags & SIDE_EVENT_FLAG_VARIADIC)) {
  69                 printf("ERROR: unexpected variadic event description\n");
  70                 abort();
  71         }
  72         enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
  73         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
  74                 // TODO: call kernel write.
  75         }
  76         if (side_unlikely(!(enabled & SIDE_EVENT_ENABLED_USER_MASK)))
  77                 return;
  78
  79         //TODO: replace tracer_call by rcu iteration on list of registered callbacks
  80         tracer_call(desc, sav_desc, NULL);
  81
  82         rcu_period = side_rcu_read_begin(&rcu_gp);
  83         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call != NULL; side_cb++)
  84                 side_cb->u.call(desc, sav_desc, side_cb->priv);
  85         side_rcu_read_end(&rcu_gp, rcu_period);
  86 }
  87
  88 void side_call_variadic(const struct side_event_description *desc,
  89         const struct side_arg_vec_description *sav_desc,
  90         const struct side_arg_dynamic_event_struct *var_struct)
  91 {
  92         const struct side_callback *side_cb;
  93         unsigned int rcu_period;
  94         uint32_t enabled;
  95
  96         if (side_unlikely(finalized))
  97                 return;
  98         if (side_unlikely(!initialized))
  99                 side_init();
 100         if (side_unlikely(!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))) {
 101                 printf("ERROR: unexpected non-variadic event description\n");
 102                 abort();
 103         }
 104         enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
 105         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
 106                 // TODO: call kernel write.
 107         }
 108         if (side_unlikely(!(enabled & SIDE_EVENT_ENABLED_USER_MASK)))
 109                 return;
 110
 111         //TODO: replace tracer_call by rcu iteration on list of registered callbacks
 112         tracer_call_variadic(desc, sav_desc, var_struct, NULL);
 113
 114         rcu_period = side_rcu_read_begin(&rcu_gp);
 115         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call_variadic != NULL; side_cb++)
 116                 side_cb->u.call_variadic(desc, sav_desc, var_struct, side_cb->priv);
 117         side_rcu_read_end(&rcu_gp, rcu_period);
 118 }
 119
 120 static
 121 const struct side_callback *side_tracer_callback_lookup(
 122                 const struct side_event_description *desc,
 123                 void (*call)(), void *priv)
 124 {
 125         const struct side_callback *cb;
 126
 127         for (cb = desc->callbacks; cb->u.call != NULL; cb++) {
 128                 if (cb->u.call == call && cb->priv == priv)
 129                         return cb;
 130         }
 131         return NULL;
 132 }
 133
 134 static
 135 int _side_tracer_callback_register(struct side_event_description *desc,
 136                 void (*call)(), void *priv)
 137 {
 138         struct side_callback *old_cb, *new_cb;
 139         int ret = SIDE_ERROR_OK;
 140         uint32_t old_nr_cb;
 141
 142         if (!call)
 143                 return SIDE_ERROR_INVAL;
 144         if (finalized)
 145                 return SIDE_ERROR_EXITING;
 146         if (!initialized)
 147                 side_init();
 148         pthread_mutex_lock(&side_lock);
 149         old_nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 150         if (old_nr_cb == SIDE_EVENT_ENABLED_USER_MASK) {
 151                 ret = SIDE_ERROR_INVAL;
 152                 goto unlock;
 153         }
 154         /* Reject duplicate (call, priv) tuples. */
 155         if (side_tracer_callback_lookup(desc, call, priv)) {
 156                 ret = SIDE_ERROR_EXIST;
 157                 goto unlock;
 158         }
 159         old_cb = (struct side_callback *) desc->callbacks;
 160         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 161         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 162         if (!new_cb) {
 163                 ret = SIDE_ERROR_NOMEM;
 164                 goto unlock;
 165         }
 166         memcpy(new_cb, old_cb, old_nr_cb);
 167         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 168                 new_cb[old_nr_cb].u.call_variadic = call;
 169         else
 170                 new_cb[old_nr_cb].u.call = call;
 171         new_cb[old_nr_cb].priv = priv;
 172         side_rcu_assign_pointer(desc->callbacks, new_cb);
 173         side_rcu_wait_grace_period(&rcu_gp);
 174         if (old_nr_cb)
 175                 free(old_cb);
 176         /* Increment concurrently with kernel setting the top bits. */
 177         (void) __atomic_add_fetch(desc->enabled, 1, __ATOMIC_RELAXED);
 178 unlock:
 179         pthread_mutex_unlock(&side_lock);
 180         return ret;
 181 }
 182
 183 int side_tracer_callback_register(struct side_event_description *desc,
 184                 void (*call)(const struct side_event_description *desc,
 185                         const struct side_arg_vec_description *sav_desc,
 186                         void *priv),
 187                 void *priv)
 188 {
 189         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 190                 return SIDE_ERROR_INVAL;
 191         return _side_tracer_callback_register(desc, call, priv);
 192 }
 193
 194 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 195                 void (*call_variadic)(const struct side_event_description *desc,
 196                         const struct side_arg_vec_description *sav_desc,
 197                         const struct side_arg_dynamic_event_struct *var_struct,
 198                         void *priv),
 199                 void *priv)
 200 {
 201         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 202                 return SIDE_ERROR_INVAL;
 203         return _side_tracer_callback_register(desc, call_variadic, priv);
 204 }
 205
 206 int _side_tracer_callback_unregister(struct side_event_description *desc,
 207                 void (*call)(), void *priv)
 208 {
 209         struct side_callback *old_cb, *new_cb;
 210         const struct side_callback *cb_pos;
 211         uint32_t pos_idx;
 212         int ret = SIDE_ERROR_OK;
 213         uint32_t old_nr_cb;
 214
 215         if (!call)
 216                 return SIDE_ERROR_INVAL;
 217         if (finalized)
 218                 return SIDE_ERROR_EXITING;
 219         if (!initialized)
 220                 side_init();
 221         pthread_mutex_lock(&side_lock);
 222         cb_pos = side_tracer_callback_lookup(desc, call, priv);
 223         if (!cb_pos) {
 224                 ret = SIDE_ERROR_NOENT;
 225                 goto unlock;
 226         }
 227         old_nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 228         old_cb = (struct side_callback *) desc->callbacks;
 229         if (old_nr_cb == 1) {
 230                 new_cb = (struct side_callback *) &side_empty_callback;
 231         } else {
 232                 pos_idx = cb_pos - desc->callbacks;
 233                 /* Remove entry at pos_idx. */
 234                 /* old_nr_cb - 1 (removed cb) + 1 (NULL) */
 235                 new_cb = (struct side_callback *) calloc(old_nr_cb, sizeof(struct side_callback));
 236                 if (!new_cb) {
 237                         ret = SIDE_ERROR_NOMEM;
 238                         goto unlock;
 239                 }
 240                 memcpy(new_cb, old_cb, pos_idx);
 241                 memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
 242         }
 243         side_rcu_assign_pointer(desc->callbacks, new_cb);
 244         side_rcu_wait_grace_period(&rcu_gp);
 245         free(old_cb);
 246         /* Decrement concurrently with kernel setting the top bits. */
 247         (void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
 248 unlock:
 249         pthread_mutex_unlock(&side_lock);
 250         return ret;
 251 }
 252
 253 int side_tracer_callback_unregister(struct side_event_description *desc,
 254                 void (*call)(const struct side_event_description *desc,
 255                         const struct side_arg_vec_description *sav_desc,
 256                         void *priv),
 257                 void *priv)
 258 {
 259         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 260                 return SIDE_ERROR_INVAL;
 261         return _side_tracer_callback_unregister(desc, call, priv);
 262 }
 263
 264 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 265                 void (*call_variadic)(const struct side_event_description *desc,
 266                         const struct side_arg_vec_description *sav_desc,
 267                         const struct side_arg_dynamic_event_struct *var_struct,
 268                         void *priv),
 269                 void *priv)
 270 {
 271         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 272                 return SIDE_ERROR_INVAL;
 273         return _side_tracer_callback_unregister(desc, call_variadic, priv);
 274 }
 275
 276 struct side_events_register_handle *side_events_register(struct side_event_description **events, uint32_t nr_events)
 277 {
 278         struct side_events_register_handle *events_handle = NULL;
 279         struct side_tracer_handle *tracer_handle;
 280
 281         if (finalized)
 282                 return NULL;
 283         if (!initialized)
 284                 side_init();
 285         events_handle = calloc(1, sizeof(struct side_events_register_handle));
 286         if (!events_handle)
 287                 return NULL;
 288         events_handle->events = events;
 289         events_handle->nr_events = nr_events;
 290
 291         pthread_mutex_lock(&side_lock);
 292         side_list_insert_node_tail(&side_events_list, &events_handle->node);
 293         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 294                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 295                         events, nr_events, tracer_handle->priv);
 296         }
 297         pthread_mutex_unlock(&side_lock);
 298         //TODO: call event batch register ioctl
 299         return events_handle;
 300 }
 301
 302 static
 303 void side_event_remove_callbacks(struct side_event_description *desc)
 304 {
 305         uint32_t nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 306         struct side_callback *old_cb;
 307
 308         if (!nr_cb)
 309                 return;
 310         old_cb = (struct side_callback *) desc->callbacks;
 311         /*
 312          * Setting the state back to 0 cb and empty callbacks out of
 313          * caution. This should not matter because instrumentation is
 314          * unreachable.
 315          */
 316         (void) __atomic_add_fetch(desc->enabled, -nr_cb, __ATOMIC_RELAXED);
 317         side_rcu_assign_pointer(desc->callbacks, &side_empty_callback);
 318         /*
 319          * No need to wait for grace period because instrumentation is
 320          * unreachable.
 321          */
 322         free(old_cb);
 323 }
 324
 325 /*
 326  * Unregister event handle. At this point, all side events in that
 327  * handle should be unreachable.
 328  */
 329 void side_events_unregister(struct side_events_register_handle *events_handle)
 330 {
 331         struct side_tracer_handle *tracer_handle;
 332         uint32_t i;
 333
 334         if (finalized)
 335                 return;
 336         if (!initialized)
 337                 side_init();
 338         pthread_mutex_lock(&side_lock);
 339         side_list_remove_node(&events_handle->node);
 340         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 341                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 342                         events_handle->events, events_handle->nr_events,
 343                         tracer_handle->priv);
 344         }
 345         for (i = 0; i < events_handle->nr_events; i++) {
 346                 struct side_event_description *event = events_handle->events[i];
 347
 348                 /* Skip NULL pointers */
 349                 if (!event)
 350                         continue;
 351                 side_event_remove_callbacks(event);
 352         }
 353         pthread_mutex_unlock(&side_lock);
 354         //TODO: call event batch unregister ioctl
 355         free(events_handle);
 356 }
 357
 358 struct side_tracer_handle *side_tracer_event_notification_register(
 359                 void (*cb)(enum side_tracer_notification notif,
 360                         struct side_event_description **events, uint32_t nr_events, void *priv),
 361                 void *priv)
 362 {
 363         struct side_tracer_handle *tracer_handle;
 364         struct side_events_register_handle *events_handle;
 365
 366         if (finalized)
 367                 return NULL;
 368         if (!initialized)
 369                 side_init();
 370         tracer_handle = calloc(1, sizeof(struct side_tracer_handle));
 371         if (!tracer_handle)
 372                 return NULL;
 373         pthread_mutex_lock(&side_lock);
 374         tracer_handle->cb = cb;
 375         tracer_handle->priv = priv;
 376         side_list_insert_node_tail(&side_tracer_list, &tracer_handle->node);
 377         side_list_for_each_entry(events_handle, &side_events_list, node) {
 378                 cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 379                         events_handle->events, events_handle->nr_events, priv);
 380         }
 381         pthread_mutex_unlock(&side_lock);
 382         return tracer_handle;
 383 }
 384
 385 void side_tracer_event_notification_unregister(struct side_tracer_handle *tracer_handle)
 386 {
 387         struct side_events_register_handle *events_handle;
 388
 389         if (finalized)
 390                 return;
 391         if (!initialized)
 392                 side_init();
 393         pthread_mutex_lock(&side_lock);
 394         side_list_for_each_entry(events_handle, &side_events_list, node) {
 395                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 396                         events_handle->events, events_handle->nr_events,
 397                         tracer_handle->priv);
 398         }
 399         side_list_remove_node(&tracer_handle->node);
 400         pthread_mutex_unlock(&side_lock);
 401 }
 402
 403 void side_init(void)
 404 {
 405         if (initialized)
 406                 return;
 407         side_rcu_gp_init(&rcu_gp);
 408         initialized = true;
 409 }
 410
 411 /*
 412  * side_exit() is executed from a library destructor. It can be called
 413  * explicitly at application exit as well. Concurrent side API use is
 414  * not expected at that point.
 415  */
 416 void side_exit(void)
 417 {
 418         struct side_events_register_handle *handle, *tmp;
 419
 420         if (finalized)
 421                 return;
 422         side_rcu_gp_exit(&rcu_gp);
 423         side_list_for_each_entry_safe(handle, tmp, &side_events_list, node)
 424                 side_events_unregister(handle);
 425         finalized = true;
 426 }