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         rcu_period = side_rcu_read_begin(&rcu_gp);
  80         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call != NULL; side_cb++)
  81                 side_cb->u.call(desc, sav_desc, side_cb->priv);
  82         side_rcu_read_end(&rcu_gp, rcu_period);
  83 }
  84
  85 void side_call_variadic(const struct side_event_description *desc,
  86         const struct side_arg_vec_description *sav_desc,
  87         const struct side_arg_dynamic_event_struct *var_struct)
  88 {
  89         const struct side_callback *side_cb;
  90         unsigned int rcu_period;
  91         uint32_t enabled;
  92
  93         if (side_unlikely(finalized))
  94                 return;
  95         if (side_unlikely(!initialized))
  96                 side_init();
  97         if (side_unlikely(!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))) {
  98                 printf("ERROR: unexpected non-variadic event description\n");
  99                 abort();
 100         }
 101         enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
 102         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
 103                 // TODO: call kernel write.
 104         }
 105         if (side_unlikely(!(enabled & SIDE_EVENT_ENABLED_USER_MASK)))
 106                 return;
 107
 108         rcu_period = side_rcu_read_begin(&rcu_gp);
 109         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call_variadic != NULL; side_cb++)
 110                 side_cb->u.call_variadic(desc, sav_desc, var_struct, side_cb->priv);
 111         side_rcu_read_end(&rcu_gp, rcu_period);
 112 }
 113
 114 static
 115 const struct side_callback *side_tracer_callback_lookup(
 116                 const struct side_event_description *desc,
 117                 void (*call)(), void *priv)
 118 {
 119         const struct side_callback *cb;
 120
 121         for (cb = desc->callbacks; cb->u.call != NULL; cb++) {
 122                 if (cb->u.call == call && cb->priv == priv)
 123                         return cb;
 124         }
 125         return NULL;
 126 }
 127
 128 static
 129 int _side_tracer_callback_register(struct side_event_description *desc,
 130                 void (*call)(), void *priv)
 131 {
 132         struct side_callback *old_cb, *new_cb;
 133         int ret = SIDE_ERROR_OK;
 134         uint32_t old_nr_cb;
 135
 136         if (!call)
 137                 return SIDE_ERROR_INVAL;
 138         if (finalized)
 139                 return SIDE_ERROR_EXITING;
 140         if (!initialized)
 141                 side_init();
 142         pthread_mutex_lock(&side_lock);
 143         old_nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 144         if (old_nr_cb == SIDE_EVENT_ENABLED_USER_MASK) {
 145                 ret = SIDE_ERROR_INVAL;
 146                 goto unlock;
 147         }
 148         /* Reject duplicate (call, priv) tuples. */
 149         if (side_tracer_callback_lookup(desc, call, priv)) {
 150                 ret = SIDE_ERROR_EXIST;
 151                 goto unlock;
 152         }
 153         old_cb = (struct side_callback *) desc->callbacks;
 154         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 155         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 156         if (!new_cb) {
 157                 ret = SIDE_ERROR_NOMEM;
 158                 goto unlock;
 159         }
 160         memcpy(new_cb, old_cb, old_nr_cb);
 161         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 162                 new_cb[old_nr_cb].u.call_variadic = call;
 163         else
 164                 new_cb[old_nr_cb].u.call = call;
 165         new_cb[old_nr_cb].priv = priv;
 166         side_rcu_assign_pointer(desc->callbacks, new_cb);
 167         side_rcu_wait_grace_period(&rcu_gp);
 168         if (old_nr_cb)
 169                 free(old_cb);
 170         /* Increment concurrently with kernel setting the top bits. */
 171         (void) __atomic_add_fetch(desc->enabled, 1, __ATOMIC_RELAXED);
 172 unlock:
 173         pthread_mutex_unlock(&side_lock);
 174         return ret;
 175 }
 176
 177 int side_tracer_callback_register(struct side_event_description *desc,
 178                 void (*call)(const struct side_event_description *desc,
 179                         const struct side_arg_vec_description *sav_desc,
 180                         void *priv),
 181                 void *priv)
 182 {
 183         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 184                 return SIDE_ERROR_INVAL;
 185         return _side_tracer_callback_register(desc, call, priv);
 186 }
 187
 188 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 189                 void (*call_variadic)(const struct side_event_description *desc,
 190                         const struct side_arg_vec_description *sav_desc,
 191                         const struct side_arg_dynamic_event_struct *var_struct,
 192                         void *priv),
 193                 void *priv)
 194 {
 195         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 196                 return SIDE_ERROR_INVAL;
 197         return _side_tracer_callback_register(desc, call_variadic, priv);
 198 }
 199
 200 int _side_tracer_callback_unregister(struct side_event_description *desc,
 201                 void (*call)(), void *priv)
 202 {
 203         struct side_callback *old_cb, *new_cb;
 204         const struct side_callback *cb_pos;
 205         uint32_t pos_idx;
 206         int ret = SIDE_ERROR_OK;
 207         uint32_t old_nr_cb;
 208
 209         if (!call)
 210                 return SIDE_ERROR_INVAL;
 211         if (finalized)
 212                 return SIDE_ERROR_EXITING;
 213         if (!initialized)
 214                 side_init();
 215         pthread_mutex_lock(&side_lock);
 216         cb_pos = side_tracer_callback_lookup(desc, call, priv);
 217         if (!cb_pos) {
 218                 ret = SIDE_ERROR_NOENT;
 219                 goto unlock;
 220         }
 221         old_nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 222         old_cb = (struct side_callback *) desc->callbacks;
 223         if (old_nr_cb == 1) {
 224                 new_cb = (struct side_callback *) &side_empty_callback;
 225         } else {
 226                 pos_idx = cb_pos - desc->callbacks;
 227                 /* Remove entry at pos_idx. */
 228                 /* old_nr_cb - 1 (removed cb) + 1 (NULL) */
 229                 new_cb = (struct side_callback *) calloc(old_nr_cb, sizeof(struct side_callback));
 230                 if (!new_cb) {
 231                         ret = SIDE_ERROR_NOMEM;
 232                         goto unlock;
 233                 }
 234                 memcpy(new_cb, old_cb, pos_idx);
 235                 memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
 236         }
 237         side_rcu_assign_pointer(desc->callbacks, new_cb);
 238         side_rcu_wait_grace_period(&rcu_gp);
 239         free(old_cb);
 240         /* Decrement concurrently with kernel setting the top bits. */
 241         (void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
 242 unlock:
 243         pthread_mutex_unlock(&side_lock);
 244         return ret;
 245 }
 246
 247 int side_tracer_callback_unregister(struct side_event_description *desc,
 248                 void (*call)(const struct side_event_description *desc,
 249                         const struct side_arg_vec_description *sav_desc,
 250                         void *priv),
 251                 void *priv)
 252 {
 253         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 254                 return SIDE_ERROR_INVAL;
 255         return _side_tracer_callback_unregister(desc, call, priv);
 256 }
 257
 258 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 259                 void (*call_variadic)(const struct side_event_description *desc,
 260                         const struct side_arg_vec_description *sav_desc,
 261                         const struct side_arg_dynamic_event_struct *var_struct,
 262                         void *priv),
 263                 void *priv)
 264 {
 265         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 266                 return SIDE_ERROR_INVAL;
 267         return _side_tracer_callback_unregister(desc, call_variadic, priv);
 268 }
 269
 270 struct side_events_register_handle *side_events_register(struct side_event_description **events, uint32_t nr_events)
 271 {
 272         struct side_events_register_handle *events_handle = NULL;
 273         struct side_tracer_handle *tracer_handle;
 274
 275         if (finalized)
 276                 return NULL;
 277         if (!initialized)
 278                 side_init();
 279         events_handle = calloc(1, sizeof(struct side_events_register_handle));
 280         if (!events_handle)
 281                 return NULL;
 282         events_handle->events = events;
 283         events_handle->nr_events = nr_events;
 284
 285         pthread_mutex_lock(&side_lock);
 286         side_list_insert_node_tail(&side_events_list, &events_handle->node);
 287         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 288                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 289                         events, nr_events, tracer_handle->priv);
 290         }
 291         pthread_mutex_unlock(&side_lock);
 292         //TODO: call event batch register ioctl
 293         return events_handle;
 294 }
 295
 296 static
 297 void side_event_remove_callbacks(struct side_event_description *desc)
 298 {
 299         uint32_t nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 300         struct side_callback *old_cb;
 301
 302         if (!nr_cb)
 303                 return;
 304         old_cb = (struct side_callback *) desc->callbacks;
 305         /*
 306          * Setting the state back to 0 cb and empty callbacks out of
 307          * caution. This should not matter because instrumentation is
 308          * unreachable.
 309          */
 310         (void) __atomic_add_fetch(desc->enabled, -nr_cb, __ATOMIC_RELAXED);
 311         side_rcu_assign_pointer(desc->callbacks, &side_empty_callback);
 312         /*
 313          * No need to wait for grace period because instrumentation is
 314          * unreachable.
 315          */
 316         free(old_cb);
 317 }
 318
 319 /*
 320  * Unregister event handle. At this point, all side events in that
 321  * handle should be unreachable.
 322  */
 323 void side_events_unregister(struct side_events_register_handle *events_handle)
 324 {
 325         struct side_tracer_handle *tracer_handle;
 326         uint32_t i;
 327
 328         if (!events_handle)
 329                 return;
 330         if (finalized)
 331                 return;
 332         if (!initialized)
 333                 side_init();
 334         pthread_mutex_lock(&side_lock);
 335         side_list_remove_node(&events_handle->node);
 336         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 337                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 338                         events_handle->events, events_handle->nr_events,
 339                         tracer_handle->priv);
 340         }
 341         for (i = 0; i < events_handle->nr_events; i++) {
 342                 struct side_event_description *event = events_handle->events[i];
 343
 344                 /* Skip NULL pointers */
 345                 if (!event)
 346                         continue;
 347                 side_event_remove_callbacks(event);
 348         }
 349         pthread_mutex_unlock(&side_lock);
 350         //TODO: call event batch unregister ioctl
 351         free(events_handle);
 352 }
 353
 354 struct side_tracer_handle *side_tracer_event_notification_register(
 355                 void (*cb)(enum side_tracer_notification notif,
 356                         struct side_event_description **events, uint32_t nr_events, void *priv),
 357                 void *priv)
 358 {
 359         struct side_tracer_handle *tracer_handle;
 360         struct side_events_register_handle *events_handle;
 361
 362         if (finalized)
 363                 return NULL;
 364         if (!initialized)
 365                 side_init();
 366         tracer_handle = calloc(1, sizeof(struct side_tracer_handle));
 367         if (!tracer_handle)
 368                 return NULL;
 369         pthread_mutex_lock(&side_lock);
 370         tracer_handle->cb = cb;
 371         tracer_handle->priv = priv;
 372         side_list_insert_node_tail(&side_tracer_list, &tracer_handle->node);
 373         side_list_for_each_entry(events_handle, &side_events_list, node) {
 374                 cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 375                         events_handle->events, events_handle->nr_events, priv);
 376         }
 377         pthread_mutex_unlock(&side_lock);
 378         return tracer_handle;
 379 }
 380
 381 void side_tracer_event_notification_unregister(struct side_tracer_handle *tracer_handle)
 382 {
 383         struct side_events_register_handle *events_handle;
 384
 385         if (finalized)
 386                 return;
 387         if (!initialized)
 388                 side_init();
 389         pthread_mutex_lock(&side_lock);
 390         side_list_for_each_entry(events_handle, &side_events_list, node) {
 391                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 392                         events_handle->events, events_handle->nr_events,
 393                         tracer_handle->priv);
 394         }
 395         side_list_remove_node(&tracer_handle->node);
 396         pthread_mutex_unlock(&side_lock);
 397 }
 398
 399 void side_init(void)
 400 {
 401         if (initialized)
 402                 return;
 403         side_rcu_gp_init(&rcu_gp);
 404         initialized = true;
 405 }
 406
 407 /*
 408  * side_exit() is executed from a library destructor. It can be called
 409  * explicitly at application exit as well. Concurrent side API use is
 410  * not expected at that point.
 411  */
 412 void side_exit(void)
 413 {
 414         struct side_events_register_handle *handle, *tmp;
 415
 416         if (finalized)
 417                 return;
 418         side_rcu_gp_exit(&rcu_gp);
 419         side_list_for_each_entry_safe(handle, tmp, &side_events_list, node)
 420                 side_events_unregister(handle);
 421         finalized = true;
 422 }