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 "rcu.h"
  10 #include "list.h"
  11
  12 /* Top 8 bits reserved for kernel tracer use. */
  13 #if SIDE_BITS_PER_LONG == 64
  14 # define SIDE_EVENT_ENABLED_KERNEL_MASK                 0xFF00000000000000ULL
  15 # define SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK      0x8000000000000000ULL
  16
  17 /* Allow 2^56 tracer references on an event. */
  18 # define SIDE_EVENT_ENABLED_USER_MASK                   0x00FFFFFFFFFFFFFFULL
  19 #else
  20 # define SIDE_EVENT_ENABLED_KERNEL_MASK                 0xFF000000UL
  21 # define SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK      0x80000000UL
  22
  23 /* Allow 2^24 tracer references on an event. */
  24 # define SIDE_EVENT_ENABLED_USER_MASK                   0x00FFFFFFUL
  25 #endif
  26
  27 struct side_events_register_handle {
  28         struct side_list_node node;
  29         struct side_event_description **events;
  30         uint32_t nr_events;
  31 };
  32
  33 struct side_tracer_handle {
  34         struct side_list_node node;
  35         void (*cb)(enum side_tracer_notification notif,
  36                 struct side_event_description **events, uint32_t nr_events, void *priv);
  37         void *priv;
  38 };
  39
  40 static struct side_rcu_gp_state rcu_gp;
  41
  42 /*
  43  * Lazy initialization for early use within library constructors.
  44  */
  45 static bool initialized;
  46 /*
  47  * Do not register/unregister any more events after destructor.
  48  */
  49 static bool finalized;
  50
  51 /*
  52  * Recursive mutex to allow tracer callbacks to use the side API.
  53  */
  54 static pthread_mutex_t side_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
  55
  56 static DEFINE_SIDE_LIST_HEAD(side_events_list);
  57 static DEFINE_SIDE_LIST_HEAD(side_tracer_list);
  58
  59 /*
  60  * The empty callback has a NULL function callback pointer, which stops
  61  * iteration on the array of callbacks immediately.
  62  */
  63 const struct side_callback side_empty_callback = { };
  64
  65 void side_call(const struct side_event_description *desc, const struct side_arg_vec *side_arg_vec)
  66 {
  67         struct side_event_state *event_state;
  68         struct side_rcu_read_state rcu_read_state;
  69         const struct side_callback *side_cb;
  70         uintptr_t enabled;
  71
  72         if (side_unlikely(finalized))
  73                 return;
  74         if (side_unlikely(!initialized))
  75                 side_init();
  76         if (side_unlikely(desc->flags & SIDE_EVENT_FLAG_VARIADIC)) {
  77                 printf("ERROR: unexpected variadic event description\n");
  78                 abort();
  79         }
  80         event_state = side_ptr_get(desc->state);
  81         enabled = __atomic_load_n(&event_state->enabled, __ATOMIC_RELAXED);
  82         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
  83                 // TODO: call kernel write.
  84         }
  85         side_rcu_read_begin(&rcu_gp, &rcu_read_state);
  86         for (side_cb = side_rcu_dereference(event_state->callbacks); side_cb->u.call != NULL; side_cb++)
  87                 side_cb->u.call(desc, side_arg_vec, side_cb->priv);
  88         side_rcu_read_end(&rcu_gp, &rcu_read_state);
  89 }
  90
  91 void side_call_variadic(const struct side_event_description *desc,
  92         const struct side_arg_vec *side_arg_vec,
  93         const struct side_arg_dynamic_struct *var_struct)
  94 {
  95         struct side_event_state *event_state;
  96         struct side_rcu_read_state rcu_read_state;
  97         const struct side_callback *side_cb;
  98         uintptr_t enabled;
  99
 100         if (side_unlikely(finalized))
 101                 return;
 102         if (side_unlikely(!initialized))
 103                 side_init();
 104         if (side_unlikely(!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))) {
 105                 printf("ERROR: unexpected non-variadic event description\n");
 106                 abort();
 107         }
 108         event_state = side_ptr_get(desc->state);
 109         enabled = __atomic_load_n(&event_state->enabled, __ATOMIC_RELAXED);
 110         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
 111                 // TODO: call kernel write.
 112         }
 113         side_rcu_read_begin(&rcu_gp, &rcu_read_state);
 114         for (side_cb = side_rcu_dereference(event_state->callbacks); side_cb->u.call_variadic != NULL; side_cb++)
 115                 side_cb->u.call_variadic(desc, side_arg_vec, var_struct, side_cb->priv);
 116         side_rcu_read_end(&rcu_gp, &rcu_read_state);
 117 }
 118
 119 static
 120 const struct side_callback *side_tracer_callback_lookup(
 121                 const struct side_event_description *desc,
 122                 void *call, void *priv)
 123 {
 124         struct side_event_state *event_state = side_ptr_get(desc->state);
 125         const struct side_callback *cb;
 126
 127         for (cb = event_state->callbacks; cb->u.call != NULL; cb++) {
 128                 if ((void *) 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_event_state *event_state;
 139         struct side_callback *old_cb, *new_cb;
 140         int ret = SIDE_ERROR_OK;
 141         uint32_t old_nr_cb;
 142
 143         if (!call)
 144                 return SIDE_ERROR_INVAL;
 145         if (finalized)
 146                 return SIDE_ERROR_EXITING;
 147         if (!initialized)
 148                 side_init();
 149         pthread_mutex_lock(&side_lock);
 150         event_state = side_ptr_get(desc->state);
 151         old_nr_cb = event_state->nr_callbacks;
 152         if (old_nr_cb == UINT32_MAX) {
 153                 ret = SIDE_ERROR_INVAL;
 154                 goto unlock;
 155         }
 156         /* Reject duplicate (call, priv) tuples. */
 157         if (side_tracer_callback_lookup(desc, call, priv)) {
 158                 ret = SIDE_ERROR_EXIST;
 159                 goto unlock;
 160         }
 161         old_cb = (struct side_callback *) event_state->callbacks;
 162         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 163         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 164         if (!new_cb) {
 165                 ret = SIDE_ERROR_NOMEM;
 166                 goto unlock;
 167         }
 168         memcpy(new_cb, old_cb, old_nr_cb);
 169         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 170                 new_cb[old_nr_cb].u.call_variadic =
 171                         (side_tracer_callback_variadic_func) call;
 172         else
 173                 new_cb[old_nr_cb].u.call =
 174                         (side_tracer_callback_func) call;
 175         new_cb[old_nr_cb].priv = priv;
 176         side_rcu_assign_pointer(event_state->callbacks, new_cb);
 177         side_rcu_wait_grace_period(&rcu_gp);
 178         if (old_nr_cb)
 179                 free(old_cb);
 180         event_state->nr_callbacks++;
 181         /* Increment concurrently with kernel setting the top bits. */
 182         if (!old_nr_cb)
 183                 (void) __atomic_add_fetch(&event_state->enabled, 1, __ATOMIC_RELAXED);
 184 unlock:
 185         pthread_mutex_unlock(&side_lock);
 186         return ret;
 187 }
 188
 189 int side_tracer_callback_register(struct side_event_description *desc,
 190                 side_tracer_callback_func call,
 191                 void *priv)
 192 {
 193         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 194                 return SIDE_ERROR_INVAL;
 195         return _side_tracer_callback_register(desc, (void *) call, priv);
 196 }
 197
 198 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 199                 side_tracer_callback_variadic_func call_variadic,
 200                 void *priv)
 201 {
 202         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 203                 return SIDE_ERROR_INVAL;
 204         return _side_tracer_callback_register(desc, (void *) call_variadic, priv);
 205 }
 206
 207 static int _side_tracer_callback_unregister(struct side_event_description *desc,
 208                 void *call, void *priv)
 209 {
 210         struct side_event_state *event_state;
 211         struct side_callback *old_cb, *new_cb;
 212         const struct side_callback *cb_pos;
 213         uint32_t pos_idx;
 214         int ret = SIDE_ERROR_OK;
 215         uint32_t old_nr_cb;
 216
 217         if (!call)
 218                 return SIDE_ERROR_INVAL;
 219         if (finalized)
 220                 return SIDE_ERROR_EXITING;
 221         if (!initialized)
 222                 side_init();
 223         pthread_mutex_lock(&side_lock);
 224         event_state = side_ptr_get(desc->state);
 225         cb_pos = side_tracer_callback_lookup(desc, call, priv);
 226         if (!cb_pos) {
 227                 ret = SIDE_ERROR_NOENT;
 228                 goto unlock;
 229         }
 230         old_nr_cb = event_state->nr_callbacks;
 231         old_cb = (struct side_callback *) event_state->callbacks;
 232         if (old_nr_cb == 1) {
 233                 new_cb = (struct side_callback *) &side_empty_callback;
 234         } else {
 235                 pos_idx = cb_pos - event_state->callbacks;
 236                 /* Remove entry at pos_idx. */
 237                 /* old_nr_cb - 1 (removed cb) + 1 (NULL) */
 238                 new_cb = (struct side_callback *) calloc(old_nr_cb, sizeof(struct side_callback));
 239                 if (!new_cb) {
 240                         ret = SIDE_ERROR_NOMEM;
 241                         goto unlock;
 242                 }
 243                 memcpy(new_cb, old_cb, pos_idx);
 244                 memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
 245         }
 246         side_rcu_assign_pointer(event_state->callbacks, new_cb);
 247         side_rcu_wait_grace_period(&rcu_gp);
 248         free(old_cb);
 249         event_state->nr_callbacks--;
 250         /* Decrement concurrently with kernel setting the top bits. */
 251         if (old_nr_cb == 1)
 252                 (void) __atomic_add_fetch(&event_state->enabled, -1, __ATOMIC_RELAXED);
 253 unlock:
 254         pthread_mutex_unlock(&side_lock);
 255         return ret;
 256 }
 257
 258 int side_tracer_callback_unregister(struct side_event_description *desc,
 259                 side_tracer_callback_func call,
 260                 void *priv)
 261 {
 262         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 263                 return SIDE_ERROR_INVAL;
 264         return _side_tracer_callback_unregister(desc, (void *) call, priv);
 265 }
 266
 267 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 268                 side_tracer_callback_variadic_func call_variadic,
 269                 void *priv)
 270 {
 271         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 272                 return SIDE_ERROR_INVAL;
 273         return _side_tracer_callback_unregister(desc, (void *) 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 = (struct side_events_register_handle *)
 286                         calloc(1, sizeof(struct side_events_register_handle));
 287         if (!events_handle)
 288                 return NULL;
 289         events_handle->events = events;
 290         events_handle->nr_events = nr_events;
 291
 292         pthread_mutex_lock(&side_lock);
 293         side_list_insert_node_tail(&side_events_list, &events_handle->node);
 294         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 295                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 296                         events, nr_events, tracer_handle->priv);
 297         }
 298         pthread_mutex_unlock(&side_lock);
 299         //TODO: call event batch register ioctl
 300         return events_handle;
 301 }
 302
 303 static
 304 void side_event_remove_callbacks(struct side_event_description *desc)
 305 {
 306         struct side_event_state *event_state = side_ptr_get(desc->state);
 307         uint32_t nr_cb = event_state->nr_callbacks;
 308         struct side_callback *old_cb;
 309
 310         if (!nr_cb)
 311                 return;
 312         old_cb = (struct side_callback *) event_state->callbacks;
 313         (void) __atomic_add_fetch(&event_state->enabled, -1, __ATOMIC_RELAXED);
 314         /*
 315          * Setting the state back to 0 cb and empty callbacks out of
 316          * caution. This should not matter because instrumentation is
 317          * unreachable.
 318          */
 319         event_state->nr_callbacks = 0;
 320         side_rcu_assign_pointer(event_state->callbacks, &side_empty_callback);
 321         /*
 322          * No need to wait for grace period because instrumentation is
 323          * unreachable.
 324          */
 325         free(old_cb);
 326 }
 327
 328 /*
 329  * Unregister event handle. At this point, all side events in that
 330  * handle should be unreachable.
 331  */
 332 void side_events_unregister(struct side_events_register_handle *events_handle)
 333 {
 334         struct side_tracer_handle *tracer_handle;
 335         uint32_t i;
 336
 337         if (!events_handle)
 338                 return;
 339         if (finalized)
 340                 return;
 341         if (!initialized)
 342                 side_init();
 343         pthread_mutex_lock(&side_lock);
 344         side_list_remove_node(&events_handle->node);
 345         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 346                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 347                         events_handle->events, events_handle->nr_events,
 348                         tracer_handle->priv);
 349         }
 350         for (i = 0; i < events_handle->nr_events; i++) {
 351                 struct side_event_description *event = events_handle->events[i];
 352
 353                 /* Skip NULL pointers */
 354                 if (!event)
 355                         continue;
 356                 side_event_remove_callbacks(event);
 357         }
 358         pthread_mutex_unlock(&side_lock);
 359         //TODO: call event batch unregister ioctl
 360         free(events_handle);
 361 }
 362
 363 struct side_tracer_handle *side_tracer_event_notification_register(
 364                 void (*cb)(enum side_tracer_notification notif,
 365                         struct side_event_description **events, uint32_t nr_events, void *priv),
 366                 void *priv)
 367 {
 368         struct side_tracer_handle *tracer_handle;
 369         struct side_events_register_handle *events_handle;
 370
 371         if (finalized)
 372                 return NULL;
 373         if (!initialized)
 374                 side_init();
 375         tracer_handle = (struct side_tracer_handle *)
 376                                 calloc(1, sizeof(struct side_tracer_handle));
 377         if (!tracer_handle)
 378                 return NULL;
 379         pthread_mutex_lock(&side_lock);
 380         tracer_handle->cb = cb;
 381         tracer_handle->priv = priv;
 382         side_list_insert_node_tail(&side_tracer_list, &tracer_handle->node);
 383         side_list_for_each_entry(events_handle, &side_events_list, node) {
 384                 cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 385                         events_handle->events, events_handle->nr_events, priv);
 386         }
 387         pthread_mutex_unlock(&side_lock);
 388         return tracer_handle;
 389 }
 390
 391 void side_tracer_event_notification_unregister(struct side_tracer_handle *tracer_handle)
 392 {
 393         struct side_events_register_handle *events_handle;
 394
 395         if (finalized)
 396                 return;
 397         if (!initialized)
 398                 side_init();
 399         pthread_mutex_lock(&side_lock);
 400         side_list_for_each_entry(events_handle, &side_events_list, node) {
 401                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 402                         events_handle->events, events_handle->nr_events,
 403                         tracer_handle->priv);
 404         }
 405         side_list_remove_node(&tracer_handle->node);
 406         pthread_mutex_unlock(&side_lock);
 407         free(tracer_handle);
 408 }
 409
 410 void side_init(void)
 411 {
 412         if (initialized)
 413                 return;
 414         side_rcu_gp_init(&rcu_gp);
 415         initialized = true;
 416 }
 417
 418 /*
 419  * side_exit() is executed from a library destructor. It can be called
 420  * explicitly at application exit as well. Concurrent side API use is
 421  * not expected at that point.
 422  */
 423 void side_exit(void)
 424 {
 425         struct side_events_register_handle *handle, *tmp;
 426
 427         if (finalized)
 428                 return;
 429         side_list_for_each_entry_safe(handle, tmp, &side_events_list, node)
 430                 side_events_unregister(handle);
 431         side_rcu_gp_exit(&rcu_gp);
 432         finalized = true;
 433 }