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 #include <assert.h>
   9
  10 #include "rcu.h"
  11 #include "list.h"
  12
  13 /* Top 8 bits reserved for kernel tracer use. */
  14 #if SIDE_BITS_PER_LONG == 64
  15 # define SIDE_EVENT_ENABLED_KERNEL_MASK                 0xFF00000000000000ULL
  16 # define SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK      0x8000000000000000ULL
  17
  18 /* Allow 2^56 tracer references on an event. */
  19 # define SIDE_EVENT_ENABLED_USER_MASK                   0x00FFFFFFFFFFFFFFULL
  20 #else
  21 # define SIDE_EVENT_ENABLED_KERNEL_MASK                 0xFF000000UL
  22 # define SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK      0x80000000UL
  23
  24 /* Allow 2^24 tracer references on an event. */
  25 # define SIDE_EVENT_ENABLED_USER_MASK                   0x00FFFFFFUL
  26 #endif
  27
  28 struct side_events_register_handle {
  29         struct side_list_node node;
  30         struct side_event_description **events;
  31         uint32_t nr_events;
  32 };
  33
  34 struct side_tracer_handle {
  35         struct side_list_node node;
  36         void (*cb)(enum side_tracer_notification notif,
  37                 struct side_event_description **events, uint32_t nr_events, void *priv);
  38         void *priv;
  39 };
  40
  41 static struct side_rcu_gp_state rcu_gp;
  42
  43 /*
  44  * Lazy initialization for early use within library constructors.
  45  */
  46 static bool initialized;
  47 /*
  48  * Do not register/unregister any more events after destructor.
  49  */
  50 static bool finalized;
  51
  52 /*
  53  * Recursive mutex to allow tracer callbacks to use the side API.
  54  */
  55 static pthread_mutex_t side_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
  56
  57 static DEFINE_SIDE_LIST_HEAD(side_events_list);
  58 static DEFINE_SIDE_LIST_HEAD(side_tracer_list);
  59
  60 /*
  61  * The empty callback has a NULL function callback pointer, which stops
  62  * iteration on the array of callbacks immediately.
  63  */
  64 const struct side_callback side_empty_callback = { };
  65
  66 void side_call(const struct side_event_state *event_state, const struct side_arg_vec *side_arg_vec)
  67 {
  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         assert(!(event_state->desc->flags & SIDE_EVENT_FLAG_VARIADIC));
  77         enabled = __atomic_load_n(&event_state->enabled, __ATOMIC_RELAXED);
  78         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
  79                 // TODO: call kernel write.
  80         }
  81         side_rcu_read_begin(&rcu_gp, &rcu_read_state);
  82         for (side_cb = side_rcu_dereference(event_state->callbacks); side_cb->u.call != NULL; side_cb++)
  83                 side_cb->u.call(event_state->desc, side_arg_vec, side_cb->priv);
  84         side_rcu_read_end(&rcu_gp, &rcu_read_state);
  85 }
  86
  87 void side_call_variadic(const struct side_event_state *event_state,
  88         const struct side_arg_vec *side_arg_vec,
  89         const struct side_arg_dynamic_struct *var_struct)
  90 {
  91         struct side_rcu_read_state rcu_read_state;
  92         const struct side_callback *side_cb;
  93         uintptr_t enabled;
  94
  95         if (side_unlikely(finalized))
  96                 return;
  97         if (side_unlikely(!initialized))
  98                 side_init();
  99         assert(event_state->desc->flags & SIDE_EVENT_FLAG_VARIADIC);
 100         enabled = __atomic_load_n(&event_state->enabled, __ATOMIC_RELAXED);
 101         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
 102                 // TODO: call kernel write.
 103         }
 104         side_rcu_read_begin(&rcu_gp, &rcu_read_state);
 105         for (side_cb = side_rcu_dereference(event_state->callbacks); side_cb->u.call_variadic != NULL; side_cb++)
 106                 side_cb->u.call_variadic(event_state->desc, side_arg_vec, var_struct, side_cb->priv);
 107         side_rcu_read_end(&rcu_gp, &rcu_read_state);
 108 }
 109
 110 static
 111 const struct side_callback *side_tracer_callback_lookup(
 112                 const struct side_event_description *desc,
 113                 void *call, void *priv)
 114 {
 115         struct side_event_state *event_state = side_ptr_get(desc->state);
 116         const struct side_callback *cb;
 117
 118         for (cb = event_state->callbacks; cb->u.call != NULL; cb++) {
 119                 if ((void *) cb->u.call == call && cb->priv == priv)
 120                         return cb;
 121         }
 122         return NULL;
 123 }
 124
 125 static
 126 int _side_tracer_callback_register(struct side_event_description *desc,
 127                 void *call, void *priv)
 128 {
 129         struct side_event_state *event_state;
 130         struct side_callback *old_cb, *new_cb;
 131         int ret = SIDE_ERROR_OK;
 132         uint32_t old_nr_cb;
 133
 134         if (!call)
 135                 return SIDE_ERROR_INVAL;
 136         if (finalized)
 137                 return SIDE_ERROR_EXITING;
 138         if (!initialized)
 139                 side_init();
 140         pthread_mutex_lock(&side_lock);
 141         event_state = side_ptr_get(desc->state);
 142         old_nr_cb = desc->nr_callbacks;
 143         if (old_nr_cb == UINT32_MAX) {
 144                 ret = SIDE_ERROR_INVAL;
 145                 goto unlock;
 146         }
 147         /* Reject duplicate (call, priv) tuples. */
 148         if (side_tracer_callback_lookup(desc, call, priv)) {
 149                 ret = SIDE_ERROR_EXIST;
 150                 goto unlock;
 151         }
 152         old_cb = (struct side_callback *) event_state->callbacks;
 153         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 154         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 155         if (!new_cb) {
 156                 ret = SIDE_ERROR_NOMEM;
 157                 goto unlock;
 158         }
 159         memcpy(new_cb, old_cb, old_nr_cb);
 160         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 161                 new_cb[old_nr_cb].u.call_variadic =
 162                         (side_tracer_callback_variadic_func) call;
 163         else
 164                 new_cb[old_nr_cb].u.call =
 165                         (side_tracer_callback_func) call;
 166         new_cb[old_nr_cb].priv = priv;
 167         side_rcu_assign_pointer(event_state->callbacks, new_cb);
 168         side_rcu_wait_grace_period(&rcu_gp);
 169         if (old_nr_cb)
 170                 free(old_cb);
 171         desc->nr_callbacks++;
 172         /* Increment concurrently with kernel setting the top bits. */
 173         if (!old_nr_cb)
 174                 (void) __atomic_add_fetch(&event_state->enabled, 1, __ATOMIC_RELAXED);
 175 unlock:
 176         pthread_mutex_unlock(&side_lock);
 177         return ret;
 178 }
 179
 180 int side_tracer_callback_register(struct side_event_description *desc,
 181                 side_tracer_callback_func call,
 182                 void *priv)
 183 {
 184         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 185                 return SIDE_ERROR_INVAL;
 186         return _side_tracer_callback_register(desc, (void *) call, priv);
 187 }
 188
 189 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 190                 side_tracer_callback_variadic_func call_variadic,
 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_variadic, priv);
 196 }
 197
 198 static int _side_tracer_callback_unregister(struct side_event_description *desc,
 199                 void *call, void *priv)
 200 {
 201         struct side_event_state *event_state;
 202         struct side_callback *old_cb, *new_cb;
 203         const struct side_callback *cb_pos;
 204         uint32_t pos_idx;
 205         int ret = SIDE_ERROR_OK;
 206         uint32_t old_nr_cb;
 207
 208         if (!call)
 209                 return SIDE_ERROR_INVAL;
 210         if (finalized)
 211                 return SIDE_ERROR_EXITING;
 212         if (!initialized)
 213                 side_init();
 214         pthread_mutex_lock(&side_lock);
 215         event_state = side_ptr_get(desc->state);
 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->nr_callbacks;
 222         old_cb = (struct side_callback *) event_state->callbacks;
 223         if (old_nr_cb == 1) {
 224                 new_cb = (struct side_callback *) &side_empty_callback;
 225         } else {
 226                 pos_idx = cb_pos - event_state->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(event_state->callbacks, new_cb);
 238         side_rcu_wait_grace_period(&rcu_gp);
 239         free(old_cb);
 240         desc->nr_callbacks--;
 241         /* Decrement concurrently with kernel setting the top bits. */
 242         if (old_nr_cb == 1)
 243                 (void) __atomic_add_fetch(&event_state->enabled, -1, __ATOMIC_RELAXED);
 244 unlock:
 245         pthread_mutex_unlock(&side_lock);
 246         return ret;
 247 }
 248
 249 int side_tracer_callback_unregister(struct side_event_description *desc,
 250                 side_tracer_callback_func call,
 251                 void *priv)
 252 {
 253         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 254                 return SIDE_ERROR_INVAL;
 255         return _side_tracer_callback_unregister(desc, (void *) call, priv);
 256 }
 257
 258 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 259                 side_tracer_callback_variadic_func call_variadic,
 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_variadic, priv);
 265 }
 266
 267 struct side_events_register_handle *side_events_register(struct side_event_description **events, uint32_t nr_events)
 268 {
 269         struct side_events_register_handle *events_handle = NULL;
 270         struct side_tracer_handle *tracer_handle;
 271
 272         if (finalized)
 273                 return NULL;
 274         if (!initialized)
 275                 side_init();
 276         events_handle = (struct side_events_register_handle *)
 277                         calloc(1, sizeof(struct side_events_register_handle));
 278         if (!events_handle)
 279                 return NULL;
 280         events_handle->events = events;
 281         events_handle->nr_events = nr_events;
 282
 283         pthread_mutex_lock(&side_lock);
 284         side_list_insert_node_tail(&side_events_list, &events_handle->node);
 285         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 286                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 287                         events, nr_events, tracer_handle->priv);
 288         }
 289         pthread_mutex_unlock(&side_lock);
 290         //TODO: call event batch register ioctl
 291         return events_handle;
 292 }
 293
 294 static
 295 void side_event_remove_callbacks(struct side_event_description *desc)
 296 {
 297         struct side_event_state *event_state = side_ptr_get(desc->state);
 298         uint32_t nr_cb = desc->nr_callbacks;
 299         struct side_callback *old_cb;
 300
 301         if (!nr_cb)
 302                 return;
 303         old_cb = (struct side_callback *) event_state->callbacks;
 304         (void) __atomic_add_fetch(&event_state->enabled, -1, __ATOMIC_RELAXED);
 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         desc->nr_callbacks = 0;
 311         side_rcu_assign_pointer(event_state->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 = (struct side_tracer_handle *)
 367                                 calloc(1, sizeof(struct side_tracer_handle));
 368         if (!tracer_handle)
 369                 return NULL;
 370         pthread_mutex_lock(&side_lock);
 371         tracer_handle->cb = cb;
 372         tracer_handle->priv = priv;
 373         side_list_insert_node_tail(&side_tracer_list, &tracer_handle->node);
 374         side_list_for_each_entry(events_handle, &side_events_list, node) {
 375                 cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 376                         events_handle->events, events_handle->nr_events, priv);
 377         }
 378         pthread_mutex_unlock(&side_lock);
 379         return tracer_handle;
 380 }
 381
 382 void side_tracer_event_notification_unregister(struct side_tracer_handle *tracer_handle)
 383 {
 384         struct side_events_register_handle *events_handle;
 385
 386         if (finalized)
 387                 return;
 388         if (!initialized)
 389                 side_init();
 390         pthread_mutex_lock(&side_lock);
 391         side_list_for_each_entry(events_handle, &side_events_list, node) {
 392                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 393                         events_handle->events, events_handle->nr_events,
 394                         tracer_handle->priv);
 395         }
 396         side_list_remove_node(&tracer_handle->node);
 397         pthread_mutex_unlock(&side_lock);
 398         free(tracer_handle);
 399 }
 400
 401 void side_init(void)
 402 {
 403         if (initialized)
 404                 return;
 405         side_rcu_gp_init(&rcu_gp);
 406         initialized = true;
 407 }
 408
 409 /*
 410  * side_exit() is executed from a library destructor. It can be called
 411  * explicitly at application exit as well. Concurrent side API use is
 412  * not expected at that point.
 413  */
 414 void side_exit(void)
 415 {
 416         struct side_events_register_handle *handle, *tmp;
 417
 418         if (finalized)
 419                 return;
 420         side_list_for_each_entry_safe(handle, tmp, &side_events_list, node)
 421                 side_events_unregister(handle);
 422         side_rcu_gp_exit(&rcu_gp);
 423         finalized = true;
 424 }