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_rcu_read_state rcu_read_state;
  68         const struct side_callback *side_cb;
  69         uintptr_t enabled;
  70
  71         if (side_unlikely(finalized))
  72                 return;
  73         if (side_unlikely(!initialized))
  74                 side_init();
  75         if (side_unlikely(desc->flags & SIDE_EVENT_FLAG_VARIADIC)) {
  76                 printf("ERROR: unexpected variadic event description\n");
  77                 abort();
  78         }
  79         enabled = __atomic_load_n(&desc->state->enabled, __ATOMIC_RELAXED);
  80         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
  81                 // TODO: call kernel write.
  82         }
  83         side_rcu_read_begin(&rcu_gp, &rcu_read_state);
  84         for (side_cb = side_rcu_dereference(desc->state->callbacks); side_cb->u.call != NULL; side_cb++)
  85                 side_cb->u.call(desc, side_arg_vec, side_cb->priv);
  86         side_rcu_read_end(&rcu_gp, &rcu_read_state);
  87 }
  88
  89 void side_call_variadic(const struct side_event_description *desc,
  90         const struct side_arg_vec *side_arg_vec,
  91         const struct side_arg_dynamic_struct *var_struct)
  92 {
  93         struct side_rcu_read_state rcu_read_state;
  94         const struct side_callback *side_cb;
  95         uintptr_t enabled;
  96
  97         if (side_unlikely(finalized))
  98                 return;
  99         if (side_unlikely(!initialized))
 100                 side_init();
 101         if (side_unlikely(!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))) {
 102                 printf("ERROR: unexpected non-variadic event description\n");
 103                 abort();
 104         }
 105         enabled = __atomic_load_n(&desc->state->enabled, __ATOMIC_RELAXED);
 106         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
 107                 // TODO: call kernel write.
 108         }
 109         side_rcu_read_begin(&rcu_gp, &rcu_read_state);
 110         for (side_cb = side_rcu_dereference(desc->state->callbacks); side_cb->u.call_variadic != NULL; side_cb++)
 111                 side_cb->u.call_variadic(desc, side_arg_vec, var_struct, side_cb->priv);
 112         side_rcu_read_end(&rcu_gp, &rcu_read_state);
 113 }
 114
 115 static
 116 const struct side_callback *side_tracer_callback_lookup(
 117                 const struct side_event_description *desc,
 118                 void *call, void *priv)
 119 {
 120         const struct side_callback *cb;
 121
 122         for (cb = desc->state->callbacks; cb->u.call != NULL; cb++) {
 123                 if ((void *) cb->u.call == call && cb->priv == priv)
 124                         return cb;
 125         }
 126         return NULL;
 127 }
 128
 129 static
 130 int _side_tracer_callback_register(struct side_event_description *desc,
 131                 void *call, void *priv)
 132 {
 133         struct side_callback *old_cb, *new_cb;
 134         int ret = SIDE_ERROR_OK;
 135         uint32_t old_nr_cb;
 136
 137         if (!call)
 138                 return SIDE_ERROR_INVAL;
 139         if (finalized)
 140                 return SIDE_ERROR_EXITING;
 141         if (!initialized)
 142                 side_init();
 143         pthread_mutex_lock(&side_lock);
 144         old_nr_cb = desc->state->nr_callbacks;
 145         if (old_nr_cb == UINT32_MAX) {
 146                 ret = SIDE_ERROR_INVAL;
 147                 goto unlock;
 148         }
 149         /* Reject duplicate (call, priv) tuples. */
 150         if (side_tracer_callback_lookup(desc, call, priv)) {
 151                 ret = SIDE_ERROR_EXIST;
 152                 goto unlock;
 153         }
 154         old_cb = (struct side_callback *) desc->state->callbacks;
 155         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 156         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 157         if (!new_cb) {
 158                 ret = SIDE_ERROR_NOMEM;
 159                 goto unlock;
 160         }
 161         memcpy(new_cb, old_cb, old_nr_cb);
 162         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 163                 new_cb[old_nr_cb].u.call_variadic =
 164                         (side_tracer_callback_variadic_func) call;
 165         else
 166                 new_cb[old_nr_cb].u.call =
 167                         (side_tracer_callback_func) call;
 168         new_cb[old_nr_cb].priv = priv;
 169         side_rcu_assign_pointer(desc->state->callbacks, new_cb);
 170         side_rcu_wait_grace_period(&rcu_gp);
 171         if (old_nr_cb)
 172                 free(old_cb);
 173         desc->state->nr_callbacks++;
 174         /* Increment concurrently with kernel setting the top bits. */
 175         if (!old_nr_cb)
 176                 (void) __atomic_add_fetch(&desc->state->enabled, 1, __ATOMIC_RELAXED);
 177 unlock:
 178         pthread_mutex_unlock(&side_lock);
 179         return ret;
 180 }
 181
 182 int side_tracer_callback_register(struct side_event_description *desc,
 183                 side_tracer_callback_func call,
 184                 void *priv)
 185 {
 186         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 187                 return SIDE_ERROR_INVAL;
 188         return _side_tracer_callback_register(desc, (void *) call, priv);
 189 }
 190
 191 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 192                 side_tracer_callback_variadic_func call_variadic,
 193                 void *priv)
 194 {
 195         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 196                 return SIDE_ERROR_INVAL;
 197         return _side_tracer_callback_register(desc, (void *) call_variadic, priv);
 198 }
 199
 200 static 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->state->nr_callbacks;
 222         old_cb = (struct side_callback *) desc->state->callbacks;
 223         if (old_nr_cb == 1) {
 224                 new_cb = (struct side_callback *) &side_empty_callback;
 225         } else {
 226                 pos_idx = cb_pos - desc->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(desc->state->callbacks, new_cb);
 238         side_rcu_wait_grace_period(&rcu_gp);
 239         free(old_cb);
 240         desc->state->nr_callbacks--;
 241         /* Decrement concurrently with kernel setting the top bits. */
 242         if (old_nr_cb == 1)
 243                 (void) __atomic_add_fetch(&desc->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         uint32_t nr_cb = desc->state->nr_callbacks;
 298         struct side_callback *old_cb;
 299
 300         if (!nr_cb)
 301                 return;
 302         old_cb = (struct side_callback *) desc->state->callbacks;
 303         (void) __atomic_add_fetch(&desc->state->enabled, -1, __ATOMIC_RELAXED);
 304         /*
 305          * Setting the state back to 0 cb and empty callbacks out of
 306          * caution. This should not matter because instrumentation is
 307          * unreachable.
 308          */
 309         desc->state->nr_callbacks = 0;
 310         side_rcu_assign_pointer(desc->state->callbacks, &side_empty_callback);
 311         /*
 312          * No need to wait for grace period because instrumentation is
 313          * unreachable.
 314          */
 315         free(old_cb);
 316 }
 317
 318 /*
 319  * Unregister event handle. At this point, all side events in that
 320  * handle should be unreachable.
 321  */
 322 void side_events_unregister(struct side_events_register_handle *events_handle)
 323 {
 324         struct side_tracer_handle *tracer_handle;
 325         uint32_t i;
 326
 327         if (!events_handle)
 328                 return;
 329         if (finalized)
 330                 return;
 331         if (!initialized)
 332                 side_init();
 333         pthread_mutex_lock(&side_lock);
 334         side_list_remove_node(&events_handle->node);
 335         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 336                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 337                         events_handle->events, events_handle->nr_events,
 338                         tracer_handle->priv);
 339         }
 340         for (i = 0; i < events_handle->nr_events; i++) {
 341                 struct side_event_description *event = events_handle->events[i];
 342
 343                 /* Skip NULL pointers */
 344                 if (!event)
 345                         continue;
 346                 side_event_remove_callbacks(event);
 347         }
 348         pthread_mutex_unlock(&side_lock);
 349         //TODO: call event batch unregister ioctl
 350         free(events_handle);
 351 }
 352
 353 struct side_tracer_handle *side_tracer_event_notification_register(
 354                 void (*cb)(enum side_tracer_notification notif,
 355                         struct side_event_description **events, uint32_t nr_events, void *priv),
 356                 void *priv)
 357 {
 358         struct side_tracer_handle *tracer_handle;
 359         struct side_events_register_handle *events_handle;
 360
 361         if (finalized)
 362                 return NULL;
 363         if (!initialized)
 364                 side_init();
 365         tracer_handle = (struct side_tracer_handle *)
 366                                 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         free(tracer_handle);
 398 }
 399
 400 void side_init(void)
 401 {
 402         if (initialized)
 403                 return;
 404         side_rcu_gp_init(&rcu_gp);
 405         initialized = true;
 406 }
 407
 408 /*
 409  * side_exit() is executed from a library destructor. It can be called
 410  * explicitly at application exit as well. Concurrent side API use is
 411  * not expected at that point.
 412  */
 413 void side_exit(void)
 414 {
 415         struct side_events_register_handle *handle, *tmp;
 416
 417         if (finalized)
 418                 return;
 419         side_list_for_each_entry_safe(handle, tmp, &side_events_list, node)
 420                 side_events_unregister(handle);
 421         side_rcu_gp_exit(&rcu_gp);
 422         finalized = true;
 423 }