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 references 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->nr_callbacks;
 144         if (old_nr_cb == UINT32_MAX) {
 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         desc->nr_callbacks++;
 171         /* Increment concurrently with kernel setting the top bits. */
 172         if (!old_nr_cb)
 173                 (void) __atomic_add_fetch(desc->enabled, 1, __ATOMIC_RELAXED);
 174 unlock:
 175         pthread_mutex_unlock(&side_lock);
 176         return ret;
 177 }
 178
 179 int side_tracer_callback_register(struct side_event_description *desc,
 180                 void (*call)(const struct side_event_description *desc,
 181                         const struct side_arg_vec_description *sav_desc,
 182                         void *priv),
 183                 void *priv)
 184 {
 185         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 186                 return SIDE_ERROR_INVAL;
 187         return _side_tracer_callback_register(desc, call, priv);
 188 }
 189
 190 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 191                 void (*call_variadic)(const struct side_event_description *desc,
 192                         const struct side_arg_vec_description *sav_desc,
 193                         const struct side_arg_dynamic_event_struct *var_struct,
 194                         void *priv),
 195                 void *priv)
 196 {
 197         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 198                 return SIDE_ERROR_INVAL;
 199         return _side_tracer_callback_register(desc, call_variadic, priv);
 200 }
 201
 202 int _side_tracer_callback_unregister(struct side_event_description *desc,
 203                 void (*call)(), void *priv)
 204 {
 205         struct side_callback *old_cb, *new_cb;
 206         const struct side_callback *cb_pos;
 207         uint32_t pos_idx;
 208         int ret = SIDE_ERROR_OK;
 209         uint32_t old_nr_cb;
 210
 211         if (!call)
 212                 return SIDE_ERROR_INVAL;
 213         if (finalized)
 214                 return SIDE_ERROR_EXITING;
 215         if (!initialized)
 216                 side_init();
 217         pthread_mutex_lock(&side_lock);
 218         cb_pos = side_tracer_callback_lookup(desc, call, priv);
 219         if (!cb_pos) {
 220                 ret = SIDE_ERROR_NOENT;
 221                 goto unlock;
 222         }
 223         old_nr_cb = desc->nr_callbacks;
 224         old_cb = (struct side_callback *) desc->callbacks;
 225         if (old_nr_cb == 1) {
 226                 new_cb = (struct side_callback *) &side_empty_callback;
 227         } else {
 228                 pos_idx = cb_pos - desc->callbacks;
 229                 /* Remove entry at pos_idx. */
 230                 /* old_nr_cb - 1 (removed cb) + 1 (NULL) */
 231                 new_cb = (struct side_callback *) calloc(old_nr_cb, sizeof(struct side_callback));
 232                 if (!new_cb) {
 233                         ret = SIDE_ERROR_NOMEM;
 234                         goto unlock;
 235                 }
 236                 memcpy(new_cb, old_cb, pos_idx);
 237                 memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
 238         }
 239         side_rcu_assign_pointer(desc->callbacks, new_cb);
 240         side_rcu_wait_grace_period(&rcu_gp);
 241         free(old_cb);
 242         desc->nr_callbacks--;
 243         /* Decrement concurrently with kernel setting the top bits. */
 244         if (old_nr_cb == 1)
 245                 (void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
 246 unlock:
 247         pthread_mutex_unlock(&side_lock);
 248         return ret;
 249 }
 250
 251 int side_tracer_callback_unregister(struct side_event_description *desc,
 252                 void (*call)(const struct side_event_description *desc,
 253                         const struct side_arg_vec_description *sav_desc,
 254                         void *priv),
 255                 void *priv)
 256 {
 257         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 258                 return SIDE_ERROR_INVAL;
 259         return _side_tracer_callback_unregister(desc, call, priv);
 260 }
 261
 262 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 263                 void (*call_variadic)(const struct side_event_description *desc,
 264                         const struct side_arg_vec_description *sav_desc,
 265                         const struct side_arg_dynamic_event_struct *var_struct,
 266                         void *priv),
 267                 void *priv)
 268 {
 269         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 270                 return SIDE_ERROR_INVAL;
 271         return _side_tracer_callback_unregister(desc, call_variadic, priv);
 272 }
 273
 274 struct side_events_register_handle *side_events_register(struct side_event_description **events, uint32_t nr_events)
 275 {
 276         struct side_events_register_handle *events_handle = NULL;
 277         struct side_tracer_handle *tracer_handle;
 278
 279         if (finalized)
 280                 return NULL;
 281         if (!initialized)
 282                 side_init();
 283         events_handle = calloc(1, sizeof(struct side_events_register_handle));
 284         if (!events_handle)
 285                 return NULL;
 286         events_handle->events = events;
 287         events_handle->nr_events = nr_events;
 288
 289         pthread_mutex_lock(&side_lock);
 290         side_list_insert_node_tail(&side_events_list, &events_handle->node);
 291         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 292                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 293                         events, nr_events, tracer_handle->priv);
 294         }
 295         pthread_mutex_unlock(&side_lock);
 296         //TODO: call event batch register ioctl
 297         return events_handle;
 298 }
 299
 300 static
 301 void side_event_remove_callbacks(struct side_event_description *desc)
 302 {
 303         uint32_t nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 304         struct side_callback *old_cb;
 305
 306         if (!nr_cb)
 307                 return;
 308         old_cb = (struct side_callback *) desc->callbacks;
 309         if (desc->nr_callbacks)
 310                 (void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
 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         desc->nr_callbacks = 0;
 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 (!events_handle)
 335                 return;
 336         if (finalized)
 337                 return;
 338         if (!initialized)
 339                 side_init();
 340         pthread_mutex_lock(&side_lock);
 341         side_list_remove_node(&events_handle->node);
 342         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 343                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 344                         events_handle->events, events_handle->nr_events,
 345                         tracer_handle->priv);
 346         }
 347         for (i = 0; i < events_handle->nr_events; i++) {
 348                 struct side_event_description *event = events_handle->events[i];
 349
 350                 /* Skip NULL pointers */
 351                 if (!event)
 352                         continue;
 353                 side_event_remove_callbacks(event);
 354         }
 355         pthread_mutex_unlock(&side_lock);
 356         //TODO: call event batch unregister ioctl
 357         free(events_handle);
 358 }
 359
 360 struct side_tracer_handle *side_tracer_event_notification_register(
 361                 void (*cb)(enum side_tracer_notification notif,
 362                         struct side_event_description **events, uint32_t nr_events, void *priv),
 363                 void *priv)
 364 {
 365         struct side_tracer_handle *tracer_handle;
 366         struct side_events_register_handle *events_handle;
 367
 368         if (finalized)
 369                 return NULL;
 370         if (!initialized)
 371                 side_init();
 372         tracer_handle = calloc(1, sizeof(struct side_tracer_handle));
 373         if (!tracer_handle)
 374                 return NULL;
 375         pthread_mutex_lock(&side_lock);
 376         tracer_handle->cb = cb;
 377         tracer_handle->priv = priv;
 378         side_list_insert_node_tail(&side_tracer_list, &tracer_handle->node);
 379         side_list_for_each_entry(events_handle, &side_events_list, node) {
 380                 cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 381                         events_handle->events, events_handle->nr_events, priv);
 382         }
 383         pthread_mutex_unlock(&side_lock);
 384         return tracer_handle;
 385 }
 386
 387 void side_tracer_event_notification_unregister(struct side_tracer_handle *tracer_handle)
 388 {
 389         struct side_events_register_handle *events_handle;
 390
 391         if (finalized)
 392                 return;
 393         if (!initialized)
 394                 side_init();
 395         pthread_mutex_lock(&side_lock);
 396         side_list_for_each_entry(events_handle, &side_events_list, node) {
 397                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 398                         events_handle->events, events_handle->nr_events,
 399                         tracer_handle->priv);
 400         }
 401         side_list_remove_node(&tracer_handle->node);
 402         pthread_mutex_unlock(&side_lock);
 403 }
 404
 405 void side_init(void)
 406 {
 407         if (initialized)
 408                 return;
 409         side_rcu_gp_init(&rcu_gp);
 410         initialized = true;
 411 }
 412
 413 /*
 414  * side_exit() is executed from a library destructor. It can be called
 415  * explicitly at application exit as well. Concurrent side API use is
 416  * not expected at that point.
 417  */
 418 void side_exit(void)
 419 {
 420         struct side_events_register_handle *handle, *tmp;
 421
 422         if (finalized)
 423                 return;
 424         side_rcu_gp_exit(&rcu_gp);
 425         side_list_for_each_entry_safe(handle, tmp, &side_events_list, node)
 426                 side_events_unregister(handle);
 427         finalized = true;
 428 }