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 static struct side_rcu_gp_state rcu_gp;
  27
  28 /*
  29  * Lazy initialization for early use within library constructors.
  30  */
  31 static bool initialized;
  32 /*
  33  * Do not register/unregister any more events after destructor.
  34  */
  35 static bool finalized;
  36
  37 static pthread_mutex_t side_lock = PTHREAD_MUTEX_INITIALIZER;
  38
  39 static DEFINE_SIDE_LIST_HEAD(side_list);
  40
  41 /*
  42  * The empty callback has a NULL function callback pointer, which stops
  43  * iteration on the array of callbacks immediately.
  44  */
  45 const struct side_callback side_empty_callback;
  46
  47 void side_init(void) __attribute__((constructor));
  48 void side_exit(void) __attribute__((destructor));
  49
  50 void side_call(const struct side_event_description *desc, const struct side_arg_vec_description *sav_desc)
  51 {
  52         const struct side_callback *side_cb;
  53         unsigned int rcu_period;
  54         uint32_t enabled;
  55
  56         if (side_unlikely(finalized))
  57                 return;
  58         if (side_unlikely(!initialized))
  59                 side_init();
  60         if (side_unlikely(desc->flags & SIDE_EVENT_FLAG_VARIADIC)) {
  61                 printf("ERROR: unexpected variadic event description\n");
  62                 abort();
  63         }
  64         enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
  65         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
  66                 // TODO: call kernel write.
  67         }
  68         if (side_unlikely(!(enabled & SIDE_EVENT_ENABLED_USER_MASK)))
  69                 return;
  70
  71         //TODO: replace tracer_call by rcu iteration on list of registered callbacks
  72         tracer_call(desc, sav_desc, NULL);
  73
  74         rcu_period = side_rcu_read_begin(&rcu_gp);
  75         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call != NULL; side_cb++)
  76                 side_cb->u.call(desc, sav_desc, side_cb->priv);
  77         side_rcu_read_end(&rcu_gp, rcu_period);
  78 }
  79
  80 void side_call_variadic(const struct side_event_description *desc,
  81         const struct side_arg_vec_description *sav_desc,
  82         const struct side_arg_dynamic_event_struct *var_struct)
  83 {
  84         const struct side_callback *side_cb;
  85         unsigned int rcu_period;
  86         uint32_t enabled;
  87
  88         if (side_unlikely(finalized))
  89                 return;
  90         if (side_unlikely(!initialized))
  91                 side_init();
  92         if (side_unlikely(!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))) {
  93                 printf("ERROR: unexpected non-variadic event description\n");
  94                 abort();
  95         }
  96         enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
  97         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
  98                 // TODO: call kernel write.
  99         }
 100         if (side_unlikely(!(enabled & SIDE_EVENT_ENABLED_USER_MASK)))
 101                 return;
 102
 103         //TODO: replace tracer_call by rcu iteration on list of registered callbacks
 104         tracer_call_variadic(desc, sav_desc, var_struct, NULL);
 105
 106         rcu_period = side_rcu_read_begin(&rcu_gp);
 107         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call_variadic != NULL; side_cb++)
 108                 side_cb->u.call_variadic(desc, sav_desc, var_struct, side_cb->priv);
 109         side_rcu_read_end(&rcu_gp, rcu_period);
 110 }
 111
 112 static
 113 const struct side_callback *side_tracer_callback_lookup(
 114                 const struct side_event_description *desc,
 115                 void (*call)(), void *priv)
 116 {
 117         const struct side_callback *cb;
 118
 119         for (cb = desc->callbacks; cb->u.call != NULL; cb++) {
 120                 if (cb->u.call == call && cb->priv == priv)
 121                         return cb;
 122         }
 123         return NULL;
 124 }
 125
 126 static
 127 int _side_tracer_callback_register(struct side_event_description *desc,
 128                 void (*call)(), void *priv)
 129 {
 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         pthread_mutex_lock(&side_lock);
 139         old_nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 140         if (old_nr_cb == SIDE_EVENT_ENABLED_USER_MASK) {
 141                 ret = SIDE_ERROR_INVAL;
 142                 goto unlock;
 143         }
 144         /* Reject duplicate (call, priv) tuples. */
 145         if (side_tracer_callback_lookup(desc, call, priv)) {
 146                 ret = SIDE_ERROR_EXIST;
 147                 goto unlock;
 148         }
 149         old_cb = (struct side_callback *) desc->callbacks;
 150         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 151         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 152         if (!new_cb) {
 153                 ret = SIDE_ERROR_NOMEM;
 154                 goto unlock;
 155         }
 156         memcpy(new_cb, old_cb, old_nr_cb);
 157         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 158                 new_cb[old_nr_cb].u.call_variadic = call;
 159         else
 160                 new_cb[old_nr_cb].u.call = call;
 161         new_cb[old_nr_cb].priv = priv;
 162         side_rcu_assign_pointer(desc->callbacks, new_cb);
 163         side_rcu_wait_grace_period(&rcu_gp);
 164         if (old_nr_cb)
 165                 free(old_cb);
 166         /* Increment concurrently with kernel setting the top bits. */
 167         (void) __atomic_add_fetch(desc->enabled, 1, __ATOMIC_RELAXED);
 168 unlock:
 169         pthread_mutex_unlock(&side_lock);
 170         return ret;
 171 }
 172
 173 int side_tracer_callback_register(struct side_event_description *desc,
 174                 void (*call)(const struct side_event_description *desc,
 175                         const struct side_arg_vec_description *sav_desc,
 176                         void *priv),
 177                 void *priv)
 178 {
 179         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 180                 return SIDE_ERROR_INVAL;
 181         return _side_tracer_callback_register(desc, call, priv);
 182 }
 183
 184 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 185                 void (*call_variadic)(const struct side_event_description *desc,
 186                         const struct side_arg_vec_description *sav_desc,
 187                         const struct side_arg_dynamic_event_struct *var_struct,
 188                         void *priv),
 189                 void *priv)
 190 {
 191         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 192                 return SIDE_ERROR_INVAL;
 193         return _side_tracer_callback_register(desc, call_variadic, priv);
 194 }
 195
 196 int _side_tracer_callback_unregister(struct side_event_description *desc,
 197                 void (*call)(), void *priv)
 198 {
 199         struct side_callback *old_cb, *new_cb;
 200         const struct side_callback *cb_pos;
 201         uint32_t pos_idx;
 202         int ret = SIDE_ERROR_OK;
 203         uint32_t old_nr_cb;
 204
 205         if (!call)
 206                 return SIDE_ERROR_INVAL;
 207         if (finalized)
 208                 return SIDE_ERROR_EXITING;
 209         pthread_mutex_lock(&side_lock);
 210         cb_pos = side_tracer_callback_lookup(desc, call, priv);
 211         if (!cb_pos) {
 212                 ret = SIDE_ERROR_NOENT;
 213                 goto unlock;
 214         }
 215         old_nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 216         old_cb = (struct side_callback *) desc->callbacks;
 217         if (old_nr_cb == 1) {
 218                 new_cb = (struct side_callback *) &side_empty_callback;
 219         } else {
 220                 pos_idx = cb_pos - desc->callbacks;
 221                 /* Remove entry at pos_idx. */
 222                 /* old_nr_cb - 1 (removed cb) + 1 (NULL) */
 223                 new_cb = (struct side_callback *) calloc(old_nr_cb, sizeof(struct side_callback));
 224                 if (!new_cb) {
 225                         ret = SIDE_ERROR_NOMEM;
 226                         goto unlock;
 227                 }
 228                 memcpy(new_cb, old_cb, pos_idx);
 229                 memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
 230         }
 231         side_rcu_assign_pointer(desc->callbacks, new_cb);
 232         side_rcu_wait_grace_period(&rcu_gp);
 233         free(old_cb);
 234         /* Decrement concurrently with kernel setting the top bits. */
 235         (void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
 236 unlock:
 237         pthread_mutex_unlock(&side_lock);
 238         return ret;
 239 }
 240
 241 int side_tracer_callback_unregister(struct side_event_description *desc,
 242                 void (*call)(const struct side_event_description *desc,
 243                         const struct side_arg_vec_description *sav_desc,
 244                         void *priv),
 245                 void *priv)
 246 {
 247         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 248                 return SIDE_ERROR_INVAL;
 249         return _side_tracer_callback_unregister(desc, call, priv);
 250 }
 251
 252 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 253                 void (*call_variadic)(const struct side_event_description *desc,
 254                         const struct side_arg_vec_description *sav_desc,
 255                         const struct side_arg_dynamic_event_struct *var_struct,
 256                         void *priv),
 257                 void *priv)
 258 {
 259         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 260                 return SIDE_ERROR_INVAL;
 261         return _side_tracer_callback_unregister(desc, call_variadic, priv);
 262 }
 263
 264 struct side_events_register_handle *side_events_register(struct side_event_description **events, uint32_t nr_events)
 265 {
 266         struct side_events_register_handle *handle = NULL;
 267
 268         if (finalized)
 269                 return NULL;
 270         handle = calloc(1, sizeof(struct side_events_register_handle));
 271         if (!handle)
 272                 return NULL;
 273         pthread_mutex_lock(&side_lock);
 274         handle->events = events;
 275         handle->nr_events = nr_events;
 276         side_list_insert_node_tail(&side_list, &handle->node);
 277         pthread_mutex_unlock(&side_lock);
 278         //TODO: call event batch register ioctl
 279         return handle;
 280 }
 281
 282 static
 283 void side_event_remove_callbacks(struct side_event_description *desc)
 284 {
 285         uint32_t nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 286         struct side_callback *old_cb;
 287
 288         if (!nr_cb)
 289                 return;
 290         old_cb = (struct side_callback *) desc->callbacks;
 291         /*
 292          * Setting the state back to 0 cb and empty callbacks out of
 293          * caution. This should not matter because instrumentation is
 294          * unreachable.
 295          */
 296         (void) __atomic_add_fetch(desc->enabled, -nr_cb, __ATOMIC_RELAXED);
 297         side_rcu_assign_pointer(desc->callbacks, &side_empty_callback);
 298         /*
 299          * No need to wait for grace period because instrumentation is
 300          * unreachable.
 301          */
 302         free(old_cb);
 303 }
 304
 305 /*
 306  * Unregister event handle. At this point, all side events in that
 307  * handle should be unreachable.
 308  */
 309 void side_events_unregister(struct side_events_register_handle *handle)
 310 {
 311         uint32_t i;
 312
 313         if (finalized)
 314                 return;
 315         pthread_mutex_lock(&side_lock);
 316         side_list_remove_node(&handle->node);
 317         for (i = 0; i < handle->nr_events; i++) {
 318                 struct side_event_description *event = handle->events[i];
 319
 320                 /* Skip NULL pointers */
 321                 if (!event)
 322                         continue;
 323                 side_event_remove_callbacks(event);
 324         }
 325         pthread_mutex_unlock(&side_lock);
 326         //TODO: call event batch unregister ioctl
 327         free(handle);
 328 }
 329
 330 void side_init(void)
 331 {
 332         if (initialized)
 333                 return;
 334         side_rcu_gp_init(&rcu_gp);
 335         initialized = true;
 336 }
 337
 338 /*
 339  * side_exit() is executed from a library destructor. It can be called
 340  * explicitly at application exit as well. Concurrent side API use is
 341  * not expected at that point.
 342  */
 343 void side_exit(void)
 344 {
 345         struct side_events_register_handle *handle, *tmp;
 346
 347         if (finalized)
 348                 return;
 349         side_rcu_gp_exit(&rcu_gp);
 350         side_list_for_each_entry_safe(handle, tmp, &side_list, node)
 351                 side_events_unregister(handle);
 352         finalized = true;
 353 }