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 static struct side_rcu_gp_state rcu_gp;
  21
  22 /*
  23  * Lazy initialization for early use within library constructors.
  24  */
  25 static bool initialized;
  26
  27 static pthread_mutex_t side_lock = PTHREAD_MUTEX_INITIALIZER;
  28
  29 static DEFINE_SIDE_LIST_HEAD(side_list);
  30
  31 static
  32 void side_init(void)
  33         __attribute__((constructor));
  34
  35 /*
  36  * The empty callback has a NULL function callback pointer, which stops
  37  * iteration on the array of callbacks immediately.
  38  */
  39 const struct side_callback side_empty_callback;
  40
  41 void side_call(const struct side_event_description *desc, const struct side_arg_vec_description *sav_desc)
  42 {
  43         const struct side_callback *side_cb;
  44         unsigned int rcu_period;
  45         uint32_t enabled;
  46
  47         if (side_unlikely(!initialized))
  48                 side_init();
  49         if (side_unlikely(desc->flags & SIDE_EVENT_FLAG_VARIADIC)) {
  50                 printf("ERROR: unexpected variadic event description\n");
  51                 abort();
  52         }
  53         enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
  54         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
  55                 // TODO: call kernel write.
  56         }
  57         if (side_unlikely(!(enabled & SIDE_EVENT_ENABLED_USER_MASK)))
  58                 return;
  59
  60         //TODO: replace tracer_call by rcu iteration on list of registered callbacks
  61         tracer_call(desc, sav_desc, NULL);
  62
  63         rcu_period = side_rcu_read_begin(&rcu_gp);
  64         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call != NULL; side_cb++)
  65                 side_cb->u.call(desc, sav_desc, side_cb->priv);
  66         side_rcu_read_end(&rcu_gp, rcu_period);
  67 }
  68
  69 void side_call_variadic(const struct side_event_description *desc,
  70         const struct side_arg_vec_description *sav_desc,
  71         const struct side_arg_dynamic_event_struct *var_struct)
  72 {
  73         const struct side_callback *side_cb;
  74         unsigned int rcu_period;
  75         uint32_t enabled;
  76
  77         if (side_unlikely(!initialized))
  78                 side_init();
  79         if (side_unlikely(!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))) {
  80                 printf("ERROR: unexpected non-variadic event description\n");
  81                 abort();
  82         }
  83         enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
  84         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
  85                 // TODO: call kernel write.
  86         }
  87         if (side_unlikely(!(enabled & SIDE_EVENT_ENABLED_USER_MASK)))
  88                 return;
  89
  90         //TODO: replace tracer_call by rcu iteration on list of registered callbacks
  91         tracer_call_variadic(desc, sav_desc, var_struct, NULL);
  92
  93         rcu_period = side_rcu_read_begin(&rcu_gp);
  94         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call_variadic != NULL; side_cb++)
  95                 side_cb->u.call_variadic(desc, sav_desc, var_struct, side_cb->priv);
  96         side_rcu_read_end(&rcu_gp, rcu_period);
  97 }
  98
  99 static
 100 const struct side_callback *side_tracer_callback_lookup(
 101                 const struct side_event_description *desc,
 102                 void (*call)(), void *priv)
 103 {
 104         const struct side_callback *cb;
 105
 106         for (cb = desc->callbacks; cb->u.call != NULL; cb++) {
 107                 if (cb->u.call == call && cb->priv == priv)
 108                         return cb;
 109         }
 110         return NULL;
 111 }
 112
 113 static
 114 int _side_tracer_callback_register(struct side_event_description *desc,
 115                 void (*call)(), void *priv)
 116 {
 117         struct side_callback *old_cb, *new_cb;
 118         int ret = SIDE_ERROR_OK;
 119         uint32_t old_nr_cb;
 120
 121         if (!call)
 122                 return SIDE_ERROR_INVAL;
 123         pthread_mutex_lock(&side_lock);
 124         old_nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 125         if (old_nr_cb == SIDE_EVENT_ENABLED_USER_MASK) {
 126                 ret = SIDE_ERROR_INVAL;
 127                 goto unlock;
 128         }
 129         /* Reject duplicate (call, priv) tuples. */
 130         if (side_tracer_callback_lookup(desc, call, priv)) {
 131                 ret = SIDE_ERROR_EXIST;
 132                 goto unlock;
 133         }
 134         old_cb = (struct side_callback *) desc->callbacks;
 135         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 136         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 137         if (!new_cb) {
 138                 ret = SIDE_ERROR_NOMEM;
 139                 goto unlock;
 140         }
 141         memcpy(new_cb, old_cb, old_nr_cb);
 142         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 143                 new_cb[old_nr_cb].u.call_variadic = call;
 144         else
 145                 new_cb[old_nr_cb].u.call = call;
 146         new_cb[old_nr_cb].priv = priv;
 147         side_rcu_assign_pointer(desc->callbacks, new_cb);
 148         side_rcu_wait_grace_period(&rcu_gp);
 149         if (old_nr_cb)
 150                 free(old_cb);
 151         /* Increment concurrently with kernel setting the top bits. */
 152         (void) __atomic_add_fetch(desc->enabled, 1, __ATOMIC_RELAXED);
 153 unlock:
 154         pthread_mutex_unlock(&side_lock);
 155         return ret;
 156 }
 157
 158 int side_tracer_callback_register(struct side_event_description *desc,
 159                 void (*call)(const struct side_event_description *desc,
 160                         const struct side_arg_vec_description *sav_desc,
 161                         void *priv),
 162                 void *priv)
 163 {
 164         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 165                 return SIDE_ERROR_INVAL;
 166         return _side_tracer_callback_register(desc, call, priv);
 167 }
 168
 169 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 170                 void (*call_variadic)(const struct side_event_description *desc,
 171                         const struct side_arg_vec_description *sav_desc,
 172                         const struct side_arg_dynamic_event_struct *var_struct,
 173                         void *priv),
 174                 void *priv)
 175 {
 176         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 177                 return SIDE_ERROR_INVAL;
 178         return _side_tracer_callback_register(desc, call_variadic, priv);
 179 }
 180
 181 int _side_tracer_callback_unregister(struct side_event_description *desc,
 182                 void (*call)(), void *priv)
 183 {
 184         struct side_callback *old_cb, *new_cb;
 185         const struct side_callback *cb_pos;
 186         uint32_t pos_idx;
 187         int ret = SIDE_ERROR_OK;
 188         uint32_t old_nr_cb;
 189
 190         if (!call)
 191                 return SIDE_ERROR_INVAL;
 192         pthread_mutex_lock(&side_lock);
 193         cb_pos = side_tracer_callback_lookup(desc, call, priv);
 194         if (!cb_pos) {
 195                 ret = SIDE_ERROR_NOENT;
 196                 goto unlock;
 197         }
 198         old_nr_cb = *desc->enabled & SIDE_EVENT_ENABLED_USER_MASK;
 199         old_cb = (struct side_callback *) desc->callbacks;
 200         if (old_nr_cb == 1) {
 201                 new_cb = (struct side_callback *) &side_empty_callback;
 202         } else {
 203                 pos_idx = cb_pos - desc->callbacks;
 204                 /* Remove entry at pos_idx. */
 205                 /* old_nr_cb - 1 (removed cb) + 1 (NULL) */
 206                 new_cb = (struct side_callback *) calloc(old_nr_cb, sizeof(struct side_callback));
 207                 if (!new_cb) {
 208                         ret = SIDE_ERROR_NOMEM;
 209                         goto unlock;
 210                 }
 211                 memcpy(new_cb, old_cb, pos_idx);
 212                 memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
 213         }
 214         side_rcu_assign_pointer(desc->callbacks, new_cb);
 215         side_rcu_wait_grace_period(&rcu_gp);
 216         free(old_cb);
 217         /* Decrement concurrently with kernel setting the top bits. */
 218         (void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
 219 unlock:
 220         pthread_mutex_unlock(&side_lock);
 221         return ret;
 222 }
 223
 224 int side_tracer_callback_unregister(struct side_event_description *desc,
 225                 void (*call)(const struct side_event_description *desc,
 226                         const struct side_arg_vec_description *sav_desc,
 227                         void *priv),
 228                 void *priv)
 229 {
 230         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 231                 return SIDE_ERROR_INVAL;
 232         return _side_tracer_callback_unregister(desc, call, priv);
 233 }
 234
 235 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 236                 void (*call_variadic)(const struct side_event_description *desc,
 237                         const struct side_arg_vec_description *sav_desc,
 238                         const struct side_arg_dynamic_event_struct *var_struct,
 239                         void *priv),
 240                 void *priv)
 241 {
 242         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 243                 return SIDE_ERROR_INVAL;
 244         return _side_tracer_callback_unregister(desc, call_variadic, priv);
 245 }
 246
 247 static
 248 void side_init(void)
 249 {
 250         if (initialized)
 251                 return;
 252         side_rcu_gp_init(&rcu_gp);
 253         initialized = true;
 254 }