Tor  0.4.8.0-alpha-dev
compat_libevent.c
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1 /* Copyright (c) 2009-2021, The Tor Project, Inc. */
2 /* See LICENSE for licensing information */
3 
4 /**
5  * \file compat_libevent.c
6  * \brief Wrappers and utility functions for Libevent.
7  */
8 
9 #include "orconfig.h"
10 #define COMPAT_LIBEVENT_PRIVATE
12 
14 #include "lib/log/log.h"
15 #include "lib/log/util_bug.h"
17 
18 #include <event2/event.h>
19 #include <event2/thread.h>
20 #include <string.h>
21 
22 /** A string which, if it appears in a libevent log, should be ignored. */
23 static const char *suppress_msg = NULL;
24 /** Callback function passed to event_set_log() so we can intercept
25  * log messages from libevent. */
26 STATIC void
27 libevent_logging_callback(int severity, const char *msg)
28 {
29  char buf[1024];
30  size_t n;
31  if (suppress_msg && strstr(msg, suppress_msg))
32  return;
33  n = strlcpy(buf, msg, sizeof(buf));
34  if (n && n < sizeof(buf) && buf[n-1] == '\n') {
35  buf[n-1] = '\0';
36  }
37  switch (severity) {
38  case _EVENT_LOG_DEBUG:
39  log_debug(LD_NOCB|LD_NET, "Message from libevent: %s", buf);
40  break;
41  case _EVENT_LOG_MSG:
42  log_info(LD_NOCB|LD_NET, "Message from libevent: %s", buf);
43  break;
44  case _EVENT_LOG_WARN:
45  log_warn(LD_NOCB|LD_GENERAL, "Warning from libevent: %s", buf);
46  break;
47  case _EVENT_LOG_ERR:
48  log_err(LD_NOCB|LD_GENERAL, "Error from libevent: %s", buf);
49  break;
50  default:
51  log_warn(LD_NOCB|LD_GENERAL, "Message [%d] from libevent: %s",
52  severity, buf);
53  break;
54  }
55 }
56 /** Set hook to intercept log messages from libevent. */
57 void
59 {
60  event_set_log_callback(libevent_logging_callback);
61 }
62 
63 /** Ignore any libevent log message that contains <b>msg</b>. */
64 void
65 suppress_libevent_log_msg(const char *msg)
66 {
67  suppress_msg = msg;
68 }
69 
70 /* Wrapper for event_free() that tolerates tor_event_free(NULL) */
71 void
72 tor_event_free_(struct event *ev)
73 {
74  if (ev == NULL)
75  return;
76  event_free(ev);
77 }
78 
79 /** Global event base for use by the main thread. */
80 static struct event_base *the_event_base = NULL;
81 
82 /**
83  * @defgroup postloop post-loop event helpers
84  *
85  * If we're not careful, Libevent can susceptible to infinite event chains:
86  * one event can activate another, whose callback activates another, whose
87  * callback activates another, ad infinitum. While this is happening,
88  * Libevent won't be checking timeouts, socket-based events, signals, and so
89  * on.
90  *
91  * We solve this problem by marking some events as "post-loop". A post-loop
92  * event behaves like any ordinary event, but any events that _it_ activates
93  * cannot run until Libevent has checked for other events at least once.
94  *
95  * @{ */
96 
97 /**
98  * An event that stops Libevent from running any more events on the current
99  * iteration of its loop, until it has re-checked for socket events, signal
100  * events, timeouts, etc.
101  */
102 static struct event *rescan_mainloop_ev = NULL;
103 
104 /**
105  * Callback to implement rescan_mainloop_ev: it simply exits the mainloop,
106  * and relies on Tor to re-enter the mainloop since no error has occurred.
107  */
108 static void
109 rescan_mainloop_cb(evutil_socket_t fd, short events, void *arg)
110 {
111  (void)fd;
112  (void)events;
113  struct event_base *the_base = arg;
114  event_base_loopbreak(the_base);
115 }
116 
117 /** @} */
118 
119 /* This is what passes for version detection on OSX. We set
120  * MACOSX_KQUEUE_IS_BROKEN to true iff we're on a version of OSX before
121  * 10.4.0 (aka 1040). */
122 #ifdef __APPLE__
123 #ifdef __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__
124 #define MACOSX_KQUEUE_IS_BROKEN \
125  (__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 1040)
126 #else
127 #define MACOSX_KQUEUE_IS_BROKEN 0
128 #endif /* defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) */
129 #endif /* defined(__APPLE__) */
130 
131 /** Initialize the Libevent library and set up the event base. */
132 void
134 {
135  tor_assert(the_event_base == NULL);
136  /* some paths below don't use torcfg, so avoid unused variable warnings */
137  (void)torcfg;
138 
139  {
140  struct event_config *cfg;
141 
142  cfg = event_config_new();
143  tor_assert(cfg);
144 
145  /* Telling Libevent not to try to turn locking on can avoid a needless
146  * socketpair() attempt. */
147  event_config_set_flag(cfg, EVENT_BASE_FLAG_NOLOCK);
148 
149  if (torcfg->num_cpus > 0)
150  event_config_set_num_cpus_hint(cfg, torcfg->num_cpus);
151 
152  /* We can enable changelist support with epoll, since we don't give
153  * Libevent any dup'd fds. This lets us avoid some syscalls. */
154  event_config_set_flag(cfg, EVENT_BASE_FLAG_EPOLL_USE_CHANGELIST);
155 
156  the_event_base = event_base_new_with_config(cfg);
157 
158  event_config_free(cfg);
159  }
160 
161  if (!the_event_base) {
162  /* LCOV_EXCL_START */
163  log_err(LD_GENERAL, "Unable to initialize Libevent: cannot continue.");
164  exit(1); // exit ok: libevent is broken.
165  /* LCOV_EXCL_STOP */
166  }
167 
168  rescan_mainloop_ev = event_new(the_event_base, -1, 0,
170  if (!rescan_mainloop_ev) {
171  /* LCOV_EXCL_START */
172  log_err(LD_GENERAL, "Unable to create rescan event: cannot continue.");
173  exit(1); // exit ok: libevent is broken.
174  /* LCOV_EXCL_STOP */
175  }
176 
177  log_info(LD_GENERAL,
178  "Initialized libevent version %s using method %s. Good.",
179  event_get_version(), tor_libevent_get_method());
180 }
181 
182 /**
183  * Return true iff the libevent module has been successfully initialized,
184  * and not subsequently shut down.
185  **/
186 bool
188 {
189  return the_event_base != NULL;
190 }
191 
192 /** Return the current Libevent event base that we're set up to use. */
193 MOCK_IMPL(struct event_base *,
195 {
196  tor_assert(the_event_base != NULL);
197  return the_event_base;
198 }
199 
200 /** Return the name of the Libevent backend we're using. */
201 const char *
203 {
204  return event_base_get_method(the_event_base);
205 }
206 
207 /** Return a string representation of the version of the currently running
208  * version of Libevent. */
209 const char *
211 {
212  return event_get_version();
213 }
214 
215 /** Return a string representation of the version of Libevent that was used
216 * at compilation time. */
217 const char *
219 {
220  return LIBEVENT_VERSION;
221 }
222 
223 /** Represents a timer that's run every N microseconds by Libevent. */
225  /** Underlying event used to implement this periodic event. */
226  struct event *ev;
227  /** The callback we'll be invoking whenever the event triggers */
228  void (*cb)(struct periodic_timer_t *, void *);
229  /** User-supplied data for the callback */
230  void *data;
231 };
232 
233 /** Libevent callback to implement a periodic event. */
234 static void
235 periodic_timer_cb(evutil_socket_t fd, short what, void *arg)
236 {
237  periodic_timer_t *timer = arg;
238  (void) what;
239  (void) fd;
240  timer->cb(timer, timer->data);
241 }
242 
243 /** Create and schedule a new timer that will run every <b>tv</b> in
244  * the event loop of <b>base</b>. When the timer fires, it will
245  * run the timer in <b>cb</b> with the user-supplied data in <b>data</b>. */
247 periodic_timer_new(struct event_base *base,
248  const struct timeval *tv,
249  void (*cb)(periodic_timer_t *timer, void *data),
250  void *data)
251 {
252  periodic_timer_t *timer;
253  tor_assert(base);
254  tor_assert(tv);
255  tor_assert(cb);
256  timer = tor_malloc_zero(sizeof(periodic_timer_t));
257  if (!(timer->ev = tor_event_new(base, -1, EV_PERSIST,
258  periodic_timer_cb, timer))) {
259  tor_free(timer);
260  return NULL;
261  }
262  timer->cb = cb;
263  timer->data = data;
264  periodic_timer_launch(timer, tv);
265  return timer;
266 }
267 
268 /**
269  * Launch the timer <b>timer</b> to run at <b>tv</b> from now, and every
270  * <b>tv</b> thereafter.
271  *
272  * If the timer is already enabled, this function does nothing.
273  */
274 void
276 {
277  tor_assert(timer);
278  if (event_pending(timer->ev, EV_TIMEOUT, NULL))
279  return;
280  event_add(timer->ev, tv);
281 }
282 
283 /**
284  * Disable the provided <b>timer</b>, but do not free it.
285  *
286  * You can reenable the same timer later with periodic_timer_launch.
287  *
288  * If the timer is already disabled, this function does nothing.
289  */
290 void
292 {
293  tor_assert(timer);
294  (void) event_del(timer->ev);
295 }
296 
297 /** Stop and free a periodic timer */
298 void
300 {
301  if (!timer)
302  return;
303  tor_event_free(timer->ev);
304  tor_free(timer);
305 }
306 
307 /**
308  * Type used to represent events that run directly from the main loop,
309  * either because they are activated from elsewhere in the code, or
310  * because they have a simple timeout.
311  *
312  * We use this type to avoid exposing Libevent's API throughout the rest
313  * of the codebase.
314  *
315  * This type can't be used for all events: it doesn't handle events that
316  * are triggered by signals or by sockets.
317  */
319  struct event *ev;
320  void (*cb)(mainloop_event_t *, void *);
321  void *userdata;
322 };
323 
324 /**
325  * Internal: Implements mainloop event using a libevent event.
326  */
327 static void
328 mainloop_event_cb(evutil_socket_t fd, short what, void *arg)
329 {
330  (void)fd;
331  (void)what;
332  mainloop_event_t *mev = arg;
333  mev->cb(mev, mev->userdata);
334 }
335 
336 /**
337  * As mainloop_event_cb, but implements a post-loop event.
338  */
339 static void
340 mainloop_event_postloop_cb(evutil_socket_t fd, short what, void *arg)
341 {
342  (void)fd;
343  (void)what;
344 
345  /* Note that if rescan_mainloop_ev is already activated,
346  * event_active() will do nothing: only the first post-loop event that
347  * happens each time through the event loop will cause it to be
348  * activated.
349  *
350  * Because event_active() puts events on a FIFO queue, every event
351  * that is made active _after_ rescan_mainloop_ev will get its
352  * callback run after rescan_mainloop_cb is called -- that is, on the
353  * next iteration of the loop.
354  */
355  event_active(rescan_mainloop_ev, EV_READ, 1);
356 
357  mainloop_event_t *mev = arg;
358  mev->cb(mev, mev->userdata);
359 }
360 
361 /**
362  * Helper for mainloop_event_new() and mainloop_event_postloop_new().
363  */
364 static mainloop_event_t *
366  void (*cb)(mainloop_event_t *, void *),
367  void *userdata)
368 {
369  tor_assert(cb);
370 
371  struct event_base *base = tor_libevent_get_base();
372  mainloop_event_t *mev = tor_malloc_zero(sizeof(mainloop_event_t));
373  mev->ev = tor_event_new(base, -1, 0,
375  mev);
376  tor_assert(mev->ev);
377  mev->cb = cb;
378  mev->userdata = userdata;
379  return mev;
380 }
381 
382 /**
383  * Create and return a new mainloop_event_t to run the function <b>cb</b>.
384  *
385  * When run, the callback function will be passed the mainloop_event_t
386  * and <b>userdata</b> as its arguments. The <b>userdata</b> pointer
387  * must remain valid for as long as the mainloop_event_t event exists:
388  * it is your responsibility to free it.
389  *
390  * The event is not scheduled by default: Use mainloop_event_activate()
391  * or mainloop_event_schedule() to make it run.
392  */
394 mainloop_event_new(void (*cb)(mainloop_event_t *, void *),
395  void *userdata)
396 {
397  return mainloop_event_new_impl(0, cb, userdata);
398 }
399 
400 /**
401  * As mainloop_event_new(), but create a post-loop event.
402  *
403  * A post-loop event behaves like any ordinary event, but any events
404  * that _it_ activates cannot run until Libevent has checked for other
405  * events at least once.
406  */
409  void *userdata)
410 {
411  return mainloop_event_new_impl(1, cb, userdata);
412 }
413 
414 /**
415  * Schedule <b>event</b> to run in the main loop, immediately. If it is
416  * not scheduled, it will run anyway. If it is already scheduled to run
417  * later, it will run now instead. This function will have no effect if
418  * the event is already scheduled to run.
419  *
420  * This function may only be called from the main thread.
421  */
422 void
424 {
425  tor_assert(event);
426  event_active(event->ev, EV_READ, 1);
427 }
428 
429 /** Schedule <b>event</b> to run in the main loop, after a delay of <b>tv</b>.
430  *
431  * If the event is scheduled for a different time, cancel it and run
432  * after this delay instead. If the event is currently pending to run
433  * <b>now</b>, has no effect.
434  *
435  * Do not call this function with <b>tv</b> == NULL -- use
436  * mainloop_event_activate() instead.
437  *
438  * This function may only be called from the main thread.
439  */
440 int
442 {
443  tor_assert(event);
444  if (BUG(tv == NULL)) {
445  // LCOV_EXCL_START
447  return 0;
448  // LCOV_EXCL_STOP
449  }
450  return event_add(event->ev, tv);
451 }
452 
453 /** Cancel <b>event</b> if it is currently active or pending. (Do nothing if
454  * the event is not currently active or pending.) */
455 void
457 {
458  if (!event)
459  return;
460  (void) event_del(event->ev);
461 }
462 
463 /** Cancel <b>event</b> and release all storage associated with it. */
464 void
466 {
467  if (!event)
468  return;
469  tor_event_free(event->ev);
470  memset(event, 0xb8, sizeof(*event));
471  tor_free(event);
472 }
473 
474 int
475 tor_init_libevent_rng(void)
476 {
477  int rv = 0;
478  char buf[256];
479  if (evutil_secure_rng_init() < 0) {
480  rv = -1;
481  }
482  crypto_rand(buf, 32);
483 #ifdef HAVE_EVUTIL_SECURE_RNG_ADD_BYTES
484  evutil_secure_rng_add_bytes(buf, 32);
485 #endif
486  evutil_secure_rng_get_bytes(buf, sizeof(buf));
487  return rv;
488 }
489 
490 /**
491  * Un-initialize libevent in preparation for an exit
492  */
493 void
495 {
496  tor_event_free(rescan_mainloop_ev);
497  if (the_event_base)
498  event_base_free(the_event_base);
499  the_event_base = NULL;
500 }
501 
502 /**
503  * Run the event loop for the provided event_base, handling events until
504  * something stops it. If <b>once</b> is set, then just poll-and-run
505  * once, then exit. Return 0 on success, -1 if an error occurred, or 1
506  * if we exited because no events were pending or active.
507  *
508  * This isn't reentrant or multithreaded.
509  */
510 int
511 tor_libevent_run_event_loop(struct event_base *base, int once)
512 {
513  const int flags = once ? EVLOOP_ONCE : 0;
514  return event_base_loop(base, flags);
515 }
516 
517 /** Tell the event loop to exit after <b>delay</b>. If <b>delay</b> is NULL,
518  * instead exit after we're done running the currently active events. */
519 void
520 tor_libevent_exit_loop_after_delay(struct event_base *base,
521  const struct timeval *delay)
522 {
523  event_base_loopexit(base, delay);
524 }
525 
526 /** Tell the event loop to exit after running whichever callback is currently
527  * active. */
528 void
530 {
531  event_base_loopbreak(base);
532 }
533 
534 #if defined(TOR_UNIT_TESTS)
535 /** For testing: called post-fork to make libevent reinitialize
536  * kernel structures. */
537 void
538 tor_libevent_postfork(void)
539 {
540  int r = event_reinit(tor_libevent_get_base());
541  tor_assert(r == 0);
542 }
543 #endif /* defined(TOR_UNIT_TESTS) */
STATIC void libevent_logging_callback(int severity, const char *msg)
void suppress_libevent_log_msg(const char *msg)
bool tor_libevent_is_initialized(void)
struct event_base * tor_libevent_get_base(void)
static mainloop_event_t * mainloop_event_new_impl(int postloop, void(*cb)(mainloop_event_t *, void *), void *userdata)
const char * tor_libevent_get_version_str(void)
mainloop_event_t * mainloop_event_postloop_new(void(*cb)(mainloop_event_t *, void *), void *userdata)
void mainloop_event_cancel(mainloop_event_t *event)
void periodic_timer_launch(periodic_timer_t *timer, const struct timeval *tv)
static struct event_base * the_event_base
const char * tor_libevent_get_method(void)
periodic_timer_t * periodic_timer_new(struct event_base *base, const struct timeval *tv, void(*cb)(periodic_timer_t *timer, void *data), void *data)
void tor_libevent_exit_loop_after_callback(struct event_base *base)
mainloop_event_t * mainloop_event_new(void(*cb)(mainloop_event_t *, void *), void *userdata)
void tor_libevent_initialize(tor_libevent_cfg_t *torcfg)
void mainloop_event_free_(mainloop_event_t *event)
int tor_libevent_run_event_loop(struct event_base *base, int once)
const char * tor_libevent_get_header_version_str(void)
static void mainloop_event_cb(evutil_socket_t fd, short what, void *arg)
void tor_libevent_exit_loop_after_delay(struct event_base *base, const struct timeval *delay)
static void periodic_timer_cb(evutil_socket_t fd, short what, void *arg)
int mainloop_event_schedule(mainloop_event_t *event, const struct timeval *tv)
void tor_libevent_free_all(void)
void periodic_timer_free_(periodic_timer_t *timer)
static const char * suppress_msg
void configure_libevent_logging(void)
void periodic_timer_disable(periodic_timer_t *timer)
void mainloop_event_activate(mainloop_event_t *event)
static void mainloop_event_postloop_cb(evutil_socket_t fd, short what, void *arg)
Header for compat_libevent.c.
Header for compat_string.c.
void crypto_rand(char *to, size_t n)
Definition: crypto_rand.c:479
Common functions for using (pseudo-)random number generators.
static void rescan_mainloop_cb(evutil_socket_t fd, short events, void *arg)
static struct event * rescan_mainloop_ev
Headers for log.c.
#define LD_NOCB
Definition: log.h:144
#define LD_NET
Definition: log.h:66
#define LD_GENERAL
Definition: log.h:62
#define tor_free(p)
Definition: malloc.h:56
struct event * ev
void(* cb)(struct periodic_timer_t *, void *)
#define STATIC
Definition: testsupport.h:32
#define MOCK_IMPL(rv, funcname, arglist)
Definition: testsupport.h:133
Macros to manage assertions, fatal and non-fatal.
#define tor_assert(expr)
Definition: util_bug.h:102