lib/tevent/tevent_signal.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3
   4    common events code for signal events
   5
   6    Copyright (C) Andrew Tridgell        2007
   7
   8      ** NOTE! The following LGPL license applies to the tevent
   9      ** library. This does NOT imply that all of Samba is released
  10      ** under the LGPL
  11
  12    This library is free software; you can redistribute it and/or
  13    modify it under the terms of the GNU Lesser General Public
  14    License as published by the Free Software Foundation; either
  15    version 3 of the License, or (at your option) any later version.
  16
  17    This library is distributed in the hope that it will be useful,
  18    but WITHOUT ANY WARRANTY; without even the implied warranty of
  19    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  20    Lesser General Public License for more details.
  21
  22    You should have received a copy of the GNU Lesser General Public
  23    License along with this library; if not, see <http://www.gnu.org/licenses/>.
  24 */
  25
  26 #include "replace.h"
  27 #include "system/filesys.h"
  28 #include "system/wait.h"
  29 #include "tevent.h"
  30 #include "tevent_internal.h"
  31 #include "tevent_util.h"
  32
  33 /* maximum number of SA_SIGINFO signals to hold in the queue.
  34   NB. This *MUST* be a power of 2, in order for the ring buffer
  35   wrap to work correctly. Thanks to Petr Vandrovec <petr@vandrovec.name>
  36   for this. */
  37
  38 #define TEVENT_SA_INFO_QUEUE_COUNT 256
  39
  40 size_t tevent_num_signals(void)
  41 {
  42         return TEVENT_NUM_SIGNALS;
  43 }
  44
  45 size_t tevent_sa_info_queue_count(void)
  46 {
  47         return TEVENT_SA_INFO_QUEUE_COUNT;
  48 }
  49
  50 struct tevent_sigcounter {
  51         uint32_t count;
  52         uint32_t seen;
  53 };
  54
  55 #if defined(HAVE___SYNC_FETCH_AND_ADD)
  56 #define TEVENT_SIG_INCREMENT(s) __sync_fetch_and_add(&((s).count), 1)
  57 #elif defined(HAVE_ATOMIC_ADD_32)
  58 #define TEVENT_SIG_INCREMENT(s) atomic_add_32(&((s).count), 1)
  59 #else
  60 #define TEVENT_SIG_INCREMENT(s) (s).count++
  61 #endif
  62 #define TEVENT_SIG_SEEN(s, n) (s).seen += (n)
  63 #define TEVENT_SIG_PENDING(s) ((s).seen != (s).count)
  64
  65 struct tevent_common_signal_list {
  66         struct tevent_common_signal_list *prev, *next;
  67         struct tevent_signal *se;
  68 };
  69
  70 /*
  71   the poor design of signals means that this table must be static global
  72 */
  73 static struct tevent_sig_state {
  74         struct tevent_common_signal_list *sig_handlers[TEVENT_NUM_SIGNALS+1];
  75         struct sigaction *oldact[TEVENT_NUM_SIGNALS+1];
  76         struct tevent_sigcounter signal_count[TEVENT_NUM_SIGNALS+1];
  77         struct tevent_sigcounter got_signal;
  78 #ifdef SA_SIGINFO
  79         /* with SA_SIGINFO we get quite a lot of info per signal */
  80         siginfo_t *sig_info[TEVENT_NUM_SIGNALS+1];
  81         struct tevent_sigcounter sig_blocked[TEVENT_NUM_SIGNALS+1];
  82 #endif
  83 } *sig_state;
  84
  85 /*
  86   return number of sigcounter events not processed yet
  87 */
  88 static uint32_t tevent_sig_count(struct tevent_sigcounter s)
  89 {
  90         return s.count - s.seen;
  91 }
  92
  93 /*
  94   signal handler - redirects to registered signals
  95 */
  96 static void tevent_common_signal_handler(int signum)
  97 {
  98         struct tevent_common_signal_list *sl;
  99         struct tevent_context *ev = NULL;
 100         int saved_errno = errno;
 101
 102         TEVENT_SIG_INCREMENT(sig_state->signal_count[signum]);
 103         TEVENT_SIG_INCREMENT(sig_state->got_signal);
 104
 105         /* Write to each unique event context. */
 106         for (sl = sig_state->sig_handlers[signum]; sl; sl = sl->next) {
 107                 if (sl->se->event_ctx && sl->se->event_ctx != ev) {
 108                         ev = sl->se->event_ctx;
 109                         tevent_common_wakeup(ev);
 110                 }
 111         }
 112
 113         errno = saved_errno;
 114 }
 115
 116 #ifdef SA_SIGINFO
 117 /*
 118   signal handler with SA_SIGINFO - redirects to registered signals
 119 */
 120 static void tevent_common_signal_handler_info(int signum, siginfo_t *info,
 121                                               void *uctx)
 122 {
 123         uint32_t count = tevent_sig_count(sig_state->signal_count[signum]);
 124         /* sig_state->signal_count[signum].seen % TEVENT_SA_INFO_QUEUE_COUNT
 125          * is the base of the unprocessed signals in the ringbuffer. */
 126         uint32_t ofs = (sig_state->signal_count[signum].seen + count) %
 127                                 TEVENT_SA_INFO_QUEUE_COUNT;
 128         sig_state->sig_info[signum][ofs] = *info;
 129
 130         tevent_common_signal_handler(signum);
 131
 132         /* handle SA_SIGINFO */
 133         if (count+1 == TEVENT_SA_INFO_QUEUE_COUNT) {
 134                 /* we've filled the info array - block this signal until
 135                    these ones are delivered */
 136 #ifdef HAVE_UCONTEXT_T
 137                 /*
 138                  * This is the only way for this to work.
 139                  * By default signum is blocked inside this
 140                  * signal handler using a temporary mask,
 141                  * but what we really need to do now is
 142                  * block it in the callers mask, so it
 143                  * stays blocked when the temporary signal
 144                  * handler mask is replaced when we return
 145                  * from here. The callers mask can be found
 146                  * in the ucontext_t passed in as the
 147                  * void *uctx argument.
 148                  */
 149                 ucontext_t *ucp = (ucontext_t *)uctx;
 150                 sigaddset(&ucp->uc_sigmask, signum);
 151 #else
 152                 /*
 153                  * WARNING !!! WARNING !!!!
 154                  *
 155                  * This code doesn't work.
 156                  * By default signum is blocked inside this
 157                  * signal handler, but calling sigprocmask
 158                  * modifies the temporary signal mask being
 159                  * used *inside* this handler, which will be
 160                  * replaced by the callers signal mask once
 161                  * we return from here. See Samba
 162                  * bug #9550 for details.
 163                  */
 164                 sigset_t set;
 165                 sigemptyset(&set);
 166                 sigaddset(&set, signum);
 167                 sigprocmask(SIG_BLOCK, &set, NULL);
 168 #endif
 169                 TEVENT_SIG_INCREMENT(sig_state->sig_blocked[signum]);
 170         }
 171 }
 172 #endif
 173
 174 static int tevent_common_signal_list_destructor(struct tevent_common_signal_list *sl)
 175 {
 176         if (sig_state->sig_handlers[sl->se->signum]) {
 177                 DLIST_REMOVE(sig_state->sig_handlers[sl->se->signum], sl);
 178         }
 179         return 0;
 180 }
 181
 182 /*
 183   destroy a signal event
 184 */
 185 static int tevent_signal_destructor(struct tevent_signal *se)
 186 {
 187         struct tevent_common_signal_list *sl =
 188                 talloc_get_type_abort(se->additional_data,
 189                 struct tevent_common_signal_list);
 190
 191         if (se->event_ctx) {
 192                 struct tevent_context *ev = se->event_ctx;
 193
 194                 DLIST_REMOVE(ev->signal_events, se);
 195         }
 196
 197         talloc_free(sl);
 198
 199         if (sig_state->sig_handlers[se->signum] == NULL) {
 200                 /* restore old handler, if any */
 201                 if (sig_state->oldact[se->signum]) {
 202                         sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 203                         talloc_free(sig_state->oldact[se->signum]);
 204                         sig_state->oldact[se->signum] = NULL;
 205                 }
 206 #ifdef SA_SIGINFO
 207                 if (se->sa_flags & SA_SIGINFO) {
 208                         if (sig_state->sig_info[se->signum]) {
 209                                 talloc_free(sig_state->sig_info[se->signum]);
 210                                 sig_state->sig_info[se->signum] = NULL;
 211                         }
 212                 }
 213 #endif
 214         }
 215
 216         return 0;
 217 }
 218
 219 /*
 220   add a signal event
 221   return NULL on failure (memory allocation error)
 222 */
 223 struct tevent_signal *tevent_common_add_signal(struct tevent_context *ev,
 224                                                TALLOC_CTX *mem_ctx,
 225                                                int signum,
 226                                                int sa_flags,
 227                                                tevent_signal_handler_t handler,
 228                                                void *private_data,
 229                                                const char *handler_name,
 230                                                const char *location)
 231 {
 232         struct tevent_signal *se;
 233         struct tevent_common_signal_list *sl;
 234         sigset_t set, oldset;
 235         int ret;
 236
 237         ret = tevent_common_wakeup_init(ev);
 238         if (ret != 0) {
 239                 errno = ret;
 240                 return NULL;
 241         }
 242
 243         if (signum >= TEVENT_NUM_SIGNALS) {
 244                 errno = EINVAL;
 245                 return NULL;
 246         }
 247
 248         /* the sig_state needs to be on a global context as it can last across
 249            multiple event contexts */
 250         if (sig_state == NULL) {
 251                 sig_state = talloc_zero(NULL, struct tevent_sig_state);
 252                 if (sig_state == NULL) {
 253                         return NULL;
 254                 }
 255         }
 256
 257         se = talloc(mem_ctx?mem_ctx:ev, struct tevent_signal);
 258         if (se == NULL) return NULL;
 259
 260         se->event_ctx           = ev;
 261         se->signum              = signum;
 262         se->sa_flags            = sa_flags;
 263         se->handler             = handler;
 264         se->private_data        = private_data;
 265         se->handler_name        = handler_name;
 266         se->location            = location;
 267         se->additional_data     = NULL;
 268
 269         sl = talloc(se, struct tevent_common_signal_list);
 270         if (!sl) {
 271                 talloc_free(se);
 272                 return NULL;
 273         }
 274         sl->se = se;
 275         se->additional_data     = sl;
 276
 277         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 278         if (!talloc_reference(se, sig_state)) {
 279                 talloc_free(se);
 280                 return NULL;
 281         }
 282
 283         /* only install a signal handler if not already installed */
 284         if (sig_state->sig_handlers[signum] == NULL) {
 285                 struct sigaction act;
 286                 ZERO_STRUCT(act);
 287                 act.sa_handler = tevent_common_signal_handler;
 288                 act.sa_flags = sa_flags;
 289 #ifdef SA_SIGINFO
 290                 if (sa_flags & SA_SIGINFO) {
 291                         act.sa_handler   = NULL;
 292                         act.sa_sigaction = tevent_common_signal_handler_info;
 293                         if (sig_state->sig_info[signum] == NULL) {
 294                                 sig_state->sig_info[signum] =
 295                                         talloc_zero_array(sig_state, siginfo_t,
 296                                                           TEVENT_SA_INFO_QUEUE_COUNT);
 297                                 if (sig_state->sig_info[signum] == NULL) {
 298                                         talloc_free(se);
 299                                         return NULL;
 300                                 }
 301                         }
 302                 }
 303 #endif
 304                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 305                 if (sig_state->oldact[signum] == NULL) {
 306                         talloc_free(se);
 307                         return NULL;
 308                 }
 309                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 310                         talloc_free(sig_state->oldact[signum]);
 311                         sig_state->oldact[signum] = NULL;
 312                         talloc_free(se);
 313                         return NULL;
 314                 }
 315         }
 316
 317         DLIST_ADD(se->event_ctx->signal_events, se);
 318
 319         /* Make sure the signal doesn't come in while we're mangling list. */
 320         sigemptyset(&set);
 321         sigaddset(&set, signum);
 322         sigprocmask(SIG_BLOCK, &set, &oldset);
 323         DLIST_ADD(sig_state->sig_handlers[signum], sl);
 324         sigprocmask(SIG_SETMASK, &oldset, NULL);
 325
 326         talloc_set_destructor(se, tevent_signal_destructor);
 327         talloc_set_destructor(sl, tevent_common_signal_list_destructor);
 328
 329         return se;
 330 }
 331
 332 struct tevent_se_exists {
 333         struct tevent_se_exists **myself;
 334 };
 335
 336 static int tevent_se_exists_destructor(struct tevent_se_exists *s)
 337 {
 338         *s->myself = NULL;
 339         return 0;
 340 }
 341
 342 /*
 343   check if a signal is pending
 344   return != 0 if a signal was pending
 345 */
 346 int tevent_common_check_signal(struct tevent_context *ev)
 347 {
 348         int i;
 349
 350         if (!sig_state || !TEVENT_SIG_PENDING(sig_state->got_signal)) {
 351                 return 0;
 352         }
 353
 354         for (i=0;i<TEVENT_NUM_SIGNALS+1;i++) {
 355                 struct tevent_common_signal_list *sl, *next;
 356                 struct tevent_sigcounter counter = sig_state->signal_count[i];
 357                 uint32_t count = tevent_sig_count(counter);
 358 #ifdef SA_SIGINFO
 359                 /* Ensure we null out any stored siginfo_t entries
 360                  * after processing for debugging purposes. */
 361                 bool clear_processed_siginfo = false;
 362 #endif
 363
 364                 if (count == 0) {
 365                         continue;
 366                 }
 367                 for (sl=sig_state->sig_handlers[i];sl;sl=next) {
 368                         struct tevent_signal *se = sl->se;
 369                         struct tevent_se_exists *exists;
 370
 371                         next = sl->next;
 372
 373                         /*
 374                          * We have to be careful to not touch "se"
 375                          * after it was deleted in its handler. Thus
 376                          * we allocate a child whose destructor will
 377                          * tell by nulling out itself that its parent
 378                          * is gone.
 379                          */
 380                         exists = talloc(se, struct tevent_se_exists);
 381                         if (exists == NULL) {
 382                                 continue;
 383                         }
 384                         exists->myself = &exists;
 385                         talloc_set_destructor(
 386                                 exists, tevent_se_exists_destructor);
 387
 388 #ifdef SA_SIGINFO
 389                         if (se->sa_flags & SA_SIGINFO) {
 390                                 uint32_t j;
 391
 392                                 clear_processed_siginfo = true;
 393
 394                                 for (j=0;j<count;j++) {
 395                                         /* sig_state->signal_count[i].seen
 396                                          * % TEVENT_SA_INFO_QUEUE_COUNT is
 397                                          * the base position of the unprocessed
 398                                          * signals in the ringbuffer. */
 399                                         uint32_t ofs = (counter.seen + j)
 400                                                 % TEVENT_SA_INFO_QUEUE_COUNT;
 401                                         se->handler(ev, se, i, 1,
 402                                                     (void*)&sig_state->sig_info[i][ofs],
 403                                                     se->private_data);
 404                                         if (!exists) {
 405                                                 break;
 406                                         }
 407                                 }
 408 #ifdef SA_RESETHAND
 409                                 if (exists && (se->sa_flags & SA_RESETHAND)) {
 410                                         talloc_free(se);
 411                                 }
 412 #endif
 413                                 talloc_free(exists);
 414                                 continue;
 415                         }
 416 #endif
 417                         se->handler(ev, se, i, count, NULL, se->private_data);
 418 #ifdef SA_RESETHAND
 419                         if (exists && (se->sa_flags & SA_RESETHAND)) {
 420                                 talloc_free(se);
 421                         }
 422 #endif
 423                         talloc_free(exists);
 424                 }
 425
 426 #ifdef SA_SIGINFO
 427                 if (clear_processed_siginfo && sig_state->sig_info[i] != NULL) {
 428                         uint32_t j;
 429                         for (j=0;j<count;j++) {
 430                                 uint32_t ofs = (counter.seen + j)
 431                                         % TEVENT_SA_INFO_QUEUE_COUNT;
 432                                 memset((void*)&sig_state->sig_info[i][ofs],
 433                                         '\0',
 434                                         sizeof(siginfo_t));
 435                         }
 436                 }
 437 #endif
 438
 439                 TEVENT_SIG_SEEN(sig_state->signal_count[i], count);
 440                 TEVENT_SIG_SEEN(sig_state->got_signal, count);
 441
 442 #ifdef SA_SIGINFO
 443                 if (TEVENT_SIG_PENDING(sig_state->sig_blocked[i])) {
 444                         /* We'd filled the queue, unblock the
 445                            signal now the queue is empty again.
 446                            Note we MUST do this after the
 447                            TEVENT_SIG_SEEN(sig_state->signal_count[i], count)
 448                            call to prevent a new signal running
 449                            out of room in the sig_state->sig_info[i][]
 450                            ring buffer. */
 451                         sigset_t set;
 452                         sigemptyset(&set);
 453                         sigaddset(&set, i);
 454                         TEVENT_SIG_SEEN(sig_state->sig_blocked[i],
 455                                  tevent_sig_count(sig_state->sig_blocked[i]));
 456                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 457                 }
 458 #endif
 459         }
 460
 461         return 1;
 462 }
 463
 464 void tevent_cleanup_pending_signal_handlers(struct tevent_signal *se)
 465 {
 466         struct tevent_common_signal_list *sl =
 467                 talloc_get_type_abort(se->additional_data,
 468                 struct tevent_common_signal_list);
 469
 470         tevent_common_signal_list_destructor(sl);
 471
 472         if (sig_state->sig_handlers[se->signum] == NULL) {
 473                 if (sig_state->oldact[se->signum]) {
 474                         sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 475                         talloc_free(sig_state->oldact[se->signum]);
 476                         sig_state->oldact[se->signum] = NULL;
 477                 }
 478         }
 479         return;
 480 }