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 #define TEVENT_NUM_SIGNALS 64
  34
  35 /* maximum number of SA_SIGINFO signals to hold in the queue.
  36   NB. This *MUST* be a power of 2, in order for the ring buffer
  37   wrap to work correctly. Thanks to Petr Vandrovec <petr@vandrovec.name>
  38   for this. */
  39
  40 #define TEVENT_SA_INFO_QUEUE_COUNT 64
  41
  42 struct tevent_sigcounter {
  43         uint32_t count;
  44         uint32_t seen;
  45 };
  46
  47 #define TEVENT_SIG_INCREMENT(s) (s).count++
  48 #define TEVENT_SIG_SEEN(s, n) (s).seen += (n)
  49 #define TEVENT_SIG_PENDING(s) ((s).seen != (s).count)
  50
  51 struct tevent_common_signal_list {
  52         struct tevent_common_signal_list *prev, *next;
  53         struct tevent_signal *se;
  54 };
  55
  56 /*
  57   the poor design of signals means that this table must be static global
  58 */
  59 static struct tevent_sig_state {
  60         struct tevent_common_signal_list *sig_handlers[TEVENT_NUM_SIGNALS+1];
  61         struct sigaction *oldact[TEVENT_NUM_SIGNALS+1];
  62         struct tevent_sigcounter signal_count[TEVENT_NUM_SIGNALS+1];
  63         struct tevent_sigcounter got_signal;
  64 #ifdef SA_SIGINFO
  65         /* with SA_SIGINFO we get quite a lot of info per signal */
  66         siginfo_t *sig_info[TEVENT_NUM_SIGNALS+1];
  67         struct tevent_sigcounter sig_blocked[TEVENT_NUM_SIGNALS+1];
  68 #endif
  69 } *sig_state;
  70
  71 /*
  72   return number of sigcounter events not processed yet
  73 */
  74 static uint32_t tevent_sig_count(struct tevent_sigcounter s)
  75 {
  76         return s.count - s.seen;
  77 }
  78
  79 /*
  80   signal handler - redirects to registered signals
  81 */
  82 static void tevent_common_signal_handler(int signum)
  83 {
  84         char c = 0;
  85         struct tevent_common_signal_list *sl;
  86         struct tevent_context *ev = NULL;
  87         int saved_errno = errno;
  88
  89         TEVENT_SIG_INCREMENT(sig_state->signal_count[signum]);
  90         TEVENT_SIG_INCREMENT(sig_state->got_signal);
  91
  92         /* Write to each unique event context. */
  93         for (sl = sig_state->sig_handlers[signum]; sl; sl = sl->next) {
  94                 if (sl->se->event_ctx && sl->se->event_ctx != ev) {
  95                         ev = sl->se->event_ctx;
  96                         /* doesn't matter if this pipe overflows */
  97                         (void) write(ev->pipe_fds[1], &c, 1);
  98                 }
  99         }
 100
 101         errno = saved_errno;
 102 }
 103
 104 #ifdef SA_SIGINFO
 105 /*
 106   signal handler with SA_SIGINFO - redirects to registered signals
 107 */
 108 static void tevent_common_signal_handler_info(int signum, siginfo_t *info,
 109                                               void *uctx)
 110 {
 111         uint32_t count = tevent_sig_count(sig_state->signal_count[signum]);
 112         /* sig_state->signal_count[signum].seen % TEVENT_SA_INFO_QUEUE_COUNT
 113          * is the base of the unprocessed signals in the ringbuffer. */
 114         uint32_t ofs = (sig_state->signal_count[signum].seen + count) %
 115                                 TEVENT_SA_INFO_QUEUE_COUNT;
 116         sig_state->sig_info[signum][ofs] = *info;
 117
 118         tevent_common_signal_handler(signum);
 119
 120         /* handle SA_SIGINFO */
 121         if (count+1 == TEVENT_SA_INFO_QUEUE_COUNT) {
 122                 /* we've filled the info array - block this signal until
 123                    these ones are delivered */
 124                 sigset_t set;
 125                 sigemptyset(&set);
 126                 sigaddset(&set, signum);
 127                 sigprocmask(SIG_BLOCK, &set, NULL);
 128                 TEVENT_SIG_INCREMENT(sig_state->sig_blocked[signum]);
 129         }
 130 }
 131 #endif
 132
 133 static int tevent_common_signal_list_destructor(struct tevent_common_signal_list *sl)
 134 {
 135         if (sig_state->sig_handlers[sl->se->signum]) {
 136                 DLIST_REMOVE(sig_state->sig_handlers[sl->se->signum], sl);
 137         }
 138         return 0;
 139 }
 140
 141 /*
 142   destroy a signal event
 143 */
 144 static int tevent_signal_destructor(struct tevent_signal *se)
 145 {
 146         struct tevent_common_signal_list *sl;
 147         sl = talloc_get_type(se->additional_data,
 148                              struct tevent_common_signal_list);
 149
 150         if (se->event_ctx) {
 151                 DLIST_REMOVE(se->event_ctx->signal_events, se);
 152         }
 153
 154         talloc_free(sl);
 155
 156         if (sig_state->sig_handlers[se->signum] == NULL) {
 157                 /* restore old handler, if any */
 158                 if (sig_state->oldact[se->signum]) {
 159                         sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 160                         sig_state->oldact[se->signum] = NULL;
 161                 }
 162 #ifdef SA_SIGINFO
 163                 if (se->sa_flags & SA_SIGINFO) {
 164                         if (sig_state->sig_info[se->signum]) {
 165                                 talloc_free(sig_state->sig_info[se->signum]);
 166                                 sig_state->sig_info[se->signum] = NULL;
 167                         }
 168                 }
 169 #endif
 170         }
 171
 172         return 0;
 173 }
 174
 175 /*
 176   this is part of the pipe hack needed to avoid the signal race condition
 177 */
 178 static void signal_pipe_handler(struct tevent_context *ev, struct tevent_fd *fde,
 179                                 uint16_t flags, void *_private)
 180 {
 181         char c[16];
 182         /* its non-blocking, doesn't matter if we read too much */
 183         (void) read(fde->fd, c, sizeof(c));
 184 }
 185
 186 /*
 187   add a signal event
 188   return NULL on failure (memory allocation error)
 189 */
 190 struct tevent_signal *tevent_common_add_signal(struct tevent_context *ev,
 191                                                TALLOC_CTX *mem_ctx,
 192                                                int signum,
 193                                                int sa_flags,
 194                                                tevent_signal_handler_t handler,
 195                                                void *private_data,
 196                                                const char *handler_name,
 197                                                const char *location)
 198 {
 199         struct tevent_signal *se;
 200         struct tevent_common_signal_list *sl;
 201         sigset_t set, oldset;
 202
 203         if (signum >= TEVENT_NUM_SIGNALS) {
 204                 errno = EINVAL;
 205                 return NULL;
 206         }
 207
 208         /* the sig_state needs to be on a global context as it can last across
 209            multiple event contexts */
 210         if (sig_state == NULL) {
 211                 sig_state = talloc_zero(NULL, struct tevent_sig_state);
 212                 if (sig_state == NULL) {
 213                         return NULL;
 214                 }
 215         }
 216
 217         se = talloc(mem_ctx?mem_ctx:ev, struct tevent_signal);
 218         if (se == NULL) return NULL;
 219
 220         se->event_ctx           = ev;
 221         se->signum              = signum;
 222         se->sa_flags            = sa_flags;
 223         se->handler             = handler;
 224         se->private_data        = private_data;
 225         se->handler_name        = handler_name;
 226         se->location            = location;
 227         se->additional_data     = NULL;
 228
 229         sl = talloc(se, struct tevent_common_signal_list);
 230         if (!sl) {
 231                 talloc_free(se);
 232                 return NULL;
 233         }
 234         sl->se = se;
 235         se->additional_data     = sl;
 236
 237         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 238         if (!talloc_reference(se, sig_state)) {
 239                 talloc_free(se);
 240                 return NULL;
 241         }
 242
 243         /* we need to setup the pipe hack handler if not already
 244            setup */
 245         if (ev->pipe_fde == NULL) {
 246                 if (pipe(ev->pipe_fds) == -1) {
 247                         talloc_free(se);
 248                         return NULL;
 249                 }
 250                 ev_set_blocking(ev->pipe_fds[0], false);
 251                 ev_set_blocking(ev->pipe_fds[1], false);
 252                 ev->pipe_fde = tevent_add_fd(ev, ev, ev->pipe_fds[0],
 253                                              TEVENT_FD_READ,
 254                                              signal_pipe_handler, NULL);
 255                 if (!ev->pipe_fde) {
 256                         close(ev->pipe_fds[0]);
 257                         close(ev->pipe_fds[1]);
 258                         talloc_free(se);
 259                         return NULL;
 260                 }
 261         }
 262
 263         /* only install a signal handler if not already installed */
 264         if (sig_state->sig_handlers[signum] == NULL) {
 265                 struct sigaction act;
 266                 ZERO_STRUCT(act);
 267                 act.sa_handler = tevent_common_signal_handler;
 268                 act.sa_flags = sa_flags;
 269 #ifdef SA_SIGINFO
 270                 if (sa_flags & SA_SIGINFO) {
 271                         act.sa_handler   = NULL;
 272                         act.sa_sigaction = tevent_common_signal_handler_info;
 273                         if (sig_state->sig_info[signum] == NULL) {
 274                                 sig_state->sig_info[signum] =
 275                                         talloc_zero_array(sig_state, siginfo_t,
 276                                                           TEVENT_SA_INFO_QUEUE_COUNT);
 277                                 if (sig_state->sig_info[signum] == NULL) {
 278                                         talloc_free(se);
 279                                         return NULL;
 280                                 }
 281                         }
 282                 }
 283 #endif
 284                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 285                 if (sig_state->oldact[signum] == NULL) {
 286                         talloc_free(se);
 287                         return NULL;
 288                 }
 289                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 290                         talloc_free(se);
 291                         return NULL;
 292                 }
 293         }
 294
 295         DLIST_ADD(se->event_ctx->signal_events, se);
 296
 297         /* Make sure the signal doesn't come in while we're mangling list. */
 298         sigemptyset(&set);
 299         sigaddset(&set, signum);
 300         sigprocmask(SIG_BLOCK, &set, &oldset);
 301         DLIST_ADD(sig_state->sig_handlers[signum], sl);
 302         sigprocmask(SIG_SETMASK, &oldset, NULL);
 303
 304         talloc_set_destructor(se, tevent_signal_destructor);
 305         talloc_set_destructor(sl, tevent_common_signal_list_destructor);
 306
 307         return se;
 308 }
 309
 310 struct tevent_se_exists {
 311         struct tevent_se_exists **myself;
 312 };
 313
 314 static int tevent_se_exists_destructor(struct tevent_se_exists *s)
 315 {
 316         *s->myself = NULL;
 317         return 0;
 318 }
 319
 320 /*
 321   check if a signal is pending
 322   return != 0 if a signal was pending
 323 */
 324 int tevent_common_check_signal(struct tevent_context *ev)
 325 {
 326         int i;
 327
 328         if (!sig_state || !TEVENT_SIG_PENDING(sig_state->got_signal)) {
 329                 return 0;
 330         }
 331
 332         for (i=0;i<TEVENT_NUM_SIGNALS+1;i++) {
 333                 struct tevent_common_signal_list *sl, *next;
 334                 struct tevent_sigcounter counter = sig_state->signal_count[i];
 335                 uint32_t count = tevent_sig_count(counter);
 336 #ifdef SA_SIGINFO
 337                 /* Ensure we null out any stored siginfo_t entries
 338                  * after processing for debugging purposes. */
 339                 bool clear_processed_siginfo = false;
 340 #endif
 341
 342                 if (count == 0) {
 343                         continue;
 344                 }
 345                 for (sl=sig_state->sig_handlers[i];sl;sl=next) {
 346                         struct tevent_signal *se = sl->se;
 347                         struct tevent_se_exists *exists;
 348
 349                         /*
 350                          * We have to be careful to not touch "se"
 351                          * after it was deleted in its handler. Thus
 352                          * we allocate a child whose destructor will
 353                          * tell by nulling out itself that its parent
 354                          * is gone.
 355                          */
 356                         exists = talloc(se, struct tevent_se_exists);
 357                         if (exists == NULL) {
 358                                 continue;
 359                         }
 360                         exists->myself = &exists;
 361                         talloc_set_destructor(
 362                                 exists, tevent_se_exists_destructor);
 363
 364                         next = sl->next;
 365 #ifdef SA_SIGINFO
 366                         if (se->sa_flags & SA_SIGINFO) {
 367                                 uint32_t j;
 368
 369                                 clear_processed_siginfo = true;
 370
 371                                 for (j=0;j<count;j++) {
 372                                         /* sig_state->signal_count[i].seen
 373                                          * % TEVENT_SA_INFO_QUEUE_COUNT is
 374                                          * the base position of the unprocessed
 375                                          * signals in the ringbuffer. */
 376                                         uint32_t ofs = (counter.seen + j)
 377                                                 % TEVENT_SA_INFO_QUEUE_COUNT;
 378                                         se->handler(ev, se, i, 1,
 379                                                     (void*)&sig_state->sig_info[i][ofs],
 380                                                     se->private_data);
 381                                         if (!exists) {
 382                                                 break;
 383                                         }
 384                                 }
 385 #ifdef SA_RESETHAND
 386                                 if (exists && (se->sa_flags & SA_RESETHAND)) {
 387                                         talloc_free(se);
 388                                 }
 389 #endif
 390                                 talloc_free(exists);
 391                                 continue;
 392                         }
 393 #endif
 394                         se->handler(ev, se, i, count, NULL, se->private_data);
 395 #ifdef SA_RESETHAND
 396                         if (exists && (se->sa_flags & SA_RESETHAND)) {
 397                                 talloc_free(se);
 398                         }
 399 #endif
 400                         talloc_free(exists);
 401                 }
 402
 403 #ifdef SA_SIGINFO
 404                 if (clear_processed_siginfo) {
 405                         uint32_t j;
 406                         for (j=0;j<count;j++) {
 407                                 uint32_t ofs = (counter.seen + j)
 408                                         % TEVENT_SA_INFO_QUEUE_COUNT;
 409                                 memset((void*)&sig_state->sig_info[i][ofs],
 410                                         '\0',
 411                                         sizeof(siginfo_t));
 412                         }
 413                 }
 414 #endif
 415
 416                 TEVENT_SIG_SEEN(sig_state->signal_count[i], count);
 417                 TEVENT_SIG_SEEN(sig_state->got_signal, count);
 418
 419 #ifdef SA_SIGINFO
 420                 if (TEVENT_SIG_PENDING(sig_state->sig_blocked[i])) {
 421                         /* We'd filled the queue, unblock the
 422                            signal now the queue is empty again.
 423                            Note we MUST do this after the
 424                            TEVENT_SIG_SEEN(sig_state->signal_count[i], count)
 425                            call to prevent a new signal running
 426                            out of room in the sig_state->sig_info[i][]
 427                            ring buffer. */
 428                         sigset_t set;
 429                         sigemptyset(&set);
 430                         sigaddset(&set, i);
 431                         TEVENT_SIG_SEEN(sig_state->sig_blocked[i],
 432                                  tevent_sig_count(sig_state->sig_blocked[i]));
 433                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 434                 }
 435 #endif
 436         }
 437
 438         return 1;
 439 }
 440
 441 void tevent_cleanup_pending_signal_handlers(struct tevent_signal *se)
 442 {
 443         struct tevent_common_signal_list *sl;
 444         sl = talloc_get_type(se->additional_data,
 445                              struct tevent_common_signal_list);
 446
 447         tevent_common_signal_list_destructor(sl);
 448
 449         if (sig_state->sig_handlers[se->signum] == NULL) {
 450                 if (sig_state->oldact[se->signum]) {
 451                         sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 452                         sig_state->oldact[se->signum] = NULL;
 453                 }
 454         }
 455         return;
 456 }