ccan/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 <ccan/tevent/tevent.h>
  27 #include <ccan/tevent/tevent_internal.h>
  28 #include <ccan/tevent/tevent_util.h>
  29 #include <signal.h>
  30 #include <errno.h>
  31 #include <unistd.h>
  32 #include <string.h>
  33
  34 #define TEVENT_NUM_SIGNALS 64
  35
  36 /* maximum number of SA_SIGINFO signals to hold in the queue.
  37   NB. This *MUST* be a power of 2, in order for the ring buffer
  38   wrap to work correctly. Thanks to Petr Vandrovec <petr@vandrovec.name>
  39   for this. */
  40
  41 #define TEVENT_SA_INFO_QUEUE_COUNT 64
  42
  43 struct tevent_sigcounter {
  44         uint32_t count;
  45         uint32_t seen;
  46 };
  47
  48 #define TEVENT_SIG_INCREMENT(s) (s).count++
  49 #define TEVENT_SIG_SEEN(s, n) (s).seen += (n)
  50 #define TEVENT_SIG_PENDING(s) ((s).seen != (s).count)
  51
  52 struct tevent_common_signal_list {
  53         struct tevent_common_signal_list *prev, *next;
  54         struct tevent_signal *se;
  55 };
  56
  57 /*
  58   the poor design of signals means that this table must be static global
  59 */
  60 static struct tevent_sig_state {
  61         struct tevent_common_signal_list *sig_handlers[TEVENT_NUM_SIGNALS+1];
  62         struct sigaction *oldact[TEVENT_NUM_SIGNALS+1];
  63         struct tevent_sigcounter signal_count[TEVENT_NUM_SIGNALS+1];
  64         struct tevent_sigcounter got_signal;
  65 #ifdef SA_SIGINFO
  66         /* with SA_SIGINFO we get quite a lot of info per signal */
  67         siginfo_t *sig_info[TEVENT_NUM_SIGNALS+1];
  68         struct tevent_sigcounter sig_blocked[TEVENT_NUM_SIGNALS+1];
  69 #endif
  70 } *sig_state;
  71
  72 /*
  73   return number of sigcounter events not processed yet
  74 */
  75 static uint32_t tevent_sig_count(struct tevent_sigcounter s)
  76 {
  77         return s.count - s.seen;
  78 }
  79
  80 /*
  81   signal handler - redirects to registered signals
  82 */
  83 static void tevent_common_signal_handler(int signum)
  84 {
  85         char c = 0;
  86         ssize_t res;
  87         struct tevent_common_signal_list *sl;
  88         struct tevent_context *ev = NULL;
  89         int saved_errno = errno;
  90
  91         TEVENT_SIG_INCREMENT(sig_state->signal_count[signum]);
  92         TEVENT_SIG_INCREMENT(sig_state->got_signal);
  93
  94         /* Write to each unique event context. */
  95         for (sl = sig_state->sig_handlers[signum]; sl; sl = sl->next) {
  96                 if (sl->se->event_ctx && sl->se->event_ctx != ev) {
  97                         ev = sl->se->event_ctx;
  98                         /* doesn't matter if this pipe overflows */
  99                         res = write(ev->pipe_fds[1], &c, 1);
 100                 }
 101         }
 102
 103         errno = saved_errno;
 104 }
 105
 106 #ifdef SA_SIGINFO
 107 /*
 108   signal handler with SA_SIGINFO - redirects to registered signals
 109 */
 110 static void tevent_common_signal_handler_info(int signum, siginfo_t *info,
 111                                               void *uctx)
 112 {
 113         uint32_t count = tevent_sig_count(sig_state->signal_count[signum]);
 114         /* sig_state->signal_count[signum].seen % TEVENT_SA_INFO_QUEUE_COUNT
 115          * is the base of the unprocessed signals in the ringbuffer. */
 116         uint32_t ofs = (sig_state->signal_count[signum].seen + count) %
 117                                 TEVENT_SA_INFO_QUEUE_COUNT;
 118         sig_state->sig_info[signum][ofs] = *info;
 119
 120         tevent_common_signal_handler(signum);
 121
 122         /* handle SA_SIGINFO */
 123         if (count+1 == TEVENT_SA_INFO_QUEUE_COUNT) {
 124                 /* we've filled the info array - block this signal until
 125                    these ones are delivered */
 126                 sigset_t set;
 127                 sigemptyset(&set);
 128                 sigaddset(&set, signum);
 129                 sigprocmask(SIG_BLOCK, &set, NULL);
 130                 TEVENT_SIG_INCREMENT(sig_state->sig_blocked[signum]);
 131         }
 132 }
 133 #endif
 134
 135 static int tevent_common_signal_list_destructor(struct tevent_common_signal_list *sl)
 136 {
 137         if (sig_state->sig_handlers[sl->se->signum]) {
 138                 DLIST_REMOVE(sig_state->sig_handlers[sl->se->signum], sl);
 139         }
 140         return 0;
 141 }
 142
 143 /*
 144   destroy a signal event
 145 */
 146 static int tevent_signal_destructor(struct tevent_signal *se)
 147 {
 148         struct tevent_common_signal_list *sl;
 149         sl = talloc_get_type(se->additional_data,
 150                              struct tevent_common_signal_list);
 151
 152         if (se->event_ctx) {
 153                 DLIST_REMOVE(se->event_ctx->signal_events, se);
 154         }
 155
 156         talloc_free(sl);
 157
 158         if (sig_state->sig_handlers[se->signum] == NULL) {
 159                 /* restore old handler, if any */
 160                 if (sig_state->oldact[se->signum]) {
 161                         sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 162                         sig_state->oldact[se->signum] = NULL;
 163                 }
 164 #ifdef SA_SIGINFO
 165                 if (se->sa_flags & SA_SIGINFO) {
 166                         if (sig_state->sig_info[se->signum]) {
 167                                 talloc_free(sig_state->sig_info[se->signum]);
 168                                 sig_state->sig_info[se->signum] = NULL;
 169                         }
 170                 }
 171 #endif
 172         }
 173
 174         return 0;
 175 }
 176
 177 /*
 178   this is part of the pipe hack needed to avoid the signal race condition
 179 */
 180 static void signal_pipe_handler(struct tevent_context *ev, struct tevent_fd *fde,
 181                                 uint16_t flags, void *_private)
 182 {
 183         char c[16];
 184         ssize_t res;
 185         /* its non-blocking, doesn't matter if we read too much */
 186         res = read(fde->fd, c, sizeof(c));
 187 }
 188
 189 /*
 190   add a signal event
 191   return NULL on failure (memory allocation error)
 192 */
 193 struct tevent_signal *tevent_common_add_signal(struct tevent_context *ev,
 194                                                TALLOC_CTX *mem_ctx,
 195                                                int signum,
 196                                                int sa_flags,
 197                                                tevent_signal_handler_t handler,
 198                                                void *private_data,
 199                                                const char *handler_name,
 200                                                const char *location)
 201 {
 202         struct tevent_signal *se;
 203         struct tevent_common_signal_list *sl;
 204         sigset_t set, oldset;
 205
 206         if (signum >= TEVENT_NUM_SIGNALS) {
 207                 errno = EINVAL;
 208                 return NULL;
 209         }
 210
 211         /* the sig_state needs to be on a global context as it can last across
 212            multiple event contexts */
 213         if (sig_state == NULL) {
 214                 sig_state = talloc_zero(NULL, struct tevent_sig_state);
 215                 if (sig_state == NULL) {
 216                         return NULL;
 217                 }
 218         }
 219
 220         se = talloc(mem_ctx?mem_ctx:ev, struct tevent_signal);
 221         if (se == NULL) return NULL;
 222
 223         se->event_ctx           = ev;
 224         se->signum              = signum;
 225         se->sa_flags            = sa_flags;
 226         se->handler             = handler;
 227         se->private_data        = private_data;
 228         se->handler_name        = handler_name;
 229         se->location            = location;
 230         se->additional_data     = NULL;
 231
 232         sl = talloc(se, struct tevent_common_signal_list);
 233         if (!sl) {
 234                 talloc_free(se);
 235                 return NULL;
 236         }
 237         sl->se = se;
 238         se->additional_data     = sl;
 239
 240         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 241         if (!talloc_reference(se, sig_state)) {
 242                 talloc_free(se);
 243                 return NULL;
 244         }
 245
 246         /* we need to setup the pipe hack handler if not already
 247            setup */
 248         if (ev->pipe_fde == NULL) {
 249                 if (pipe(ev->pipe_fds) == -1) {
 250                         talloc_free(se);
 251                         return NULL;
 252                 }
 253                 ev_set_blocking(ev->pipe_fds[0], false);
 254                 ev_set_blocking(ev->pipe_fds[1], false);
 255                 ev->pipe_fde = tevent_add_fd(ev, ev, ev->pipe_fds[0],
 256                                              TEVENT_FD_READ,
 257                                              signal_pipe_handler, NULL);
 258                 if (!ev->pipe_fde) {
 259                         close(ev->pipe_fds[0]);
 260                         close(ev->pipe_fds[1]);
 261                         talloc_free(se);
 262                         return NULL;
 263                 }
 264         }
 265
 266         /* only install a signal handler if not already installed */
 267         if (sig_state->sig_handlers[signum] == NULL) {
 268                 struct sigaction act;
 269                 ZERO_STRUCT(act);
 270                 act.sa_handler = tevent_common_signal_handler;
 271                 act.sa_flags = sa_flags;
 272 #ifdef SA_SIGINFO
 273                 if (sa_flags & SA_SIGINFO) {
 274                         act.sa_handler   = NULL;
 275                         act.sa_sigaction = tevent_common_signal_handler_info;
 276                         if (sig_state->sig_info[signum] == NULL) {
 277                                 sig_state->sig_info[signum] =
 278                                         talloc_zero_array(sig_state, siginfo_t,
 279                                                           TEVENT_SA_INFO_QUEUE_COUNT);
 280                                 if (sig_state->sig_info[signum] == NULL) {
 281                                         talloc_free(se);
 282                                         return NULL;
 283                                 }
 284                         }
 285                 }
 286 #endif
 287                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 288                 if (sig_state->oldact[signum] == NULL) {
 289                         talloc_free(se);
 290                         return NULL;
 291                 }
 292                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 293                         talloc_free(se);
 294                         return NULL;
 295                 }
 296         }
 297
 298         DLIST_ADD(se->event_ctx->signal_events, se);
 299
 300         /* Make sure the signal doesn't come in while we're mangling list. */
 301         sigemptyset(&set);
 302         sigaddset(&set, signum);
 303         sigprocmask(SIG_BLOCK, &set, &oldset);
 304         DLIST_ADD(sig_state->sig_handlers[signum], sl);
 305         sigprocmask(SIG_SETMASK, &oldset, NULL);
 306
 307         talloc_set_destructor(se, tevent_signal_destructor);
 308         talloc_set_destructor(sl, tevent_common_signal_list_destructor);
 309
 310         return se;
 311 }
 312
 313
 314 /*
 315   check if a signal is pending
 316   return != 0 if a signal was pending
 317 */
 318 int tevent_common_check_signal(struct tevent_context *ev)
 319 {
 320         int i;
 321
 322         if (!sig_state || !TEVENT_SIG_PENDING(sig_state->got_signal)) {
 323                 return 0;
 324         }
 325
 326         for (i=0;i<TEVENT_NUM_SIGNALS+1;i++) {
 327                 struct tevent_common_signal_list *sl, *next;
 328                 struct tevent_sigcounter counter = sig_state->signal_count[i];
 329                 uint32_t count = tevent_sig_count(counter);
 330 #ifdef SA_SIGINFO
 331                 /* Ensure we null out any stored siginfo_t entries
 332                  * after processing for debugging purposes. */
 333                 bool clear_processed_siginfo = false;
 334 #endif
 335
 336                 if (count == 0) {
 337                         continue;
 338                 }
 339                 for (sl=sig_state->sig_handlers[i];sl;sl=next) {
 340                         struct tevent_signal *se = sl->se;
 341                         next = sl->next;
 342 #ifdef SA_SIGINFO
 343                         if (se->sa_flags & SA_SIGINFO) {
 344                                 uint32_t j;
 345
 346                                 clear_processed_siginfo = true;
 347
 348                                 for (j=0;j<count;j++) {
 349                                         /* sig_state->signal_count[i].seen
 350                                          * % TEVENT_SA_INFO_QUEUE_COUNT is
 351                                          * the base position of the unprocessed
 352                                          * signals in the ringbuffer. */
 353                                         uint32_t ofs = (counter.seen + j)
 354                                                 % TEVENT_SA_INFO_QUEUE_COUNT;
 355                                         se->handler(ev, se, i, 1,
 356                                                     (void*)&sig_state->sig_info[i][ofs],
 357                                                     se->private_data);
 358                                 }
 359                                 if (se->sa_flags & SA_RESETHAND) {
 360                                         talloc_free(se);
 361                                 }
 362                                 continue;
 363                         }
 364 #endif
 365                         se->handler(ev, se, i, count, NULL, se->private_data);
 366                         if (se->sa_flags & SA_RESETHAND) {
 367                                 talloc_free(se);
 368                         }
 369                 }
 370
 371 #ifdef SA_SIGINFO
 372                 if (clear_processed_siginfo) {
 373                         uint32_t j;
 374                         for (j=0;j<count;j++) {
 375                                 uint32_t ofs = (counter.seen + j)
 376                                         % TEVENT_SA_INFO_QUEUE_COUNT;
 377                                 memset((void*)&sig_state->sig_info[i][ofs],
 378                                         '\0',
 379                                         sizeof(siginfo_t));
 380                         }
 381                 }
 382 #endif
 383
 384                 TEVENT_SIG_SEEN(sig_state->signal_count[i], count);
 385                 TEVENT_SIG_SEEN(sig_state->got_signal, count);
 386
 387 #ifdef SA_SIGINFO
 388                 if (TEVENT_SIG_PENDING(sig_state->sig_blocked[i])) {
 389                         /* We'd filled the queue, unblock the
 390                            signal now the queue is empty again.
 391                            Note we MUST do this after the
 392                            TEVENT_SIG_SEEN(sig_state->signal_count[i], count)
 393                            call to prevent a new signal running
 394                            out of room in the sig_state->sig_info[i][]
 395                            ring buffer. */
 396                         sigset_t set;
 397                         sigemptyset(&set);
 398                         sigaddset(&set, i);
 399                         TEVENT_SIG_SEEN(sig_state->sig_blocked[i],
 400                                  tevent_sig_count(sig_state->sig_blocked[i]));
 401                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 402                 }
 403 #endif
 404         }
 405
 406         return 1;
 407 }
 408
 409 void tevent_cleanup_pending_signal_handlers(struct tevent_signal *se)
 410 {
 411         struct tevent_common_signal_list *sl;
 412         sl = talloc_get_type(se->additional_data,
 413                              struct tevent_common_signal_list);
 414
 415         tevent_common_signal_list_destructor(sl);
 416
 417         if (sig_state->sig_handlers[se->signum] == NULL) {
 418                 if (sig_state->oldact[se->signum]) {
 419                         sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 420                         sig_state->oldact[se->signum] = NULL;
 421                 }
 422         }
 423         return;
 424 }