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