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