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