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