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         int pipe_hack[2];
  61 #ifdef SA_SIGINFO
  62         /* with SA_SIGINFO we get quite a lot of info per signal */
  63         siginfo_t *sig_info[NUM_SIGNALS+1];
  64         struct sigcounter sig_blocked[NUM_SIGNALS+1];
  65 #endif
  66 } *sig_state;
  67
  68 /*
  69   return number of sigcounter events not processed yet
  70 */
  71 static uint32_t sig_count(struct sigcounter s)
  72 {
  73         if (s.count >= s.seen) {
  74                 return s.count - s.seen;
  75         }
  76         return 1 + (0xFFFFFFFF & ~(s.seen - s.count));
  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         SIG_INCREMENT(sig_state->signal_count[signum]);
  87         SIG_INCREMENT(sig_state->got_signal);
  88         /* doesn't matter if this pipe overflows */
  89         res = write(sig_state->pipe_hack[1], &c, 1);
  90 }
  91
  92 #ifdef SA_SIGINFO
  93 /*
  94   signal handler with SA_SIGINFO - redirects to registered signals
  95 */
  96 static void tevent_common_signal_handler_info(int signum, siginfo_t *info,
  97                                               void *uctx)
  98 {
  99         uint32_t count = sig_count(sig_state->signal_count[signum]);
 100         /* sig_state->signal_count[signum].seen % SA_INFO_QUEUE_COUNT
 101          * is the base of the unprocessed signals in the ringbuffer. */
 102         uint32_t ofs = (sig_state->signal_count[signum].seen + count) %
 103                                 SA_INFO_QUEUE_COUNT;
 104         sig_state->sig_info[signum][ofs] = *info;
 105
 106         tevent_common_signal_handler(signum);
 107
 108         /* handle SA_SIGINFO */
 109         if (count+1 == SA_INFO_QUEUE_COUNT) {
 110                 /* we've filled the info array - block this signal until
 111                    these ones are delivered */
 112                 sigset_t set;
 113                 sigemptyset(&set);
 114                 sigaddset(&set, signum);
 115                 sigprocmask(SIG_BLOCK, &set, NULL);
 116                 SIG_INCREMENT(sig_state->sig_blocked[signum]);
 117         }
 118 }
 119 #endif
 120
 121 static int tevent_common_signal_list_destructor(struct tevent_common_signal_list *sl)
 122 {
 123         DLIST_REMOVE(sig_state->sig_handlers[sl->se->signum], sl);
 124         return 0;
 125 }
 126
 127 /*
 128   destroy a signal event
 129 */
 130 static int tevent_signal_destructor(struct tevent_signal *se)
 131 {
 132         struct tevent_common_signal_list *sl;
 133         sl = talloc_get_type(se->additional_data,
 134                              struct tevent_common_signal_list);
 135
 136         if (se->event_ctx) {
 137                 DLIST_REMOVE(se->event_ctx->signal_events, se);
 138         }
 139
 140         talloc_free(sl);
 141
 142         if (sig_state->sig_handlers[se->signum] == NULL) {
 143                 /* restore old handler, if any */
 144                 sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 145                 sig_state->oldact[se->signum] = NULL;
 146 #ifdef SA_SIGINFO
 147                 if (se->sa_flags & SA_SIGINFO) {
 148                         talloc_free(sig_state->sig_info[se->signum]);
 149                         sig_state->sig_info[se->signum] = NULL;
 150                 }
 151 #endif
 152         }
 153
 154         return 0;
 155 }
 156
 157 /*
 158   this is part of the pipe hack needed to avoid the signal race condition
 159 */
 160 static void signal_pipe_handler(struct tevent_context *ev, struct tevent_fd *fde,
 161                                 uint16_t flags, void *private)
 162 {
 163         char c[16];
 164         ssize_t res;
 165         /* its non-blocking, doesn't matter if we read too much */
 166         res = read(sig_state->pipe_hack[0], c, sizeof(c));
 167 }
 168
 169 /*
 170   add a signal event
 171   return NULL on failure (memory allocation error)
 172 */
 173 struct tevent_signal *tevent_common_add_signal(struct tevent_context *ev,
 174                                                TALLOC_CTX *mem_ctx,
 175                                                int signum,
 176                                                int sa_flags,
 177                                                tevent_signal_handler_t handler,
 178                                                void *private_data,
 179                                                const char *handler_name,
 180                                                const char *location)
 181 {
 182         struct tevent_signal *se;
 183         struct tevent_common_signal_list *sl;
 184
 185         if (signum >= NUM_SIGNALS) {
 186                 errno = EINVAL;
 187                 return NULL;
 188         }
 189
 190         /* the sig_state needs to be on a global context as it can last across
 191            multiple event contexts */
 192         if (sig_state == NULL) {
 193                 sig_state = talloc_zero(talloc_autofree_context(), struct sig_state);
 194                 if (sig_state == NULL) {
 195                         return NULL;
 196                 }
 197         }
 198
 199         se = talloc(mem_ctx?mem_ctx:ev, struct tevent_signal);
 200         if (se == NULL) return NULL;
 201
 202         se->event_ctx           = ev;
 203         se->signum              = signum;
 204         se->sa_flags            = sa_flags;
 205         se->handler             = handler;
 206         se->private_data        = private_data;
 207         se->handler_name        = handler_name;
 208         se->location            = location;
 209         se->additional_data     = NULL;
 210
 211         sl = talloc(se, struct tevent_common_signal_list);
 212         if (!sl) {
 213                 talloc_free(se);
 214                 return NULL;
 215         }
 216         sl->se = se;
 217         se->additional_data     = sl;
 218
 219         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 220         if (!talloc_reference(se, sig_state)) {
 221                 talloc_free(se);
 222                 return NULL;
 223         }
 224
 225         /* only install a signal handler if not already installed */
 226         if (sig_state->sig_handlers[signum] == NULL) {
 227                 struct sigaction act;
 228                 ZERO_STRUCT(act);
 229                 act.sa_handler = tevent_common_signal_handler;
 230                 act.sa_flags = sa_flags;
 231 #ifdef SA_SIGINFO
 232                 if (sa_flags & SA_SIGINFO) {
 233                         act.sa_handler   = NULL;
 234                         act.sa_sigaction = tevent_common_signal_handler_info;
 235                         if (sig_state->sig_info[signum] == NULL) {
 236                                 sig_state->sig_info[signum] = talloc_zero_array(sig_state, siginfo_t, SA_INFO_QUEUE_COUNT);
 237                                 if (sig_state->sig_info[signum] == NULL) {
 238                                         talloc_free(se);
 239                                         return NULL;
 240                                 }
 241                         }
 242                 }
 243 #endif
 244                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 245                 if (sig_state->oldact[signum] == NULL) {
 246                         talloc_free(se);
 247                         return NULL;
 248                 }
 249                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 250                         talloc_free(se);
 251                         return NULL;
 252                 }
 253         }
 254
 255         DLIST_ADD(se->event_ctx->signal_events, se);
 256         DLIST_ADD(sig_state->sig_handlers[signum], sl);
 257
 258         talloc_set_destructor(se, tevent_signal_destructor);
 259         talloc_set_destructor(sl, tevent_common_signal_list_destructor);
 260
 261         /* we need to setup the pipe hack handler if not already
 262            setup */
 263         if (ev->pipe_fde == NULL) {
 264                 if (sig_state->pipe_hack[0] == 0 &&
 265                     sig_state->pipe_hack[1] == 0) {
 266                         if (pipe(sig_state->pipe_hack) == -1) {
 267                                 talloc_free(se);
 268                                 return NULL;
 269                         }
 270                         ev_set_blocking(sig_state->pipe_hack[0], false);
 271                         ev_set_blocking(sig_state->pipe_hack[1], false);
 272                 }
 273                 ev->pipe_fde = tevent_add_fd(ev, ev, sig_state->pipe_hack[0],
 274                                              TEVENT_FD_READ, signal_pipe_handler, NULL);
 275                 if (!ev->pipe_fde) {
 276                         talloc_free(se);
 277                         return NULL;
 278                 }
 279         }
 280
 281         return se;
 282 }
 283
 284
 285 /*
 286   check if a signal is pending
 287   return != 0 if a signal was pending
 288 */
 289 int tevent_common_check_signal(struct tevent_context *ev)
 290 {
 291         int i;
 292
 293         if (!sig_state || !SIG_PENDING(sig_state->got_signal)) {
 294                 return 0;
 295         }
 296
 297         for (i=0;i<NUM_SIGNALS+1;i++) {
 298                 struct tevent_common_signal_list *sl, *next;
 299                 struct sigcounter counter = sig_state->signal_count[i];
 300                 uint32_t count = sig_count(counter);
 301 #ifdef SA_SIGINFO
 302                 /* Ensure we null out any stored siginfo_t entries
 303                  * after processing for debugging purposes. */
 304                 bool clear_processed_siginfo = false;
 305 #endif
 306
 307                 if (count == 0) {
 308                         continue;
 309                 }
 310                 for (sl=sig_state->sig_handlers[i];sl;sl=next) {
 311                         struct tevent_signal *se = sl->se;
 312                         next = sl->next;
 313 #ifdef SA_SIGINFO
 314                         if (se->sa_flags & SA_SIGINFO) {
 315                                 uint32_t j;
 316
 317                                 clear_processed_siginfo = true;
 318
 319                                 for (j=0;j<count;j++) {
 320                                         /* sig_state->signal_count[i].seen
 321                                          * % SA_INFO_QUEUE_COUNT is
 322                                          * the base position of the unprocessed
 323                                          * signals in the ringbuffer. */
 324                                         uint32_t ofs = (counter.seen + j)
 325                                                 % SA_INFO_QUEUE_COUNT;
 326                                         se->handler(ev, se, i, 1,
 327                                                     (void*)&sig_state->sig_info[i][ofs],
 328                                                     se->private_data);
 329                                 }
 330                                 if (se->sa_flags & SA_RESETHAND) {
 331                                         talloc_free(se);
 332                                 }
 333                                 continue;
 334                         }
 335 #endif
 336                         se->handler(ev, se, i, count, NULL, se->private_data);
 337                         if (se->sa_flags & SA_RESETHAND) {
 338                                 talloc_free(se);
 339                         }
 340                 }
 341
 342 #ifdef SA_SIGINFO
 343                 if (clear_processed_siginfo) {
 344                         uint32_t j;
 345                         for (j=0;j<count;j++) {
 346                                 uint32_t ofs = (counter.seen + j)
 347                                         % SA_INFO_QUEUE_COUNT;
 348                                 memset((void*)&sig_state->sig_info[i][ofs],
 349                                         '\0',
 350                                         sizeof(siginfo_t));
 351                         }
 352                 }
 353 #endif
 354
 355                 SIG_SEEN(sig_state->signal_count[i], count);
 356                 SIG_SEEN(sig_state->got_signal, count);
 357
 358 #ifdef SA_SIGINFO
 359                 if (SIG_PENDING(sig_state->sig_blocked[i])) {
 360                         /* We'd filled the queue, unblock the
 361                            signal now the queue is empty again.
 362                            Note we MUST do this after the
 363                            SIG_SEEN(sig_state->signal_count[i], count)
 364                            call to prevent a new signal running
 365                            out of room in the sig_state->sig_info[i][]
 366                            ring buffer. */
 367                         sigset_t set;
 368                         sigemptyset(&set);
 369                         sigaddset(&set, i);
 370                         SIG_SEEN(sig_state->sig_blocked[i],
 371                                  sig_count(sig_state->sig_blocked[i]));
 372                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 373                 }
 374 #endif
 375         }
 376
 377         return 1;
 378 }