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