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 && sl->se->event_ctx != ev) {
  96                         ev = sl->se->event_ctx;
  97                         /* doesn't matter if this pipe overflows */
  98                         res = write(ev->pipe_fds[1], &c, 1);
  99                 }
 100         }
 101
 102         errno = saved_errno;
 103 }
 104
 105 #ifdef SA_SIGINFO
 106 /*
 107   signal handler with SA_SIGINFO - redirects to registered signals
 108 */
 109 static void tevent_common_signal_handler_info(int signum, siginfo_t *info,
 110                                               void *uctx)
 111 {
 112         uint32_t count = sig_count(sig_state->signal_count[signum]);
 113         /* sig_state->signal_count[signum].seen % SA_INFO_QUEUE_COUNT
 114          * is the base of the unprocessed signals in the ringbuffer. */
 115         uint32_t ofs = (sig_state->signal_count[signum].seen + count) %
 116                                 SA_INFO_QUEUE_COUNT;
 117         sig_state->sig_info[signum][ofs] = *info;
 118
 119         tevent_common_signal_handler(signum);
 120
 121         /* handle SA_SIGINFO */
 122         if (count+1 == SA_INFO_QUEUE_COUNT) {
 123                 /* we've filled the info array - block this signal until
 124                    these ones are delivered */
 125                 sigset_t set;
 126                 sigemptyset(&set);
 127                 sigaddset(&set, signum);
 128                 sigprocmask(SIG_BLOCK, &set, NULL);
 129                 SIG_INCREMENT(sig_state->sig_blocked[signum]);
 130         }
 131 }
 132 #endif
 133
 134 static int tevent_common_signal_list_destructor(struct tevent_common_signal_list *sl)
 135 {
 136         DLIST_REMOVE(sig_state->sig_handlers[sl->se->signum], sl);
 137         return 0;
 138 }
 139
 140 /*
 141   destroy a signal event
 142 */
 143 static int tevent_signal_destructor(struct tevent_signal *se)
 144 {
 145         struct tevent_common_signal_list *sl;
 146         sl = talloc_get_type(se->additional_data,
 147                              struct tevent_common_signal_list);
 148
 149         if (se->event_ctx) {
 150                 DLIST_REMOVE(se->event_ctx->signal_events, se);
 151         }
 152
 153         talloc_free(sl);
 154
 155         if (sig_state->sig_handlers[se->signum] == NULL) {
 156                 /* restore old handler, if any */
 157                 sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 158                 sig_state->oldact[se->signum] = NULL;
 159 #ifdef SA_SIGINFO
 160                 if (se->sa_flags & SA_SIGINFO) {
 161                         talloc_free(sig_state->sig_info[se->signum]);
 162                         sig_state->sig_info[se->signum] = NULL;
 163                 }
 164 #endif
 165         }
 166
 167         return 0;
 168 }
 169
 170 /*
 171   this is part of the pipe hack needed to avoid the signal race condition
 172 */
 173 static void signal_pipe_handler(struct tevent_context *ev, struct tevent_fd *fde,
 174                                 uint16_t flags, void *_private)
 175 {
 176         char c[16];
 177         ssize_t res;
 178         /* its non-blocking, doesn't matter if we read too much */
 179         res = read(fde->fd, c, sizeof(c));
 180 }
 181
 182 /*
 183   add a signal event
 184   return NULL on failure (memory allocation error)
 185 */
 186 struct tevent_signal *tevent_common_add_signal(struct tevent_context *ev,
 187                                                TALLOC_CTX *mem_ctx,
 188                                                int signum,
 189                                                int sa_flags,
 190                                                tevent_signal_handler_t handler,
 191                                                void *private_data,
 192                                                const char *handler_name,
 193                                                const char *location)
 194 {
 195         struct tevent_signal *se;
 196         struct tevent_common_signal_list *sl;
 197         sigset_t set, oldset;
 198
 199         if (signum >= NUM_SIGNALS) {
 200                 errno = EINVAL;
 201                 return NULL;
 202         }
 203
 204         /* the sig_state needs to be on a global context as it can last across
 205            multiple event contexts */
 206         if (sig_state == NULL) {
 207                 sig_state = talloc_zero(talloc_autofree_context(), struct sig_state);
 208                 if (sig_state == NULL) {
 209                         return NULL;
 210                 }
 211         }
 212
 213         se = talloc(mem_ctx?mem_ctx:ev, struct tevent_signal);
 214         if (se == NULL) return NULL;
 215
 216         se->event_ctx           = ev;
 217         se->signum              = signum;
 218         se->sa_flags            = sa_flags;
 219         se->handler             = handler;
 220         se->private_data        = private_data;
 221         se->handler_name        = handler_name;
 222         se->location            = location;
 223         se->additional_data     = NULL;
 224
 225         sl = talloc(se, struct tevent_common_signal_list);
 226         if (!sl) {
 227                 talloc_free(se);
 228                 return NULL;
 229         }
 230         sl->se = se;
 231         se->additional_data     = sl;
 232
 233         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 234         if (!talloc_reference(se, sig_state)) {
 235                 talloc_free(se);
 236                 return NULL;
 237         }
 238
 239         /* we need to setup the pipe hack handler if not already
 240            setup */
 241         if (ev->pipe_fde == NULL) {
 242                 if (pipe(ev->pipe_fds) == -1) {
 243                         talloc_free(se);
 244                         return NULL;
 245                 }
 246                 ev_set_blocking(ev->pipe_fds[0], false);
 247                 ev_set_blocking(ev->pipe_fds[1], false);
 248                 ev->pipe_fde = tevent_add_fd(ev, ev, ev->pipe_fds[0],
 249                                              TEVENT_FD_READ,
 250                                              signal_pipe_handler, NULL);
 251                 if (!ev->pipe_fde) {
 252                         close(ev->pipe_fds[0]);
 253                         close(ev->pipe_fds[1]);
 254                         talloc_free(se);
 255                         return NULL;
 256                 }
 257         }
 258
 259         /* only install a signal handler if not already installed */
 260         if (sig_state->sig_handlers[signum] == NULL) {
 261                 struct sigaction act;
 262                 ZERO_STRUCT(act);
 263                 act.sa_handler = tevent_common_signal_handler;
 264                 act.sa_flags = sa_flags;
 265 #ifdef SA_SIGINFO
 266                 if (sa_flags & SA_SIGINFO) {
 267                         act.sa_handler   = NULL;
 268                         act.sa_sigaction = tevent_common_signal_handler_info;
 269                         if (sig_state->sig_info[signum] == NULL) {
 270                                 sig_state->sig_info[signum] = talloc_zero_array(sig_state, siginfo_t, SA_INFO_QUEUE_COUNT);
 271                                 if (sig_state->sig_info[signum] == NULL) {
 272                                         talloc_free(se);
 273                                         return NULL;
 274                                 }
 275                         }
 276                 }
 277 #endif
 278                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 279                 if (sig_state->oldact[signum] == NULL) {
 280                         talloc_free(se);
 281                         return NULL;
 282                 }
 283                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 284                         talloc_free(se);
 285                         return NULL;
 286                 }
 287         }
 288
 289         DLIST_ADD(se->event_ctx->signal_events, se);
 290
 291         /* Make sure the signal doesn't come in while we're mangling list. */
 292         sigemptyset(&set);
 293         sigaddset(&set, signum);
 294         sigprocmask(SIG_BLOCK, &set, &oldset);
 295         DLIST_ADD(sig_state->sig_handlers[signum], sl);
 296         sigprocmask(SIG_SETMASK, &oldset, NULL);
 297
 298         talloc_set_destructor(se, tevent_signal_destructor);
 299         talloc_set_destructor(sl, tevent_common_signal_list_destructor);
 300
 301         return se;
 302 }
 303
 304
 305 /*
 306   check if a signal is pending
 307   return != 0 if a signal was pending
 308 */
 309 int tevent_common_check_signal(struct tevent_context *ev)
 310 {
 311         int i;
 312
 313         if (!sig_state || !SIG_PENDING(sig_state->got_signal)) {
 314                 return 0;
 315         }
 316
 317         for (i=0;i<NUM_SIGNALS+1;i++) {
 318                 struct tevent_common_signal_list *sl, *next;
 319                 struct sigcounter counter = sig_state->signal_count[i];
 320                 uint32_t count = sig_count(counter);
 321 #ifdef SA_SIGINFO
 322                 /* Ensure we null out any stored siginfo_t entries
 323                  * after processing for debugging purposes. */
 324                 bool clear_processed_siginfo = false;
 325 #endif
 326
 327                 if (count == 0) {
 328                         continue;
 329                 }
 330                 for (sl=sig_state->sig_handlers[i];sl;sl=next) {
 331                         struct tevent_signal *se = sl->se;
 332                         next = sl->next;
 333 #ifdef SA_SIGINFO
 334                         if (se->sa_flags & SA_SIGINFO) {
 335                                 uint32_t j;
 336
 337                                 clear_processed_siginfo = true;
 338
 339                                 for (j=0;j<count;j++) {
 340                                         /* sig_state->signal_count[i].seen
 341                                          * % SA_INFO_QUEUE_COUNT is
 342                                          * the base position of the unprocessed
 343                                          * signals in the ringbuffer. */
 344                                         uint32_t ofs = (counter.seen + j)
 345                                                 % SA_INFO_QUEUE_COUNT;
 346                                         se->handler(ev, se, i, 1,
 347                                                     (void*)&sig_state->sig_info[i][ofs],
 348                                                     se->private_data);
 349                                 }
 350                                 if (se->sa_flags & SA_RESETHAND) {
 351                                         talloc_free(se);
 352                                 }
 353                                 continue;
 354                         }
 355 #endif
 356                         se->handler(ev, se, i, count, NULL, se->private_data);
 357                         if (se->sa_flags & SA_RESETHAND) {
 358                                 talloc_free(se);
 359                         }
 360                 }
 361
 362 #ifdef SA_SIGINFO
 363                 if (clear_processed_siginfo) {
 364                         uint32_t j;
 365                         for (j=0;j<count;j++) {
 366                                 uint32_t ofs = (counter.seen + j)
 367                                         % SA_INFO_QUEUE_COUNT;
 368                                 memset((void*)&sig_state->sig_info[i][ofs],
 369                                         '\0',
 370                                         sizeof(siginfo_t));
 371                         }
 372                 }
 373 #endif
 374
 375                 SIG_SEEN(sig_state->signal_count[i], count);
 376                 SIG_SEEN(sig_state->got_signal, count);
 377
 378 #ifdef SA_SIGINFO
 379                 if (SIG_PENDING(sig_state->sig_blocked[i])) {
 380                         /* We'd filled the queue, unblock the
 381                            signal now the queue is empty again.
 382                            Note we MUST do this after the
 383                            SIG_SEEN(sig_state->signal_count[i], count)
 384                            call to prevent a new signal running
 385                            out of room in the sig_state->sig_info[i][]
 386                            ring buffer. */
 387                         sigset_t set;
 388                         sigemptyset(&set);
 389                         sigaddset(&set, i);
 390                         SIG_SEEN(sig_state->sig_blocked[i],
 391                                  sig_count(sig_state->sig_blocked[i]));
 392                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 393                 }
 394 #endif
 395         }
 396
 397         return 1;
 398 }