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 #ifdef SA_SIGINFO
  61         /* with SA_SIGINFO we get quite a lot of info per signal */
  62         siginfo_t *sig_info[NUM_SIGNALS+1];
  63         struct sigcounter sig_blocked[NUM_SIGNALS+1];
  64 #endif
  65 } *sig_state;
  66
  67 /*
  68   return number of sigcounter events not processed yet
  69 */
  70 static uint32_t sig_count(struct sigcounter s)
  71 {
  72         return s.count - s.seen;
  73 }
  74
  75 /*
  76   signal handler - redirects to registered signals
  77 */
  78 static void tevent_common_signal_handler(int signum)
  79 {
  80         char c = 0;
  81         ssize_t res;
  82         struct tevent_common_signal_list *sl;
  83         struct tevent_context *ev = NULL;
  84
  85         SIG_INCREMENT(sig_state->signal_count[signum]);
  86         SIG_INCREMENT(sig_state->got_signal);
  87
  88         if (sig_state->sig_handlers[signum] != NULL) {
  89                 ev = sig_state->sig_handlers[signum]->se->event_ctx;
  90                 /* doesn't matter if this pipe overflows */
  91                 res = write(ev->pipe_fds[1], &c, 1);
  92         }
  93
  94         /* Write to each unique event context. */
  95         for (sl = sig_state->sig_handlers[signum]; sl; sl = sl->next) {
  96                 if (sl->se->event_ctx != ev) {
  97                         /* doesn't matter if this pipe overflows */
  98                         res = write(ev->pipe_fds[1], &c, 1);
  99                         ev = sl->se->event_ctx;
 100                 }
 101         }
 102 }
 103
 104 #ifdef SA_SIGINFO
 105 /*
 106   signal handler with SA_SIGINFO - redirects to registered signals
 107 */
 108 static void tevent_common_signal_handler_info(int signum, siginfo_t *info,
 109                                               void *uctx)
 110 {
 111         uint32_t count = sig_count(sig_state->signal_count[signum]);
 112         /* sig_state->signal_count[signum].seen % SA_INFO_QUEUE_COUNT
 113          * is the base of the unprocessed signals in the ringbuffer. */
 114         uint32_t ofs = (sig_state->signal_count[signum].seen + count) %
 115                                 SA_INFO_QUEUE_COUNT;
 116         sig_state->sig_info[signum][ofs] = *info;
 117
 118         tevent_common_signal_handler(signum);
 119
 120         /* handle SA_SIGINFO */
 121         if (count+1 == SA_INFO_QUEUE_COUNT) {
 122                 /* we've filled the info array - block this signal until
 123                    these ones are delivered */
 124                 sigset_t set;
 125                 sigemptyset(&set);
 126                 sigaddset(&set, signum);
 127                 sigprocmask(SIG_BLOCK, &set, NULL);
 128                 SIG_INCREMENT(sig_state->sig_blocked[signum]);
 129         }
 130 }
 131 #endif
 132
 133 static int tevent_common_signal_list_destructor(struct tevent_common_signal_list *sl)
 134 {
 135         DLIST_REMOVE(sig_state->sig_handlers[sl->se->signum], sl);
 136         return 0;
 137 }
 138
 139 /*
 140   destroy a signal event
 141 */
 142 static int tevent_signal_destructor(struct tevent_signal *se)
 143 {
 144         struct tevent_common_signal_list *sl;
 145         sl = talloc_get_type(se->additional_data,
 146                              struct tevent_common_signal_list);
 147
 148         if (se->event_ctx) {
 149                 DLIST_REMOVE(se->event_ctx->signal_events, se);
 150         }
 151
 152         talloc_free(sl);
 153
 154         if (sig_state->sig_handlers[se->signum] == NULL) {
 155                 /* restore old handler, if any */
 156                 sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 157                 sig_state->oldact[se->signum] = NULL;
 158 #ifdef SA_SIGINFO
 159                 if (se->sa_flags & SA_SIGINFO) {
 160                         talloc_free(sig_state->sig_info[se->signum]);
 161                         sig_state->sig_info[se->signum] = NULL;
 162                 }
 163 #endif
 164         }
 165
 166         return 0;
 167 }
 168
 169 /*
 170   this is part of the pipe hack needed to avoid the signal race condition
 171 */
 172 static void signal_pipe_handler(struct tevent_context *ev, struct tevent_fd *fde,
 173                                 uint16_t flags, void *_private)
 174 {
 175         char c[16];
 176         ssize_t res;
 177         /* its non-blocking, doesn't matter if we read too much */
 178         res = read(fde->fd, c, sizeof(c));
 179 }
 180
 181 /*
 182   add a signal event
 183   return NULL on failure (memory allocation error)
 184 */
 185 struct tevent_signal *tevent_common_add_signal(struct tevent_context *ev,
 186                                                TALLOC_CTX *mem_ctx,
 187                                                int signum,
 188                                                int sa_flags,
 189                                                tevent_signal_handler_t handler,
 190                                                void *private_data,
 191                                                const char *handler_name,
 192                                                const char *location)
 193 {
 194         struct tevent_signal *se;
 195         struct tevent_common_signal_list *sl;
 196         sigset_t set, oldset;
 197
 198         if (signum >= NUM_SIGNALS) {
 199                 errno = EINVAL;
 200                 return NULL;
 201         }
 202
 203         /* the sig_state needs to be on a global context as it can last across
 204            multiple event contexts */
 205         if (sig_state == NULL) {
 206                 sig_state = talloc_zero(talloc_autofree_context(), struct sig_state);
 207                 if (sig_state == NULL) {
 208                         return NULL;
 209                 }
 210         }
 211
 212         se = talloc(mem_ctx?mem_ctx:ev, struct tevent_signal);
 213         if (se == NULL) return NULL;
 214
 215         se->event_ctx           = ev;
 216         se->signum              = signum;
 217         se->sa_flags            = sa_flags;
 218         se->handler             = handler;
 219         se->private_data        = private_data;
 220         se->handler_name        = handler_name;
 221         se->location            = location;
 222         se->additional_data     = NULL;
 223
 224         sl = talloc(se, struct tevent_common_signal_list);
 225         if (!sl) {
 226                 talloc_free(se);
 227                 return NULL;
 228         }
 229         sl->se = se;
 230         se->additional_data     = sl;
 231
 232         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 233         if (!talloc_reference(se, sig_state)) {
 234                 talloc_free(se);
 235                 return NULL;
 236         }
 237
 238         /* we need to setup the pipe hack handler if not already
 239            setup */
 240         if (ev->pipe_fde == NULL) {
 241                 if (pipe(ev->pipe_fds) == -1) {
 242                         talloc_free(se);
 243                         return NULL;
 244                 }
 245                 ev_set_blocking(ev->pipe_fds[0], false);
 246                 ev_set_blocking(ev->pipe_fds[1], false);
 247                 ev->pipe_fde = tevent_add_fd(ev, ev, ev->pipe_fds[0],
 248                                              TEVENT_FD_READ,
 249                                              signal_pipe_handler, NULL);
 250                 if (!ev->pipe_fde) {
 251                         close(ev->pipe_fds[0]);
 252                         close(ev->pipe_fds[1]);
 253                         talloc_free(se);
 254                         return NULL;
 255                 }
 256         }
 257
 258         /* only install a signal handler if not already installed */
 259         if (sig_state->sig_handlers[signum] == NULL) {
 260                 struct sigaction act;
 261                 ZERO_STRUCT(act);
 262                 act.sa_handler = tevent_common_signal_handler;
 263                 act.sa_flags = sa_flags;
 264 #ifdef SA_SIGINFO
 265                 if (sa_flags & SA_SIGINFO) {
 266                         act.sa_handler   = NULL;
 267                         act.sa_sigaction = tevent_common_signal_handler_info;
 268                         if (sig_state->sig_info[signum] == NULL) {
 269                                 sig_state->sig_info[signum] = talloc_zero_array(sig_state, siginfo_t, SA_INFO_QUEUE_COUNT);
 270                                 if (sig_state->sig_info[signum] == NULL) {
 271                                         talloc_free(se);
 272                                         return NULL;
 273                                 }
 274                         }
 275                 }
 276 #endif
 277                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 278                 if (sig_state->oldact[signum] == NULL) {
 279                         talloc_free(se);
 280                         return NULL;
 281                 }
 282                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 283                         talloc_free(se);
 284                         return NULL;
 285                 }
 286         }
 287
 288         DLIST_ADD(se->event_ctx->signal_events, se);
 289
 290         /* Make sure the signal doesn't come in while we're mangling list. */
 291         sigemptyset(&set);
 292         sigaddset(&set, signum);
 293         sigprocmask(SIG_BLOCK, &set, &oldset);
 294         DLIST_ADD(sig_state->sig_handlers[signum], sl);
 295         sigprocmask(SIG_SETMASK, &oldset, NULL);
 296
 297         talloc_set_destructor(se, tevent_signal_destructor);
 298         talloc_set_destructor(sl, tevent_common_signal_list_destructor);
 299
 300         return se;
 301 }
 302
 303
 304 /*
 305   check if a signal is pending
 306   return != 0 if a signal was pending
 307 */
 308 int tevent_common_check_signal(struct tevent_context *ev)
 309 {
 310         int i;
 311
 312         if (!sig_state || !SIG_PENDING(sig_state->got_signal)) {
 313                 return 0;
 314         }
 315
 316         for (i=0;i<NUM_SIGNALS+1;i++) {
 317                 struct tevent_common_signal_list *sl, *next;
 318                 struct sigcounter counter = sig_state->signal_count[i];
 319                 uint32_t count = sig_count(counter);
 320 #ifdef SA_SIGINFO
 321                 /* Ensure we null out any stored siginfo_t entries
 322                  * after processing for debugging purposes. */
 323                 bool clear_processed_siginfo = false;
 324 #endif
 325
 326                 if (count == 0) {
 327                         continue;
 328                 }
 329                 for (sl=sig_state->sig_handlers[i];sl;sl=next) {
 330                         struct tevent_signal *se = sl->se;
 331                         next = sl->next;
 332 #ifdef SA_SIGINFO
 333                         if (se->sa_flags & SA_SIGINFO) {
 334                                 uint32_t j;
 335
 336                                 clear_processed_siginfo = true;
 337
 338                                 for (j=0;j<count;j++) {
 339                                         /* sig_state->signal_count[i].seen
 340                                          * % SA_INFO_QUEUE_COUNT is
 341                                          * the base position of the unprocessed
 342                                          * signals in the ringbuffer. */
 343                                         uint32_t ofs = (counter.seen + j)
 344                                                 % SA_INFO_QUEUE_COUNT;
 345                                         se->handler(ev, se, i, 1,
 346                                                     (void*)&sig_state->sig_info[i][ofs],
 347                                                     se->private_data);
 348                                 }
 349                                 if (se->sa_flags & SA_RESETHAND) {
 350                                         talloc_free(se);
 351                                 }
 352                                 continue;
 353                         }
 354 #endif
 355                         se->handler(ev, se, i, count, NULL, se->private_data);
 356                         if (se->sa_flags & SA_RESETHAND) {
 357                                 talloc_free(se);
 358                         }
 359                 }
 360
 361 #ifdef SA_SIGINFO
 362                 if (clear_processed_siginfo) {
 363                         uint32_t j;
 364                         for (j=0;j<count;j++) {
 365                                 uint32_t ofs = (counter.seen + j)
 366                                         % SA_INFO_QUEUE_COUNT;
 367                                 memset((void*)&sig_state->sig_info[i][ofs],
 368                                         '\0',
 369                                         sizeof(siginfo_t));
 370                         }
 371                 }
 372 #endif
 373
 374                 SIG_SEEN(sig_state->signal_count[i], count);
 375                 SIG_SEEN(sig_state->got_signal, count);
 376
 377 #ifdef SA_SIGINFO
 378                 if (SIG_PENDING(sig_state->sig_blocked[i])) {
 379                         /* We'd filled the queue, unblock the
 380                            signal now the queue is empty again.
 381                            Note we MUST do this after the
 382                            SIG_SEEN(sig_state->signal_count[i], count)
 383                            call to prevent a new signal running
 384                            out of room in the sig_state->sig_info[i][]
 385                            ring buffer. */
 386                         sigset_t set;
 387                         sigemptyset(&set);
 388                         sigaddset(&set, i);
 389                         SIG_SEEN(sig_state->sig_blocked[i],
 390                                  sig_count(sig_state->sig_blocked[i]));
 391                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 392                 }
 393 #endif
 394         }
 395
 396         return 1;
 397 }