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