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    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  20 */
  21
  22 #include "replace.h"
  23 #include "system/filesys.h"
  24 #include "system/wait.h"
  25 #include "tevent.h"
  26 #include "tevent_internal.h"
  27 #include "tevent_util.h"
  28
  29 #define NUM_SIGNALS 64
  30
  31 /* maximum number of SA_SIGINFO signals to hold in the queue */
  32 #define SA_INFO_QUEUE_COUNT 100
  33
  34 struct sigcounter {
  35         uint32_t count;
  36         uint32_t seen;
  37 };
  38
  39 #define SIG_INCREMENT(s) (s).count++
  40 #define SIG_SEEN(s, n) (s).seen += (n)
  41 #define SIG_PENDING(s) ((s).seen != (s).count)
  42
  43 struct tevent_common_signal_list {
  44         struct tevent_common_signal_list *prev, *next;
  45         struct tevent_signal *se;
  46 };
  47
  48 /*
  49   the poor design of signals means that this table must be static global
  50 */
  51 static struct sig_state {
  52         struct tevent_common_signal_list *sig_handlers[NUM_SIGNALS+1];
  53         struct sigaction *oldact[NUM_SIGNALS+1];
  54         struct sigcounter signal_count[NUM_SIGNALS+1];
  55         struct sigcounter got_signal;
  56         int pipe_hack[2];
  57 #ifdef SA_SIGINFO
  58         /* with SA_SIGINFO we get quite a lot of info per signal */
  59         siginfo_t *sig_info[NUM_SIGNALS+1];
  60         struct sigcounter sig_blocked[NUM_SIGNALS+1];
  61 #endif
  62 } *sig_state;
  63
  64 /*
  65   return number of sigcounter events not processed yet
  66 */
  67 static uint32_t sig_count(struct sigcounter s)
  68 {
  69         if (s.count >= s.seen) {
  70                 return s.count - s.seen;
  71         }
  72         return 1 + (0xFFFFFFFF & ~(s.seen - s.count));
  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         SIG_INCREMENT(sig_state->signal_count[signum]);
  82         SIG_INCREMENT(sig_state->got_signal);
  83         /* doesn't matter if this pipe overflows */
  84         write(sig_state->pipe_hack[1], &c, 1);
  85 }
  86
  87 #ifdef SA_SIGINFO
  88 /*
  89   signal handler with SA_SIGINFO - redirects to registered signals
  90 */
  91 static void tevent_common_signal_handler_info(int signum, siginfo_t *info,
  92                                               void *uctx)
  93 {
  94         uint32_t count = sig_count(sig_state->signal_count[signum]);
  95         sig_state->sig_info[signum][count] = *info;
  96
  97         tevent_common_signal_handler(signum);
  98
  99         /* handle SA_SIGINFO */
 100         if (count+1 == SA_INFO_QUEUE_COUNT) {
 101                 /* we've filled the info array - block this signal until
 102                    these ones are delivered */
 103                 sigset_t set;
 104                 sigemptyset(&set);
 105                 sigaddset(&set, signum);
 106                 sigprocmask(SIG_BLOCK, &set, NULL);
 107                 SIG_INCREMENT(sig_state->sig_blocked[signum]);
 108         }
 109 }
 110 #endif
 111
 112 static int tevent_common_signal_list_destructor(struct tevent_common_signal_list *sl)
 113 {
 114         DLIST_REMOVE(sig_state->sig_handlers[sl->se->signum], sl);
 115         return 0;
 116 }
 117
 118 /*
 119   destroy a signal event
 120 */
 121 static int tevent_signal_destructor(struct tevent_signal *se)
 122 {
 123         struct tevent_common_signal_list *sl;
 124         sl = talloc_get_type(se->additional_data,
 125                              struct tevent_common_signal_list);
 126
 127         if (se->event_ctx) {
 128                 DLIST_REMOVE(se->event_ctx->signal_events, se);
 129         }
 130
 131         talloc_free(sl);
 132
 133         if (sig_state->sig_handlers[se->signum] == NULL) {
 134                 /* restore old handler, if any */
 135                 sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 136                 sig_state->oldact[se->signum] = NULL;
 137 #ifdef SA_SIGINFO
 138                 if (se->sa_flags & SA_SIGINFO) {
 139                         talloc_free(sig_state->sig_info[se->signum]);
 140                         sig_state->sig_info[se->signum] = NULL;
 141                 }
 142 #endif
 143         }
 144
 145         return 0;
 146 }
 147
 148 /*
 149   this is part of the pipe hack needed to avoid the signal race condition
 150 */
 151 static void signal_pipe_handler(struct tevent_context *ev, struct tevent_fd *fde,
 152                                 uint16_t flags, void *private)
 153 {
 154         char c[16];
 155         /* its non-blocking, doesn't matter if we read too much */
 156         read(sig_state->pipe_hack[0], c, sizeof(c));
 157 }
 158
 159 /*
 160   add a signal event
 161   return NULL on failure (memory allocation error)
 162 */
 163 struct tevent_signal *tevent_common_add_signal(struct tevent_context *ev,
 164                                                TALLOC_CTX *mem_ctx,
 165                                                int signum,
 166                                                int sa_flags,
 167                                                tevent_signal_handler_t handler,
 168                                                void *private_data,
 169                                                const char *handler_name,
 170                                                const char *location)
 171 {
 172         struct tevent_signal *se;
 173         struct tevent_common_signal_list *sl;
 174
 175         if (signum >= NUM_SIGNALS) {
 176                 errno = EINVAL;
 177                 return NULL;
 178         }
 179
 180         /* the sig_state needs to be on a global context as it can last across
 181            multiple event contexts */
 182         if (sig_state == NULL) {
 183                 sig_state = talloc_zero(talloc_autofree_context(), struct sig_state);
 184                 if (sig_state == NULL) {
 185                         return NULL;
 186                 }
 187         }
 188
 189         se = talloc(mem_ctx?mem_ctx:ev, struct tevent_signal);
 190         if (se == NULL) return NULL;
 191
 192         se->event_ctx           = ev;
 193         se->signum              = signum;
 194         se->sa_flags            = sa_flags;
 195         se->handler             = handler;
 196         se->private_data        = private_data;
 197         se->handler_name        = handler_name;
 198         se->location            = location;
 199         se->additional_data     = NULL;
 200
 201         sl = talloc(se, struct tevent_common_signal_list);
 202         if (!sl) {
 203                 talloc_free(se);
 204                 return NULL;
 205         }
 206         sl->se = se;
 207         se->additional_data     = sl;
 208
 209         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 210         if (!talloc_reference(se, sig_state)) {
 211                 talloc_free(se);
 212                 return NULL;
 213         }
 214
 215         /* only install a signal handler if not already installed */
 216         if (sig_state->sig_handlers[signum] == NULL) {
 217                 struct sigaction act;
 218                 ZERO_STRUCT(act);
 219                 act.sa_handler = tevent_common_signal_handler;
 220                 act.sa_flags = sa_flags;
 221 #ifdef SA_SIGINFO
 222                 if (sa_flags & SA_SIGINFO) {
 223                         act.sa_handler   = NULL;
 224                         act.sa_sigaction = tevent_common_signal_handler_info;
 225                         if (sig_state->sig_info[signum] == NULL) {
 226                                 sig_state->sig_info[signum] = talloc_array(sig_state, siginfo_t, SA_INFO_QUEUE_COUNT);
 227                                 if (sig_state->sig_info[signum] == NULL) {
 228                                         talloc_free(se);
 229                                         return NULL;
 230                                 }
 231                         }
 232                 }
 233 #endif
 234                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 235                 if (sig_state->oldact[signum] == NULL) {
 236                         talloc_free(se);
 237                         return NULL;
 238                 }
 239                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 240                         talloc_free(se);
 241                         return NULL;
 242                 }
 243         }
 244
 245         DLIST_ADD(se->event_ctx->signal_events, se);
 246         DLIST_ADD(sig_state->sig_handlers[signum], sl);
 247
 248         talloc_set_destructor(se, tevent_signal_destructor);
 249         talloc_set_destructor(sl, tevent_common_signal_list_destructor);
 250
 251         /* we need to setup the pipe hack handler if not already
 252            setup */
 253         if (ev->pipe_fde == NULL) {
 254                 if (sig_state->pipe_hack[0] == 0 &&
 255                     sig_state->pipe_hack[1] == 0) {
 256                         pipe(sig_state->pipe_hack);
 257                         ev_set_blocking(sig_state->pipe_hack[0], false);
 258                         ev_set_blocking(sig_state->pipe_hack[1], false);
 259                 }
 260                 ev->pipe_fde = tevent_add_fd(ev, ev, sig_state->pipe_hack[0],
 261                                              TEVENT_FD_READ, signal_pipe_handler, NULL);
 262                 if (!ev->pipe_fde) {
 263                         talloc_free(se);
 264                         return NULL;
 265                 }
 266         }
 267
 268         return se;
 269 }
 270
 271
 272 /*
 273   check if a signal is pending
 274   return != 0 if a signal was pending
 275 */
 276 int tevent_common_check_signal(struct tevent_context *ev)
 277 {
 278         int i;
 279
 280         if (!sig_state || !SIG_PENDING(sig_state->got_signal)) {
 281                 return 0;
 282         }
 283
 284         for (i=0;i<NUM_SIGNALS+1;i++) {
 285                 struct tevent_common_signal_list *sl, *next;
 286                 struct sigcounter counter = sig_state->signal_count[i];
 287                 uint32_t count = sig_count(counter);
 288
 289                 if (count == 0) {
 290                         continue;
 291                 }
 292                 for (sl=sig_state->sig_handlers[i];sl;sl=next) {
 293                         struct tevent_signal *se = sl->se;
 294                         next = sl->next;
 295 #ifdef SA_SIGINFO
 296                         if (se->sa_flags & SA_SIGINFO) {
 297                                 int j;
 298                                 for (j=0;j<count;j++) {
 299                                         /* note the use of the sig_info array as a
 300                                            ring buffer */
 301                                         int ofs = ((count-1) + j) % SA_INFO_QUEUE_COUNT;
 302                                         se->handler(ev, se, i, 1,
 303                                                     (void*)&sig_state->sig_info[i][ofs],
 304                                                     se->private_data);
 305                                 }
 306                                 if (SIG_PENDING(sig_state->sig_blocked[i])) {
 307                                         /* we'd filled the queue, unblock the
 308                                            signal now */
 309                                         sigset_t set;
 310                                         sigemptyset(&set);
 311                                         sigaddset(&set, i);
 312                                         SIG_SEEN(sig_state->sig_blocked[i],
 313                                                  sig_count(sig_state->sig_blocked[i]));
 314                                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 315                                 }
 316                                 if (se->sa_flags & SA_RESETHAND) {
 317                                         talloc_free(se);
 318                                 }
 319                                 continue;
 320                         }
 321 #endif
 322                         se->handler(ev, se, i, count, NULL, se->private_data);
 323                         if (se->sa_flags & SA_RESETHAND) {
 324                                 talloc_free(se);
 325                         }
 326                 }
 327                 SIG_SEEN(sig_state->signal_count[i], count);
 328                 SIG_SEEN(sig_state->got_signal, count);
 329         }
 330
 331         return 1;
 332 }