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 10
  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
  44 /*
  45   the poor design of signals means that this table must be static global
  46 */
  47 static struct sig_state {
  48         struct signal_event *sig_handlers[NUM_SIGNALS+1];
  49         struct sigaction *oldact[NUM_SIGNALS+1];
  50         struct sigcounter signal_count[NUM_SIGNALS+1];
  51         struct sigcounter got_signal;
  52         int pipe_hack[2];
  53 #ifdef SA_SIGINFO
  54         /* with SA_SIGINFO we get quite a lot of info per signal */
  55         siginfo_t *sig_info[NUM_SIGNALS+1];
  56         struct sigcounter sig_blocked[NUM_SIGNALS+1];
  57 #endif
  58 } *sig_state;
  59
  60 /*
  61   return number of sigcounter events not processed yet
  62 */
  63 static uint32_t sig_count(struct sigcounter s)
  64 {
  65         if (s.count >= s.seen) {
  66                 return s.count - s.seen;
  67         }
  68         return 1 + (0xFFFFFFFF & ~(s.seen - s.count));
  69 }
  70
  71 /*
  72   signal handler - redirects to registered signals
  73 */
  74 static void signal_handler(int signum)
  75 {
  76         char c = 0;
  77         SIG_INCREMENT(sig_state->signal_count[signum]);
  78         SIG_INCREMENT(sig_state->got_signal);
  79         /* doesn't matter if this pipe overflows */
  80         write(sig_state->pipe_hack[1], &c, 1);
  81 }
  82
  83 #ifdef SA_SIGINFO
  84 /*
  85   signal handler with SA_SIGINFO - redirects to registered signals
  86 */
  87 static void signal_handler_info(int signum, siginfo_t *info, void *uctx)
  88 {
  89         uint32_t count = sig_count(sig_state->signal_count[signum]);
  90         sig_state->sig_info[signum][count] = *info;
  91
  92         signal_handler(signum);
  93
  94         /* handle SA_SIGINFO */
  95         if (count+1 == SA_INFO_QUEUE_COUNT) {
  96                 /* we've filled the info array - block this signal until
  97                    these ones are delivered */
  98                 sigset_t set;
  99                 sigemptyset(&set);
 100                 sigaddset(&set, signum);
 101                 sigprocmask(SIG_BLOCK, &set, NULL);
 102                 SIG_INCREMENT(sig_state->sig_blocked[signum]);
 103         }
 104 }
 105 #endif
 106
 107 /*
 108   destroy a signal event
 109 */
 110 static int signal_event_destructor(struct signal_event *se)
 111 {
 112         se->event_ctx->num_signal_handlers--;
 113         DLIST_REMOVE(sig_state->sig_handlers[se->signum], se);
 114         if (sig_state->sig_handlers[se->signum] == NULL) {
 115                 /* restore old handler, if any */
 116                 sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 117                 sig_state->oldact[se->signum] = NULL;
 118 #ifdef SA_SIGINFO
 119                 if (se->sa_flags & SA_SIGINFO) {
 120                         talloc_free(sig_state->sig_info[se->signum]);
 121                         sig_state->sig_info[se->signum] = NULL;
 122                 }
 123 #endif
 124         }
 125         return 0;
 126 }
 127
 128 /*
 129   this is part of the pipe hack needed to avoid the signal race condition
 130 */
 131 static void signal_pipe_handler(struct tevent_context *ev, struct tevent_fd *fde,
 132                                 uint16_t flags, void *private)
 133 {
 134         char c[16];
 135         /* its non-blocking, doesn't matter if we read too much */
 136         read(sig_state->pipe_hack[0], c, sizeof(c));
 137 }
 138
 139 /*
 140   add a signal event
 141   return NULL on failure (memory allocation error)
 142 */
 143 struct signal_event *common_event_add_signal(struct tevent_context *ev,
 144                                              TALLOC_CTX *mem_ctx,
 145                                              int signum,
 146                                              int sa_flags,
 147                                              event_signal_handler_t handler,
 148                                              void *private_data)
 149 {
 150         struct signal_event *se;
 151
 152         if (signum >= NUM_SIGNALS) {
 153                 return NULL;
 154         }
 155
 156         /* the sig_state needs to be on a global context as it can last across
 157            multiple event contexts */
 158         if (sig_state == NULL) {
 159                 sig_state = talloc_zero(talloc_autofree_context(), struct sig_state);
 160                 if (sig_state == NULL) {
 161                         return NULL;
 162                 }
 163         }
 164
 165         se = talloc(mem_ctx?mem_ctx:ev, struct signal_event);
 166         if (se == NULL) return NULL;
 167
 168         se->event_ctx           = ev;
 169         se->handler             = handler;
 170         se->private_data        = private_data;
 171         se->signum              = signum;
 172         se->sa_flags            = sa_flags;
 173
 174         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 175         if (!talloc_reference(se, sig_state)) {
 176                 return NULL;
 177         }
 178
 179         /* only install a signal handler if not already installed */
 180         if (sig_state->sig_handlers[signum] == NULL) {
 181                 struct sigaction act;
 182                 ZERO_STRUCT(act);
 183                 act.sa_handler   = signal_handler;
 184                 act.sa_flags = sa_flags;
 185 #ifdef SA_SIGINFO
 186                 if (sa_flags & SA_SIGINFO) {
 187                         act.sa_handler   = NULL;
 188                         act.sa_sigaction = signal_handler_info;
 189                         if (sig_state->sig_info[signum] == NULL) {
 190                                 sig_state->sig_info[signum] = talloc_array(sig_state, siginfo_t, SA_INFO_QUEUE_COUNT);
 191                                 if (sig_state->sig_info[signum] == NULL) {
 192                                         talloc_free(se);
 193                                         return NULL;
 194                                 }
 195                         }
 196                 }
 197 #endif
 198                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 199                 if (sig_state->oldact[signum] == NULL) {
 200                         talloc_free(se);
 201                         return NULL;
 202                 }
 203                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 204                         talloc_free(se);
 205                         return NULL;
 206                 }
 207         }
 208
 209         DLIST_ADD(sig_state->sig_handlers[signum], se);
 210
 211         talloc_set_destructor(se, signal_event_destructor);
 212
 213         /* we need to setup the pipe hack handler if not already
 214            setup */
 215         if (ev->pipe_fde == NULL) {
 216                 if (sig_state->pipe_hack[0] == 0 &&
 217                     sig_state->pipe_hack[1] == 0) {
 218                         pipe(sig_state->pipe_hack);
 219                         ev_set_blocking(sig_state->pipe_hack[0], false);
 220                         ev_set_blocking(sig_state->pipe_hack[1], false);
 221                 }
 222                 ev->pipe_fde = event_add_fd(ev, ev, sig_state->pipe_hack[0],
 223                                             EVENT_FD_READ, signal_pipe_handler, NULL);
 224         }
 225         ev->num_signal_handlers++;
 226
 227         return se;
 228 }
 229
 230
 231 /*
 232   check if a signal is pending
 233   return != 0 if a signal was pending
 234 */
 235 int common_event_check_signal(struct tevent_context *ev)
 236 {
 237         int i;
 238
 239         if (!sig_state || !SIG_PENDING(sig_state->got_signal)) {
 240                 return 0;
 241         }
 242
 243         for (i=0;i<NUM_SIGNALS+1;i++) {
 244                 struct signal_event *se, *next;
 245                 struct sigcounter counter = sig_state->signal_count[i];
 246                 uint32_t count = sig_count(counter);
 247
 248                 if (count == 0) {
 249                         continue;
 250                 }
 251                 for (se=sig_state->sig_handlers[i];se;se=next) {
 252                         next = se->next;
 253 #ifdef SA_SIGINFO
 254                         if (se->sa_flags & SA_SIGINFO) {
 255                                 int j;
 256                                 for (j=0;j<count;j++) {
 257                                         /* note the use of the sig_info array as a
 258                                            ring buffer */
 259                                         int ofs = ((count-1) + j) % SA_INFO_QUEUE_COUNT;
 260                                         se->handler(ev, se, i, 1,
 261                                                     (void*)&sig_state->sig_info[i][ofs],
 262                                                     se->private_data);
 263                                 }
 264                                 if (SIG_PENDING(sig_state->sig_blocked[i])) {
 265                                         /* we'd filled the queue, unblock the
 266                                            signal now */
 267                                         sigset_t set;
 268                                         sigemptyset(&set);
 269                                         sigaddset(&set, i);
 270                                         SIG_SEEN(sig_state->sig_blocked[i],
 271                                                  sig_count(sig_state->sig_blocked[i]));
 272                                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 273                                 }
 274                                 if (se->sa_flags & SA_RESETHAND) {
 275                                         talloc_free(se);
 276                                 }
 277                                 continue;
 278                         }
 279 #endif
 280                         se->handler(ev, se, i, count, NULL, se->private_data);
 281                         if (se->sa_flags & SA_RESETHAND) {
 282                                 talloc_free(se);
 283                         }
 284                 }
 285                 SIG_SEEN(sig_state->signal_count[i], count);
 286                 SIG_SEEN(sig_state->got_signal, count);
 287         }
 288
 289         return 1;
 290 }