source/lib/events/events_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 #if _SAMBA_BUILD_
  23 #include "includes.h"
  24 #include "lib/util/dlinklist.h"
  25 #else
  26 #include <signal.h>
  27 #include "replace.h"
  28 #include "events_util.h"
  29 #endif
  30 #include "system/filesys.h"
  31 #include "system/select.h"
  32 #include "events.h"
  33 #include "events_internal.h"
  34
  35 #define NUM_SIGNALS 64
  36
  37 /* maximum number of SA_SIGINFO signals to hold in the queue */
  38 #define SA_INFO_QUEUE_COUNT 10
  39
  40 struct sigcounter {
  41         uint32_t count;
  42         uint32_t seen;
  43 };
  44
  45 #define SIG_INCREMENT(s) (s).count++
  46 #define SIG_SEEN(s, n) (s).seen += (n)
  47 #define SIG_PENDING(s) ((s).seen != (s).count)
  48
  49
  50 /*
  51   the poor design of signals means that this table must be static global
  52 */
  53 static struct sig_state {
  54         struct signal_event *sig_handlers[NUM_SIGNALS];
  55         struct sigaction *oldact[NUM_SIGNALS];
  56         struct sigcounter signal_count[NUM_SIGNALS];
  57         struct sigcounter got_signal;
  58         int pipe_hack[2];
  59 #ifdef SA_SIGINFO
  60         /* with SA_SIGINFO we get quite a lot of info per signal */
  61         siginfo_t *sig_info[NUM_SIGNALS];
  62         struct sigcounter sig_blocked[NUM_SIGNALS];
  63 #endif
  64 } *sig_state;
  65
  66 /*
  67   return number of sigcounter events not processed yet
  68 */
  69 static uint32_t sig_count(struct sigcounter s)
  70 {
  71         if (s.count >= s.seen) {
  72                 return s.count - s.seen;
  73         }
  74         return 1 + (0xFFFFFFFF & ~(s.seen - s.count));
  75 }
  76
  77 /*
  78   signal handler - redirects to registered signals
  79 */
  80 static void signal_handler(int signum)
  81 {
  82         char c = 0;
  83         SIG_INCREMENT(sig_state->signal_count[signum]);
  84         SIG_INCREMENT(sig_state->got_signal);
  85         /* doesn't matter if this pipe overflows */
  86         write(sig_state->pipe_hack[1], &c, 1);
  87 }
  88
  89 #ifdef SA_SIGINFO
  90 /*
  91   signal handler with SA_SIGINFO - redirects to registered signals
  92 */
  93 static void signal_handler_info(int signum, siginfo_t *info, void *uctx)
  94 {
  95         uint32_t count = sig_count(sig_state->signal_count[signum]);
  96         sig_state->sig_info[signum][count] = *info;
  97
  98         signal_handler(signum);
  99
 100         /* handle SA_SIGINFO */
 101         if (count+1 == SA_INFO_QUEUE_COUNT) {
 102                 /* we've filled the info array - block this signal until
 103                    these ones are delivered */
 104                 sigset_t set;
 105                 sigemptyset(&set);
 106                 sigaddset(&set, signum);
 107                 sigprocmask(SIG_BLOCK, &set, NULL);
 108                 SIG_INCREMENT(sig_state->sig_blocked[signum]);
 109         }
 110 }
 111 #endif
 112
 113 /*
 114   destroy a signal event
 115 */
 116 static int signal_event_destructor(struct signal_event *se)
 117 {
 118         se->event_ctx->num_signal_handlers--;
 119         DLIST_REMOVE(sig_state->sig_handlers[se->signum], se);
 120         if (sig_state->sig_handlers[se->signum] == NULL) {
 121                 /* restore old handler, if any */
 122                 sigaction(se->signum, sig_state->oldact[se->signum], NULL);
 123                 sig_state->oldact[se->signum] = NULL;
 124 #ifdef SA_SIGINFO
 125                 if (se->sa_flags & SA_SIGINFO) {
 126                         talloc_free(sig_state->sig_info[se->signum]);
 127                         sig_state->sig_info[se->signum] = NULL;
 128                 }
 129 #endif
 130         }
 131         return 0;
 132 }
 133
 134 /*
 135   this is part of the pipe hack needed to avoid the signal race condition
 136 */
 137 static void signal_pipe_handler(struct event_context *ev, struct fd_event *fde,
 138                                 uint16_t flags, void *private)
 139 {
 140         char c[16];
 141         /* its non-blocking, doesn't matter if we read too much */
 142         read(sig_state->pipe_hack[0], c, sizeof(c));
 143 }
 144
 145 /*
 146   add a signal event
 147   return NULL on failure (memory allocation error)
 148 */
 149 struct signal_event *common_event_add_signal(struct event_context *ev,
 150                                              TALLOC_CTX *mem_ctx,
 151                                              int signum,
 152                                              int sa_flags,
 153                                              event_signal_handler_t handler,
 154                                              void *private_data)
 155 {
 156         struct signal_event *se;
 157
 158         if (signum >= NUM_SIGNALS) {
 159                 return NULL;
 160         }
 161
 162         /* the sig_state needs to be on a global context as it can last across
 163            multiple event contexts */
 164         if (sig_state == NULL) {
 165                 sig_state = talloc_zero(talloc_autofree_context(), struct sig_state);
 166                 if (sig_state == NULL) {
 167                         return NULL;
 168                 }
 169         }
 170
 171         se = talloc(mem_ctx?mem_ctx:ev, struct signal_event);
 172         if (se == NULL) return NULL;
 173
 174         se->event_ctx           = ev;
 175         se->handler             = handler;
 176         se->private_data        = private_data;
 177         se->signum              = signum;
 178         se->sa_flags            = sa_flags;
 179
 180         /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
 181         if (!talloc_reference(se, sig_state)) {
 182                 return NULL;
 183         }
 184
 185         /* only install a signal handler if not already installed */
 186         if (sig_state->sig_handlers[signum] == NULL) {
 187                 struct sigaction act;
 188                 ZERO_STRUCT(act);
 189                 act.sa_handler   = signal_handler;
 190                 act.sa_flags = sa_flags;
 191 #ifdef SA_SIGINFO
 192                 if (sa_flags & SA_SIGINFO) {
 193                         act.sa_handler   = NULL;
 194                         act.sa_sigaction = signal_handler_info;
 195                         if (sig_state->sig_info[signum] == NULL) {
 196                                 sig_state->sig_info[signum] = talloc_array(sig_state, siginfo_t, SA_INFO_QUEUE_COUNT);
 197                                 if (sig_state->sig_info[signum] == NULL) {
 198                                         talloc_free(se);
 199                                         return NULL;
 200                                 }
 201                         }
 202                 }
 203 #endif
 204                 sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
 205                 if (sig_state->oldact[signum] == NULL) {
 206                         talloc_free(se);
 207                         return NULL;
 208                 }
 209                 if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
 210                         talloc_free(se);
 211                         return NULL;
 212                 }
 213         }
 214
 215         DLIST_ADD(sig_state->sig_handlers[signum], se);
 216
 217         talloc_set_destructor(se, signal_event_destructor);
 218
 219         /* we need to setup the pipe hack handler if not already
 220            setup */
 221         if (ev->pipe_fde == NULL) {
 222                 if (sig_state->pipe_hack[0] == 0 &&
 223                     sig_state->pipe_hack[1] == 0) {
 224                         pipe(sig_state->pipe_hack);
 225                         set_blocking(sig_state->pipe_hack[0], false);
 226                         set_blocking(sig_state->pipe_hack[1], false);
 227                 }
 228                 ev->pipe_fde = event_add_fd(ev, ev, sig_state->pipe_hack[0],
 229                                             EVENT_FD_READ, signal_pipe_handler, NULL);
 230         }
 231         ev->num_signal_handlers++;
 232
 233         return se;
 234 }
 235
 236
 237 /*
 238   check if a signal is pending
 239   return != 0 if a signal was pending
 240 */
 241 int common_event_check_signal(struct event_context *ev)
 242 {
 243         int i;
 244
 245         if (!sig_state || !SIG_PENDING(sig_state->got_signal)) {
 246                 return 0;
 247         }
 248
 249         for (i=0;i<NUM_SIGNALS+1;i++) {
 250                 struct signal_event *se, *next;
 251                 struct sigcounter counter = sig_state->signal_count[i];
 252                 uint32_t count = sig_count(counter);
 253
 254                 if (count == 0) {
 255                         continue;
 256                 }
 257                 for (se=sig_state->sig_handlers[i];se;se=next) {
 258                         next = se->next;
 259 #ifdef SA_SIGINFO
 260                         if (se->sa_flags & SA_SIGINFO) {
 261                                 int j;
 262                                 for (j=0;j<count;j++) {
 263                                         /* note the use of the sig_info array as a
 264                                            ring buffer */
 265                                         int ofs = ((count-1) + j) % SA_INFO_QUEUE_COUNT;
 266                                         se->handler(ev, se, i, 1,
 267                                                     (void*)&sig_state->sig_info[i][ofs],
 268                                                     se->private_data);
 269                                 }
 270                                 if (SIG_PENDING(sig_state->sig_blocked[i])) {
 271                                         /* we'd filled the queue, unblock the
 272                                            signal now */
 273                                         sigset_t set;
 274                                         sigemptyset(&set);
 275                                         sigaddset(&set, i);
 276                                         SIG_SEEN(sig_state->sig_blocked[i],
 277                                                  sig_count(sig_state->sig_blocked[i]));
 278                                         sigprocmask(SIG_UNBLOCK, &set, NULL);
 279                                 }
 280                                 if (se->sa_flags & SA_RESETHAND) {
 281                                         talloc_free(se);
 282                                 }
 283                                 continue;
 284                         }
 285 #endif
 286                         se->handler(ev, se, i, count, NULL, se->private_data);
 287                         if (se->sa_flags & SA_RESETHAND) {
 288                                 talloc_free(se);
 289                         }
 290                 }
 291                 SIG_SEEN(sig_state->signal_count[i], count);
 292                 SIG_SEEN(sig_state->got_signal, count);
 293         }
 294
 295         return 1;
 296 }