lib/fatal-signal.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 #include <config.h>
  17 #include "fatal-signal.h"
  18 #include <assert.h>
  19 #include <errno.h>
  20 #include <signal.h>
  21 #include <stdbool.h>
  22 #include <stdio.h>
  23 #include <stdint.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <unistd.h>
  27 #include "poll-loop.h"
  28 #include "shash.h"
  29 #include "sset.h"
  30 #include "socket-util.h"
  31 #include "util.h"
  32 #include "vlog.h"
  33
  34 VLOG_DEFINE_THIS_MODULE(fatal_signal);
  35
  36 /* Signals to catch. */
  37 static const int fatal_signals[] = { SIGTERM, SIGINT, SIGHUP, SIGALRM };
  38
  39 /* Signals to catch as a sigset_t. */
  40 static sigset_t fatal_signal_set;
  41
  42 /* Hooks to call upon catching a signal */
  43 struct hook {
  44     void (*hook_cb)(void *aux);
  45     void (*cancel_cb)(void *aux);
  46     void *aux;
  47     bool run_at_exit;
  48 };
  49 #define MAX_HOOKS 32
  50 static struct hook hooks[MAX_HOOKS];
  51 static size_t n_hooks;
  52
  53 static int signal_fds[2];
  54 static volatile sig_atomic_t stored_sig_nr = SIG_ATOMIC_MAX;
  55
  56 static void fatal_signal_init(void);
  57 static void atexit_handler(void);
  58 static void call_hooks(int sig_nr);
  59
  60 static void
  61 fatal_signal_init(void)
  62 {
  63     static bool inited = false;
  64
  65     if (!inited) {
  66         size_t i;
  67
  68         inited = true;
  69
  70         if (pipe(signal_fds)) {
  71             ovs_fatal(errno, "could not create pipe");
  72         }
  73         set_nonblocking(signal_fds[0]);
  74         set_nonblocking(signal_fds[1]);
  75
  76         sigemptyset(&fatal_signal_set);
  77         for (i = 0; i < ARRAY_SIZE(fatal_signals); i++) {
  78             int sig_nr = fatal_signals[i];
  79             struct sigaction old_sa;
  80
  81             sigaddset(&fatal_signal_set, sig_nr);
  82             if (sigaction(sig_nr, NULL, &old_sa)) {
  83                 ovs_fatal(errno, "sigaction");
  84             }
  85             if (old_sa.sa_handler == SIG_DFL
  86                 && signal(sig_nr, fatal_signal_handler) == SIG_ERR) {
  87                 ovs_fatal(errno, "signal");
  88             }
  89         }
  90         atexit(atexit_handler);
  91     }
  92 }
  93
  94 /* Registers 'hook_cb' to be called when a process termination signal is
  95  * raised.  If 'run_at_exit' is true, 'hook_cb' is also called during normal
  96  * process termination, e.g. when exit() is called or when main() returns.
  97  *
  98  * 'hook_cb' is not called immediately from the signal handler but rather the
  99  * next time the poll loop iterates, so it is freed from the usual restrictions
 100  * on signal handler functions.
 101  *
 102  * If the current process forks, fatal_signal_fork() may be called to clear the
 103  * parent process's fatal signal hooks, so that 'hook_cb' is only called when
 104  * the child terminates, not when the parent does.  When fatal_signal_fork() is
 105  * called, it calls the 'cancel_cb' function if it is nonnull, passing 'aux',
 106  * to notify that the hook has been canceled.  This allows the hook to free
 107  * memory, etc. */
 108 void
 109 fatal_signal_add_hook(void (*hook_cb)(void *aux), void (*cancel_cb)(void *aux),
 110                       void *aux, bool run_at_exit)
 111 {
 112     fatal_signal_init();
 113
 114     assert(n_hooks < MAX_HOOKS);
 115     hooks[n_hooks].hook_cb = hook_cb;
 116     hooks[n_hooks].cancel_cb = cancel_cb;
 117     hooks[n_hooks].aux = aux;
 118     hooks[n_hooks].run_at_exit = run_at_exit;
 119     n_hooks++;
 120 }
 121
 122 /* Handles fatal signal number 'sig_nr'.
 123  *
 124  * Ordinarily this is the actual signal handler.  When other code needs to
 125  * handle one of our signals, however, it can register for that signal and, if
 126  * and when necessary, call this function to do fatal signal processing for it
 127  * and terminate the process.  Currently only timeval.c does this, for SIGALRM.
 128  * (It is not important whether the other code sets up its signal handler
 129  * before or after this file, because this file will only set up a signal
 130  * handler in the case where the signal has its default handling.)  */
 131 void
 132 fatal_signal_handler(int sig_nr)
 133 {
 134     ignore(write(signal_fds[1], "", 1));
 135     stored_sig_nr = sig_nr;
 136 }
 137
 138 /* Check whether a fatal signal has occurred and, if so, call the fatal signal
 139  * hooks and exit.
 140  *
 141  * This function is called automatically by poll_block(), but specialized
 142  * programs that may not always call poll_block() on a regular basis should
 143  * also call it periodically.  (Therefore, any function with "block" in its
 144  * name should call fatal_signal_run() each time it is called, either directly
 145  * or through poll_block(), because such functions can only used by specialized
 146  * programs that can afford to block outside their main loop around
 147  * poll_block().)
 148  */
 149 void
 150 fatal_signal_run(void)
 151 {
 152     int sig_nr;
 153
 154     fatal_signal_init();
 155
 156     sig_nr = stored_sig_nr;
 157     if (sig_nr != SIG_ATOMIC_MAX) {
 158         call_hooks(sig_nr);
 159
 160         /* Re-raise the signal with the default handling so that the program
 161          * termination status reflects that we were killed by this signal */
 162         signal(sig_nr, SIG_DFL);
 163         raise(sig_nr);
 164     }
 165 }
 166
 167 void
 168 fatal_signal_wait(void)
 169 {
 170     fatal_signal_init();
 171     poll_fd_wait(signal_fds[0], POLLIN);
 172 }
 173
 174 static void
 175 atexit_handler(void)
 176 {
 177     call_hooks(0);
 178 }
 179
 180 static void
 181 call_hooks(int sig_nr)
 182 {
 183     static volatile sig_atomic_t recurse = 0;
 184     if (!recurse) {
 185         size_t i;
 186
 187         recurse = 1;
 188
 189         for (i = 0; i < n_hooks; i++) {
 190             struct hook *h = &hooks[i];
 191             if (sig_nr || h->run_at_exit) {
 192                 h->hook_cb(h->aux);
 193             }
 194         }
 195     }
 196 }
 197 \f
 198 /* Files to delete on exit. */
 199 static struct sset files = SSET_INITIALIZER(&files);
 200
 201 /* Has a hook function been registered with fatal_signal_add_hook() (and not
 202  * cleared by fatal_signal_fork())? */
 203 static bool added_hook;
 204
 205 static void unlink_files(void *aux);
 206 static void cancel_files(void *aux);
 207 static void do_unlink_files(void);
 208
 209 /* Registers 'file' to be unlinked when the program terminates via exit() or a
 210  * fatal signal. */
 211 void
 212 fatal_signal_add_file_to_unlink(const char *file)
 213 {
 214     if (!added_hook) {
 215         added_hook = true;
 216         fatal_signal_add_hook(unlink_files, cancel_files, NULL, true);
 217     }
 218
 219     sset_add(&files, file);
 220 }
 221
 222 /* Unregisters 'file' from being unlinked when the program terminates via
 223  * exit() or a fatal signal. */
 224 void
 225 fatal_signal_remove_file_to_unlink(const char *file)
 226 {
 227     sset_find_and_delete(&files, file);
 228 }
 229
 230 /* Like fatal_signal_remove_file_to_unlink(), but also unlinks 'file'.
 231  * Returns 0 if successful, otherwise a positive errno value. */
 232 int
 233 fatal_signal_unlink_file_now(const char *file)
 234 {
 235     int error = unlink(file) ? errno : 0;
 236     if (error) {
 237         VLOG_WARN("could not unlink \"%s\" (%s)", file, strerror(error));
 238     }
 239
 240     fatal_signal_remove_file_to_unlink(file);
 241
 242     return error;
 243 }
 244
 245 static void
 246 unlink_files(void *aux OVS_UNUSED)
 247 {
 248     do_unlink_files();
 249 }
 250
 251 static void
 252 cancel_files(void *aux OVS_UNUSED)
 253 {
 254     sset_clear(&files);
 255     added_hook = false;
 256 }
 257
 258 static void
 259 do_unlink_files(void)
 260 {
 261     const char *file;
 262
 263     SSET_FOR_EACH (file, &files) {
 264         unlink(file);
 265     }
 266 }
 267 \f
 268 /* Clears all of the fatal signal hooks without executing them.  If any of the
 269  * hooks passed a 'cancel_cb' function to fatal_signal_add_hook(), then those
 270  * functions will be called, allowing them to free resources, etc.
 271  *
 272  * Following a fork, one of the resulting processes can call this function to
 273  * allow it to terminate without calling the hooks registered before calling
 274  * this function.  New hooks registered after calling this function will take
 275  * effect normally. */
 276 void
 277 fatal_signal_fork(void)
 278 {
 279     size_t i;
 280
 281     for (i = 0; i < n_hooks; i++) {
 282         struct hook *h = &hooks[i];
 283         if (h->cancel_cb) {
 284             h->cancel_cb(h->aux);
 285         }
 286     }
 287     n_hooks = 0;
 288
 289     /* Raise any signals that we have already received with the default
 290      * handler. */
 291     if (stored_sig_nr != SIG_ATOMIC_MAX) {
 292         raise(stored_sig_nr);
 293     }
 294 }