lib/fatal-signal.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira, Inc.
   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 <errno.h>
  19 #include <signal.h>
  20 #include <stdbool.h>
  21 #include <stdio.h>
  22 #include <stdint.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <unistd.h>
  26 #include "poll-loop.h"
  27 #include "shash.h"
  28 #include "sset.h"
  29 #include "signals.h"
  30 #include "socket-util.h"
  31 #include "util.h"
  32 #include "vlog.h"
  33
  34 #include "type-props.h"
  35
  36 #ifndef SIG_ATOMIC_MAX
  37 #define SIG_ATOMIC_MAX TYPE_MAXIMUM(sig_atomic_t)
  38 #endif
  39
  40 VLOG_DEFINE_THIS_MODULE(fatal_signal);
  41
  42 /* Signals to catch. */
  43 static const int fatal_signals[] = { SIGTERM, SIGINT, SIGHUP, SIGALRM };
  44
  45 /* Signals to catch as a sigset_t. */
  46 static sigset_t fatal_signal_set;
  47
  48 /* Hooks to call upon catching a signal */
  49 struct hook {
  50     void (*hook_cb)(void *aux);
  51     void (*cancel_cb)(void *aux);
  52     void *aux;
  53     bool run_at_exit;
  54 };
  55 #define MAX_HOOKS 32
  56 static struct hook hooks[MAX_HOOKS];
  57 static size_t n_hooks;
  58
  59 static int signal_fds[2];
  60 static volatile sig_atomic_t stored_sig_nr = SIG_ATOMIC_MAX;
  61
  62 static void fatal_signal_init(void);
  63 static void atexit_handler(void);
  64 static void call_hooks(int sig_nr);
  65
  66 static void
  67 fatal_signal_init(void)
  68 {
  69     static bool inited = false;
  70
  71     if (!inited) {
  72         size_t i;
  73
  74         inited = true;
  75
  76         xpipe_nonblocking(signal_fds);
  77
  78         sigemptyset(&fatal_signal_set);
  79         for (i = 0; i < ARRAY_SIZE(fatal_signals); i++) {
  80             int sig_nr = fatal_signals[i];
  81             struct sigaction old_sa;
  82
  83             sigaddset(&fatal_signal_set, sig_nr);
  84             xsigaction(sig_nr, NULL, &old_sa);
  85             if (old_sa.sa_handler == SIG_DFL
  86                 && signal(sig_nr, fatal_signal_handler) == SIG_ERR) {
  87                 VLOG_FATAL("signal failed (%s)", strerror(errno));
  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     ovs_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     sig_atomic_t sig_nr;
 153
 154     fatal_signal_init();
 155
 156     sig_nr = stored_sig_nr;
 157     if (sig_nr != SIG_ATOMIC_MAX) {
 158         VLOG_WARN("terminating with signal %d (%s)",
 159                   (int)sig_nr, signal_name(sig_nr));
 160         call_hooks(sig_nr);
 161
 162         /* Re-raise the signal with the default handling so that the program
 163          * termination status reflects that we were killed by this signal */
 164         signal(sig_nr, SIG_DFL);
 165         raise(sig_nr);
 166     }
 167 }
 168
 169 void
 170 fatal_signal_wait(void)
 171 {
 172     fatal_signal_init();
 173     poll_fd_wait(signal_fds[0], POLLIN);
 174 }
 175
 176 static void
 177 atexit_handler(void)
 178 {
 179     call_hooks(0);
 180 }
 181
 182 static void
 183 call_hooks(int sig_nr)
 184 {
 185     static volatile sig_atomic_t recurse = 0;
 186     if (!recurse) {
 187         size_t i;
 188
 189         recurse = 1;
 190
 191         for (i = 0; i < n_hooks; i++) {
 192             struct hook *h = &hooks[i];
 193             if (sig_nr || h->run_at_exit) {
 194                 h->hook_cb(h->aux);
 195             }
 196         }
 197     }
 198 }
 199 \f
 200 /* Files to delete on exit. */
 201 static struct sset files = SSET_INITIALIZER(&files);
 202
 203 /* Has a hook function been registered with fatal_signal_add_hook() (and not
 204  * cleared by fatal_signal_fork())? */
 205 static bool added_hook;
 206
 207 static void unlink_files(void *aux);
 208 static void cancel_files(void *aux);
 209 static void do_unlink_files(void);
 210
 211 /* Registers 'file' to be unlinked when the program terminates via exit() or a
 212  * fatal signal. */
 213 void
 214 fatal_signal_add_file_to_unlink(const char *file)
 215 {
 216     if (!added_hook) {
 217         added_hook = true;
 218         fatal_signal_add_hook(unlink_files, cancel_files, NULL, true);
 219     }
 220
 221     sset_add(&files, file);
 222 }
 223
 224 /* Unregisters 'file' from being unlinked when the program terminates via
 225  * exit() or a fatal signal. */
 226 void
 227 fatal_signal_remove_file_to_unlink(const char *file)
 228 {
 229     sset_find_and_delete(&files, file);
 230 }
 231
 232 /* Like fatal_signal_remove_file_to_unlink(), but also unlinks 'file'.
 233  * Returns 0 if successful, otherwise a positive errno value. */
 234 int
 235 fatal_signal_unlink_file_now(const char *file)
 236 {
 237     int error = unlink(file) ? errno : 0;
 238     if (error) {
 239         VLOG_WARN("could not unlink \"%s\" (%s)", file, strerror(error));
 240     }
 241
 242     fatal_signal_remove_file_to_unlink(file);
 243
 244     return error;
 245 }
 246
 247 static void
 248 unlink_files(void *aux OVS_UNUSED)
 249 {
 250     do_unlink_files();
 251 }
 252
 253 static void
 254 cancel_files(void *aux OVS_UNUSED)
 255 {
 256     sset_clear(&files);
 257     added_hook = false;
 258 }
 259
 260 static void
 261 do_unlink_files(void)
 262 {
 263     const char *file;
 264
 265     SSET_FOR_EACH (file, &files) {
 266         unlink(file);
 267     }
 268 }
 269 \f
 270 /* Clears all of the fatal signal hooks without executing them.  If any of the
 271  * hooks passed a 'cancel_cb' function to fatal_signal_add_hook(), then those
 272  * functions will be called, allowing them to free resources, etc.
 273  *
 274  * Following a fork, one of the resulting processes can call this function to
 275  * allow it to terminate without calling the hooks registered before calling
 276  * this function.  New hooks registered after calling this function will take
 277  * effect normally. */
 278 void
 279 fatal_signal_fork(void)
 280 {
 281     size_t i;
 282
 283     for (i = 0; i < n_hooks; i++) {
 284         struct hook *h = &hooks[i];
 285         if (h->cancel_cb) {
 286             h->cancel_cb(h->aux);
 287         }
 288     }
 289     n_hooks = 0;
 290
 291     /* Raise any signals that we have already received with the default
 292      * handler. */
 293     if (stored_sig_nr != SIG_ATOMIC_MAX) {
 294         raise(stored_sig_nr);
 295     }
 296 }