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         char namebuf[SIGNAL_NAME_BUFSIZE];
 159
 160         VLOG_WARN("terminating with signal %d (%s)",
 161                   (int)sig_nr, signal_name(sig_nr, namebuf, sizeof namebuf));
 162         call_hooks(sig_nr);
 163
 164         /* Re-raise the signal with the default handling so that the program
 165          * termination status reflects that we were killed by this signal */
 166         signal(sig_nr, SIG_DFL);
 167         raise(sig_nr);
 168     }
 169 }
 170
 171 void
 172 fatal_signal_wait(void)
 173 {
 174     fatal_signal_init();
 175     poll_fd_wait(signal_fds[0], POLLIN);
 176 }
 177
 178 static void
 179 atexit_handler(void)
 180 {
 181     call_hooks(0);
 182 }
 183
 184 static void
 185 call_hooks(int sig_nr)
 186 {
 187     static volatile sig_atomic_t recurse = 0;
 188     if (!recurse) {
 189         size_t i;
 190
 191         recurse = 1;
 192
 193         for (i = 0; i < n_hooks; i++) {
 194             struct hook *h = &hooks[i];
 195             if (sig_nr || h->run_at_exit) {
 196                 h->hook_cb(h->aux);
 197             }
 198         }
 199     }
 200 }
 201 \f
 202 /* Files to delete on exit. */
 203 static struct sset files = SSET_INITIALIZER(&files);
 204
 205 /* Has a hook function been registered with fatal_signal_add_hook() (and not
 206  * cleared by fatal_signal_fork())? */
 207 static bool added_hook;
 208
 209 static void unlink_files(void *aux);
 210 static void cancel_files(void *aux);
 211 static void do_unlink_files(void);
 212
 213 /* Registers 'file' to be unlinked when the program terminates via exit() or a
 214  * fatal signal. */
 215 void
 216 fatal_signal_add_file_to_unlink(const char *file)
 217 {
 218     if (!added_hook) {
 219         added_hook = true;
 220         fatal_signal_add_hook(unlink_files, cancel_files, NULL, true);
 221     }
 222
 223     sset_add(&files, file);
 224 }
 225
 226 /* Unregisters 'file' from being unlinked when the program terminates via
 227  * exit() or a fatal signal. */
 228 void
 229 fatal_signal_remove_file_to_unlink(const char *file)
 230 {
 231     sset_find_and_delete(&files, file);
 232 }
 233
 234 /* Like fatal_signal_remove_file_to_unlink(), but also unlinks 'file'.
 235  * Returns 0 if successful, otherwise a positive errno value. */
 236 int
 237 fatal_signal_unlink_file_now(const char *file)
 238 {
 239     int error = unlink(file) ? errno : 0;
 240     if (error) {
 241         VLOG_WARN("could not unlink \"%s\" (%s)", file, strerror(error));
 242     }
 243
 244     fatal_signal_remove_file_to_unlink(file);
 245
 246     return error;
 247 }
 248
 249 static void
 250 unlink_files(void *aux OVS_UNUSED)
 251 {
 252     do_unlink_files();
 253 }
 254
 255 static void
 256 cancel_files(void *aux OVS_UNUSED)
 257 {
 258     sset_clear(&files);
 259     added_hook = false;
 260 }
 261
 262 static void
 263 do_unlink_files(void)
 264 {
 265     const char *file;
 266
 267     SSET_FOR_EACH (file, &files) {
 268         unlink(file);
 269     }
 270 }
 271 \f
 272 /* Clears all of the fatal signal hooks without executing them.  If any of the
 273  * hooks passed a 'cancel_cb' function to fatal_signal_add_hook(), then those
 274  * functions will be called, allowing them to free resources, etc.
 275  *
 276  * Following a fork, one of the resulting processes can call this function to
 277  * allow it to terminate without calling the hooks registered before calling
 278  * this function.  New hooks registered after calling this function will take
 279  * effect normally. */
 280 void
 281 fatal_signal_fork(void)
 282 {
 283     size_t i;
 284
 285     for (i = 0; i < n_hooks; i++) {
 286         struct hook *h = &hooks[i];
 287         if (h->cancel_cb) {
 288             h->cancel_cb(h->aux);
 289         }
 290     }
 291     n_hooks = 0;
 292
 293     /* Raise any signals that we have already received with the default
 294      * handler. */
 295     if (stored_sig_nr != SIG_ATOMIC_MAX) {
 296         raise(stored_sig_nr);
 297     }
 298 }