lib/fatal-signal.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010 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 "socket-util.h"
  30 #include "util.h"
  31
  32 #define THIS_MODULE VLM_fatal_signal
  33 #include "vlog.h"
  34
  35 /* Signals to catch. */
  36 static const int fatal_signals[] = { SIGTERM, SIGINT, SIGHUP, SIGALRM };
  37
  38 /* Signals to catch as a sigset_t. */
  39 static sigset_t fatal_signal_set;
  40
  41 /* Hooks to call upon catching a signal */
  42 struct hook {
  43     void (*hook_cb)(void *aux);
  44     void (*cancel_cb)(void *aux);
  45     void *aux;
  46     bool run_at_exit;
  47 };
  48 #define MAX_HOOKS 32
  49 static struct hook hooks[MAX_HOOKS];
  50 static size_t n_hooks;
  51
  52 static int signal_fds[2];
  53 static volatile sig_atomic_t stored_sig_nr = SIG_ATOMIC_MAX;
  54
  55 static void fatal_signal_init(void);
  56 static void atexit_handler(void);
  57 static void call_hooks(int sig_nr);
  58
  59 static void
  60 fatal_signal_init(void)
  61 {
  62     static bool inited = false;
  63
  64     if (!inited) {
  65         size_t i;
  66
  67         inited = true;
  68
  69         if (pipe(signal_fds)) {
  70             ovs_fatal(errno, "could not create pipe");
  71         }
  72         set_nonblocking(signal_fds[0]);
  73         set_nonblocking(signal_fds[1]);
  74
  75         sigemptyset(&fatal_signal_set);
  76         for (i = 0; i < ARRAY_SIZE(fatal_signals); i++) {
  77             int sig_nr = fatal_signals[i];
  78             struct sigaction old_sa;
  79
  80             sigaddset(&fatal_signal_set, sig_nr);
  81             if (sigaction(sig_nr, NULL, &old_sa)) {
  82                 ovs_fatal(errno, "sigaction");
  83             }
  84             if (old_sa.sa_handler == SIG_DFL
  85                 && signal(sig_nr, fatal_signal_handler) == SIG_ERR) {
  86                 ovs_fatal(errno, "signal");
  87             }
  88         }
  89         atexit(atexit_handler);
  90     }
  91 }
  92
  93 /* Registers 'hook_cb' to be called when a process termination signal is
  94  * raised.  If 'run_at_exit' is true, 'hook_cb' is also called during normal
  95  * process termination, e.g. when exit() is called or when main() returns.
  96  *
  97  * 'hook_cb' is not called immediately from the signal handler but rather the
  98  * next time the poll loop iterates, so it is freed from the usual restrictions
  99  * on signal handler functions.
 100  *
 101  * If the current process forks, fatal_signal_fork() may be called to clear the
 102  * parent process's fatal signal hooks, so that 'hook_cb' is only called when
 103  * the child terminates, not when the parent does.  When fatal_signal_fork() is
 104  * called, it calls the 'cancel_cb' function if it is nonnull, passing 'aux',
 105  * to notify that the hook has been canceled.  This allows the hook to free
 106  * memory, etc. */
 107 void
 108 fatal_signal_add_hook(void (*hook_cb)(void *aux), void (*cancel_cb)(void *aux),
 109                       void *aux, bool run_at_exit)
 110 {
 111     fatal_signal_init();
 112
 113     assert(n_hooks < MAX_HOOKS);
 114     hooks[n_hooks].hook_cb = hook_cb;
 115     hooks[n_hooks].cancel_cb = cancel_cb;
 116     hooks[n_hooks].aux = aux;
 117     hooks[n_hooks].run_at_exit = run_at_exit;
 118     n_hooks++;
 119 }
 120
 121 /* Handles fatal signal number 'sig_nr'.
 122  *
 123  * Ordinarily this is the actual signal handler.  When other code needs to
 124  * handle one of our signals, however, it can register for that signal and, if
 125  * and when necessary, call this function to do fatal signal processing for it
 126  * and terminate the process.  Currently only timeval.c does this, for SIGALRM.
 127  * (It is not important whether the other code sets up its signal handler
 128  * before or after this file, because this file will only set up a signal
 129  * handler in the case where the signal has its default handling.)  */
 130 void
 131 fatal_signal_handler(int sig_nr)
 132 {
 133     ignore(write(signal_fds[1], "", 1));
 134     stored_sig_nr = sig_nr;
 135 }
 136
 137 /* Check whether a fatal signal has occurred and, if so, call the fatal signal
 138  * hooks and exit.
 139  *
 140  * This function is called automatically by poll_block(), but specialized
 141  * programs that may not always call poll_block() on a regular basis should
 142  * also call it periodically.  (Therefore, any function with "block" in its
 143  * name should call fatal_signal_run() each time it is called, either directly
 144  * or through poll_block(), because such functions can only used by specialized
 145  * programs that can afford to block outside their main loop around
 146  * poll_block().)
 147  */
 148 void
 149 fatal_signal_run(void)
 150 {
 151     int sig_nr;
 152
 153     fatal_signal_init();
 154
 155     sig_nr = stored_sig_nr;
 156     if (sig_nr != SIG_ATOMIC_MAX) {
 157         call_hooks(sig_nr);
 158
 159         /* Re-raise the signal with the default handling so that the program
 160          * termination status reflects that we were killed by this signal */
 161         signal(sig_nr, SIG_DFL);
 162         raise(sig_nr);
 163     }
 164 }
 165
 166 void
 167 fatal_signal_wait(void)
 168 {
 169     fatal_signal_init();
 170     poll_fd_wait(signal_fds[0], POLLIN);
 171 }
 172
 173 static void
 174 atexit_handler(void)
 175 {
 176     call_hooks(0);
 177 }
 178
 179 static void
 180 call_hooks(int sig_nr)
 181 {
 182     static volatile sig_atomic_t recurse = 0;
 183     if (!recurse) {
 184         size_t i;
 185
 186         recurse = 1;
 187
 188         for (i = 0; i < n_hooks; i++) {
 189             struct hook *h = &hooks[i];
 190             if (sig_nr || h->run_at_exit) {
 191                 h->hook_cb(h->aux);
 192             }
 193         }
 194     }
 195 }
 196 \f
 197 /* Files to delete on exit.  (The 'data' member of each node is unused.) */
 198 static struct shash files = SHASH_INITIALIZER(&files);
 199
 200 /* Has a hook function been registered with fatal_signal_add_hook() (and not
 201  * cleared by fatal_signal_fork())? */
 202 static bool added_hook;
 203
 204 static void unlink_files(void *aux);
 205 static void cancel_files(void *aux);
 206 static void do_unlink_files(void);
 207
 208 /* Registers 'file' to be unlinked when the program terminates via exit() or a
 209  * fatal signal. */
 210 void
 211 fatal_signal_add_file_to_unlink(const char *file)
 212 {
 213     if (!added_hook) {
 214         added_hook = true;
 215         fatal_signal_add_hook(unlink_files, cancel_files, NULL, true);
 216     }
 217
 218     shash_add_once(&files, file, NULL);
 219 }
 220
 221 /* Unregisters 'file' from being unlinked when the program terminates via
 222  * exit() or a fatal signal. */
 223 void
 224 fatal_signal_remove_file_to_unlink(const char *file)
 225 {
 226     struct shash_node *node;
 227
 228     node = shash_find(&files, file);
 229     if (node) {
 230         shash_delete(&files, node);
 231     }
 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     shash_clear(&files);
 259     added_hook = false;
 260 }
 261
 262 static void
 263 do_unlink_files(void)
 264 {
 265     struct shash_node *node;
 266
 267     SHASH_FOR_EACH (node, &files) {
 268         unlink(node->name);
 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 }