lib/fatal-signal.c

   1 /*
   2  * Copyright (c) 2008, 2009 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 <stdlib.h>
  24 #include <string.h>
  25 #include <unistd.h>
  26 #include "shash.h"
  27 #include "util.h"
  28
  29 /* Signals to catch. */
  30 static const int fatal_signals[] = { SIGTERM, SIGINT, SIGHUP, SIGALRM };
  31
  32 /* Signals to catch as a sigset_t. */
  33 static sigset_t fatal_signal_set;
  34
  35 /* Hooks to call upon catching a signal */
  36 struct hook {
  37     void (*func)(void *aux);
  38     void *aux;
  39     bool run_at_exit;
  40 };
  41 #define MAX_HOOKS 32
  42 static struct hook hooks[MAX_HOOKS];
  43 static size_t n_hooks;
  44
  45 /* Number of nesting signal blockers. */
  46 static int block_level = 0;
  47
  48 /* Signal mask saved by outermost signal blocker. */
  49 static sigset_t saved_signal_mask;
  50
  51 /* Disabled by fatal_signal_fork()? */
  52 static bool disabled;
  53
  54 static void call_sigprocmask(int how, sigset_t* new_set, sigset_t* old_set);
  55 static void atexit_handler(void);
  56 static void call_hooks(int sig_nr);
  57
  58 /* Registers 'hook' to be called when a process termination signal is raised.
  59  * If 'run_at_exit' is true, 'hook' is also called during normal process
  60  * termination, e.g. when exit() is called or when main() returns. */
  61 void
  62 fatal_signal_add_hook(void (*func)(void *aux), void *aux, bool run_at_exit)
  63 {
  64     fatal_signal_block();
  65     assert(n_hooks < MAX_HOOKS);
  66     hooks[n_hooks].func = func;
  67     hooks[n_hooks].aux = aux;
  68     hooks[n_hooks].run_at_exit = run_at_exit;
  69     n_hooks++;
  70     fatal_signal_unblock();
  71 }
  72
  73 /* Blocks program termination signals until fatal_signal_unblock() is called.
  74  * May be called multiple times with nesting; if so, fatal_signal_unblock()
  75  * must be called the same number of times to unblock signals.
  76  *
  77  * This is needed while adjusting a data structure that will be accessed by a
  78  * fatal signal hook, so that the hook is not invoked while the data structure
  79  * is in an inconsistent state. */
  80 void
  81 fatal_signal_block(void)
  82 {
  83     static bool inited = false;
  84     if (!inited) {
  85         size_t i;
  86
  87         inited = true;
  88         sigemptyset(&fatal_signal_set);
  89         for (i = 0; i < ARRAY_SIZE(fatal_signals); i++) {
  90             int sig_nr = fatal_signals[i];
  91             struct sigaction old_sa;
  92
  93             sigaddset(&fatal_signal_set, sig_nr);
  94             if (sigaction(sig_nr, NULL, &old_sa)) {
  95                 ovs_fatal(errno, "sigaction");
  96             }
  97             if (old_sa.sa_handler == SIG_DFL
  98                 && signal(sig_nr, fatal_signal_handler) == SIG_ERR) {
  99                 ovs_fatal(errno, "signal");
 100             }
 101         }
 102         atexit(atexit_handler);
 103     }
 104
 105     if (++block_level == 1) {
 106         call_sigprocmask(SIG_BLOCK, &fatal_signal_set, &saved_signal_mask);
 107     }
 108 }
 109
 110 /* Unblocks program termination signals blocked by fatal_signal_block() is
 111  * called.  If multiple calls to fatal_signal_block() are nested,
 112  * fatal_signal_unblock() must be called the same number of times to unblock
 113  * signals. */
 114 void
 115 fatal_signal_unblock(void)
 116 {
 117     assert(block_level > 0);
 118     if (--block_level == 0) {
 119         call_sigprocmask(SIG_SETMASK, &saved_signal_mask, NULL);
 120     }
 121 }
 122
 123 /* Handles fatal signal number 'sig_nr'.
 124  *
 125  * Ordinarily this is the actual signal handler.  When other code needs to
 126  * handle one of our signals, however, it can register for that signal and, if
 127  * and when necessary, call this function to do fatal signal processing for it
 128  * and terminate the process.  Currently only timeval.c does this, for SIGALRM.
 129  * (It is not important whether the other code sets up its signal handler
 130  * before or after this file, because this file will only set up a signal
 131  * handler in the case where the signal has its default handling.)  */
 132 void
 133 fatal_signal_handler(int sig_nr)
 134 {
 135     call_hooks(sig_nr);
 136
 137     /* Re-raise the signal with the default handling so that the program
 138      * termination status reflects that we were killed by this signal */
 139     signal(sig_nr, SIG_DFL);
 140     raise(sig_nr);
 141 }
 142
 143 static void
 144 atexit_handler(void)
 145 {
 146     if (!disabled) {
 147         call_hooks(0);
 148     }
 149 }
 150
 151 static void
 152 call_hooks(int sig_nr)
 153 {
 154     static volatile sig_atomic_t recurse = 0;
 155     if (!recurse) {
 156         size_t i;
 157
 158         recurse = 1;
 159
 160         for (i = 0; i < n_hooks; i++) {
 161             struct hook *h = &hooks[i];
 162             if (sig_nr || h->run_at_exit) {
 163                 h->func(h->aux);
 164             }
 165         }
 166     }
 167 }
 168 \f
 169 static struct shash files = SHASH_INITIALIZER(&files);
 170
 171 static void unlink_files(void *aux);
 172 static void do_unlink_files(void);
 173
 174 /* Registers 'file' to be unlinked when the program terminates via exit() or a
 175  * fatal signal. */
 176 void
 177 fatal_signal_add_file_to_unlink(const char *file)
 178 {
 179     static bool added_hook = false;
 180     if (!added_hook) {
 181         added_hook = true;
 182         fatal_signal_add_hook(unlink_files, NULL, true);
 183     }
 184
 185     fatal_signal_block();
 186     if (!shash_find(&files, file)) {
 187         shash_add(&files, file, NULL);
 188     }
 189     fatal_signal_unblock();
 190 }
 191
 192 /* Unregisters 'file' from being unlinked when the program terminates via
 193  * exit() or a fatal signal. */
 194 void
 195 fatal_signal_remove_file_to_unlink(const char *file)
 196 {
 197     struct shash_node *node;
 198
 199     fatal_signal_block();
 200     node = shash_find(&files, file);
 201     if (node) {
 202         shash_delete(&files, node);
 203     }
 204     fatal_signal_unblock();
 205 }
 206
 207 static void
 208 unlink_files(void *aux UNUSED)
 209 {
 210     do_unlink_files();
 211 }
 212
 213 static void
 214 do_unlink_files(void)
 215 {
 216     struct shash_node *node;
 217
 218     SHASH_FOR_EACH (node, &files) {
 219         unlink(node->name);
 220     }
 221 }
 222 \f
 223 /* Disables the fatal signal hook mechanism.  Following a fork, one of the
 224  * resulting processes can call this function to allow it to terminate without
 225  * triggering fatal signal processing or removing files.  Fatal signal
 226  * processing is still enabled in the other process. */
 227 void
 228 fatal_signal_fork(void)
 229 {
 230     size_t i;
 231
 232     disabled = true;
 233
 234     for (i = 0; i < ARRAY_SIZE(fatal_signals); i++) {
 235         int sig_nr = fatal_signals[i];
 236         if (signal(sig_nr, SIG_DFL) == SIG_IGN) {
 237             signal(sig_nr, SIG_IGN);
 238         }
 239     }
 240 }
 241 \f
 242 static void
 243 call_sigprocmask(int how, sigset_t* new_set, sigset_t* old_set)
 244 {
 245     int error = sigprocmask(how, new_set, old_set);
 246     if (error) {
 247         fprintf(stderr, "sigprocmask: %s\n", strerror(errno));
 248     }
 249 }