Import from old repository commit 61ef2b42a9c4ba8e1600f15bb0236765edc2ad45.

lib/fatal-signal.c

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+/*
+ * Copyright (c) 2008, 2009 Nicira Networks.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#include <config.h>
+#include "fatal-signal.h"
+#include <assert.h>
+#include <errno.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include "util.h"
+
+/* Signals to catch. */
+static const int fatal_signals[] = { SIGTERM, SIGINT, SIGHUP, SIGALRM };
+
+/* Signals to catch as a sigset_t. */
+static sigset_t fatal_signal_set;
+
+/* Hooks to call upon catching a signal */
+struct hook {
+    void (*func)(void *aux);
+    void *aux;
+    bool run_at_exit;
+};
+#define MAX_HOOKS 32
+static struct hook hooks[MAX_HOOKS];
+static size_t n_hooks;
+
+/* Number of nesting signal blockers. */
+static int block_level = 0;
+
+/* Signal mask saved by outermost signal blocker. */
+static sigset_t saved_signal_mask;
+
+/* Disabled by fatal_signal_fork()? */
+static bool disabled;
+
+static void call_sigprocmask(int how, sigset_t* new_set, sigset_t* old_set);
+static void atexit_handler(void);
+static void call_hooks(int sig_nr);
+
+/* Registers 'hook' to be called when a process termination signal is raised.
+ * If 'run_at_exit' is true, 'hook' is also called during normal process
+ * termination, e.g. when exit() is called or when main() returns. */
+void
+fatal_signal_add_hook(void (*func)(void *aux), void *aux, bool run_at_exit)
+{
+    fatal_signal_block();
+    assert(n_hooks < MAX_HOOKS);
+    hooks[n_hooks].func = func;
+    hooks[n_hooks].aux = aux;
+    hooks[n_hooks].run_at_exit = run_at_exit;
+    n_hooks++;
+    fatal_signal_unblock();
+}
+
+/* Blocks program termination signals until fatal_signal_unblock() is called.
+ * May be called multiple times with nesting; if so, fatal_signal_unblock()
+ * must be called the same number of times to unblock signals.
+ *
+ * This is needed while adjusting a data structure that will be accessed by a
+ * fatal signal hook, so that the hook is not invoked while the data structure
+ * is in an inconsistent state. */
+void
+fatal_signal_block(void)
+{
+    static bool inited = false;
+    if (!inited) {
+        size_t i;
+
+        inited = true;
+        sigemptyset(&fatal_signal_set);
+        for (i = 0; i < ARRAY_SIZE(fatal_signals); i++) {
+            int sig_nr = fatal_signals[i];
+            struct sigaction old_sa;
+
+            sigaddset(&fatal_signal_set, sig_nr);
+            if (sigaction(sig_nr, NULL, &old_sa)) {
+                ovs_fatal(errno, "sigaction");
+            }
+            if (old_sa.sa_handler == SIG_DFL
+                && signal(sig_nr, fatal_signal_handler) == SIG_ERR) {
+                ovs_fatal(errno, "signal");
+            }
+        }
+        atexit(atexit_handler);
+    }
+
+    if (++block_level == 1) {
+        call_sigprocmask(SIG_BLOCK, &fatal_signal_set, &saved_signal_mask);
+    }
+}
+
+/* Unblocks program termination signals blocked by fatal_signal_block() is
+ * called.  If multiple calls to fatal_signal_block() are nested,
+ * fatal_signal_unblock() must be called the same number of times to unblock
+ * signals. */
+void
+fatal_signal_unblock(void)
+{
+    assert(block_level > 0);
+    if (--block_level == 0) {
+        call_sigprocmask(SIG_SETMASK, &saved_signal_mask, NULL);
+    }
+}
+
+/* Handles fatal signal number 'sig_nr'.
+ *
+ * Ordinarily this is the actual signal handler.  When other code needs to
+ * handle one of our signals, however, it can register for that signal and, if
+ * and when necessary, call this function to do fatal signal processing for it
+ * and terminate the process.  Currently only timeval.c does this, for SIGALRM.
+ * (It is not important whether the other code sets up its signal handler
+ * before or after this file, because this file will only set up a signal
+ * handler in the case where the signal has its default handling.)  */
+void
+fatal_signal_handler(int sig_nr)
+{
+    call_hooks(sig_nr);
+
+    /* Re-raise the signal with the default handling so that the program
+     * termination status reflects that we were killed by this signal */
+    signal(sig_nr, SIG_DFL);
+    raise(sig_nr);
+}
+
+static void
+atexit_handler(void)
+{
+    if (!disabled) {
+        call_hooks(0);
+    }
+}
+
+static void
+call_hooks(int sig_nr)
+{
+    static volatile sig_atomic_t recurse = 0;
+    if (!recurse) {
+        size_t i;
+
+        recurse = 1;
+
+        for (i = 0; i < n_hooks; i++) {
+            struct hook *h = &hooks[i];
+            if (sig_nr || h->run_at_exit) {
+                h->func(h->aux);
+            }
+        }
+    }
+}
+
+static char **files;
+static size_t n_files, max_files;
+
+static void unlink_files(void *aux);
+static void do_unlink_files(void);
+
+/* Registers 'file' to be unlinked when the program terminates via exit() or a
+ * fatal signal. */
+void
+fatal_signal_add_file_to_unlink(const char *file)
+{
+    static bool added_hook = false;
+    if (!added_hook) {
+        added_hook = true;
+        fatal_signal_add_hook(unlink_files, NULL, true);
+    }
+
+    fatal_signal_block();
+    if (n_files >= max_files) {
+        files = x2nrealloc(files, &max_files, sizeof *files);
+    }
+    files[n_files++] = xstrdup(file);
+    fatal_signal_unblock();
+}
+
+/* Unregisters 'file' from being unlinked when the program terminates via
+ * exit() or a fatal signal. */
+void
+fatal_signal_remove_file_to_unlink(const char *file)
+{
+    size_t i;
+
+    fatal_signal_block();
+    for (i = 0; i < n_files; i++) {
+        if (!strcmp(files[i], file)) {
+            free(files[i]);
+            files[i] = files[--n_files];
+            break;
+        }
+    }
+    fatal_signal_unblock();
+}
+
+static void
+unlink_files(void *aux UNUSED)
+{
+    do_unlink_files(); 
+}
+
+static void
+do_unlink_files(void)
+{
+    size_t i;
+
+    for (i = 0; i < n_files; i++) {
+        unlink(files[i]);
+    }
+}
+
+/* Disables the fatal signal hook mechanism.  Following a fork, one of the
+ * resulting processes can call this function to allow it to terminate without
+ * triggering fatal signal processing or removing files.  Fatal signal
+ * processing is still enabled in the other process. */
+void
+fatal_signal_fork(void)
+{
+    size_t i;
+
+    disabled = true;
+
+    for (i = 0; i < ARRAY_SIZE(fatal_signals); i++) {
+        int sig_nr = fatal_signals[i];
+        if (signal(sig_nr, SIG_DFL) == SIG_IGN) {
+            signal(sig_nr, SIG_IGN);
+        }
+    }
+}
+
+static void
+call_sigprocmask(int how, sigset_t* new_set, sigset_t* old_set)
+{
+    int error = sigprocmask(how, new_set, old_set);
+    if (error) {
+        fprintf(stderr, "sigprocmask: %s\n", strerror(errno));
+    }
+}