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Diffstat (limited to 'lib/fatal-signal.c')
-rw-r--r-- | lib/fatal-signal.c | 253 |
1 files changed, 253 insertions, 0 deletions
diff --git a/lib/fatal-signal.c b/lib/fatal-signal.c new file mode 100644 index 000000000..ccb7fe451 --- /dev/null +++ b/lib/fatal-signal.c @@ -0,0 +1,253 @@ +/* + * 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)); + } +} |