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https://git.busybox.net/busybox.git
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init: improve handling of signals racing with each other
Before this change, a request to reboot could be "overwritten" by e.g. SIGHUP. function old new delta init_main 709 793 +84 packed_usage 33273 33337 +64 run_actions 109 117 +8 stop_handler 87 88 +1 check_delayed_sigs 340 335 -5 run 214 198 -16 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 4/2 up/down: 157/-21) Total: 136 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
parent
113c776f4d
commit
356f23de20
280
init/init.c
280
init/init.c
@ -210,6 +210,8 @@ struct globals {
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#if !ENABLE_FEATURE_INIT_SYSLOG
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const char *log_console;
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#endif
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sigset_t delayed_sigset;
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struct timespec zero_ts;
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} FIX_ALIASING;
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#define G (*(struct globals*)bb_common_bufsiz1)
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#define INIT_G() do { \
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@ -411,14 +413,8 @@ static int open_stdio_to_tty(const char* tty_name)
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static void reset_sighandlers_and_unblock_sigs(void)
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{
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bb_signals(0
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+ (1 << SIGUSR1)
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+ (1 << SIGUSR2)
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+ (1 << SIGTERM)
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+ (1 << SIGQUIT)
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+ (1 << SIGINT)
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+ (1 << SIGHUP)
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+ (1 << SIGTSTP)
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+ (1 << SIGSTOP)
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| (1 << SIGTSTP)
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| (1 << SIGSTOP)
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, SIG_DFL);
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sigprocmask_allsigs(SIG_UNBLOCK);
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}
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@ -484,16 +480,13 @@ static pid_t run(const struct init_action *a)
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{
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pid_t pid;
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/* Careful: don't be affected by a signal in vforked child */
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sigprocmask_allsigs(SIG_BLOCK);
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if (BB_MMU && (a->action_type & ASKFIRST))
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pid = fork();
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else
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pid = vfork();
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if (pid < 0)
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message(L_LOG | L_CONSOLE, "can't fork");
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if (pid) {
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sigprocmask_allsigs(SIG_UNBLOCK);
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if (pid < 0)
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message(L_LOG | L_CONSOLE, "can't fork");
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return pid; /* Parent or error */
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}
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@ -587,9 +580,11 @@ static void waitfor(pid_t pid)
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while (1) {
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pid_t wpid = wait(NULL);
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mark_terminated(wpid);
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/* Unsafe. SIGTSTP handler might have wait'ed it already */
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/*if (wpid == pid) break;*/
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/* More reliable: */
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if (wpid == pid) /* this was the process we waited for */
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break;
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/* The above is not reliable enough: SIGTSTP handler might have
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* wait'ed it already. Double check, exit if process is gone:
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*/
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if (kill(pid, 0))
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break;
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}
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@ -798,23 +793,17 @@ static void run_shutdown_and_kill_processes(void)
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* Delayed handlers just set a flag variable. The variable is checked
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* in the main loop and acted upon.
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*
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* halt/poweroff/reboot and restart have immediate handlers.
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* They only traverse linked list of struct action's, never modify it,
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* this should be safe to do even in signal handler. Also they
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* never return.
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*
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* SIGSTOP and SIGTSTP have immediate handlers. They just wait
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* for SIGCONT to happen.
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*
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* halt/poweroff/reboot and restart have delayed handlers.
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*
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* SIGHUP has a delayed handler, because modifying linked list
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* of struct action's from a signal handler while it is manipulated
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* by the program may be disastrous.
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*
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* Ctrl-Alt-Del has a delayed handler. Not a must, but allowing
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* it to happen even somewhere inside "sysinit" would be a bit awkward.
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*
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* There is a tiny probability that SIGHUP and Ctrl-Alt-Del will collide
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* and only one will be remembered and acted upon.
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*/
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/* The SIGPWR/SIGUSR[12]/SIGTERM handler */
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@ -898,11 +887,9 @@ static void exec_restart_action(void)
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*/
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static void stop_handler(int sig UNUSED_PARAM)
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{
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smallint saved_bb_got_signal;
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int saved_errno;
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int saved_errno = errno;
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saved_bb_got_signal = bb_got_signal;
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saved_errno = errno;
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bb_got_signal = 0;
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signal(SIGCONT, record_signo);
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while (1) {
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@ -916,12 +903,12 @@ static void stop_handler(int sig UNUSED_PARAM)
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*/
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wpid = wait_any_nohang(NULL);
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mark_terminated(wpid);
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sleep(1);
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if (wpid <= 0) /* no processes exited? sleep a bit */
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sleep(1);
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}
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signal(SIGCONT, SIG_DFL);
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errno = saved_errno;
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bb_got_signal = saved_bb_got_signal;
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}
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#if ENABLE_FEATURE_USE_INITTAB
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@ -986,43 +973,39 @@ static void reload_inittab(void)
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}
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#endif
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static int check_delayed_sigs(void)
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static void check_delayed_sigs(struct timespec *ts)
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{
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int sigs_seen = 0;
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int sig = sigtimedwait(&G.delayed_sigset, /* siginfo_t */ NULL, ts);
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if (sig <= 0)
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return;
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while (1) {
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smallint sig = bb_got_signal;
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/* The signal "sig" was caught */
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if (!sig)
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return sigs_seen;
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bb_got_signal = 0;
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sigs_seen = 1;
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#if ENABLE_FEATURE_USE_INITTAB
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if (sig == SIGHUP)
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reload_inittab();
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if (sig == SIGHUP)
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reload_inittab();
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#endif
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if (sig == SIGINT)
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run_actions(CTRLALTDEL);
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if (sig == SIGQUIT) {
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exec_restart_action();
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/* returns only if no restart action defined */
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}
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if ((1 << sig) & (0
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#ifdef SIGPWR
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+ (1 << SIGPWR)
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#endif
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+ (1 << SIGUSR1)
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+ (1 << SIGUSR2)
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+ (1 << SIGTERM)
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)) {
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halt_reboot_pwoff(sig);
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}
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if (sig == SIGINT)
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run_actions(CTRLALTDEL);
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if (sig == SIGQUIT) {
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exec_restart_action();
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/* returns only if no restart action defined */
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}
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if ((1 << sig) & (0
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#ifdef SIGPWR
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| (1 << SIGPWR)
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#endif
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| (1 << SIGUSR1)
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| (1 << SIGUSR2)
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| (1 << SIGTERM)
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)) {
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halt_reboot_pwoff(sig);
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}
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/* if (sig == SIGCHLD) do nothing */
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}
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#if DEBUG_SEGV_HANDLER
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static
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void handle_sigsegv(int sig, siginfo_t *info, void *ucontext)
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static void handle_sigsegv(int sig, siginfo_t *info, void *ucontext)
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{
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long ip;
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ucontext_t *uc;
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@ -1049,50 +1032,62 @@ void handle_sigsegv(int sig, siginfo_t *info, void *ucontext)
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static void sleep_much(void)
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{
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sleep(30 * 24*60*60);
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sleep(30 * 24*60*60);
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}
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int init_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int init_main(int argc UNUSED_PARAM, char **argv)
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{
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struct sigaction sa;
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INIT_G();
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/* Some users send poweroff signals to init VERY early.
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* To handle this, mask signals early.
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*/
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/* sigemptyset(&G.delayed_sigset); - done by INIT_G() */
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sigaddset(&G.delayed_sigset, SIGINT); /* Ctrl-Alt-Del */
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sigaddset(&G.delayed_sigset, SIGQUIT); /* re-exec another init */
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#ifdef SIGPWR
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sigaddset(&G.delayed_sigset, SIGPWR); /* halt */
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#endif
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sigaddset(&G.delayed_sigset, SIGUSR1); /* halt */
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sigaddset(&G.delayed_sigset, SIGTERM); /* reboot */
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sigaddset(&G.delayed_sigset, SIGUSR2); /* poweroff */
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#if ENABLE_FEATURE_USE_INITTAB
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sigaddset(&G.delayed_sigset, SIGHUP); /* reread /etc/inittab */
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#endif
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sigaddset(&G.delayed_sigset, SIGCHLD); /* make sigtimedwait() exit on SIGCHLD */
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sigprocmask(SIG_BLOCK, &G.delayed_sigset, NULL);
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#if DEBUG_SEGV_HANDLER
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memset(&sa, 0, sizeof(sa));
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sa.sa_sigaction = handle_sigsegv;
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sa.sa_flags = SA_SIGINFO;
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sigaction_set(SIGSEGV, &sa);
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sigaction_set(SIGILL, &sa);
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sigaction_set(SIGFPE, &sa);
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sigaction_set(SIGBUS, &sa);
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#endif
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if (argv[1] && strcmp(argv[1], "-q") == 0) {
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return kill(1, SIGHUP);
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}
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#if DEBUG_SEGV_HANDLER
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{
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struct sigaction sa;
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memset(&sa, 0, sizeof(sa));
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sa.sa_sigaction = handle_sigsegv;
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sa.sa_flags = SA_SIGINFO;
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sigaction(SIGSEGV, &sa, NULL);
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sigaction(SIGILL, &sa, NULL);
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sigaction(SIGFPE, &sa, NULL);
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sigaction(SIGBUS, &sa, NULL);
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#if !DEBUG_INIT
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/* Expect to be invoked as init with PID=1 or be invoked as linuxrc */
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if (getpid() != 1
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&& (!ENABLE_LINUXRC || applet_name[0] != 'l') /* not linuxrc? */
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) {
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bb_simple_error_msg_and_die("must be run as PID 1");
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}
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#endif
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if (!DEBUG_INIT) {
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/* Some users send poweroff signals to init VERY early.
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* To handle this, mask signals early,
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* and unmask them only after signal handlers are installed.
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*/
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sigprocmask_allsigs(SIG_BLOCK);
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/* Expect to be invoked as init with PID=1 or be invoked as linuxrc */
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if (getpid() != 1
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&& (!ENABLE_LINUXRC || applet_name[0] != 'l') /* not linuxrc? */
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) {
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bb_simple_error_msg_and_die("must be run as PID 1");
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}
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#ifdef RB_DISABLE_CAD
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/* Turn off rebooting via CTL-ALT-DEL - we get a
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* SIGINT on CAD so we can shut things down gracefully... */
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reboot(RB_DISABLE_CAD); /* misnomer */
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# ifdef RB_DISABLE_CAD
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/* Turn off rebooting via CTL-ALT-DEL - we get a
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* SIGINT on CAD so we can shut things down gracefully... */
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reboot(RB_DISABLE_CAD); /* misnomer */
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# endif
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#endif
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}
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/* If, say, xmalloc would ever die, we don't want to oops kernel
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* by exiting.
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@ -1156,106 +1151,65 @@ int init_main(int argc UNUSED_PARAM, char **argv)
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}
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#endif
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if (ENABLE_FEATURE_INIT_MODIFY_CMDLINE) {
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/* Make the command line just say "init" - that's all, nothing else */
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strncpy(argv[0], "init", strlen(argv[0]));
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/* Wipe argv[1]-argv[N] so they don't clutter the ps listing */
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while (*++argv)
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nuke_str(*argv);
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}
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/* Set up signal handlers */
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if (!DEBUG_INIT) {
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struct sigaction sa;
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/* Stop handler must allow only SIGCONT inside itself */
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memset(&sa, 0, sizeof(sa));
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sigfillset(&sa.sa_mask);
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sigdelset(&sa.sa_mask, SIGCONT);
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sa.sa_handler = stop_handler;
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/* NB: sa_flags doesn't have SA_RESTART.
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* It must be able to interrupt wait().
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*/
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sigaction_set(SIGTSTP, &sa); /* pause */
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/* Does not work as intended, at least in 2.6.20.
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* SIGSTOP is simply ignored by init:
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*/
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sigaction_set(SIGSTOP, &sa); /* pause */
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/* These signals must interrupt wait(),
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* setting handler without SA_RESTART flag.
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*/
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bb_signals_recursive_norestart(0
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+ (1 << SIGINT) /* Ctrl-Alt-Del */
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+ (1 << SIGQUIT) /* re-exec another init */
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#ifdef SIGPWR
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+ (1 << SIGPWR) /* halt */
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#if ENABLE_FEATURE_INIT_MODIFY_CMDLINE
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/* Make the command line just say "init" - that's all, nothing else */
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strncpy(argv[0], "init", strlen(argv[0]));
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/* Wipe argv[1]-argv[N] so they don't clutter the ps listing */
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while (*++argv)
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nuke_str(*argv);
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#endif
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+ (1 << SIGUSR1) /* halt */
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+ (1 << SIGTERM) /* reboot */
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+ (1 << SIGUSR2) /* poweroff */
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#if ENABLE_FEATURE_USE_INITTAB
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+ (1 << SIGHUP) /* reread /etc/inittab */
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#endif
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, record_signo);
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sigprocmask_allsigs(SIG_UNBLOCK);
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}
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/* Set up STOP signal handlers */
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/* Stop handler must allow only SIGCONT inside itself */
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memset(&sa, 0, sizeof(sa));
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sigfillset(&sa.sa_mask);
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sigdelset(&sa.sa_mask, SIGCONT);
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sa.sa_handler = stop_handler;
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sa.sa_flags = SA_RESTART;
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sigaction_set(SIGTSTP, &sa); /* pause */
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/* Does not work as intended, at least in 2.6.20.
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* SIGSTOP is simply ignored by init
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* (NB: behavior might differ under strace):
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*/
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sigaction_set(SIGSTOP, &sa); /* pause */
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/* Now run everything that needs to be run */
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/* First run the sysinit command */
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run_actions(SYSINIT);
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check_delayed_sigs();
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check_delayed_sigs(&G.zero_ts);
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/* Next run anything that wants to block */
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run_actions(WAIT);
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check_delayed_sigs();
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check_delayed_sigs(&G.zero_ts);
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/* Next run anything to be run only once */
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run_actions(ONCE);
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/* Now run the looping stuff for the rest of forever.
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*/
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/* Now run the looping stuff for the rest of forever */
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while (1) {
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int maybe_WNOHANG;
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maybe_WNOHANG = check_delayed_sigs();
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/* (Re)run the respawn/askfirst stuff */
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run_actions(RESPAWN | ASKFIRST);
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maybe_WNOHANG |= check_delayed_sigs();
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/* Don't consume all CPU time - sleep a bit */
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sleep(1);
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maybe_WNOHANG |= check_delayed_sigs();
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/* Wait for any signal (typically it's SIGCHLD) */
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check_delayed_sigs(NULL); /* NULL timespec makes it wait */
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/* Wait for any child process(es) to exit.
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*
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* If check_delayed_sigs above reported that a signal
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* was caught, wait will be nonblocking. This ensures
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* that if SIGHUP has reloaded inittab, respawn and askfirst
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* actions will not be delayed until next child death.
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*/
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if (maybe_WNOHANG)
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maybe_WNOHANG = WNOHANG;
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/* Wait for any child process(es) to exit */
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while (1) {
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pid_t wpid;
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struct init_action *a;
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/* If signals happen _in_ the wait, they interrupt it,
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* bb_signals_recursive_norestart set them up that way
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*/
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wpid = waitpid(-1, NULL, maybe_WNOHANG);
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wpid = waitpid(-1, NULL, WNOHANG);
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if (wpid <= 0)
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break;
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a = mark_terminated(wpid);
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if (a) {
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message(L_LOG, "process '%s' (pid %d) exited. "
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message(L_LOG, "process '%s' (pid %u) exited. "
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"Scheduling for restart.",
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a->command, wpid);
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a->command, (unsigned)wpid);
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}
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/* See if anyone else is waiting to be reaped */
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maybe_WNOHANG = WNOHANG;
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}
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/* Don't consume all CPU time - sleep a bit */
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sleep(1);
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} /* while (1) */
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}
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@ -1268,11 +1222,17 @@ int init_main(int argc UNUSED_PARAM, char **argv)
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//usage: "Init is the first process started during boot. It never exits."
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//usage: IF_FEATURE_USE_INITTAB(
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//usage: "\n""It (re)spawns children according to /etc/inittab."
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//usage: "\n""Signals:"
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//usage: "\n""HUP: reload /etc/inittab"
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//usage: )
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//usage: IF_NOT_FEATURE_USE_INITTAB(
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//usage: "\n""This version of init doesn't use /etc/inittab,"
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//usage: "\n""has fixed set of processed to run."
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//usage: "\n""Signals:"
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//usage: )
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//usage: "\n""TSTP: stop respawning until CONT"
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//usage: "\n""QUIT: re-exec another init"
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//usage: "\n""USR1/TERM/USR2/INT: run halt/reboot/poweroff/Ctrl-Alt-Del script"
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//usage:
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//usage:#define init_notes_usage
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//usage: "This version of init is designed to be run only by the kernel.\n"
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