Option to restart the cild process #186

Dockerfile

@@ -13,6 +13,8 @@ ARG CC
 
 # Persist ARGs into the image
 
+RUN ln -s /usr/bin/python3 /usr/bin/python
+
 ENV ARCH_SUFFIX="$ARCH_SUFFIX" \
     ARCH_NATIVE="$ARCH_NATIVE" \
     CC="$CC"

ci/install_deps.sh

@@ -6,7 +6,7 @@ set -o xtrace
 DEPS=(
   build-essential git gdb valgrind cmake rpm file
   libcap-dev python3-dev python3-pip python3-setuptools
-  hardening-includes gnupg
+  hardening-includes gnupg curl
 )
 
 case "${ARCH_SUFFIX-}" in
@@ -26,5 +26,7 @@ apt-get update
 apt-get install --no-install-recommends --yes "${DEPS[@]}"
 rm -rf /var/lib/apt/lists/*
 
-python3 -m pip install --upgrade pip
+curl -fsSL -o- https://bootstrap.pypa.io/pip/3.5/get-pip.py | python3.5
+#python3 -m pip install --upgrade pip
 python3 -m pip install virtualenv
+python3 -m pip install importlib-metadata==2.1.0

src/tini.c

@@ -44,6 +44,8 @@
 #define STATUS_MAX 255
 #define STATUS_MIN 0
 
+#define RESPAWN_CHILD -2
+
 typedef struct {
    sigset_t* const sigmask_ptr;
    struct sigaction* const sigttin_action_ptr;
@@ -90,11 +92,11 @@ static int32_t expect_status[(STATUS_MAX - STATUS_MIN + 1) / 32];
 
 #ifdef PR_SET_CHILD_SUBREAPER
 #define HAS_SUBREAPER 1
-#define OPT_STRING "p:hvwgle:s"
+#define OPT_STRING "p:hvwgle:r:t:s"
 #define SUBREAPER_ENV_VAR "TINI_SUBREAPER"
 #else
 #define HAS_SUBREAPER 0
-#define OPT_STRING "p:hvwgle:"
+#define OPT_STRING "p:hvwgle:r:t:"
 #endif
 
 #define VERBOSITY_ENV_VAR "TINI_VERBOSITY"
@@ -128,6 +130,10 @@ To fix the problem, "
 #endif
 "run Tini as PID 1.";
 
+static unsigned int restart_signal = 0;
+static unsigned int child_term_signal = SIGTERM;
+static bool is_restarting = false;
+
 int restore_signals(const signal_configuration_t* const sigconf_ptr) {
 	if (sigprocmask(SIG_SETMASK, sigconf_ptr->sigmask_ptr, NULL)) {
 		PRINT_FATAL("Restoring child signal mask failed: '%s'", strerror(errno));
@@ -248,6 +254,9 @@ void print_usage(char* const name, FILE* const file) {
 	fprintf(file, "  -w: Print a warning when processes are getting reaped.\n");
 	fprintf(file, "  -g: Send signals to the child's process group.\n");
 	fprintf(file, "  -e EXIT_CODE: Remap EXIT_CODE (from 0 to 255) to 0 (can be repeated).\n");
+	fprintf(file, "  -r RESTART_SIGNAL: Restart(terminate and start) child process on RESTART_SIGNAL, e.g. \"-r SIGUSR1\".\n");
+	fprintf(file, "  -t CHILD_TERM_SIGNAL: Signal to terminate the child process for a restart, defaults to SIGTERM, e.g. \"-t SIGTERM\".\n");
+	fprintf(file, "  -e EXIT_CODE: Remap EXIT_CODE (from 0 to 255) to 0 (can be repeated).\n");
 	fprintf(file, "  -l: Show license and exit.\n");
 #endif
 
@@ -273,13 +282,13 @@ void print_license(FILE* const file) {
     }
 }
 
-int set_pdeathsig(char* const arg) {
+int set_signal_number(char* const signal_name, unsigned int* signal_number) {
 	size_t i;
 
 	for (i = 0; i < ARRAY_LEN(signal_names); i++) {
-		if (strcmp(signal_names[i].name, arg) == 0) {
+		if (strcmp(signal_names[i].name, signal_name) == 0) {
 			/* Signals start at value "1" */
-			parent_death_signal = signal_names[i].number;
+			*signal_number = signal_names[i].number;
 			return 0;
 		}
 	}
@@ -329,13 +338,35 @@ int parse_args(const int argc, char* const argv[], char* (**child_args_ptr_ptr)[
 				break;
 #endif
 			case 'p':
-				if (set_pdeathsig(optarg)) {
+				if (set_signal_number(optarg, &parent_death_signal)) {
 					PRINT_FATAL("Not a valid option for -p: %s", optarg);
 					*parse_fail_exitcode_ptr = 1;
 					return 1;
 				}
 				break;
 
+			case 'r':
+				if (set_signal_number(optarg, &restart_signal)) {
+					PRINT_FATAL("Not a valid option for -r: %s", optarg);
+					*parse_fail_exitcode_ptr = 1;
+					return 1;
+				}
+
+				if (restart_signal == SIGCHLD) {
+					PRINT_FATAL("SIGCHLD not a valid option for -r: %s", optarg);
+					*parse_fail_exitcode_ptr = 1;
+					return 1;
+				}
+				break;
+
+			case 't':
+				if (set_signal_number(optarg, &child_term_signal)) {
+					PRINT_FATAL("Not a valid option for -t: %s", optarg);
+					*parse_fail_exitcode_ptr = 1;
+					return 1;
+				}
+				break;
+
 			case 'v':
 				verbosity++;
 				break;
@@ -498,6 +529,10 @@ int configure_signals(sigset_t* const parent_sigset_ptr, const signal_configurat
 	return 0;
 }
 
+bool is_restart_enabled() {
+	return restart_signal != 0;
+}
+
 int wait_and_forward_signal(sigset_t const* const parent_sigset_ptr, pid_t const child_pid) {
 	siginfo_t sig;
 
@@ -521,6 +556,17 @@ int wait_and_forward_signal(sigset_t const* const parent_sigset_ptr, pid_t const
 				PRINT_DEBUG("Received SIGCHLD");
 				break;
 			default:
+					if (restart_signal == (unsigned)sig.si_signo && is_restart_enabled()) {
+					PRINT_DEBUG("Received process restart signal: %d", sig.si_signo);
+					// Shutdown the child process.
+					// Success full termination will be known when corresponding
+					// SIGCHLD is received.
+					PRINT_DEBUG("Terminating child process with pid %d", child_pid);
+					kill(child_pid, child_term_signal);
+					is_restarting = true;
+					break;
+				}
+
 				PRINT_DEBUG("Passing signal: '%s'", strsignal(sig.si_signo));
 				/* Forward anything else */
 				if (kill(kill_process_group ? -child_pid : child_pid, sig.si_signo)) {
@@ -542,6 +588,8 @@ int reap_zombies(const pid_t child_pid, int* const child_exitcode_ptr) {
 	pid_t current_pid;
 	int current_status;
 
+	*child_exitcode_ptr = -1;
+
 	while (1) {
 		current_pid = waitpid(-1, &current_status, WNOHANG);
 
@@ -588,6 +636,14 @@ int reap_zombies(const pid_t child_pid, int* const child_exitcode_ptr) {
 					if (INT32_BITFIELD_TEST(expect_status, *child_exitcode_ptr)) {
 						*child_exitcode_ptr = 0;
 					}
+
+					if (is_restarting && *child_exitcode_ptr == 0) {
+						/* The child process exited normally with a success exit
+						 * code 0 and we are restarting. Indicate repsawn of the child.
+						 */
+						*child_exitcode_ptr = RESPAWN_CHILD;
+					}
+					is_restarting = false;
 				} else if (warn_on_reap > 0) {
 					PRINT_WARNING("Reaped zombie process with pid=%i", current_pid);
 				}
@@ -603,7 +659,6 @@ int reap_zombies(const pid_t child_pid, int* const child_exitcode_ptr) {
 	return 0;
 }
 
-
 int main(int argc, char *argv[]) {
 	pid_t child_pid;
 
@@ -660,7 +715,10 @@ int main(int argc, char *argv[]) {
 	if (spawn_ret) {
 		return spawn_ret;
 	}
-	free(child_args_ptr);
+
+	if (!is_restart_enabled()) {
+		free(child_args_ptr);
+	}
 
 	while (1) {
 		/* Wait for one signal, and forward it */
@@ -673,8 +731,13 @@ int main(int argc, char *argv[]) {
 			return 1;
 		}
 
-		if (child_exitcode != -1) {
-			PRINT_TRACE("Exiting: child has exited");
+		if (is_restart_enabled() && child_exitcode == RESPAWN_CHILD) {
+			spawn_ret = spawn(&child_sigconf, *child_args_ptr, &child_pid);
+			if (spawn_ret) {
+				return spawn_ret;
+			}
+		} else if (child_exitcode != -1) {
+			PRINT_TRACE("Exiting: child has exited %d", child_exitcode);
 			return child_exitcode;
 		}
 	}

test/restart/restart-test.py

@@ -0,0 +1,28 @@
+#!/usr/bin/env python
+import signal
+import os
+import sys
+import time
+
+
+def sigterm_handler(sig, frame):
+    print("SIGTERM received - exiting gracefully")
+    sys.exit(0)
+
+
+def sigusr1_handler(sig, frame):
+    print("SIGUSR1 received - exiting")
+    sys.exit(1)
+
+
+def main():
+    signal.signal(signal.SIGTERM, sigterm_handler)
+    signal.signal(signal.SIGUSR1, sigusr1_handler)
+    print("#")
+    print("Starting")
+    while True:
+        time.sleep(1)
+
+
+if __name__ == "__main__":
+    main()