Use pthread_atfork() to restore signals and NOFILE limit

This ensures these functions are always called (even when a library
such as wlroots or libc perform the fork) and removes the need to
manually call them.

include/sway/server.h

@@ -164,9 +164,6 @@ void server_fini(struct sway_server *server);
 bool server_start(struct sway_server *server);
 void server_run(struct sway_server *server);
 
-void restore_nofile_limit(void);
-void restore_signals(void);
-
 void handle_new_output(struct wl_listener *listener, void *data);
 
 void handle_idle_inhibitor_v1(struct wl_listener *listener, void *data);

meson.build

@@ -79,7 +79,7 @@ libudev = wlroots_features['libinput_backend'] ? dependency('libudev') : null_de
 math = cc.find_library('m')
 rt = cc.find_library('rt')
 xcb_icccm = wlroots_features['xwayland'] ? dependency('xcb-icccm') : null_dep
-threads = dependency('threads') # for pthread_setschedparam
+threads = dependency('threads') # for pthread_setschedparam and pthread_atfork
 
 if get_option('sd-bus-provider') == 'auto'
 	if not get_option('tray').disabled()

sway/commands/exec_always.c

@@ -51,8 +51,6 @@ struct cmd_results *cmd_exec_process(int argc, char **argv) {
 	// Fork process
 	pid_t child = fork();
 	if (child == 0) {
-		restore_nofile_limit();
-		restore_signals();
 		setsid();
 
 		if (ctx) {

sway/config/bar.c

@@ -213,8 +213,6 @@ static void invoke_swaybar(struct bar_config *bar) {
 		sway_log(SWAY_ERROR, "Failed to create fork for swaybar");
 		return;
 	} else if (pid == 0) {
-		restore_nofile_limit();
-		restore_signals();
 		if (!sway_set_cloexec(sockets[1], false)) {
 			_exit(EXIT_FAILURE);
 		}

sway/config/output.c

@@ -1060,8 +1060,6 @@ static bool _spawn_swaybg(char **command) {
 		sway_log_errno(SWAY_ERROR, "fork failed");
 		return false;
 	} else if (pid == 0) {
-		restore_nofile_limit();
-		restore_signals();
 		if (!sway_set_cloexec(sockets[1], false)) {
 			_exit(EXIT_FAILURE);
 		}

sway/main.c

@@ -1,5 +1,6 @@
 #include <getopt.h>
 #include <pango/pangocairo.h>
+#include <pthread.h>
 #include <signal.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -121,6 +122,16 @@ static bool detect_suid(void) {
 	return true;
 }
 
+static void restore_nofile_limit(void) {
+	if (original_nofile_rlimit.rlim_cur == 0) {
+		return;
+	}
+	if (setrlimit(RLIMIT_NOFILE, &original_nofile_rlimit) != 0) {
+		sway_log_errno(SWAY_ERROR, "Failed to restore max open files limit: "
+			"setrlimit(NOFILE) failed");
+	}
+}
+
 static void increase_nofile_limit(void) {
 	if (getrlimit(RLIMIT_NOFILE, &original_nofile_rlimit) != 0) {
 		sway_log_errno(SWAY_ERROR, "Failed to bump max open files limit: "
@@ -135,17 +146,10 @@ static void increase_nofile_limit(void) {
 			"setrlimit(NOFILE) failed");
 		sway_log(SWAY_INFO, "Running with %d max open files",
 			(int)original_nofile_rlimit.rlim_cur);
-	}
-}
-
-void restore_nofile_limit(void) {
-	if (original_nofile_rlimit.rlim_cur == 0) {
 		return;
 	}
-	if (setrlimit(RLIMIT_NOFILE, &original_nofile_rlimit) != 0) {
-		sway_log_errno(SWAY_ERROR, "Failed to restore max open files limit: "
-			"setrlimit(NOFILE) failed");
-	}
+
+	pthread_atfork(NULL, NULL, restore_nofile_limit);
 }
 
 static int term_signal(int signal, void *data) {
@@ -153,6 +157,14 @@ static int term_signal(int signal, void *data) {
 	return 0;
 }
 
+static void restore_signals(void) {
+	sigset_t set;
+	sigemptyset(&set);
+	sigprocmask(SIG_SETMASK, &set, NULL);
+	signal(SIGCHLD, SIG_DFL);
+	signal(SIGPIPE, SIG_DFL);
+}
+
 static void init_signals(void) {
 	wl_event_loop_add_signal(server.wl_event_loop, SIGTERM, term_signal, NULL);
 	wl_event_loop_add_signal(server.wl_event_loop, SIGINT, term_signal, NULL);
@@ -162,14 +174,8 @@ static void init_signals(void) {
 
 	// prevent ipc write errors from crashing sway
 	signal(SIGPIPE, SIG_IGN);
-}
 
-void restore_signals(void) {
-	sigset_t set;
-	sigemptyset(&set);
-	sigprocmask(SIG_SETMASK, &set, NULL);
-	signal(SIGCHLD, SIG_DFL);
-	signal(SIGPIPE, SIG_DFL);
+	pthread_atfork(NULL, NULL, restore_signals);
 }
 
 void enable_debug_flag(const char *flag) {

sway/swaynag.c

@@ -63,7 +63,6 @@ bool swaynag_spawn(const char *swaynag_command,
 		sway_log(SWAY_ERROR, "Failed to create fork for swaynag");
 		goto failed;
 	} else if (pid == 0) {
-		restore_nofile_limit();
 		if (!sway_set_cloexec(sockets[1], false)) {
 			_exit(EXIT_FAILURE);
 		}
@@ -148,4 +147,3 @@ void swaynag_show(struct swaynag_instance *swaynag) {
 		close(swaynag->fd[1]);
 	}
 }
-