fix: handle SIGTERM for graceful graphical shutdown

Sending SIGTERM to X.org is necessary to avoid graphical lock-up.

Makefile

@@ -17,10 +17,10 @@ LDFLAGS?=-Wl,--gc-sections
 
 LIBS=-lpam
 
-_DEPS = version.h log.h util.h ui.h ui_state.h config.h pam.h desktop.h desktop_exec.h auth.h ofield.h efield.h keys.h users.h sessions.h chvt.h macros.h launch_state.h
+_DEPS = version.h log.h util.h ui.h ui_state.h config.h pam.h desktop.h desktop_exec.h auth.h ofield.h efield.h keys.h users.h sessions.h chvt.h macros.h launch_state.h signal_handler.h
 DEPS = $(patsubst %,$(IDIR)/%,$(_DEPS))
 
-_OBJ = main.o log.o util.o ui.o ui_state.o config.o pam.o desktop.o desktop_exec.o auth.o ofield.o efield.o users.o sessions.o chvt.o launch_state.o
+_OBJ = main.o log.o util.o ui.o ui_state.o config.o pam.o desktop.o desktop_exec.o auth.o ofield.o efield.o users.o sessions.o chvt.o launch_state.o signal_handler.o
 OBJ = $(patsubst %,$(ODIR)/%,$(_OBJ))
 
 INFO_GIT_REV?=$$(git describe --long --tags --always || echo '?')

include/signal_handler.h

@@ -0,0 +1,3 @@
+// handle SIGTERM by sending SIGTERM to all children, resulting
+// in a graceful graphical shutdown
+void setup_sigterm();

src/main.c

@@ -12,12 +12,14 @@
 #include "log.h"
 #include "macros.h"
 #include "sessions.h"
+#include "signal_handler.h"
 #include "ui.h"
 #include "users.h"
 #include "util.h"
 #include "version.h"
 
 #define DATESTR_MAXBUFSIZE 0x20
+
 int main(int argc, char* argv[]) {
   // Logger
   char* log_output = getenv("LIDM_LOG");
@@ -85,6 +87,8 @@ int main(int argc, char* argv[]) {
   struct Vector users = get_human_users();
   struct Vector sessions = get_avaliable_sessions();
 
+  setup_sigterm();
+
   int ret = load(&users, &sessions);
   if (ret == 0) execl(argv[0], argv[0], NULL);
 }

src/signal_handler.c

@@ -0,0 +1,26 @@
+#include <errno.h>
+#include <stddef.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+static void handle_sigterm(int) {
+  signal(SIGTERM, SIG_IGN);
+
+  kill(-getpgrp(), SIGTERM);
+
+  int status;
+  while (waitpid(-1, &status, 0) > 0 || errno == EINTR) {
+  }
+
+  _exit(0);
+}
+
+void setup_sigterm() {
+  setpgid(0, 0);
+
+  struct sigaction sa;
+  sa.sa_handler = handle_sigterm;
+  sigemptyset(&sa.sa_mask);
+  sa.sa_flags = 0;
+  sigaction(SIGTERM, &sa, NULL);
+}