main: Use signalfd instead of raw signals

Copied from ConnMan's commit 6ad51830 where Daniel Wagner was
explaining:

   "It's unsafe to call syslog in the terminated signal handler
    because syslog takes a lock. So when the signal handler
    kicks in and we were already in syslog, we have a nice
    deadlock."

diff --git a/src/main.c b/src/main.c
index 1a0f297..9765b19 100644 (file)
--- a/src/main.c
+++ b/src/main.c
@@ -28,6 +28,7 @@
 #include <unistd.h>
 #include <string.h>
 #include <signal.h>
+#include <sys/signalfd.h>
 
 #include <gdbus.h>
 
@@ -91,16 +92,72 @@ static GMainLoop *main_loop = NULL;
 
 static volatile sig_atomic_t __terminated = 0;
 
-static void sig_term(int sig)
+static gboolean signal_handler(GIOChannel *channel, GIOCondition cond,
+                                                       gpointer user_data)
 {
-       if (__terminated > 0)
-               return;
+       struct signalfd_siginfo si;
+       ssize_t result;
+       int fd;
 
-       __terminated = 1;
+       if (cond & (G_IO_NVAL | G_IO_ERR | G_IO_HUP))
+               return FALSE;
 
-       near_info("Terminating");
+       fd = g_io_channel_unix_get_fd(channel);
 
-       g_main_loop_quit(main_loop);
+       result = read(fd, &si, sizeof(si));
+       if (result != sizeof(si))
+               return FALSE;
+
+       switch (si.ssi_signo) {
+       case SIGINT:
+       case SIGTERM:
+               if (__terminated == 0) {
+                       near_info("Terminating");
+                       g_main_loop_quit(main_loop);
+               }
+
+               __terminated = 1;
+               break;
+       }
+
+       return TRUE;
+}
+
+static guint setup_signalfd(void)
+{
+       GIOChannel *channel;
+       guint source;
+       sigset_t mask;
+       int fd;
+
+       sigemptyset(&mask);
+       sigaddset(&mask, SIGINT);
+       sigaddset(&mask, SIGTERM);
+
+       if (sigprocmask(SIG_BLOCK, &mask, NULL) < 0) {
+               perror("Failed to set signal mask");
+               return 0;
+       }
+
+       fd = signalfd(-1, &mask, 0);
+       if (fd < 0) {
+               perror("Failed to create signal descriptor");
+               return 0;
+       }
+
+       channel = g_io_channel_unix_new(fd);
+
+       g_io_channel_set_close_on_unref(channel, TRUE);
+       g_io_channel_set_encoding(channel, NULL, NULL);
+       g_io_channel_set_buffered(channel, FALSE);
+
+       source = g_io_add_watch(channel,
+                               G_IO_IN | G_IO_HUP | G_IO_ERR | G_IO_NVAL,
+                               signal_handler, NULL);
+
+       g_io_channel_unref(channel);
+
+       return source;
 }
 
 static void disconnect_callback(DBusConnection *conn, void *user_data)
@@ -161,7 +218,7 @@ int main(int argc, char *argv[])
        DBusConnection *conn;
        DBusError err;
        GKeyFile *config;
-       struct sigaction sa;
+       guint signal;
 
        context = g_option_context_new(NULL);
        g_option_context_add_main_entries(context, options, NULL);
@@ -184,6 +241,8 @@ int main(int argc, char *argv[])
 
        main_loop = g_main_loop_new(NULL, FALSE);
 
+       signal = setup_signalfd();
+
        dbus_error_init(&err);
 
        conn = g_dbus_setup_bus(DBUS_BUS_SYSTEM, NFC_SERVICE, &err);
@@ -228,13 +287,10 @@ int main(int argc, char *argv[])
                }
        }
 
-       memset(&sa, 0, sizeof(sa));
-       sa.sa_handler = sig_term;
-       sigaction(SIGINT, &sa, NULL);
-       sigaction(SIGTERM, &sa, NULL);
-
        g_main_loop_run(main_loop);
 
+       g_source_remove(signal);
+
        __near_plugin_cleanup();
 
        __near_agent_cleanup();