signal handling: remove dead code

Remove the code which existed at times when we weren't
running everything inside an event loop, so required
alternative ways of signal handling in and out of an
event loop.

Reset signal handlers when handling fatal signals,
to avoid an infinite loop.

src/main.cc

@@ -211,22 +211,6 @@ sig_fatal_cb(int signo)
 	abort();
 }
 
-/**
- * This SIGTERM handler is only used before the main event loop started to
- * cleanup server pid file. The handler is replaced by ev_signal after the boot.
- * @sa signal_start
- */
-static void
-sig_term_cb(int signo)
-{
-	psignal(signo, "");
-	/* unlink pidfile. */
-	if (pid_file != NULL)
-		unlink(pid_file);
-
-	_exit(EXIT_SUCCESS);
-}
-
 static void
 signal_free(void)
 {
@@ -239,6 +223,9 @@ signal_free(void)
 static void
 signal_reset()
 {
+	for (int i = 0; i < ev_sig_count; i++)
+		ev_signal_stop(loop(), &ev_sigs[i]);
+
 	struct sigaction sa;
 
 	/* Reset all signals to their defaults. */
@@ -254,9 +241,6 @@ signal_reset()
 	    sigaction(SIGFPE, &sa, NULL) == -1)
 		say_syserror("sigaction");
 
-	for (int i = 0; i < ev_sig_count; i++)
-		ev_signal_stop(loop(), &ev_sigs[i]);
-
 	/* Unblock any signals blocked by libev. */
 	sigset_t sigset;
 	sigfillset(&sigset);
@@ -286,6 +270,12 @@ signal_init(void)
 	if (sigaction(SIGPIPE, &sa, 0) == -1)
 		panic_syserror("sigaction");
 
+	/*
+	 * SA_RESETHAND resets handler action to the default
+	 * one when entering handler.
+	 * SA_NODEFER allows receiving the same signal during handler.
+	 */
+	sa.sa_flags = SA_RESETHAND | SA_NODEFER;
 	sa.sa_handler = sig_fatal_cb;
 
 	if (sigaction(SIGSEGV, &sa, 0) == -1 ||
@@ -293,14 +283,6 @@ signal_init(void)
 		panic_syserror("sigaction");
 	}
 
-	sa.sa_handler = sig_term_cb;
-	if (sigaction(SIGUSR1, &sa, 0) == -1 ||
-	    sigaction(SIGINT, &sa, 0) == -1  ||
-	    sigaction(SIGTERM, &sa, 0) == -1 ||
-	    sigaction(SIGHUP, &sa, 0) == -1) {
-		panic_syserror("sigaction");
-	}
-
 	ev_signal_init(&ev_sigs[0], sig_snapshot, SIGUSR1);
 	ev_signal_init(&ev_sigs[1], signal_cb, SIGINT);
 	ev_signal_init(&ev_sigs[2], signal_cb, SIGTERM);