rc: use /etc/hostname if available

This is significantly less overhead than an init script.

src/openrc/rc.c

@@ -473,12 +473,33 @@ handle_signal(int sig)
 	errno = serrno;
 }
 
+static void
+do_early_hostname(void)
+{
+#ifdef __linux__
+	/* Set hostname if available */
+	char *buffer = NULL;
+	size_t len;
+
+	if (rc_getfile(RC_SYSCONFDIR "/hostname", &buffer, &len)) {
+		if (buffer[len - 2] == '\n')
+			buffer[--len - 1] = '\0';
+		if (sethostname(buffer, len)) {
+			/* ignore */;
+		}
+		free(buffer);
+	}
+#endif
+}
+
 static void
 do_sysinit(void)
 {
 	struct utsname uts;
 	const char *sys;
 
+	do_early_hostname();
+
 	/* exec init-early.sh if it exists
 	 * This should just setup the console to use the correct
 	 * font. Maybe it should setup the keyboard too? */