classes: rootfs-postcommands: autologin root on serial-getty

when debug-tweaks or empty-root-password are part of the
IMAGE_FEATURES, save some of the developers time by not having to type
the (then still sole) 'root' username on the serial consoleafter each
and every reboot

by inserting '--autologin root' into the command line of the
responsible 'getty' service

Signed-off-by: Johannes Schneider <johannes.schneider@leica-geosystems.com>

meta/classes/rootfs-postcommands.bbclass

@@ -8,6 +8,9 @@ ROOTFS_POSTPROCESS_COMMAND += '${@bb.utils.contains_any("IMAGE_FEATURES", [ 'deb
 # Allow dropbear/openssh to accept root logins if debug-tweaks or allow-root-login is enabled
 ROOTFS_POSTPROCESS_COMMAND += '${@bb.utils.contains_any("IMAGE_FEATURES", [ 'debug-tweaks', 'allow-root-login' ], "ssh_allow_root_login; ", "",d)}'
 
+# Autologin the root user on the serial console, if debug-tweaks or empty-root-password are active
+ROOTFS_POSTPROCESS_COMMAND += '${@bb.utils.contains_any("IMAGE_FEATURES", [ 'debug-tweaks', 'empty-root-password' ], "serial_autologin_root; ", "",d)}'
+
 # Enable postinst logging if debug-tweaks or post-install-logging is enabled
 ROOTFS_POSTPROCESS_COMMAND += '${@bb.utils.contains_any("IMAGE_FEATURES", [ 'debug-tweaks', 'post-install-logging' ], "postinst_enable_logging; ", "",d)}'
 
@@ -196,6 +199,18 @@ ssh_allow_root_login () {
 	fi
 }
 
+#
+# Autologin the 'root' user on the serial terminal,
+# if empty-root-password is enabled
+#
+serial_root_autologin () {
+	if [ -e ${IMAGE_ROOTFS}${systemd_system_unitdir}/serial-getty@.service ]; then
+		sed -i '/^\s*ExecStart\b/ s/getty /&--autologin root /' \
+			"${IMAGE_ROOTFS}${systemd_system_unitdir}/serial-getty@.service"
+	fi
+}
+
+
 python sort_passwd () {
     import rootfspostcommands
     rootfspostcommands.sort_passwd(d.expand('${IMAGE_ROOTFS}${sysconfdir}'))