package/busybox: add systemd service for telnetd

Signed-off-by: Sam Voss <sam.voss@collins.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[yann.morin.1998@free.fr:
  - introduce BUSYBOX_INSTALL_TELNET_SERVICE
  - move _INSTALL_INIT_SYSTEMD alphabetically between openrc and sysv
  - drop the comment about Type=simple  (Arnout)
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

buildroot-2021.05/package/busybox/busybox.mk

@@ -332,6 +332,12 @@ define BUSYBOX_INSTALL_TELNET_SCRIPT
 			$(TARGET_DIR)/etc/init.d/S50telnet ; \
 	fi
 endef
+define BUSYBOX_INSTALL_TELNET_SERVICE
+	if grep -q CONFIG_FEATURE_TELNETD_STANDALONE=y $(@D)/.config; then \
+		$(INSTALL) -D -m 0644 package/busybox/telnetd.service \
+			$(TARGET_DIR)/usr/lib/systemd/system/telnetd.service ; \
+	fi
+endef
 
 # Add /bin/{a,hu}sh to /etc/shells otherwise some login tools like dropbear
 # can reject the user connection. See man shells.
@@ -384,6 +390,10 @@ define BUSYBOX_INSTALL_INIT_OPENRC
 	$(BUSYBOX_INSTALL_TELNET_SCRIPT)
 endef
 
+define BUSYBOX_INSTALL_INIT_SYSTEMD
+	$(BUSYBOX_INSTALL_TELNET_SERVICE)
+endef
+
 define BUSYBOX_INSTALL_INIT_SYSV
 	$(BUSYBOX_INSTALL_MDEV_SCRIPT)
 	$(BUSYBOX_INSTALL_LOGGING_SCRIPT)

buildroot-2021.05/package/busybox/telnetd.service

+[Unit]
+Description=Telnetd Service
+After=network.target
+
+[Service]
+Type=simple
+ExecStart=/usr/sbin/telnetd -F
+
+[Install]
+WantedBy=multi-user.target