package/mender: adding a writable location

Mender needs /var/lib/mender to be writable at the service start, the
path is hardcoded and thus we cannot change it.
This patch solves the problem using the same approach we have for
dropbear.

Signed-off-by: Angelo Compagnucci <angelo@amarulasolutions.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: <aduskett@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/mender/mender.mk

@@ -49,6 +49,8 @@ define MENDER_INSTALL_CONFIG_FILES
 		$(INSTALL) -D -m 0755 $(@D)/support/mender-inventory-$(f) \
 			$(TARGET_DIR)/usr/share/mender/inventory/mender-inventory-$(f)
 	)
+
+	ln -snf /var/run/mender $(TARGET_DIR)/var/lib/mender
 endef
 
 MENDER_POST_INSTALL_TARGET_HOOKS += MENDER_INSTALL_CONFIG_FILES

package/mender/mender.service

@@ -6,7 +6,17 @@ After=systemd-resolved.service
 Type=idle
 User=root
 Group=root
-ExecStartPre=/bin/mkdir -p -m 0700 /data/mender
+ExecStartPre=/bin/sh -c '\
+if [ -L /var/lib/mender \
+     -a "$(readlink /var/lib/mender)" = "/var/run/mender" ]; then \
+    if rm -f /var/lib/mender >/dev/null 2>&1; then \
+        mkdir -p /var/lib/mender; \
+    else \
+        echo "No persistent location to store mender data. Data will be lost\
+        echo "at reboot. Are you sure this is what you want to do?"; \
+        mkdir -p "$(readlink /var/lib/mender)"; \
+    fi; \
+fi'
 ExecStart=/usr/bin/mender -daemon
 Restart=on-abort