samba36: add package with hotplug.d script for auto sharing

The new samba36-hotplug package provides a hotplug.d script for the
"mount" subsystem. It automatically shares every mounted block device.

It works by updating /var/run/config/samba file which:
1) Is read by procd init script
2) Gets wiped on reboot providing a consistent state
3) Can be safely updated without flash wearing or conflicting with user
   changes being made in /etc/config/samba

Cc: Rosy Song <rosysong@rosinson.com>
Cc: Jo-Philipp Wich <jo@mein.io>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

package/network/services/samba36/Makefile

@@ -43,6 +43,12 @@ define Package/samba36-server
   DEPENDS:=+USE_GLIBC:librt $(ICONV_DEPENDS)
 endef
 
+define Package/samba36-hotplug
+  $(call Package/samba/Default)
+  TITLE+= hotplug script for auto sharing
+  DEPENDS:=+blockd
+endef
+
 define Package/samba36-client
   $(call Package/samba/Default)
   TITLE+= client
@@ -161,6 +167,11 @@ define Package/samba36-server/install
 	$(LN) samba_multicall $(1)/usr/sbin/smbpasswd
 endef
 
+define Package/samba36-hotplug/install
+	$(INSTALL_DIR) $(1)/etc/hotplug.d/mount
+	$(INSTALL_CONF) ./files/samba.hotplug $(1)/etc/hotplug.d/mount/60-samba
+endef
+
 define Package/samba36-client/install
 	$(INSTALL_DIR) $(1)/usr/sbin
 	$(INSTALL_BIN) $(PKG_BUILD_BIN)/smbclient $(1)/usr/sbin
@@ -174,5 +185,6 @@ endef
 
 $(eval $(call BuildPackage,samba36-client))
 $(eval $(call BuildPackage,samba36-server))
+$(eval $(call BuildPackage,samba36-hotplug))
 $(eval $(call BuildPackage,samba36-net))
 

package/network/services/samba36/files/samba.hotplug

@@ -0,0 +1,56 @@
+#!/bin/sh
+
+. /usr/share/libubox/jshn.sh
+
+device_get_vars() {
+	json_init
+	json_load "$(ubus call block info)"
+
+	json_select devices
+
+	json_get_keys keys
+	for key in $keys
+	do
+		json_select $key
+
+		json_get_var device device
+		[ "$device" = "$1" ] && {
+			shift
+			json_get_vars $@
+			json_select ..
+			break
+		}
+
+		json_select ..
+	done
+
+	json_select ..
+}
+
+[ -f /var/run/config/samba ] || {
+	mkdir -p /var/run/config && touch /var/run/config/samba
+}
+
+[ "$ACTION" = "add" ] && {
+	device_get_vars $DEVICE label mount
+	[ -n "$mount" ] && {
+		uci -c /var/run/config batch <<-EOF
+			set samba.$DEVICE="sambashare"
+			set samba.$DEVICE.name="$label"
+			set samba.$DEVICE.path="$mount"
+			set samba.$DEVICE.browseable="yes"
+			set samba.$DEVICE.read_only="yes"
+			set samba.$DEVICE.guest_ok="yes"
+			commit samba
+		EOF
+		/etc/init.d/samba reload
+	}
+}
+
+[ "$ACTION" = "remove" ] && {
+	uci -c /var/run/config batch <<-EOF
+		delete samba.$DEVICE
+		commit samba
+	EOF
+	/etc/init.d/samba reload
+}