lxd/metadata: update metadata configuration

Signed-off-by: Gabriel Mougard <[email protected]>

doc/config_options.txt

@@ -2359,6 +2359,14 @@ Specify either a cron expression (`<minute> <hour> <dom> <month> <dow>`), a comm
 
 <!-- config group instance-snapshots end -->
 <!-- config group instance-volatile start -->
+```{config:option} volatile.<disk_dev_name>.last_state.created instance-volatile
+:shortdesc: "Path of the directory created from mounting a `disk` device"
+:type: "string"
+If mounting a host directory through a `disk` device creates the target directory, this option contains the path of this newly created target directory.
+For example, if the target directory is `/opt` and `/opt` already exists in the instance, this key is not set.
+However, if the target directory is `/opt/foo` and `/opt/foo` doesn't exist in the instance, this key is set to `/opt/foo`.
+```
+
 ```{config:option} volatile.<name>.apply_quota instance-volatile
 :shortdesc: "Disk quota"
 :type: "string"

lxd/metadata/configuration.json

@@ -2665,6 +2665,13 @@
 			},
 			"volatile": {
 				"keys": [
+					{
+						"volatile.\u003cdisk_dev_name\u003e.last_state.created": {
+							"longdesc": "If mounting a host directory through a `disk` device creates the target directory, this option contains the path of this newly created target directory.\nFor example, if the target directory is `/opt` and `/opt` already exists in the instance, this key is not set.\nHowever, if the target directory is `/opt/foo` and `/opt/foo` doesn't exist in the instance, this key is set to `/opt/foo`.",
+							"shortdesc": "Path of the directory created from mounting a `disk` device",
+							"type": "string"
+						}
+					},
 					{
 						"volatile.\u003cname\u003e.apply_quota": {
 							"longdesc": "The disk quota is applied the next time the instance starts.",