How to get LLD discovered entities via Zabbix API?

[macgaffin2]

We can get the LLD discovered items via item.get.
but, I want to get LLD discovered entities,such as:
File Systems: "/", "/opt"......
Interfaces: "eth0", "eth1"......
CPUs: "cpu0", "cpu1"......

I tried querying item.get API with:
{
"host": "Zabbix server",
"output": "extend",
"search": {
"key_": "vfs.fs.discovery"
},
"sortfield": "name"
}

but I got response:
{
"jsonrpc": "2.0",
"result": "[]",
"id": 0
}

It seems nothing here!

And I tried creating an item with key "vfs.fs.discovery", but Zabbix says --
Item with key "vfs.fs.discovery" already exists on "Zabbix server".

How could I approach the goal!

Thank you!