Remove leaks in the xenopsd <-> xapi caches

We have two caches:

  Xapi_cache: contains the latest pool VM metadata, translated into
     xenopsd format. Whenever the user changes the VM's name_label
     (for example), this is used to update the xenopsd metadata for
     next reboot.

  Xenops_cache: contains the latest runtime VM state, as queried
     from xenopsd. This is used to minimise the number of writes
     to the pool database.

The cache lifetime is tied to the lifetime of the metadata in xenopsd:
whenever we add to xenopsd we initialise the cache; whenever we remove
from xenopsd we remove from the cache.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>

ocaml/xapi/xapi_vm.ml

@@ -288,7 +288,7 @@ let power_state_reset ~__context ~vm =
 					true
 				end else begin
 					(* Delete the metadata from xenopsd *)
-					Xapi_xenops.delete_metadata_from_xenopsd ~__context id;
+					Xapi_xenops.Xenopsd_metadata.delete ~__context id;
 					false
 				end
 			with _ -> false in

ocaml/xapi/xapi_vm_migrate.ml

@@ -80,7 +80,10 @@ let pool_migrate ~__context ~vm ~host ~options =
 				(* XXX: PR-1255: the live flag *)
 				info "xenops: VM.migrate %s to %s" vm' xenops_url;
 				XenopsAPI.VM.migrate dbg vm' [] [] xenops_url |> wait_for_task dbg |> success_task dbg |> ignore;
-				(try XenopsAPI.VM.remove dbg vm' with e -> debug "xenops: VM.remove %s: caught %s" vm' (Printexc.to_string e));
+				(* Delete all record of this VM locally (including caches) *)
+				Xapi_xenops.Xenopsd_metadata.delete ~__context vm';
+				(* Flush xenopsd events through: we don't want the pool database to
+				   be updated on this host ever again. *)
 				Xapi_xenops.Event.wait dbg ()
 			)
 		);
@@ -90,14 +93,10 @@ let pool_migrate ~__context ~vm ~host ~options =
 		let _, state = XenopsAPI.VM.stat dbg vm' in
 		if Xenops_interface.(state.Vm.power_state = Suspended) then begin
 			debug "xenops: %s: shutting down suspended VM" vm';
-			(* This will remove any traces, but the VM may still be 'suspended' *)
 			Xapi_xenops.shutdown ~__context ~self:vm None;
-			(* Remove the VM metadata from xenopsd *)
-			(try XenopsAPI.VM.remove dbg vm' with e -> debug "xenops: VM.remove %s: caught %s" vm' (Printexc.to_string e))
 		end;
 		raise e
 	end;
-	Xapi_xenops.remove_caches vm';
 	Rrdd_proxy.migrate_rrd ~__context ~vm_uuid:vm' ~host_uuid:(Ref.string_of host) ();
 	(* We will have missed important events because we set resident_on late.
 	   This was deliberate: resident_on is used by the pool master to reserve
@@ -428,9 +427,8 @@ let migrate_send'  ~__context ~vm ~dest ~live ~vdi_map ~vif_map ~options =
 				Xapi_xenops.with_migrating_away vm_uuid
 					(fun () ->
 						XenopsAPI.VM.migrate dbg vm_uuid xenops_vdi_map xenops_vif_map xenops |> wait_for_task dbg |> success_task dbg |> ignore;
-						(try XenopsAPI.VM.remove dbg vm_uuid with e -> debug "Caught %s while removing VM %s from metadata" (Printexc.to_string e) vm_uuid);
+						Xapi_xenops.Xenopsd_metadata.delete ~__context vm_uuid;
 						Xapi_xenops.Event.wait dbg ())
-
 			with
 				| Xenops_interface.Does_not_exist ("VM",_) ->
 					()	
@@ -496,7 +494,7 @@ let migrate_send'  ~__context ~vm ~dest ~live ~vdi_map ~vif_map ~options =
 	with e ->
 		error "Caught %s: cleaning up" (Printexc.to_string e);
 
-		Xapi_xenops.remove_caches vm_uuid;
+		(* This resets the caches to empty: *)
 		Xapi_xenops.add_caches vm_uuid;
 		Xapi_xenops.refresh_vm ~__context ~self:vm;
 
@@ -667,7 +665,7 @@ let handler req fd _ =
 			Xapi_network.with_networks_attached_for_vm ~__context ~vm (fun () ->
 				Xapi_xenops.transform_xenops_exn ~__context (fun () ->
 					debug "Sending VM %s configuration to xenopsd" (Ref.string_of vm);
-					let id = Xapi_xenops.push_metadata_to_xenopsd ~__context ~upgrade:true ~self:vm in
+					let id = Xapi_xenops.Xenopsd_metadata.push ~__context ~upgrade:true ~self:vm in
 					info "xenops: VM.receive_memory %s" id;
 					let uri = Printf.sprintf "/services/xenops/memory/%s" id in
 					let memory_limit = free_memory_required_kib |> Memory.bytes_of_kib |> Int64.to_string in