IH-728: Refactor tracing logic

Previously a task was constructed based on the log and tracing of a dbg
of the type Debug_info.t, and then later on a dbg is constructed based
on the previously constructued task. Instead of that, just convert the
first dbg into a string and thread it through the call.

Signed-off-by: Vincent Liu <[email protected]>

ocaml/xapi/storage_migrate.ml

@@ -456,12 +456,6 @@ let add_to_sm_config vdi_info key value =
   let vdi_info = remove_from_sm_config vdi_info key in
   {vdi_info with sm_config= (key, value) :: vdi_info.sm_config}
 
-let dbg_and_tracing_of_task task =
-  Debug_info.make
-    ~log:(Storage_task.get_dbg task)
-    ~tracing:(Storage_task.tracing task)
-  |> Debug_info.to_string
-
 (** This module [MigrateLocal] consists of the concrete implementations of the 
 migration part of SMAPI. Functions inside this module are sender driven, which means
 they tend to be executed on the sender side. although there is not a hard rule
@@ -716,7 +710,7 @@ module MigrateLocal = struct
     | e ->
         raise (Storage_error (Internal_error (Printexc.to_string e)))
 
-  let start ~task ~dbg:_ ~sr ~vdi ~dp ~url ~dest ~verify_dest =
+  let start ~task ~dbg ~sr ~vdi ~dp ~url ~dest ~verify_dest =
     SXM.info "%s sr:%s vdi:%s url:%s dest:%s verify_dest:%B" __FUNCTION__
       (Storage_interface.Sr.string_of sr)
       (Storage_interface.Vdi.string_of vdi)
@@ -730,7 +724,6 @@ module MigrateLocal = struct
           (Storage_utils.connection_args_of_uri ~verify_dest url)
     end)) in
     (* Find the local VDI *)
-    let dbg = dbg_and_tracing_of_task task in
     let vdis = Local.SR.scan dbg sr in
     let local_vdi =
       try List.find (fun x -> x.vdi = vdi) vdis
@@ -1383,14 +1376,14 @@ let with_task_and_thread ~dbg f =
 
 let copy ~dbg ~sr ~vdi ~url ~dest ~verify_dest =
   with_task_and_thread ~dbg (fun task ->
-      MigrateLocal.copy_into_sr ~task ~dbg:dbg.Debug_info.log ~sr ~vdi ~url
-        ~dest ~verify_dest
+      MigrateLocal.copy_into_sr ~task ~dbg:(Debug_info.to_string dbg) ~sr ~vdi
+        ~url ~dest ~verify_dest
   )
 
 let start ~dbg ~sr ~vdi ~dp ~url ~dest ~verify_dest =
   with_task_and_thread ~dbg (fun task ->
-      MigrateLocal.start ~task ~dbg:dbg.Debug_info.log ~sr ~vdi ~dp ~url ~dest
-        ~verify_dest
+      MigrateLocal.start ~task ~dbg:(Debug_info.to_string dbg) ~sr ~vdi ~dp ~url
+        ~dest ~verify_dest
   )
 
 (* XXX: PR-1255: copy the xenopsd 'raise Exception' pattern *)