IH-728: Refactor SXM code, Pt1 (#6084)

The Storage migration code is too messy to be maintainable, making the
developing experience quite bad. This is the first attempt to make it
less spaghetti.

I am intending to do this in several stages. This PR is just for those
that are mostly "safe" operations that can probably be checked
statically by the compiler. More risky changes on the way...

Best reviewed by commit.

ocaml/xapi-idl/storage/storage_interface.ml

@@ -976,28 +976,12 @@ module StorageAPI (R : RPC) = struct
         ~description:["when true, verify remote server certificate"]
         Types.bool
 
-    (** [copy_into task sr vdi url sr2] copies the data from [vdi] into a remote
-        system [url]'s [sr2] *)
-    let copy_into =
-      let dest_vdi_p = Param.mk ~name:"dest_vdi" Vdi.t in
-      declare "DATA.copy_into" []
-        (dbg_p
-        @-> sr_p
-        @-> vdi_p
-        @-> url_p
-        @-> dest_p
-        @-> dest_vdi_p
-        @-> verify_dest_p
-        @-> returning task_id_p err
-        )
-
     let copy =
       let result_p = Param.mk ~name:"task_id" Task.id in
       declare "DATA.copy" []
         (dbg_p
         @-> sr_p
         @-> vdi_p
-        @-> dp_p
         @-> url_p
         @-> dest_p
         @-> verify_dest_p
@@ -1344,23 +1328,11 @@ module type Server_impl = sig
   val get_by_name : context -> dbg:debug_info -> name:string -> sr * vdi_info
 
   module DATA : sig
-    val copy_into :
-         context
-      -> dbg:debug_info
-      -> sr:sr
-      -> vdi:vdi
-      -> url:string
-      -> dest:sr
-      -> dest_vdi:vdi
-      -> verify_dest:bool
-      -> Task.id
-
     val copy :
          context
       -> dbg:debug_info
       -> sr:sr
       -> vdi:vdi
-      -> dp:dp
       -> url:string
       -> dest:sr
       -> verify_dest:bool
@@ -1549,11 +1521,8 @@ module Server (Impl : Server_impl) () = struct
         Impl.VDI.list_changed_blocks () ~dbg ~sr ~vdi_from ~vdi_to
     ) ;
     S.get_by_name (fun dbg name -> Impl.get_by_name () ~dbg ~name) ;
-    S.DATA.copy_into (fun dbg sr vdi url dest dest_vdi verify_dest ->
-        Impl.DATA.copy_into () ~dbg ~sr ~vdi ~url ~dest ~dest_vdi ~verify_dest
-    ) ;
-    S.DATA.copy (fun dbg sr vdi dp url dest verify_dest ->
-        Impl.DATA.copy () ~dbg ~sr ~vdi ~dp ~url ~dest ~verify_dest
+    S.DATA.copy (fun dbg sr vdi url dest verify_dest ->
+        Impl.DATA.copy () ~dbg ~sr ~vdi ~url ~dest ~verify_dest
     ) ;
     S.DATA.MIRROR.start (fun dbg sr vdi dp url dest verify_dest ->
         Impl.DATA.MIRROR.start () ~dbg ~sr ~vdi ~dp ~url ~dest ~verify_dest

ocaml/xapi-idl/storage/storage_skeleton.ml

@@ -152,9 +152,7 @@ end
 let get_by_name ctx ~dbg ~name = u "get_by_name"
 
 module DATA = struct
-  let copy_into ctx ~dbg ~sr ~vdi ~url ~dest ~dest_vdi = u "DATA.copy_into"
-
-  let copy ctx ~dbg ~sr ~vdi ~dp ~url ~dest = u "DATA.copy"
+  let copy ctx ~dbg ~sr ~vdi ~url ~dest = u "DATA.copy"
 
   module MIRROR = struct
     (** [start task sr vdi url sr2] creates a VDI in remote [url]'s [sr2] and

ocaml/xapi-storage-script/main.ml

@@ -1739,7 +1739,6 @@ let bind ~volume_script_dir =
   S.VDI.get_url (u "VDI.get_url") ;
   S.DATA.MIRROR.start (u "DATA.MIRROR.start") ;
   S.Policy.get_backend_vm (u "Policy.get_backend_vm") ;
-  S.DATA.copy_into (u "DATA.copy_into") ;
   S.DATA.MIRROR.receive_cancel (u "DATA.MIRROR.receive_cancel") ;
   S.SR.update_snapshot_info_src (u "SR.update_snapshot_info_src") ;
   S.DATA.MIRROR.stop (u "DATA.MIRROR.stop") ;