CP-45016: Implement a new nbd proxy handler

The new http handler nbd_proxy accepts a connection from an nbd client,
and acts as a proxy between the client and the nbd server of the
underlying storage backend, as returned by get_nbd_server.

This proxy is used in place of the old style of fd passing to tapdisks
for VDI copying during storage migration, since the new nbd server from
qemu-dp does not support accepting fds.

This might also be used in the future for outbound storage migration for
mirroring.

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

ocaml/xapi/storage_migrate.ml

@@ -529,15 +529,15 @@ module MigrateLocal = struct
       let dest_vdi_url =
         let url' = Http.Url.of_string url in
         Http.Url.set_uri url'
-          (Printf.sprintf "%s/nbd/%s/%s/%s/%s" (Http.Url.get_uri url')
+          (Printf.sprintf "%s/nbdproxy/%s/%s/%s/%s" (Http.Url.get_uri url')
              (Storage_interface.Vm.string_of vm)
              (Storage_interface.Sr.string_of dest)
              (Storage_interface.Vdi.string_of dest_vdi)
              remote_dp
           )
         |> Http.Url.to_string
       in
-      debug "copy remote NBD URL = %s" dest_vdi_url ;
+      debug "%s copy remote NBD URL = %s" __FUNCTION__ dest_vdi_url ;
       let id = State.copy_id_of (sr, vdi) in
       debug "Persisting state for copy (id=%s)" id ;
       State.add id
@@ -762,7 +762,7 @@ module MigrateLocal = struct
         ; watchdog= None
         }
     in
- 
+
     State.add mirror_id (State.Send_op alm) ;
     debug "%s Added mirror %s to active local mirrors" __FUNCTION__ mirror_id ;
     (* A list of cleanup actions to perform if the operation should fail. *)
@@ -1383,6 +1383,30 @@ let nbd_handler req s ?(vm = "0") sr vdi dp =
     )
     (fun () -> Unix.close control_fd)
 
+(** nbd_proxy is a http handler but will turn the http connection into an nbd connection.
+It proxies the connection between the sender and the generic nbd server, as returned
+by [get_nbd_server dp sr vdi vm]. *)
+let nbd_proxy req s vm sr vdi dp =
+  debug "%s: vm=%s sr=%s vdi=%s dp=%s" __FUNCTION__ vm sr vdi dp ;
+  let sr, vdi = Storage_interface.(Sr.of_string sr, Vdi.of_string vdi) in
+  req.Http.Request.close <- true ;
+  let vm = Vm.of_string vm in
+  let path =
+    Storage_utils.transform_storage_exn (fun () ->
+        Local.DATA.MIRROR.get_nbd_server "nbd" dp sr vdi vm
+    )
+  in
+  debug "%s got nbd server path %s" __FUNCTION__ path ;
+  Http_svr.headers s (Http.http_200_ok () @ ["Transfer-encoding: nbd"]) ;
+  let control_fd = Unix.socket Unix.PF_UNIX Unix.SOCK_STREAM 0 in
+  finally
+    (fun () ->
+      Unix.connect control_fd (Unix.ADDR_UNIX path) ;
+      debug "%s about to proxy between two fd" __FUNCTION__ ;
+      Unixext.proxy s control_fd
+    )
+    (fun () -> Unix.close control_fd)
+
 let with_task_and_thread ~dbg f =
   let task =
     Storage_task.add tasks dbg.Debug_info.log (fun task ->

ocaml/xapi/xapi_services.ml

@@ -206,6 +206,9 @@ let put_handler (req : Http.Request.t) s _ =
       | [""; services; "SM"; "nbd"; vm; sr; vdi; dp] when services = _services
         ->
           Storage_migrate.nbd_handler req s ~vm sr vdi dp
+      | [""; services; "SM"; "nbdproxy"; vm; sr; vdi; dp]
+        when services = _services ->
+          Storage_migrate.nbd_proxy req s vm sr vdi dp
       | _ ->
           Http_svr.headers s (Http.http_404_missing ~version:"1.0" ()) ;
           req.Http.Request.close <- true