Merge pull request #93 from xapi-project/more-tunnelling

Vgs: a more accurate lv_count

Author: djs55

test/test.ml

@@ -36,8 +36,20 @@ let vgcreate =
     Lwt_main.run t 
   )
 
+let vgs_offline =
+  "vgs <device>: check that we can read metadata without xenvmd." >::
+  (fun () ->
+    with_temp_file (fun filename ->
+      xenvm [ "vgcreate"; vg; filename ] |> ignore_string;
+      mkdir_rec "/etc/xenvm.d" 0o0644;
+      xenvm [ "set-vg-info"; "--pvpath"; filename; "-S"; "/tmp/xenvmd"; vg; "--local-allocator-path"; "/tmp/xenvm-local-allocator"; "--uri"; "file://local/services/xenvmd/"^vg ] |> ignore_string;
+      xenvm [ "vgs"; vg ] |> ignore_string
+    )
+  )
+
 let no_xenvmd_suite = "Commands which should work without xenvmd" >::: [
   vgcreate;
+  vgs_offline;
 ]
 
 let assert_lv_exists ?expected_size_in_extents name =
@@ -115,11 +127,31 @@ let lvchange_n =
   assert_equal ~printer:string_of_bool false (dm_exists name);
   xenvm [ "lvremove"; vg ^ "/test" ] |> ignore_string
 
+let parse_int x =
+  int_of_string (String.trim x)
+
+let vgs_online =
+  "vgs <device>: check that we can read fresh metadata with xenvmd." >::
+  (fun () ->
+    let metadata = Lwt_main.run (Client.get ()) in
+    let count = xenvm [ "vgs"; "/dev/" ^ vg; "--noheadings"; "-o"; "lv_count" ] |> parse_int in
+    let expected = Lvm.Vg.LVs.cardinal metadata.Lvm.Vg.lvs in
+    assert_equal ~printer:string_of_int expected count;
+    (* The new LV will be cached: *)
+    xenvm [ "lvcreate"; "-n"; "test"; "-L"; "3"; vg ] |> ignore_string;
+    (* This should use the network, not the on-disk metadata: *)
+    let count = xenvm [ "vgs"; "/dev/" ^ vg; "--noheadings"; "-o"; "lv_count" ] |> parse_int in
+    (* Did we see the new volume? *)
+    assert_equal ~printer:string_of_int (expected+1) count;
+    xenvm [ "lvremove"; vg ^ "/test" ] |> ignore_string
+  )
+
 let xenvmd_suite = "Commands which require xenvmd" >::: [
   lvcreate_L;
   lvcreate_l;
   lvcreate_percent;
   lvchange_n;
+  vgs_online;
 ]
 
 let _ =

xenvm/vgs.ml

@@ -41,20 +41,28 @@ let vgs copts noheadings nosuffix units fields vg_names =
         let local_device = match info with
         | Some info -> info.local_device (* If we've got a default, use that *)
         | None -> failwith "Need to know the local device!" in
-        Lwt.catch
-          (fun () ->
-            with_block local_device
-              (fun x ->
-                Vg_IO.connect [ x ] `RO >>|= fun vg ->
-                return (Vg_IO.metadata_of vg) 
+        (* First try a network connection to get the most up to date information.
+           We currently don't replay the redo log when opening the VG read/only--
+           see [mirage/mirage-block-volume#68]. *)
+        Lwt.catch Client.get
+          (fun e ->
+            stderr "WARNING: failed to contact xenvmd; falling back to reading the disk metadata"
+            >>= fun () ->
+            Lwt.catch
+              (fun () ->
+                with_block local_device
+                  (fun x ->
+                   Vg_IO.connect [ x ] `RO >>|= fun vg ->
+                    return (Vg_IO.metadata_of vg) 
+                  )
               )
+              (fun _ ->
+                stderr "  Volume group \"%s\" not found" vg_name
+                >>= fun () ->
+                stderr "  Skipping volume group %s" vg_name
+                >>= fun () ->
+                exit 1)
           )
-          (fun _ ->
-            stderr "  Volume group \"%s\" not found" vg_name
-            >>= fun () ->
-            stderr "  Skipping volume group %s" vg_name
-            >>= fun () ->
-            exit 1)
         >>= fun vg ->
       Lwt.return (info,vg)) vg_names >>= fun vgs ->
     let rows = List.concat (List.map do_row vgs) in