daemon/inspect_fs_windows.ml: Add debugging for MBR drive mappings

The function 'map_registry_disk_blob_gpt' immediately below this one
has a debugging statement.  Add the equivalent to the function
'map_registry_disk_blob_mbr'.

The output looks like:

  map_registry_disk_blob_mbr: searching for MBR disk ID 31 32 33 34
  map_registry_disk_blob_mbr: searching for MBR partition offset 00 00 00 10 00 00 00 00

daemon/inspect_fs_windows.ml

@@ -376,6 +376,10 @@ and map_registry_disk_blob_mbr devices blob =
      * disk with this disk ID.
      *)
     let diskid = String.sub blob 0 4 in
+    if verbose () then
+      eprintf "map_registry_disk_blob_mbr: searching for MBR disk ID %s\n%!"
+        (hex_of_string diskid);
+
     let device =
       List.find (
         fun dev ->
@@ -388,6 +392,10 @@ and map_registry_disk_blob_mbr devices blob =
      * partition byte offset from Parted.part_list.
      *)
     let offset = String.sub blob 4 8 in
+    if verbose () then
+      eprintf "map_registry_disk_blob_mbr: searching for MBR partition offset \
+               %s\n%!"
+        (hex_of_string offset);
     let offset = int_of_le64 offset in
     let partitions = Parted.part_list device in
     let partition =

daemon/utils.ml

@@ -291,3 +291,7 @@ let parse_key_value_strings ?unquote lines =
   match unquote with
   | None -> lines
   | Some f -> List.map (fun (k, v) -> (k, f v)) lines
+
+let hex_of_string s =
+  let bytes = String.map_chars (fun c -> sprintf "%02x" (Char.code c)) s in
+  String.concat " " bytes

daemon/utils.mli

@@ -121,5 +121,9 @@ val parse_key_value_strings : ?unquote:(string -> string) -> string list -> (str
     it is applied on the values as unquote function.  Empty lines,
     or that start with a comment character [#], are ignored. *)
 
+val hex_of_string : string -> string
+(** Return a string as a list of hex bytes.
+    Use this for debugging msgs only. *)
+
 (**/**)
 val get_verbose_flag : unit -> bool