qcow-stream-tool: Use tail-recursive List.rev_map in read_headers

Otherwise we overflow the stack on large QCOW files:

    qcow-stream-tool: internal error, uncaught exception:
    Stack overflow
    Raised by primitive operation at Dune__exe__Qcow_stream_tool.Impl.read_headers.(fun) in file "ocaml/qcow-stream-tool/qcow_stream_tool.ml", line 23, characters 12-24
    Called from Stdlib__List.map in file "list.ml", line 92, characters 32-39
    Called from Stdlib__List.map in file "list.ml", line 92, characters 32-39
    ....

List.rev + List.rev_map is not terribly efficient, but more efficient than
reverting back to handling the QCOW file as raw without knowing which clusters
are allocated.

Signed-off-by: Andrii Sultanov <[email protected]>

Author: last-genius

ocaml/qcow-stream-tool/qcow_stream_tool.ml

@@ -14,15 +14,17 @@ module Impl = struct
       in
       let clusters = Qcow_types.Cluster.Map.bindings data_cluster_map in
       let clusters =
-        List.map
-          (fun (_, virt_address) ->
-            let ( >> ) = Int64.shift_right_logical in
-            let address =
-              Int64.to_int (virt_address >> Int32.to_int cluster_bits)
-            in
-            `Int address
+        List.rev
+          (List.rev_map
+             (fun (_, virt_address) ->
+               let ( >> ) = Int64.shift_right_logical in
+               let address =
+                 Int64.to_int (virt_address >> Int32.to_int cluster_bits)
+               in
+               `Int address
+             )
+             clusters
           )
-          clusters
       in
       let json =
         `Assoc