[Libguestfs] [PATCH 2/2] v2v: remove the 'graphicsmodedisabled' entry in ESP BCD

[Pavel Butsykin]

Guest tools for Windows in Parallels / Virtuozzo Server 6 contain a
paravirtualized video driver, which wants to take full control of the video
mode. To avoid excessive video mode switches in UEFI VMs it executes
"bcdedit /set {current} graphicsmodedisabled true".

When such a VM is imported into a QEMU/KVM-based hypervisor, the
standard video drivers in Windows do not set the video mode as they
expect it to have already been configured by the bootloader.  As a result,
the VM runs with black screen.

So patch the BCD store (which is a Windows registry hive with a special
structure, located on the EFI system partition) to clear this setting.

Signed-off-by: Pavel Butsykin <pbutsykin at virtuozzo.com>
---
 v2v/convert_windows.ml | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/v2v/convert_windows.ml b/v2v/convert_windows.ml
index 62bb536..8579240 100644
--- a/v2v/convert_windows.ml
+++ b/v2v/convert_windows.ml
@@ -466,6 +466,45 @@ if errorlevel 3010 exit /b 0
         ignore (g#pwrite_device rootpart bytes 0x1a_L)
       )
     )
+
+  and fix_win_esp () =
+    let fix_win_uefi_bcd esp_path =
+      try
+        let bcd_path = "/EFI/Microsoft/Boot/BCD" in
+        Windows.with_hive_write g (esp_path ^ bcd_path) (
+          (* Remove the 'graphicsmodedisabled' key in BCD *)
+          fun root ->
+          let path = ["Objects"; "{9dea862c-5cdd-4e70-acc1-f32b344d4795}";
+                      "Elements"; "23000003"] in
+          let boot_mgr_default_link =
+            match Windows.get_node g root path with
+            | None -> raise Not_found
+            | Some node -> node in
+          let current_boot_entry = g#hivex_value_utf8 (
+            g#hivex_node_get_value boot_mgr_default_link "Element") in
+          let path = ["Objects"; current_boot_entry; "Elements"; "16000046"] in
+          match Windows.get_node g root path with
+          | None -> raise Not_found
+          | Some graphics_mode_disabled ->
+            g#hivex_node_delete_child graphics_mode_disabled
+        );
+      with
+        Not_found -> ()
+    in
+
+    let esp_temp_path = g#mkdtemp "/Windows/Temp/ESP_XXXXXX" in
+
+    match inspect.i_uefi with
+    | None -> ()
+    | Some uefi_list ->
+      List.iter (
+        fun dev_path ->
+        g#mount dev_path esp_temp_path;
+        fix_win_uefi_bcd esp_temp_path;
+        g#umount esp_temp_path;
+      ) uefi_list;
+
+    g#rmdir esp_temp_path;
   in
 
   (* Firstboot configuration. *)
@@ -480,6 +519,8 @@ if errorlevel 3010 exit /b 0
 
   fix_ntfs_heads ();
 
+  fix_win_esp ();
+
   (* Warn if installation of virtio block drivers might conflict with
    * group policy or AV software causing a boot 0x7B error (RHBZ#1260689).
    *)
-- 
2.8.3