[PATCH v2] xen/efi: Use blexit() instead of BUG_ON() in read_file()

[Szymon Acedański <accek@xxxxxxxxxxxxxxxxxxxxxx>]

Follow-up to 880e40b187aa, which added a BUG_ON() guard in read_file().

But as Jan pointed out, before ExitBootServices BUG_ON()
is not functional. It results in a hang with no message.

On the other hand blexit() prints a message and returns back
to the bootloader.

Fixes: 880e40b187aa ("xen/efi: Fix boot from a device without a file system")
Reported-by: Jan Beulich <jbeulich@xxxxxxxx>
Signed-off-by: Szymon Acedański <accek@xxxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Changes in v2:
- Drop the Link: tag; use Reported-by: and Fixes: instead. (Jan)

blexit() has been chosen over PrintErrMesg(), as the latter
is predominantly used in cases where an EFI call fails
(and it prints the status).

 xen/common/efi/boot.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
index 2971ea8696d1..8f24df9bc23a 100644
--- a/xen/common/efi/boot.c
+++ b/xen/common/efi/boot.c
@@ -849,7 +849,8 @@ static bool __init read_file(EFI_FILE_HANDLE dir_handle, 
CHAR16 *name,
     if ( !name )
         PrintErrMesg(L"No filename", EFI_OUT_OF_RESOURCES);
 
-    BUG_ON(!dir_handle);
+    if ( !dir_handle )
+        blexit(L"BUG: !dir_handle in read_file()");
 
     what = L"Open";
     ret = dir_handle->Open(dir_handle, &FileHandle, name,
-- 
2.53.0