MdeModulePkg/BdsDxe: fall back to a Boot Manager Menu loop before hanging

Under the following scenario:

- no UEFI bootable application available anywhere in the system,
- ... not even for the default platform recovery option,
- no shell is built into the firmware image,
- but UiApp is available in the firmware image,

we should preferably not just hang in BdsEntry() with:

   DEBUG ((EFI_D_ERROR, "[Bds] Unable to boot!\n"));
   CpuDeadLoop ();

while the user sits at the TianoCore logo page, wondering what's going on.
Print an informative message to the console, wait for a keypress, and then
return to the Boot Manager Menu forever.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1515418
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=513
Suggested-by: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>

MdeModulePkg/Universal/BdsDxe/BdsEntry.c

@@ -685,6 +685,55 @@ BdsAllocateMemoryForPerformanceData (
   }
 }
 
+/**
+  Enter an infinite loop of calling the Boot Manager Menu.
+
+  This is a last resort alternative to BdsEntry() giving up for good. This
+  function never returns.
+
+  @param[in] BootManagerMenu  The EFI_BOOT_MANAGER_LOAD_OPTION located and/or
+                              created by the EfiBootManagerGetBootManagerMenu()
+                              call in BdsEntry().
+**/
+VOID
+BdsBootManagerMenuLoop (
+  IN EFI_BOOT_MANAGER_LOAD_OPTION *BootManagerMenu
+  )
+{
+  EFI_INPUT_KEY Key;
+
+  //
+  // Normally BdsDxe does not print anything to the system console, but this is
+  // a last resort -- the end-user will likely not see any DEBUG messages
+  // logged in this situation.
+  //
+  // AsciiPrint() will NULL-check gST->ConOut internally. We check gST->ConIn
+  // here to see if it makes sense to request and wait for a keypress.
+  //
+  if (gST->ConIn != NULL) {
+    AsciiPrint (
+      "%a: No bootable option or device was found.\n"
+      "%a: Press any key to enter the Boot Manager Menu.\n",
+      gEfiCallerBaseName,
+      gEfiCallerBaseName
+      );
+    BdsWaitForSingleEvent (gST->ConIn->WaitForKey, 0);
+
+    //
+    // Drain any queued keys.
+    //
+    while (!EFI_ERROR (gST->ConIn->ReadKeyStroke (gST->ConIn, &Key))) {
+      //
+      // just throw away Key
+      //
+    }
+  }
+
+  for (;;) {
+    EfiBootManagerBoot (BootManagerMenu);
+  }
+}
+
 /**
 
   Service routine for BdsInstance->Entry(). Devices are connected, the
@@ -1088,16 +1137,19 @@ BdsEntry (
     } while (BootSuccess);
   }
 
-  if (BootManagerMenuStatus != EFI_NOT_FOUND) {
-    EfiBootManagerFreeLoadOption (&BootManagerMenu);
-  }
-
   if (!BootSuccess) {
     LoadOptions = EfiBootManagerGetLoadOptions (&LoadOptionCount, LoadOptionTypePlatformRecovery);
     ProcessLoadOptions (LoadOptions, LoadOptionCount);
     EfiBootManagerFreeLoadOptions (LoadOptions, LoadOptionCount);
   }
 
+  //
+  // If BootManagerMenu is available, fall back to it indefinitely.
+  //
+  if (BootManagerMenuStatus != EFI_NOT_FOUND) {
+    BdsBootManagerMenuLoop (&BootManagerMenu);
+  }
+
   DEBUG ((EFI_D_ERROR, "[Bds] Unable to boot!\n"));
   CpuDeadLoop ();
 }