OVMF: Add support for saving the NV variables to disk following each SetVariable call.

Note:
* This only works before ExitBootServices
* For OVMF, variables are only preserved on the disk if there
  is a hard disk connected which has a writeable FAT file system.

The Ovmf/Library/EmuVariableFvbLib library will look for the
gUefiOvmfPkgTokenSpaceGuid.PcdEmuVariableEvent PCD to be set to
a non-zero value.  If set, it is treated as an event handle, and
each write to the EmuVariableFvb will cause the event to be
signaled.

In this change, the OVMF platform BDS library sets up this event,
and sets the PCD so that after each write to the EMU Variable FVB,
the non-volatile variables will be saved out to the file system.

The end result is that NV variables that are written prior to the
ExitBootServices call should be preserved by storing them on the
disk.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@9318 6f19259b-4bc3-4df7-8a09-765794883524

1 files changed, 30 insertions, 0 deletions

diff --git a/OvmfPkg/Library/NvVarsFileLib/NvVarsFileLib.c b/OvmfPkg/Library/NvVarsFileLib/NvVarsFileLib.c
index 94e00e0bdb..62fee6f031 100644
--- a/OvmfPkg/Library/NvVarsFileLib/NvVarsFileLib.c
+++ b/OvmfPkg/Library/NvVarsFileLib/NvVarsFileLib.c
@@ -16,6 +16,8 @@
 #include <Library/DebugLib.h>
 #include <Library/NvVarsFileLib.h>
 
+EFI_HANDLE    mNvVarsFileLibFsHandle = NULL;
+
 
 /**
   Attempts to connect the NvVarsFileLib to the specified file system.
@@ -46,8 +48,36 @@ ConnectNvVarsToFileSystem (
   // to have connected successfully.
   //
   Status = SaveNvVarsToFs (FsHandle);
+  if (!EFI_ERROR (Status)) {
+    mNvVarsFileLibFsHandle = FsHandle;
+  }
 
   return Status;
 }
 
 
+/**
+  Update non-volatile variables stored on the file system.
+
+  @return     The EFI_STATUS while attempting to update the variable on
+              the connected file system.
+  @retval     EFI_SUCCESS - The non-volatile variables were saved to the disk
+  @retval     EFI_NOT_STARTED - A file system has not been connected
+
+**/
+EFI_STATUS
+EFIAPI
+UpdateNvVarsOnFileSystem (
+  )
+{
+  if (mNvVarsFileLibFsHandle == NULL) {
+    //
+    // A file system had not been connected to the library.
+    //
+    return EFI_NOT_STARTED;
+  } else {
+    return SaveNvVarsToFs (mNvVarsFileLibFsHandle);
+  }
+}
+
+