OvmfPkg: PlatformDxe: utility functions for saving / loading configuration

The two functions introduced here allow the saving and loading of platform
configuration to/from the non-volatile variable store.

The PLATFORM_CONFIG structure and the two functions that take it / return
it are generally meant for any DXE or UEFI driver that needs to access
platform configuration. For now we keep this small "library" internal to
PlatformDxe.

The PLATFORM_CONFIG wire format is intended only to grow over time (as
long as the variable GUID remains unchanged). At the introduction of new
fields, new feature flags must be added, and recognized in
PlatformConfigLoad().

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15365 6f19259b-4bc3-4df7-8a09-765794883524

OvmfPkg/PlatformDxe/Platform.inf

@@ -26,6 +26,7 @@
 
 [Sources]
   Platform.c
+  PlatformConfig.c
 
 [Packages]
   MdePkg/MdePkg.dec
@@ -33,9 +34,17 @@
   OvmfPkg/OvmfPkg.dec
 
 [LibraryClasses]
+  BaseMemoryLib
   DebugLib
+  MemoryAllocationLib
   UefiBootServicesTableLib
+  UefiLib
+  UefiRuntimeServicesTableLib
   UefiDriverEntryPoint
 
+[Guids]
+  gOvmfPlatformConfigGuid
+
 [Depex]
-  TRUE
+  gEfiVariableArchProtocolGuid      AND
+  gEfiVariableWriteArchProtocolGuid

OvmfPkg/PlatformDxe/PlatformConfig.c

@@ -0,0 +1,131 @@
+/** @file
+
+  Utility functions for serializing (persistently storing) and deserializing
+  OVMF's platform configuration.
+
+  Copyright (C) 2014, Red Hat, Inc.
+
+  This program and the accompanying materials are licensed and made available
+  under the terms and conditions of the BSD License which accompanies this
+  distribution. The full text of the license may be found at
+  http://opensource.org/licenses/bsd-license.php
+
+  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
+  WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+
+#include <Library/BaseMemoryLib.h>
+#include <Library/DebugLib.h>
+#include <Library/MemoryAllocationLib.h>
+#include <Library/UefiLib.h>
+#include <Library/UefiRuntimeServicesTableLib.h>
+#include <Guid/OvmfPlatformConfig.h>
+
+#include "PlatformConfig.h"
+
+//
+// Name of the UEFI variable that we use for persistent storage.
+//
+STATIC CHAR16 mVariableName[] = L"PlatformConfig";
+
+
+/**
+  Serialize and persistently save platform configuration.
+
+  @param[in] PlatformConfig  The platform configuration to serialize and save.
+
+  @return  Status codes returned by gRT->SetVariable().
+**/
+EFI_STATUS
+EFIAPI
+PlatformConfigSave (
+  IN PLATFORM_CONFIG *PlatformConfig
+  )
+{
+  EFI_STATUS Status;
+
+  //
+  // We could implement any kind of translation here, as part of serialization.
+  // For example, we could expose the platform configuration in separate
+  // variables with human-readable contents, allowing other tools to access
+  // them more easily. For now, just save a binary dump.
+  //
+  Status = gRT->SetVariable (mVariableName, &gOvmfPlatformConfigGuid,
+                  EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS |
+                    EFI_VARIABLE_RUNTIME_ACCESS,
+                  sizeof *PlatformConfig, PlatformConfig);
+  return Status;
+}
+
+
+/**
+  Load and deserialize platform configuration.
+
+  When the function fails, output parameters are indeterminate.
+
+  @param[out] PlatformConfig    The platform configuration to receive the
+                                loaded data.
+
+  @param[out] OptionalElements  This bitmap describes the presence of optional
+                                configuration elements that have been loaded.
+                                PLATFORM_CONFIG_F_DOWNGRADE means that some
+                                unknown elements, present in the wire format,
+                                have been ignored.
+
+  @retval  EFI_SUCCESS         Loading & deserialization successful.
+  @return                      Error codes returned by GetVariable2().
+**/
+EFI_STATUS
+EFIAPI
+PlatformConfigLoad (
+  OUT PLATFORM_CONFIG *PlatformConfig,
+  OUT UINT64          *OptionalElements
+  )
+{
+  VOID       *Data;
+  UINTN      DataSize;
+  EFI_STATUS Status;
+
+  //
+  // Any translation done in PlatformConfigSave() would have to be mirrored
+  // here. For now, just load the binary dump.
+  //
+  // Versioning of the binary wire format is implemented based on size
+  // (only incremental changes, ie. new fields), and on GUID.
+  // (Incompatible changes require a GUID change.)
+  //
+  Status = GetVariable2 (mVariableName, &gOvmfPlatformConfigGuid, &Data,
+             &DataSize);
+  if (EFI_ERROR (Status)) {
+    return Status;
+  }
+
+  *OptionalElements = 0;
+  if (DataSize > sizeof *PlatformConfig) {
+    //
+    // Handle firmware downgrade -- keep only leading part.
+    //
+    CopyMem (PlatformConfig, Data, sizeof *PlatformConfig);
+    *OptionalElements |= PLATFORM_CONFIG_F_DOWNGRADE;
+  } else {
+    CopyMem (PlatformConfig, Data, DataSize);
+
+    //
+    // Handle firmware upgrade -- zero out missing fields.
+    //
+    ZeroMem ((UINT8 *)PlatformConfig + DataSize,
+      sizeof *PlatformConfig - DataSize);
+  }
+
+  //
+  // Based on DataSize, report the optional features that we recognize.
+  //
+  if (DataSize >= (OFFSET_OF (PLATFORM_CONFIG, VerticalResolution) +
+                   sizeof PlatformConfig->VerticalResolution)) {
+    *OptionalElements |= PLATFORM_CONFIG_F_GRAPHICS_RESOLUTION;
+  }
+
+  FreePool (Data);
+  return EFI_SUCCESS;
+}

OvmfPkg/PlatformDxe/PlatformConfig.h

@@ -0,0 +1,59 @@
+/** @file
+
+  Utility functions for serializing (persistently storing) and deserializing
+  OVMF's platform configuration.
+
+  Copyright (C) 2014, Red Hat, Inc.
+
+  This program and the accompanying materials are licensed and made available
+  under the terms and conditions of the BSD License which accompanies this
+  distribution. The full text of the license may be found at
+  http://opensource.org/licenses/bsd-license.php
+
+  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
+  WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+
+#ifndef _PLATFORM_CONFIG_H_
+#define _PLATFORM_CONFIG_H_
+
+#include <Base.h>
+
+//
+// This structure participates in driver configuration. It does not
+// (necessarily) reflect the wire format in the persistent store.
+//
+#pragma pack(1)
+typedef struct {
+  //
+  // preferred graphics console resolution when booting
+  //
+  UINT32 HorizontalResolution;
+  UINT32 VerticalResolution;
+} PLATFORM_CONFIG;
+#pragma pack()
+
+//
+// Please see the API documentation near the function definitions.
+//
+EFI_STATUS
+EFIAPI
+PlatformConfigSave (
+  IN PLATFORM_CONFIG *PlatformConfig
+  );
+
+EFI_STATUS
+EFIAPI
+PlatformConfigLoad (
+  OUT PLATFORM_CONFIG *PlatformConfig,
+  OUT UINT64          *OptionalElements
+  );
+
+//
+// Feature flags for OptionalElements.
+//
+#define PLATFORM_CONFIG_F_GRAPHICS_RESOLUTION BIT0
+#define PLATFORM_CONFIG_F_DOWNGRADE           BIT63
+
+#endif // _PLATFORM_CONFIG_H_