OvmfPkg: Add QemuFwCfgLibNull

Add a null implementation library for QemuFwCfgLib, in order to
support building PciHostBridgeLib for bhyve.

Signed-off-by: Rebecca Cran <rebecca@bsdio.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200503230910.26783-1-rebecca@bsdio.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLibNull.inf

@@ -0,0 +1,30 @@
+## @file
+#
+#  Null implementation of the fw_cfg library.
+#
+#  Copyright (C) 2020, Rebecca Cran <rebecca@bsdio.com>
+#  Copyright (C) 2013, Red Hat, Inc.
+#  Copyright (c) 2008 - 2012, Intel Corporation. All rights reserved.<BR>
+#  Copyright (c) 2017, AMD Incorporated. All rights reserved.<BR>
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x00010005
+  BASE_NAME                      = QemuFwCfgLibNull
+  FILE_GUID                      = B9D1A1F2-01E2-4732-982D-C7F9ED51AC6B
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = QemuFwCfgLib
+
+[Sources]
+  QemuFwCfgNull.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+  OvmfPkg/OvmfPkg.dec
+
+[LibraryClasses]
+  DebugLib

OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgNull.c

@@ -0,0 +1,209 @@
+/** @file
+
+  Null implementation of the fw_cfg library.
+
+  Copyright (C) 2020, Rebecca Cran <rebecca@bsdio.com>
+  Copyright (C) 2013, Red Hat, Inc.
+  Copyright (c) 2011 - 2013, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2017, Advanced Micro Devices. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#include <Library/DebugLib.h>
+#include <Library/QemuFwCfgLib.h>
+
+/**
+  Returns a boolean indicating if the firmware configuration interface
+  is available or not.
+
+  This function may change fw_cfg state.
+
+  @retval    TRUE   The interface is available
+  @retval    FALSE  The interface is not available
+
+**/
+BOOLEAN
+EFIAPI
+QemuFwCfgIsAvailable (
+  VOID
+  )
+{
+  return FALSE;
+}
+
+
+/**
+  Selects a firmware configuration item for reading.
+
+  Following this call, any data read from this item will start from
+  the beginning of the configuration item's data.
+
+  @param[in] QemuFwCfgItem - Firmware Configuration item to read
+
+**/
+VOID
+EFIAPI
+QemuFwCfgSelectItem (
+  IN FIRMWARE_CONFIG_ITEM   QemuFwCfgItem
+  )
+{
+  ASSERT (FALSE);
+}
+
+
+/**
+  Reads firmware configuration bytes into a buffer
+
+  If called multiple times, then the data read will
+  continue at the offset of the firmware configuration
+  item where the previous read ended.
+
+  @param[in] Size - Size in bytes to read
+  @param[in] Buffer - Buffer to store data into
+
+**/
+VOID
+EFIAPI
+QemuFwCfgReadBytes (
+  IN UINTN                  Size,
+  IN VOID                   *Buffer  OPTIONAL
+  )
+{
+  ASSERT (FALSE);
+}
+
+
+/**
+  Writes firmware configuration bytes from a buffer
+
+  If called multiple times, then the data written will
+  continue at the offset of the firmware configuration
+  item where the previous write ended.
+
+  @param[in] Size - Size in bytes to write
+  @param[in] Buffer - Buffer to read data from
+
+**/
+VOID
+EFIAPI
+QemuFwCfgWriteBytes (
+  IN UINTN                  Size,
+  IN VOID                   *Buffer
+  )
+{
+  ASSERT (FALSE);
+}
+
+
+/**
+  Skip bytes in the firmware configuration item.
+
+  Increase the offset of the firmware configuration item without transferring
+  bytes between the item and a caller-provided buffer. Subsequent read, write
+  or skip operations will commence at the increased offset.
+
+  @param[in] Size  Number of bytes to skip.
+**/
+VOID
+EFIAPI
+QemuFwCfgSkipBytes (
+  IN UINTN                  Size
+  )
+{
+  ASSERT (FALSE);
+}
+
+
+/**
+  Reads a UINT8 firmware configuration value
+
+  @return    Value of Firmware Configuration item read
+
+**/
+UINT8
+EFIAPI
+QemuFwCfgRead8 (
+  VOID
+  )
+{
+  ASSERT (FALSE);
+  return 0;
+}
+
+
+/**
+  Reads a UINT16 firmware configuration value
+
+  @return    Value of Firmware Configuration item read
+
+**/
+UINT16
+EFIAPI
+QemuFwCfgRead16 (
+  VOID
+  )
+{
+  ASSERT (FALSE);
+  return 0;
+}
+
+
+/**
+  Reads a UINT32 firmware configuration value
+
+  @return    Value of Firmware Configuration item read
+
+**/
+UINT32
+EFIAPI
+QemuFwCfgRead32 (
+  VOID
+  )
+{
+  ASSERT (FALSE);
+  return 0;
+}
+
+
+/**
+  Reads a UINT64 firmware configuration value
+
+  @return    Value of Firmware Configuration item read
+
+**/
+UINT64
+EFIAPI
+QemuFwCfgRead64 (
+  VOID
+  )
+{
+  ASSERT (FALSE);
+  return 0;
+}
+
+
+/**
+  Find the configuration item corresponding to the firmware configuration file.
+
+  @param[in]  Name - Name of file to look up.
+  @param[out] Item - Configuration item corresponding to the file, to be passed
+                     to QemuFwCfgSelectItem ().
+  @param[out] Size - Number of bytes in the file.
+
+  @return    RETURN_SUCCESS       If file is found.
+             RETURN_NOT_FOUND     If file is not found.
+             RETURN_UNSUPPORTED   If firmware configuration is unavailable.
+
+**/
+RETURN_STATUS
+EFIAPI
+QemuFwCfgFindFile (
+  IN   CONST CHAR8           *Name,
+  OUT  FIRMWARE_CONFIG_ITEM  *Item,
+  OUT  UINTN                 *Size
+  )
+{
+  return RETURN_UNSUPPORTED;
+}
+