system76-edk2/MdeModulePkg/Core/Dxe/FwVol/FwVol.c

/** @file
  Firmware File System driver that produce Firmware Volume protocol.
  Layers on top of Firmware Block protocol to produce a file abstraction
  of FV based files.

Copyright (c) 2006 - 2014, Intel Corporation. All rights reserved.<BR>
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 "DxeMain.h"
#include "FwVolDriver.h"


//
// Protocol notify related globals
//
VOID          *gEfiFwVolBlockNotifyReg;
EFI_EVENT     gEfiFwVolBlockEvent;

FV_DEVICE mFvDevice = {
  FV2_DEVICE_SIGNATURE,
  NULL,
  NULL,
  {
    FvGetVolumeAttributes,
    FvSetVolumeAttributes,
    FvReadFile,
    FvReadFileSection,
    FvWriteFile,
    FvGetNextFile,   
	sizeof (UINTN),
    NULL,
    FvGetVolumeInfo,
    FvSetVolumeInfo
  },
  NULL,
  NULL,
  NULL,
  NULL,
  { NULL, NULL },
  0,
  0,
  FALSE,
  FALSE
};


//
// FFS helper functions
//
/**
  Read data from Firmware Block by FVB protocol Read. 
  The data may cross the multi block ranges.

  @param  Fvb                   The FW_VOL_BLOCK_PROTOCOL instance from which to read data.
  @param  StartLba              Pointer to StartLba.
                                On input, the start logical block index from which to read.
                                On output,the end logical block index after reading.
  @param  Offset                Pointer to Offset
                                On input, offset into the block at which to begin reading.
                                On output, offset into the end block after reading.
  @param  DataSize              Size of data to be read.
  @param  Data                  Pointer to Buffer that the data will be read into.

  @retval EFI_SUCCESS           Successfully read data from firmware block.
  @retval others
**/
EFI_STATUS
ReadFvbData (
  IN     EFI_FIRMWARE_VOLUME_BLOCK_PROTOCOL     *Fvb,
  IN OUT EFI_LBA                                *StartLba,
  IN OUT UINTN                                  *Offset,
  IN     UINTN                                  DataSize,
  OUT    UINT8                                  *Data
  )
{
  UINTN                       BlockSize;
  UINTN                       NumberOfBlocks;
  UINTN                       BlockIndex;
  UINTN                       ReadDataSize;
  EFI_STATUS                  Status;
  
  //
  // Try read data in current block
  //
  BlockIndex   = 0;
  ReadDataSize = DataSize;
  Status = Fvb->Read (Fvb, *StartLba, *Offset, &ReadDataSize, Data);
  if (Status == EFI_SUCCESS) {
    *Offset  += DataSize;
    return EFI_SUCCESS;
  } else if (Status != EFI_BAD_BUFFER_SIZE) {
    //
    // other error will direct return
    //
    return Status;
  }
  
  //
  // Data crosses the blocks, read data from next block
  //
  DataSize -= ReadDataSize;
  Data     += ReadDataSize;
  *StartLba = *StartLba + 1;
  while (DataSize > 0) {
    Status = Fvb->GetBlockSize (Fvb, *StartLba, &BlockSize, &NumberOfBlocks);
    if (EFI_ERROR (Status)) {
      return Status;
    }

    //
    // Read data from the crossing blocks
    //
    BlockIndex = 0; 
    while (BlockIndex < NumberOfBlocks && DataSize >= BlockSize) {
      Status = Fvb->Read (Fvb, *StartLba + BlockIndex, 0, &BlockSize, Data);
      if (EFI_ERROR (Status)) {
        return Status;
      }
      Data += BlockSize;
      DataSize -= BlockSize;
      BlockIndex ++;
    }
    
    //
    // Data doesn't exceed the current block range.
    //
    if (DataSize < BlockSize) {
      break;
    }
    
    //
    // Data must be got from the next block range.
    //
    *StartLba += NumberOfBlocks;
  }
  
  //
  // read the remaining data
  //
  if (DataSize > 0) {
    Status = Fvb->Read (Fvb, *StartLba + BlockIndex, 0, &DataSize, Data);
    if (EFI_ERROR (Status)) {
      return Status;
    }
  }
  
  //
  // Update Lba and Offset used by the following read.
  //
  *StartLba += BlockIndex;
  *Offset   = DataSize;

  return EFI_SUCCESS;
}

/**
  Given the supplied FW_VOL_BLOCK_PROTOCOL, allocate a buffer for output and
  copy the real length volume header into it.

  @param  Fvb                   The FW_VOL_BLOCK_PROTOCOL instance from which to
                                read the volume header
  @param  FwVolHeader           Pointer to pointer to allocated buffer in which
                                the volume header is returned.

  @retval EFI_OUT_OF_RESOURCES  No enough buffer could be allocated.
  @retval EFI_SUCCESS           Successfully read volume header to the allocated
                                buffer.
  @retval EFI_INVALID_PARAMETER The FV Header signature is not as expected or
                                the file system could not be understood.

**/
EFI_STATUS
GetFwVolHeader (
  IN     EFI_FIRMWARE_VOLUME_BLOCK_PROTOCOL     *Fvb,
  OUT    EFI_FIRMWARE_VOLUME_HEADER             **FwVolHeader
  )
{
  EFI_STATUS                  Status;
  EFI_FIRMWARE_VOLUME_HEADER  TempFvh;
  UINTN                       FvhLength;
  EFI_LBA                     StartLba;
  UINTN                       Offset;
  UINT8                       *Buffer;
  
  //
  // Read the standard FV header
  //
  StartLba = 0;
  Offset   = 0;
  FvhLength = sizeof (EFI_FIRMWARE_VOLUME_HEADER);
  Status = ReadFvbData (Fvb, &StartLba, &Offset, FvhLength, (UINT8 *)&TempFvh);
  if (EFI_ERROR (Status)) {
    return Status;
  }

  //
  // Validate FV Header signature, if not as expected, continue.
  //
  if (TempFvh.Signature != EFI_FVH_SIGNATURE) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // Check to see that the file system is indeed formatted in a way we can
  // understand it...
  //
  if ((!CompareGuid (&TempFvh.FileSystemGuid, &gEfiFirmwareFileSystem2Guid)) &&
      (!CompareGuid (&TempFvh.FileSystemGuid, &gEfiFirmwareFileSystem3Guid))) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // Allocate a buffer for the caller
  //
  *FwVolHeader = AllocatePool (TempFvh.HeaderLength);
  if (*FwVolHeader == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }

  //
  // Copy the standard header into the buffer
  //
  CopyMem (*FwVolHeader, &TempFvh, sizeof (EFI_FIRMWARE_VOLUME_HEADER));

  //
  // Read the rest of the header
  //
  FvhLength = TempFvh.HeaderLength - sizeof (EFI_FIRMWARE_VOLUME_HEADER);
  Buffer = (UINT8 *)*FwVolHeader + sizeof (EFI_FIRMWARE_VOLUME_HEADER);
  Status = ReadFvbData (Fvb, &StartLba, &Offset, FvhLength, Buffer);
  if (EFI_ERROR (Status)) {
    //
    // Read failed so free buffer
    //
    CoreFreePool (*FwVolHeader);
  }

  return Status;
}



/**
  Free FvDevice resource when error happens

  @param  FvDevice              pointer to the FvDevice to be freed.

**/
VOID
FreeFvDeviceResource (
  IN FV_DEVICE  *FvDevice
  )
{
  FFS_FILE_LIST_ENTRY         *FfsFileEntry;
  LIST_ENTRY                  *NextEntry;

  //
  // Free File List Entry
  //
  FfsFileEntry = (FFS_FILE_LIST_ENTRY *)FvDevice->FfsFileListHeader.ForwardLink;
  while (&FfsFileEntry->Link != &FvDevice->FfsFileListHeader) {
    NextEntry = (&FfsFileEntry->Link)->ForwardLink;

    if (FfsFileEntry->StreamHandle != 0) {
      //
      // Close stream and free resources from SEP
      //
      CloseSectionStream (FfsFileEntry->StreamHandle, FALSE);
    }

    if (FfsFileEntry->FileCached) {
      //
      // Free the cached file buffer.
      //
      CoreFreePool (FfsFileEntry->FfsHeader);
    }

    CoreFreePool (FfsFileEntry);

    FfsFileEntry = (FFS_FILE_LIST_ENTRY *) NextEntry;
  }

  if (!FvDevice->IsMemoryMapped) {
    //
    // Free the cached FV buffer.
    //
    CoreFreePool (FvDevice->CachedFv);
  }

  //
  // Free Volume Header
  //
  CoreFreePool (FvDevice->FwVolHeader);

  return;
}



/**
  Check if an FV is consistent and allocate cache for it.

  @param  FvDevice              A pointer to the FvDevice to be checked.

  @retval EFI_OUT_OF_RESOURCES  No enough buffer could be allocated.
  @retval EFI_SUCCESS           FV is consistent and cache is allocated.
  @retval EFI_VOLUME_CORRUPTED  File system is corrupted.

**/
EFI_STATUS
FvCheck (
  IN OUT FV_DEVICE  *FvDevice
  )
{
  EFI_STATUS                            Status;
  EFI_FIRMWARE_VOLUME_BLOCK_PROTOCOL    *Fvb;
  EFI_FIRMWARE_VOLUME_HEADER            *FwVolHeader;
  EFI_FIRMWARE_VOLUME_EXT_HEADER        *FwVolExtHeader;
  EFI_FVB_ATTRIBUTES_2                  FvbAttributes;
  EFI_FV_BLOCK_MAP_ENTRY                *BlockMap;
  FFS_FILE_LIST_ENTRY                   *FfsFileEntry;
  EFI_FFS_FILE_HEADER                   *FfsHeader;
  UINT8                                 *CacheLocation;
  UINTN                                 LbaOffset;
  UINTN                                 HeaderSize;
  UINTN                                 Index;
  EFI_LBA                               LbaIndex;
  UINTN                                 Size;
  EFI_FFS_FILE_STATE                    FileState;
  UINT8                                 *TopFvAddress;
  UINTN                                 TestLength;
  EFI_PHYSICAL_ADDRESS                  PhysicalAddress;
  BOOLEAN                               FileCached;
  UINTN                                 WholeFileSize;
  EFI_FFS_FILE_HEADER                   *CacheFfsHeader;

  FileCached = FALSE;
  CacheFfsHeader = NULL;

  Fvb = FvDevice->Fvb;
  FwVolHeader = FvDevice->FwVolHeader;

  Status = Fvb->GetAttributes (Fvb, &FvbAttributes);
  if (EFI_ERROR (Status)) {
    return Status;
  }

  //
  // Size is the size of the FV minus the head. We have already allocated
  // the header to check to make sure the volume is valid
  //
  Size = (UINTN)(FwVolHeader->FvLength - FwVolHeader->HeaderLength);
  if ((FvbAttributes & EFI_FVB2_MEMORY_MAPPED) != 0) {
    FvDevice->IsMemoryMapped = TRUE;

    Status = Fvb->GetPhysicalAddress (Fvb, &PhysicalAddress);
    if (EFI_ERROR (Status)) {
      return Status;
    }

    //
    // Don't cache memory mapped FV really.
    //
    FvDevice->CachedFv = (UINT8 *) (UINTN) (PhysicalAddress + FwVolHeader->HeaderLength);
  } else {
    FvDevice->IsMemoryMapped = FALSE;
    FvDevice->CachedFv = AllocatePool (Size);

    if (FvDevice->CachedFv == NULL) {
      return EFI_OUT_OF_RESOURCES;
    }
  }

  //
  // Remember a pointer to the end fo the CachedFv
  //
  FvDevice->EndOfCachedFv = FvDevice->CachedFv + Size;

  if (!FvDevice->IsMemoryMapped) {
    //
    // Copy FV minus header into memory using the block map we have all ready
    // read into memory.
    //
    BlockMap = FwVolHeader->BlockMap;
    CacheLocation = FvDevice->CachedFv;
    LbaIndex = 0;
    LbaOffset = 0;
    HeaderSize = FwVolHeader->HeaderLength;
    while ((BlockMap->NumBlocks != 0) || (BlockMap->Length != 0)) {
      Index = 0;
      Size  = BlockMap->Length;
      if (HeaderSize > 0) {
        //
        // Skip header size
        //
        for (; Index < BlockMap->NumBlocks && HeaderSize >= BlockMap->Length; Index ++) {
          HeaderSize -= BlockMap->Length;
          LbaIndex ++;
        }

        //
        // Check whether FvHeader is crossing the multi block range.
        //
        if (Index >= BlockMap->NumBlocks) {
          BlockMap++;
          continue;
        } else if (HeaderSize > 0) {
          LbaOffset = HeaderSize;
          Size = BlockMap->Length - HeaderSize;
          HeaderSize = 0;
        }
      }
    
      //
      // read the FV data  
      //
      for (; Index < BlockMap->NumBlocks; Index ++) {
        Status = Fvb->Read (Fvb,
                        LbaIndex,
                        LbaOffset,
                        &Size,
                        CacheLocation
                        );

        //
        // Not check EFI_BAD_BUFFER_SIZE, for Size = BlockMap->Length
        //
        if (EFI_ERROR (Status)) {
          goto Done;
        }

        LbaIndex++;
        CacheLocation += Size;

        //
        // After we skip Fv Header always read from start of block
        //
        LbaOffset = 0;
        Size  = BlockMap->Length;
      }

      BlockMap++;
    }
  }

  //
  // Scan to check the free space & File list
  //
  if ((FvbAttributes & EFI_FVB2_ERASE_POLARITY) != 0) {
    FvDevice->ErasePolarity = 1;
  } else {
    FvDevice->ErasePolarity = 0;
  }


  //
  // go through the whole FV cache, check the consistence of the FV.
  // Make a linked list of all the Ffs file headers
  //
  Status = EFI_SUCCESS;
  InitializeListHead (&FvDevice->FfsFileListHeader);

  //
  // Build FFS list
  //
  if (FwVolHeader->ExtHeaderOffset != 0) {
    //
    // Searching for files starts on an 8 byte aligned boundary after the end of the Extended Header if it exists.
    //
    FwVolExtHeader = (EFI_FIRMWARE_VOLUME_EXT_HEADER *) (FvDevice->CachedFv + (FwVolHeader->ExtHeaderOffset - FwVolHeader->HeaderLength));
    FfsHeader = (EFI_FFS_FILE_HEADER *) ((UINT8 *) FwVolExtHeader + FwVolExtHeader->ExtHeaderSize);
    FfsHeader = (EFI_FFS_FILE_HEADER *) ALIGN_POINTER (FfsHeader, 8);
  } else {
    FfsHeader = (EFI_FFS_FILE_HEADER *) (FvDevice->CachedFv);
  }
  TopFvAddress = FvDevice->EndOfCachedFv;
  while (((UINTN) FfsHeader >= (UINTN) FvDevice->CachedFv) && ((UINTN) FfsHeader <= (UINTN) ((UINTN) TopFvAddress - sizeof (EFI_FFS_FILE_HEADER)))) {

    if (FileCached) {
      CoreFreePool (CacheFfsHeader);
      FileCached = FALSE;
    }

    TestLength = TopFvAddress - ((UINT8 *) FfsHeader);
    if (TestLength > sizeof (EFI_FFS_FILE_HEADER)) {
      TestLength = sizeof (EFI_FFS_FILE_HEADER);
    }

    if (IsBufferErased (FvDevice->ErasePolarity, FfsHeader, TestLength)) {
      //
      // We have found the free space so we are done!
      //
      goto Done;
    }

    if (!IsValidFfsHeader (FvDevice->ErasePolarity, FfsHeader, &FileState)) {
      if ((FileState == EFI_FILE_HEADER_INVALID) ||
          (FileState == EFI_FILE_HEADER_CONSTRUCTION)) {
        if (IS_FFS_FILE2 (FfsHeader)) {
          if (!FvDevice->IsFfs3Fv) {
            DEBUG ((EFI_D_ERROR, "Found a FFS3 formatted file: %g in a non-FFS3 formatted FV.\n", &FfsHeader->Name));
          }
          FfsHeader = (EFI_FFS_FILE_HEADER *) ((UINT8 *) FfsHeader + sizeof (EFI_FFS_FILE_HEADER2));
        } else {
          FfsHeader = (EFI_FFS_FILE_HEADER *) ((UINT8 *) FfsHeader + sizeof (EFI_FFS_FILE_HEADER));
        }
        continue;
      } else {
        //
        // File system is corrputed
        //
        Status = EFI_VOLUME_CORRUPTED;
        goto Done;
      }
    }

    CacheFfsHeader = FfsHeader;
    if ((CacheFfsHeader->Attributes & FFS_ATTRIB_CHECKSUM) == FFS_ATTRIB_CHECKSUM) {
      if (FvDevice->IsMemoryMapped) {
        //
        // Memory mapped FV has not been cached.
        // Here is to cache FFS file to memory buffer for following checksum calculating.
        // And then, the cached file buffer can be also used for FvReadFile.
        //
        WholeFileSize = IS_FFS_FILE2 (CacheFfsHeader) ? FFS_FILE2_SIZE (CacheFfsHeader): FFS_FILE_SIZE (CacheFfsHeader);
        CacheFfsHeader = AllocateCopyPool (WholeFileSize, CacheFfsHeader);
        if (CacheFfsHeader == NULL) {
          Status = EFI_OUT_OF_RESOURCES;
          goto Done;
        }
        FileCached = TRUE;
      }
    }

    if (!IsValidFfsFile (FvDevice->ErasePolarity, CacheFfsHeader)) {
      //
      // File system is corrupted
      //
      Status = EFI_VOLUME_CORRUPTED;
      goto Done;
    }

    if (IS_FFS_FILE2 (CacheFfsHeader)) {
      ASSERT (FFS_FILE2_SIZE (CacheFfsHeader) > 0x00FFFFFF);
      if (!FvDevice->IsFfs3Fv) {
        DEBUG ((EFI_D_ERROR, "Found a FFS3 formatted file: %g in a non-FFS3 formatted FV.\n", &CacheFfsHeader->Name));
        FfsHeader = (EFI_FFS_FILE_HEADER *) ((UINT8 *) FfsHeader + FFS_FILE2_SIZE (CacheFfsHeader));
        //
        // Adjust pointer to the next 8-byte aligned boundry.
        //
        FfsHeader = (EFI_FFS_FILE_HEADER *) (((UINTN) FfsHeader + 7) & ~0x07);
        continue;
      }
    }

    FileState = GetFileState (FvDevice->ErasePolarity, CacheFfsHeader);

    //
    // check for non-deleted file
    //
    if (FileState != EFI_FILE_DELETED) {
      //
      // Create a FFS list entry for each non-deleted file
      //
      FfsFileEntry = AllocateZeroPool (sizeof (FFS_FILE_LIST_ENTRY));
      if (FfsFileEntry == NULL) {
        Status = EFI_OUT_OF_RESOURCES;
        goto Done;
      }

      FfsFileEntry->FfsHeader = CacheFfsHeader;
      FfsFileEntry->FileCached = FileCached;
      FileCached = FALSE;
      InsertTailList (&FvDevice->FfsFileListHeader, &FfsFileEntry->Link);
    }

    if (IS_FFS_FILE2 (CacheFfsHeader)) {
      FfsHeader = (EFI_FFS_FILE_HEADER *) ((UINT8 *) FfsHeader + FFS_FILE2_SIZE (CacheFfsHeader));
    } else {
      FfsHeader = (EFI_FFS_FILE_HEADER *) ((UINT8 *) FfsHeader + FFS_FILE_SIZE (CacheFfsHeader));
    }

    //
    // Adjust pointer to the next 8-byte aligned boundry.
    //
    FfsHeader = (EFI_FFS_FILE_HEADER *)(((UINTN)FfsHeader + 7) & ~0x07);

  }

Done:
  if (EFI_ERROR (Status)) {
    if (FileCached) {
      CoreFreePool (CacheFfsHeader);
      FileCached = FALSE;
    }
    FreeFvDeviceResource (FvDevice);
  }

  return Status;
}



/**
  This notification function is invoked when an instance of the
  EFI_FIRMWARE_VOLUME_BLOCK_PROTOCOL is produced.  It layers an instance of the
  EFI_FIRMWARE_VOLUME2_PROTOCOL on the same handle.  This is the function where
  the actual initialization of the EFI_FIRMWARE_VOLUME2_PROTOCOL is done.

  @param  Event                 The event that occured
  @param  Context               For EFI compatiblity.  Not used.

**/
VOID
EFIAPI
NotifyFwVolBlock (
  IN  EFI_EVENT Event,
  IN  VOID      *Context
  )
{
  EFI_HANDLE                            Handle;
  EFI_STATUS                            Status;
  UINTN                                 BufferSize;
  EFI_FIRMWARE_VOLUME_BLOCK_PROTOCOL    *Fvb;
  EFI_FIRMWARE_VOLUME2_PROTOCOL         *Fv;
  FV_DEVICE                             *FvDevice;
  EFI_FIRMWARE_VOLUME_HEADER            *FwVolHeader;
  //
  // Examine all new handles
  //
  for (;;) {
    //
    // Get the next handle
    //
    BufferSize = sizeof (Handle);
    Status = CoreLocateHandle (
              ByRegisterNotify,
              NULL,
              gEfiFwVolBlockNotifyReg,
              &BufferSize,
              &Handle
              );

    //
    // If not found, we're done
    //
    if (EFI_NOT_FOUND == Status) {
      break;
    }

    if (EFI_ERROR (Status)) {
      continue;
    }

    //
    // Get the FirmwareVolumeBlock protocol on that handle
    //
    Status = CoreHandleProtocol (Handle, &gEfiFirmwareVolumeBlockProtocolGuid, (VOID **)&Fvb);
    ASSERT_EFI_ERROR (Status);
    ASSERT (Fvb != NULL);

    //
    // Make sure the Fv Header is O.K.
    //
    Status = GetFwVolHeader (Fvb, &FwVolHeader);
    if (EFI_ERROR (Status)) {
      continue;
    }
    ASSERT (FwVolHeader != NULL);

    if (!VerifyFvHeaderChecksum (FwVolHeader)) {
      CoreFreePool (FwVolHeader);
      continue;
    }

    //
    // Check if there is an FV protocol already installed in that handle
    //
    Status = CoreHandleProtocol (Handle, &gEfiFirmwareVolume2ProtocolGuid, (VOID **)&Fv);
    if (!EFI_ERROR (Status)) {
      //
      // Update Fv to use a new Fvb
      //
      FvDevice = BASE_CR (Fv, FV_DEVICE, Fv);
      if (FvDevice->Signature == FV2_DEVICE_SIGNATURE) {
        //
        // Only write into our device structure if it's our device structure
        //
        FvDevice->Fvb = Fvb;
      }

    } else {
      //
      // No FwVol protocol on the handle so create a new one
      //
      FvDevice = AllocateCopyPool (sizeof (FV_DEVICE), &mFvDevice);
      if (FvDevice == NULL) {
        return;
      }

      FvDevice->Fvb             = Fvb;
      FvDevice->Handle          = Handle;
      FvDevice->FwVolHeader     = FwVolHeader;
      FvDevice->IsFfs3Fv        = CompareGuid (&FwVolHeader->FileSystemGuid, &gEfiFirmwareFileSystem3Guid);
      FvDevice->Fv.ParentHandle = Fvb->ParentHandle;

      if (Fvb->ParentHandle != NULL) {
        //
        // Inherit the authentication status from FVB.
        //
        FvDevice->AuthenticationStatus = GetFvbAuthenticationStatus (Fvb);
      }
      
      if (!EFI_ERROR (FvCheck (FvDevice))) {
        //
        // Install an New FV protocol on the existing handle
        //
        Status = CoreInstallProtocolInterface (
                    &Handle,
                    &gEfiFirmwareVolume2ProtocolGuid,
                    EFI_NATIVE_INTERFACE,
                    &FvDevice->Fv
                    );
        ASSERT_EFI_ERROR (Status);
      } else {
        //
        // Free FvDevice Buffer for the corrupt FV image.
        //
        CoreFreePool (FvDevice);
      }
    }
  }

  return;
}



/**
  This routine is the driver initialization entry point.  It registers
  a notification function.  This notification function are responsible
  for building the FV stack dynamically.

  @param  ImageHandle           The image handle.
  @param  SystemTable           The system table.

  @retval EFI_SUCCESS           Function successfully returned.

**/
EFI_STATUS
EFIAPI
FwVolDriverInit (
  IN EFI_HANDLE                   ImageHandle,
  IN EFI_SYSTEM_TABLE             *SystemTable
  )
{
  gEfiFwVolBlockEvent = EfiCreateProtocolNotifyEvent (
                          &gEfiFirmwareVolumeBlockProtocolGuid,
                          TPL_CALLBACK,
                          NotifyFwVolBlock,
                          NULL,
                          &gEfiFwVolBlockNotifyReg
                          );
  return EFI_SUCCESS;
}