diskio.c

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  Private   = DISK_IO_PRIVATE_DATA_FROM_THIS (This);

  BlockIo   = Private->BlockIo;
  Media     = BlockIo->Media;
  BlockSize = Media->BlockSize;

  if (Media->MediaId != MediaId) {
    return EFI_MEDIA_CHANGED;
  }

  WorkingBuffer     = Buffer;
  WorkingBufferSize = BufferSize;

  //
  // Allocate a temporary buffer for operation
  //
  DataBufferSize = BlockSize * DATA_BUFFER_BLOCK_NUM;

  if (Media->IoAlign > 1) {
    PreData = EfiLibAllocatePool (DataBufferSize + Media->IoAlign);
    Data    = PreData - ((UINTN) PreData & (Media->IoAlign - 1)) + Media->IoAlign;
  } else {
    PreData = EfiLibAllocatePool (DataBufferSize);
    Data    = PreData;
  }

  if (PreData == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }

  Lba                 = DivU64x32 (Offset, BlockSize, &UnderRun);

  Length              = BlockSize - UnderRun;
  TransactionComplete = FALSE;

  Status              = EFI_SUCCESS;
  if (UnderRun != 0) {
    //
    // Offset starts in the middle of an Lba, so read the entire block.
    //
    Status = BlockIo->ReadBlocks (
                        BlockIo,
                        MediaId,
                        Lba,
                        BlockSize,
                        Data
                        );

    if (EFI_ERROR (Status)) {
      goto Done;
    }

    if (Length > BufferSize) {
      Length              = BufferSize;
      TransactionComplete = TRUE;
    }

    EfiCopyMem (WorkingBuffer, Data + UnderRun, Length);

    WorkingBuffer += Length;

    WorkingBufferSize -= Length;
    if (WorkingBufferSize == 0) {
      goto Done;
    }

    Lba += 1;
  }

  OverRunLba = Lba + DivU64x32 (WorkingBufferSize, BlockSize, &OverRun);

  if (!TransactionComplete && WorkingBufferSize >= BlockSize) {
    //
    // If the DiskIo maps directly to a BlockIo device do the read.
    //
    if (OverRun != 0) {
      WorkingBufferSize -= OverRun;
    }
    //
    // Check buffer alignment
    //
    IsBufferAligned = (UINTN) WorkingBuffer & (UINTN) (Media->IoAlign - 1);

    if (Media->IoAlign <= 1 || IsBufferAligned == 0) {
      //
      // Alignment is satisfied, so read them together
      //
      Status = BlockIo->ReadBlocks (
                          BlockIo,
                          MediaId,
                          Lba,
                          WorkingBufferSize,
                          WorkingBuffer
                          );

      if (EFI_ERROR (Status)) {
        goto Done;
      }

      WorkingBuffer += WorkingBufferSize;

    } else {
      //
      // Use the allocated buffer instead of the original buffer
      // to avoid alignment issue.
      // Here, the allocated buffer (8-byte align) can satisfy the alignment
      //
      LastRead = FALSE;
      do {
        if (WorkingBufferSize <= DataBufferSize) {
          //
          // It is the last calling to readblocks in this loop
          //
          DataBufferSize  = WorkingBufferSize;
          LastRead        = TRUE;
        }

        Status = BlockIo->ReadBlocks (
                            BlockIo,
                            MediaId,
                            Lba,
                            DataBufferSize,
                            Data
                            );
        if (EFI_ERROR (Status)) {
          goto Done;
        }

        EfiCopyMem (WorkingBuffer, Data, DataBufferSize);
        WorkingBufferSize -= DataBufferSize;
        WorkingBuffer += DataBufferSize;
        Lba += DATA_BUFFER_BLOCK_NUM;
      } while (!LastRead);
    }
  }

  if (!TransactionComplete && OverRun != 0) {
    //
    // Last read is not a complete block.
    //
    Status = BlockIo->ReadBlocks (
                        BlockIo,
                        MediaId,
                        OverRunLba,
                        BlockSize,
                        Data
                        );

    if (EFI_ERROR (Status)) {
      goto Done;
    }

    EfiCopyMem (WorkingBuffer, Data, OverRun);
  }

Done:
  if (PreData != NULL) {
    gBS->FreePool (PreData);
  }

  return Status;
}

EFI_STATUS
EFIAPI
DiskIoWriteDisk (
  IN EFI_DISK_IO_PROTOCOL  *This,
  IN UINT32                MediaId,
  IN UINT64                Offset,
  IN UINTN                 BufferSize,
  IN VOID                  *Buffer
  )
/*++

  Routine Description:
    Read BufferSize bytes from Offset into Buffer.

    Writes may require a read modify write to support writes that are not 
    aligned on sector boundaries. There are three cases:
    
      UnderRun - The first byte is not on a sector boundary or the write request
                 is less than a sector in length. Read modify write is required.

      Aligned  - A write of N contiguous sectors.

      OverRun  - The last byte is not on a sector boundary. Read modified write 
                 required.

  Arguments:
    This       - Protocol instance pointer.
    MediaId    - Id of the media, changes every time the media is replaced. 
    Offset     - The starting byte offset to read from.
    BufferSize - Size of Buffer.
    Buffer     - Buffer containing read data.

  Returns:
    EFI_SUCCESS           - The data was written correctly to the device.
    EFI_WRITE_PROTECTED   - The device can not be written to.
    EFI_DEVICE_ERROR      - The device reported an error while performing the write.
    EFI_NO_MEDIA          - There is no media in the device.
    EFI_MEDIA_CHNAGED     - The MediaId does not matched the current device.
    EFI_INVALID_PARAMETER - The write request contains device addresses that are not 
                            valid for the device.
    EFI_OUT_OF_RESOURCES

--*/
{
  EFI_STATUS            Status;
  DISK_IO_PRIVATE_DATA  *Private;
  EFI_BLOCK_IO_PROTOCOL *BlockIo;
  EFI_BLOCK_IO_MEDIA    *Media;
  UINT32                BlockSize;
  UINT64                Lba;
  UINT64                OverRunLba;
  UINTN                 UnderRun;
  UINTN                 OverRun;
  BOOLEAN               TransactionComplete;
  UINTN                 WorkingBufferSize;
  UINT8                 *WorkingBuffer;
  UINTN                 Length;
  UINT8                 *Data;
  UINT8                 *PreData;
  UINTN                 IsBufferAligned;
  UINTN                 DataBufferSize;
  BOOLEAN               LastWrite;

  Private   = DISK_IO_PRIVATE_DATA_FROM_THIS (This);

  BlockIo   = Private->BlockIo;
  Media     = BlockIo->Media;
  BlockSize = Media->BlockSize;

  if (Media->ReadOnly) {
    return EFI_WRITE_PROTECTED;
  }

  if (Media->MediaId != MediaId) {
    return EFI_MEDIA_CHANGED;
  }

  DataBufferSize = BlockSize * DATA_BUFFER_BLOCK_NUM;

  if (Media->IoAlign > 1) {
    PreData = EfiLibAllocatePool (DataBufferSize + Media->IoAlign);
    Data    = PreData - ((UINTN) PreData & (Media->IoAlign - 1)) + Media->IoAlign;
  } else {
    PreData = EfiLibAllocatePool (DataBufferSize);
    Data    = PreData;
  }

  if (PreData == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }

  WorkingBuffer       = Buffer;
  WorkingBufferSize   = BufferSize;

  Lba                 = DivU64x32 (Offset, BlockSize, &UnderRun);

  Length              = BlockSize - UnderRun;
  TransactionComplete = FALSE;

  Status              = EFI_SUCCESS;
  if (UnderRun != 0) {
    //
    // Offset starts in the middle of an Lba, so do read modify write.
    //
    Status = BlockIo->ReadBlocks (
                        BlockIo,
                        MediaId,
                        Lba,
                        BlockSize,
                        Data
                        );

    if (EFI_ERROR (Status)) {
      goto Done;
    }

    if (Length > BufferSize) {
      Length              = BufferSize;
      TransactionComplete = TRUE;
    }

    EfiCopyMem (Data + UnderRun, WorkingBuffer, Length);

    Status = BlockIo->WriteBlocks (
                        BlockIo,
                        MediaId,
                        Lba,
                        BlockSize,
                        Data
                        );
    if (EFI_ERROR (Status)) {
      goto Done;
    }

    WorkingBuffer += Length;
    WorkingBufferSize -= Length;
    if (WorkingBufferSize == 0) {
      goto Done;
    }

    Lba += 1;
  }

  OverRunLba = Lba + DivU64x32 (WorkingBufferSize, BlockSize, &OverRun);

  if (!TransactionComplete && WorkingBufferSize >= BlockSize) {
    //
    // If the DiskIo maps directly to a BlockIo device do the write.
    //
    if (OverRun != 0) {
      WorkingBufferSize -= OverRun;
    }
    //
    // Check buffer alignment
    //
    IsBufferAligned = (UINTN) WorkingBuffer & (UINTN) (Media->IoAlign - 1);

    if (Media->IoAlign <= 1 || IsBufferAligned == 0) {
      //
      // Alignment is satisfied, so write them together
      //
      Status = BlockIo->WriteBlocks (
                          BlockIo,
                          MediaId,
                          Lba,
                          WorkingBufferSize,
                          WorkingBuffer
                          );

      if (EFI_ERROR (Status)) {
        goto Done;
      }

      WorkingBuffer += WorkingBufferSize;

    } else {
      //
      // The buffer parameter is not aligned with the request
      // So use the allocated instead.
      // It can fit almost all the cases.
      //
      LastWrite = FALSE;
      do {
        if (WorkingBufferSize <= DataBufferSize) {
          //
          // It is the last calling to writeblocks in this loop
          //
          DataBufferSize  = WorkingBufferSize;
          LastWrite       = TRUE;
        }

        EfiCopyMem (Data, WorkingBuffer, DataBufferSize);
        Status = BlockIo->WriteBlocks (
                            BlockIo,
                            MediaId,
                            Lba,
                            DataBufferSize,
                            Data
                            );
        if (EFI_ERROR (Status)) {
          goto Done;
        }

        WorkingBufferSize -= DataBufferSize;
        WorkingBuffer += DataBufferSize;
        Lba += DATA_BUFFER_BLOCK_NUM;
      } while (!LastWrite);
    }
  }

  if (!TransactionComplete && OverRun != 0) {
    //
    // Last bit is not a complete block, so do a read modify write.
    //
    Status = BlockIo->ReadBlocks (
                        BlockIo,
                        MediaId,
                        OverRunLba,
                        BlockSize,
                        Data
                        );

    if (EFI_ERROR (Status)) {
      goto Done;
    }

    EfiCopyMem (Data, WorkingBuffer, OverRun);

    Status = BlockIo->WriteBlocks (
                        BlockIo,
                        MediaId,
                        OverRunLba,
                        BlockSize,
                        Data
                        );
    if (EFI_ERROR (Status)) {
      goto Done;
    }
  }

Done:
  if (PreData != NULL) {
    gBS->FreePool (PreData);
  }

  return Status;
}