今天拿到了 Microsoft Surface 3 ，
測試一個EFI程序的時候總是出問題，
后來查了一下，發現在使用EFI_BLOCK_IO 取得外接USB閃存大小的時候
也就是 BlkIo->Media->LastBlock 取得的大小會比實際的多出來一個
估計是寫固件的人理解出了問題。
這里是定義
/**
Block IO read only mode data and updated only via members of BlockIO
**/
typedef struct {
///
/// The curent media Id. If the media changes, this value is changed.
///
UINT32 MediaId;
///
/// TRUE if the media is removable; otherwise, FALSE.
///
BOOLEAN RemovableMedia;
///
/// TRUE if there is a media currently present in the device;
/// othersise, FALSE. THis field shows the media present status
/// as of the most recent ReadBlocks() or WriteBlocks() call.
///
BOOLEAN MediaPresent;
///
/// TRUE if LBA 0 is the first block of a partition; otherwise
/// FALSE. For media with only one partition this would be TRUE.
///
BOOLEAN LogicalPartition;
///
/// TRUE if the media is marked read-only otherwise, FALSE.
/// This field shows the read-only status as of the most recent WriteBlocks () call.
///
BOOLEAN ReadOnly;
///
/// TRUE if the WriteBlock () function caches write data.
///
BOOLEAN WriteCaching;
///
/// The intrinsic block size of the device. If the media changes, then
/// this field is updated.
///
UINT32 BlockSize;
///
/// Supplies the alignment requirement for any buffer to read or write block(s).
///
UINT32 IoAlign;
///
/// The last logical block address on the device.
/// If the media changes, then this field is updated.
///
EFI_LBA LastBlock;
///
/// Only present if EFI_BLOCK_IO_PROTOCOL.Revision is greater than or equal to
/// EFI_BLOCK_IO_PROTOCOL_REVISION2. Returns the first LBA is aligned to
/// a physical block boundary.
///
EFI_LBA LowestAlignedLba;
///
/// Only present if EFI_BLOCK_IO_PROTOCOL.Revision is greater than or equal to
/// EFI_BLOCK_IO_PROTOCOL_REVISION2. Returns the number of logical blocks
/// per physical block.
///
UINT32 LogicalBlocksPerPhysicalBlock;
///
/// Only present if EFI_BLOCK_IO_PROTOCOL.Revision is greater than or equal to
/// EFI_BLOCK_IO_PROTOCOL_REVISION3. Returns the optimal transfer length
/// granularity as a number of logical blocks.
///
UINT32 OptimalTransferLengthGranularity;
} EFI_BLOCK_IO_MEDIA;
其中那個
LastBlock是這樣說明的 /// The last logical block address on the device.
所以應該是總的block 數-1.
不知道微軟的工程師為什么會有這樣的錯誤