【UEFI基础】块设备访问

朴灿烈づ我的快乐病毒、 2023-10-17 08:47 111阅读 0赞

## 接口说明 ##

UEFI下的基本块设备访问接口是以下的几个：

gEfiBlockIoProtocolGuid;
    ///
    ///  This protocol provides control over block devices.
    ///
    struct _EFI_BLOCK_IO_PROTOCOL {
      ///
      /// The revision to which the block IO interface adheres. All future
      /// revisions must be backwards compatible. If a future version is not
      /// back wards compatible, it is not the same GUID.
      ///
      UINT64              Revision;
      ///
      /// Pointer to the EFI_BLOCK_IO_MEDIA data for this device.
      ///
      EFI_BLOCK_IO_MEDIA  *Media;
    
      EFI_BLOCK_RESET     Reset;
      EFI_BLOCK_READ      ReadBlocks;
      EFI_BLOCK_WRITE     WriteBlocks;
      EFI_BLOCK_FLUSH     FlushBlocks;
    
    };

以及

gEfiDiskIoProtocolGuid;
    ///
    /// This protocol is used to abstract Block I/O interfaces.
    ///
    struct _EFI_DISK_IO_PROTOCOL {
      ///
      /// The revision to which the disk I/O interface adheres. All future
      /// revisions must be backwards compatible. If a future version is not
      /// backwards compatible, it is not the same GUID.
      ///
      UINT64          Revision;
      EFI_DISK_READ   ReadDisk;
      EFI_DISK_WRITE  WriteDisk;
    };

其中DiskIoProtocol对应的是一个UEFI Driver Model。它依赖于BlockIoProtocol：

EFI_STATUS
    EFIAPI
    DiskIoDriverBindingSupported (
      IN EFI_DRIVER_BINDING_PROTOCOL  *This,
      IN EFI_HANDLE                   ControllerHandle,
      IN EFI_DEVICE_PATH_PROTOCOL     *RemainingDevicePath OPTIONAL
      )
    {
      EFI_STATUS            Status;
      EFI_BLOCK_IO_PROTOCOL *BlockIo;
    
      //
      // Open the IO Abstraction(s) needed to perform the supported test.
      //
      Status = gBS->OpenProtocol (
                      ControllerHandle,
                      &gEfiBlockIoProtocolGuid,
                      (VOID **) &BlockIo,
                      This->DriverBindingHandle,
                      ControllerHandle,
                      EFI_OPEN_PROTOCOL_BY_DRIVER
                      );
      if (EFI_ERROR (Status)) {
        return Status;
      }

一般我们使用的时候会用DiskIoProtocol来读写块设备，而不是使用BlockIoProtocol，不过BlockIoProtocol并不是没有用，因为在DiskIoProtocol的读写接口中都需要使用到BlockIoProtocol的参数：

/**
      Read BufferSize bytes from Offset into Buffer.
    
      @param  This                  Protocol instance pointer.
      @param  MediaId               Id of the media, changes every time the media is replaced.
      @param  Offset                The starting byte offset to read from
      @param  BufferSize            Size of Buffer
      @param  Buffer                Buffer containing read data
    
      @retval EFI_SUCCESS           The data was read correctly from the device.
      @retval EFI_DEVICE_ERROR      The device reported an error while performing the read.
      @retval EFI_NO_MEDIA          There is no media in the device.
      @retval EFI_MEDIA_CHNAGED     The MediaId does not matched the current device.
      @retval EFI_INVALID_PARAMETER The read request contains device addresses that are not
                                    valid for the device.
    
    **/
    typedef
    EFI_STATUS
    (EFIAPI *EFI_DISK_READ)(
      IN EFI_DISK_IO_PROTOCOL         *This,
      IN UINT32                       MediaId,
      IN UINT64                       Offset,
      IN UINTN                        BufferSize,
      OUT VOID                        *Buffer
      );

其中的MediaId就是在BlockIoProtocol中定义的EFI\_BLOCK\_IO\_MEDIA结构体中：

/**
      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;

另外，它们都对应有一个2版本，算是加强版，这里不具体说明。

无论是BlockIoProtocol还是DiskIoProtocol，其实都只是UEFI层的抽象，具体的IO实现还需要块设备驱动自己做，驱动的最后会安装BlockIoProtocol。

之后才有DiskIoProtocol的进一步封装。