什么是protocol從字面意思上看，protocol是server和client之間的一種約定，雙方根據這種約定互通信息。這里的server和client是一種廣義的稱呼，提供服務的稱為server，使用服務的稱為client。 TCP是一種protocol， client(應用程序)通過一組函數來壓包和解包，壓包和解包是server提供的服務。COM也是一種protocol，client通過
CoCreateInstance(...)和GUID獲得指向COM對象的指針，然后使用該指針獲得COM對象提供的服務， GUID標示了這個COM對象。現在我們對protocol有了概念上的理解，那么具體到UEFI里，protocol是什么樣子呢？ 如何標示一個protocol？如何得到protocol對應的對象？...容我慢慢道來.
在講protocol什么樣子之前，還要插幾句C與C++的區(qū)別。我們知道UEFI是用C來開發(fā)的，C是面向過程的一種語言。而管理和使用UEFI眾多的protocol完全使用面向過程的思想會使程序變得復雜。protocol作為一種對象來設計管理會比較直觀。因而UEFI中的Protocol引入了面向對象的思想，用struct來模擬class, Protocol用struct來實現，用函數指針(Protocol的成員變量)模擬成員函數，此種函數的第一參數必須是指向Protocol的指針，用來模擬this指針。
Protocol的摸樣
以EFI_DISKIO_PROTOCOL 來看看Protocol的樣子。 MdePkg/Include/Protocol/BlockIo.h
///
/// 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;
};
extern EFI_GUID gEfiBlockIoProtocolGuid;
MdePkg/Include/Protocol/BlockIo.h
#define EFI_BLOCK_IO_PROTOCOL_GUID \
{ \
0x964e5b21, 0x6459, 0x11d2, {0x8e, 0x39, 0x0, 0xa0, 0xc9, 0x69, 0x72, 0x3b } \
}
typedef struct _EFI_BLOCK_IO_PROTOCOL EFI_BLOCK_IO_PROTOCOL;
EFI_BLOCK_IO_PROTOCOL 有兩個成員變量，四個成員函數(當然從C的角度來看，“成員函數”叫法不準確，它實際上也是一個成員變量，只是這個變量是函數指針). gEfiBlockIoProtocolGuid({0x964e5b21, 0x6459, 0x11d2, {0x8e, 0x39, 0x0, 0xa0, 0xc9, 0x69, 0x72, 0x3b })標示了EFI_BLOCK_IO_PROTOCOL 。
來看成員函數的聲明
/**
Read BufferSize bytes from Lba into Buffer.
@param This Indicates a pointer to the calling context.
@param MediaId Id of the media, changes every time the media is replaced.
@param Lba The starting Logical Block Address to read from
@param BufferSize Size of Buffer, must be a multiple of device block size.
@param Buffer A pointer to the destination buffer for the data. The caller is
responsible for either having implicit or explicit ownership of the buffer.
@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_CHANGED The MediaId does not matched the current device.
@retval EFI_BAD_BUFFER_SIZE The Buffer was not a multiple of the block size of the device.
@retval EFI_INVALID_PARAMETER The read request contains LBAs that are not valid,
or the buffer is not on proper alignment.
**/
typedef
EFI_STATUS
(EFIAPI *EFI_BLOCK_READ)(
IN EFI_BLOCK_IO_PROTOCOL *This,
IN UINT32 MediaId,
IN EFI_LBA Lba,
IN UINTN BufferSize,
OUT VOID *Buffer
);
EFI_BLOCK_READ具體用法我們先不看，我們來看它的第一個參數，指向
EFI_BLOCK_IO_PROTOCOL 對象自己的this指針，這是成員函數區(qū)別于一般函數的重要特征。
如何使用Protocol 使用Protocol之前，我們要弄清楚Protocol位于什么地方。首先我們要來認識一下EFI_HANDLE，
///
/// A collection of related interfaces.
///
typedef VOID *EFI_HANDLE;
EFI_HANDLE是指向某種對象的指針，UEFI用它來表示某個對象。 UEFI掃描總線后，會為每個設備建立一個Controller對象，用于控制設備，所有該設備的驅動以protocol的形式安裝到這個controller中，這個Controller就是一個EFI_HANDLE對象。 當我們將一個.efi文件加載到內存中，UEFI也會為該文件建立一個Image對象（此Image非圖像的意識), 這個Image對象也是一個EFI_HANDLE對象。 在UEFI內部，EFI_HANDLE被理解為IHANDLE
///
/// IHANDLE - contains a list of protocol handles
///
typedef struct {
UINTN Signature;
/// All handles list of IHANDLE
LIST_ENTRY AllHandles;
/// List of PROTOCOL_INTERFACE's for this handle
LIST_ENTRY Protocols;
UINTN LocateRequest;
/// The Handle Database Key value when this handle was last created or modified
UINT64 Key;
} IHANDLE;
每個IHANDLE中都有一個Protocols鏈表，存放屬于自己的protocol。所有的IHANDLE通過AllHandles鏈接起來。
要使用Protocol，首先要找到protocol對象，可以通過BootServices的OpenProtocol(...), HandleProtocl(...), LocateProtocol(...)獲得。
typedef
/**
Queries a handle to determine if it supports a specified protocol. If the protocol is supported by the
handle, it opens the protocol on behalf of the calling agent.
@param Handle The handle for the protocol interface that is being opened.
@param Protocol The published unique identifier of the protocol.
@param Interface Supplies the address where a pointer to the corresponding Protocol
Interface is returned.
@param AgentHandle The handle of the agent that is opening the protocol interface
specified by Protocol and Interface.
@param ControllerHandle If the agent that is opening a protocol is a driver that follows the
UEFI Driver Model, then this parameter is the controller handle
that requires the protocol interface. If the agent does not follow
the UEFI Driver Model, then this parameter is optional and may
be NULL.
@param Attributes The open mode of the protocol interface specified by Handle
and Protocol.
@retval EFI_SUCCESS An item was added to the open list for the protocol interface, and the
protocol interface was returned in Interface.
@retval EFI_UNSUPPORTED Handle does not support Protocol.
@retval EFI_INVALID_PARAMETER One or more parameters are invalid.
@retval EFI_ACCESS_DENIED Required attributes can't be supported in current environment.
@retval EFI_ALREADY_STARTED Item on the open list already has requierd attributes whose agent
handle is the same as AgentHandle.
**/
EFI_STATUS
(EFIAPI *EFI_OPEN_PROTOCOL)(
IN EFI_HANDLE Handle,
IN EFI_GUID *Protocol,
OUT VOID **Interface, OPTIONAL
IN EFI_HANDLE AgentHandle,
IN EFI_HANDLE ControllerHandle,
IN UINT32 Attributes
);
Handle是Protocol的提供者，如果Handle的Protocols鏈表中有該Potocol，Protocol對象的指針寫到*Interface
，并返回EFI_SUCCESS；否則 返回
EFI_UNSUPPORTED 。
如果在驅動中調用OpenProtocol()， AgentHandle是擁有該
EFI_DRIVER_BINDING_PROTOCOL對象的Handle；ControllerHandle是擁有該驅動的Controller。
如果調用OpenProtocol的是應用程序，那么AgentHandle是該應用對應的Handle，也就main函數的第一個參數。 ControllerHandle此時可以忽略。
Attributes可以取以下5種值。
#define EFI_OPEN_PROTOCOL_BY_HANDLE_PROTOCOL 0x00000001
#define EFI_OPEN_PROTOCOL_GET_PROTOCOL 0x00000002
#define EFI_OPEN_PROTOCOL_TEST_PROTOCOL 0x00000004
#define EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER 0x00000008
#define EFI_OPEN_PROTOCOL_BY_DRIVER 0x00000010
#define EFI_OPEN_PROTOCOL_EXCLUSIVE 0x00000020
HandleProtocol是OpenProtocol的簡化版，因為大部分情況下我們都不需要關心AgentHandle，
ControllerHandle和Attributes。
EFI_STATUS
EFIAPI
CoreHandleProtocol (
IN EFI_HANDLE UserHandle,
IN EFI_GUID *Protocol,
OUT VOID **Interface
)
{
return CoreOpenProtocol (
UserHandle,
Protocol,
Interface,
gDxeCoreImageHandle,
NULL,
EFI_OPEN_PROTOCOL_BY_HANDLE_PROTOCOL
);
}
LocateProtocol(...)是從內核中找出指定Protocol的第一個實例。
typedef
EFI_STATUS
LocateProtocol (
IN EFI_GUID *Protocol,
IN VOID *Registration OPTIONAL,
OUT VOID **Interface
);
UEFI內核中某個Protocol的實例可能不止一個，例如每個硬盤及每個分區(qū)都有一個EFI_DISK_IO_PROTOCOL實例。LocateProtocol順序搜索HANDLE鏈表，返回找到的第一個該Protocol的實例。
我們可以用BootServices提供的其它函數處理HANDLE和Protocol。
typedef
EFI_STATUS
LocateHandleBuffer (
IN EFI_LOCATE_SEARCH_TYPE SearchType,
IN EFI_GUID *Protocol OPTIONAL,
IN VOID *SearchKey OPTIONAL,
IN OUT UINTN *NoHandles,
OUT EFI_HANDLE **Buffer
); 可以獲得所有支持指定Protocol的HANDLE，
SearchType 有三種：AllHandles(查找所有HANDLE), ByRegisterNotify, ByProtocol（查找支持指定Protocol的HANDLE）。NoHandles是找到的HANDLE的數量， Buffer數組由UEFI復雜分配，由用戶負責釋放。
typedef
EFI_STATUS
LocateHandle (
IN EFI_LOCATE_SEARCH_TYPE SearchType,
IN EFI_GUID *Protocol OPTIONAL,
IN VOID *SearchKey OPTIONAL,
IN OUT UINTN *BufferSize,
OUT EFI_HANDLE *Buffer
);
與LocateHandleBuffer相似，只是用戶負責分配和釋放Buffer數組。
typedef
EFI_STATUS
ProtocolsPerHandle (
IN EFI_HANDLE Handle,
OUT EFI_GUID ***ProtocolBuffer,
OUT UINTN *ProtocolBufferCount
);
獲得指定Handle所支持的所有Protocol， UEFI負責分配內存給
ProtocolBuffer，用戶負責釋放該內存。
typedef
EFI_STATUS
(EFIAPI *EFI_OPEN_PROTOCOL_INFORMATION) (
IN EFI_HANDLE Handle,
IN EFI_GUID *Protocol,
OUT EFI_OPEN_PROTOCOL_INFORMATION_ENTRY **EntryBuffer,
OUT UINTN *EntryCount
);
typedef struct {
EFI_HANDLE AgentHandle;
EFI_HANDLE ControllerHandle;
UINT32 Attributes;
UINT32 OpenCount;
} EFI_OPEN_PROTOCOL_INFORMATION_ENTRY;
OpenProtocolInformation()獲得指定Handle中指定Protocol的打開信息。
SPEC2.3.1第165頁有很好的例子演示了怎么打開一個Protocol，
EFI_BOOT_SERVICES *gBS;
EFI_HANDLE ImageHandle;
EFI_DRIVER_BINDING_PROTOCOL *This;
IN EFI_HANDLE ControllerHandle,
extern EFI_GUID gEfiXyzIoProtocol;
EFI_XYZ_IO_PROTOCOL *XyzIo;
EFI_STATUS Status;
Status = gBS->OpenProtocol (
ControllerHandle,
&gEfiXyzIoProtocol,
&XyzIo,
ImageHandle,
NULL,
EFI_OPEN_PROTOCOL_BY_HANDLE_PROTOCOL
);
Status = gBS->OpenProtocol (
ControllerHandle,
&gEfiXyzIoProtocol,
&XyzIo,
This->DriverBindingHandle,
ControllerHandle,
EFI_OPEN_PROTOCOL_GET_PROTOCOL
);
打開Protocol之后就可以使用了，最后要通過CloseProtocol關閉打開的Protocol。
typedef
EFI_STATUS
(EFIAPI *EFI_CLOSE_PROTOCOL) (
IN EFI_HANDLE Handle,
IN EFI_GUID *Protocol,
IN EFI_HANDLE AgentHandle,
IN EFI_HANDLE ControllerHandle
);
通過HandleProtocol和LocateProtocol打開的Protocol因為沒有指定AgentHandle，所以無法關閉。如果一定要去關閉它，要調用OpenProtocolInformation()獲得AgentHandle和ControllerHandle，然后關閉它。
下面看一個完整的例子，用EFI_DISK_IO_PROTOCOL讀取GPT硬盤的分區(qū)表
#include <Uefi.h>
#include <Base.h>
#include <Library/UefiLib.h>
#include <Library/BaseLib.h>
#include <Library/BaseMemoryLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/PrintLib.h>
#include <Protocol/DiskIo.h>
#include <Protocol/BlockIo.h>
#include <Protocol/DevicePath.h>
#include <Uefi/UefiGpt.h>
#include <Library/DevicePathLib.h>
EFI_STATUSEFIAPIUefiMain( IN EFI_HANDLE ImageHandle, IN EFI_SYSTEM_TABLE *SystemTable ){ EFI_STATUS Status; UINTN HandleIndex, HandleCount; EFI_HANDLE *DiskControllerHandles = NULL; EFI_DISK_IO_PROTOCOL *DiskIo; /*找到所有提供
EFI_DISK_IO_PROTOCOL 的Controller */ Status = gBS->LocateHandleBuffer( ByProtocol, &gEfiDiskIoProtocolGuid, NULL, &HandleCount, &DiskControllerHandles); if (!EFI_ERROR(Status)) { CHAR8 gptHeaderBuf[512];
EFI_PARTITION_TABLE_HEADER* gptHeader = (EFI_PARTITION_TABLE_HEADER*
)gpHeaderBuf;
for (HandleIndex = 0; HandleIndex < HandleCount; HandleIndex++) { /*打開EFI_DISK_IO_PROTOCOL */ Status = gBS->HandleProtocol( DiskControllerHandles[HandleIndex], &gEfiDiskIoProtocolGuid, (VOID**)&DiskIo); if (!EFI_ERROR(Status)){ { EFI_DEVICE_PATH_PROTOCOL *DiskDevicePath; EFI_DEVICE_PATH_TO_TEXT_PROTOCOL *Device2TextProtocol = 0; CHAR16* TextDevicePath = 0; /*1. 打開EFI_DEVICE_PATH_PROTOCOL */ Status = gBS->OpenProtocol( DiskControllerHandles[HandleIndex], &gEfiDevicePathProtocolGuid, (VOID**)&DiskDevicePath, ImageHandle, NULL, EFI_OPEN_PROTOCOL_GET_PROTOCOL ); if(!EFI_ERROR(Status)){ if(Device2TextProtocol == 0) Status = gBS->LocateProtocol( &gEfiDevicePathToTextProtocolGuid, NULL, (VOID**)&Device2TextProtocol ); /*2. 使用
EFI_DEVICE_PATH_PROTOCOL 得到文本格式的Device Path */ TextDevicePath = Device2TextProtocol->ConvertDevicePathToText(DiskDevicePath, TRUE, TRUE); Print(L"%s\n", TextDevicePath); if(TextDevicePath)gBS->FreePool(TextDevicePath); /*3. 關閉 EFI_DEVICE_PATH_PROTOCO */ Status = gBS->CloseProtocol( DiskControllerHandles[HandleIndex], &gEfiDevicePathProtocolGuid, ImageHandle, ); } } { EFI_BLOCK_IO_PROTOCOL* BlockIo = *(EFI_BLOCK_IO_PROTOCOL**) (DiskIo + 1); EFI_BLOCK_IO_MEDIA* Media = BlockIo->Media; /*讀1號扇區(qū)。 */ Status = DiskIo->ReadDisk(DiskIo, Media->MediaId, 512, 512, gptHeader); /*檢查GPT標志。 */ if((!EFI_ERROR(Status)) &&( gptHeader -> Header.Signature == 0x5452415020494645)){ UINT32 CRCsum; UINT32 GPTHeaderCRCsum = (gptHeader->Header.CRC32); gptHeader->Header.CRC32 = 0; gBS -> CalculateCrc32(gptHeader , (gptHeader->Header.HeaderSize), &CRCsum); if(GPTHeaderCRCsum == CRCsum){ // Find out a GPT Header
} } } } } gBS->FreePool(DiskControllerHandles); }}