Step to UEFI (74） ----- 通过 OpenVolume访问FSx上的文件

题目有点绕口，简单的说目标就是：我打算用 EFI_SIMPLE_FILE_SYSTEM_PROTOCOL 中的 OpenVolume 打开 FsX: 上面的文件怎么办？
实现的思路是：

1. 查找系统中所有支持 FS Protocol的Device
2. 对于每一个有 FS Protocol 的 Device 用 DevicePathFromHandle 取得 DevicePath
3. 再用 GetFsName 功能取得 FS0 ，FS1 这样的名称，然后判断是否为我们希望的名称
4. 如果是的话，再取得这个设备上的 SimpleFileSystem protocol
5. 最后用 OpenVolue 打开文件。

具体代码：

#include  <Uefi.h>
#include  <Library/UefiLib.h>
#include  <Library/ShellCEntryLib.h>

#include  <stdio.h>
#include  <stdlib.h>
#include  <wchar.h>

#include <Protocol/EfiShell.h>
#include <Library/ShellLib.h>

#include <Protocol/SimpleFileSystem.h>
#include <Protocol/BlockIo.h>
#include <Library/DevicePathLib.h>
#include <Library/HandleParsingLib.h>
#include <Library/SortLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/BaseMemoryLib.h>

extern EFI_BOOT_SERVICES         *gBS;

extern EFI_SHELL_ENVIRONMENT2    *mEfiShellEnvironment2;
extern EFI_HANDLE				 gImageHandle;

EFI_STATUS
EFIAPI
PerformSingleMappingDisplay(
  IN CONST EFI_HANDLE Handle
  )
{
	EFI_DEVICE_PATH_PROTOCOL  *DevPath;
	CHAR16                    *CurrentName;
	CHAR16					*FSNAME=L"fsnt1";
	EFI_SIMPLE_FILE_SYSTEM_PROTOCOL *SimpleFileSystem;
	EFI_FILE_INFO     		*FileInfo = NULL;
	EFI_STATUS                Status;
	EFI_FILE_PROTOCOL   		*FileProtocol;
	EFI_FILE_HANDLE     		FileHandle;
	UINTN 					FileDataLength;
	CHAR16 					*FileData;

	CurrentName = NULL;
    DevPath = DevicePathFromHandle(Handle);
  
  //4. Covnver DevicePath to FSx (E.x FS2, FSNT1.....)
  mEfiShellEnvironment2->GetFsName(DevPath,FALSE,&CurrentName);

  //5. If the "FSx" string is what we want 
  if (StrCmp(CurrentName,FSNAME)==0) {
		Print (L"%s \r\n", CurrentName);  		
		
		//6. Open the SimpleFileSystem Protocol on it
		Status = gBS->OpenProtocol(
								Handle,
                                &gEfiSimpleFileSystemProtocolGuid,
                                (VOID**)&SimpleFileSystem,
								gImageHandle,
								NULL,
								EFI_OPEN_PROTOCOL_GET_PROTOCOL
                                );
		if (EFI_ERROR(Status)) {
			Print (L"LocateProtocol SimpleFileSystem Error \r\n");  	
			return (EFI_NOT_FOUND);
		}
	   
	    //7. Use OpenVolue to get FileProtocol
		Status = SimpleFileSystem->OpenVolume(SimpleFileSystem, &FileProtocol);
		if (EFI_ERROR(Status)) {
			Print (L"SimpleFileSystem OpenVolume Error \r\n");
			return Status;
		}
    
		//8. At last we can operate file by FileProtocol
		Status = FileProtocol->Open(FileProtocol, 
                              &FileHandle, 
                              L"Hello.txt",
                              EFI_FILE_MODE_READ,
                              0);
		if (EFI_ERROR(Status)) {
			Print (L"FileProtocol Open Error [%r]\r\n",Status);
			return Status;
		}
    
		FileInfo = ShellGetFileInfo( (SHELL_FILE_HANDLE)FileHandle);	
		Print(L"Filesize [%ld] bytes\n",FileInfo-> FileSize);
		FileDataLength=(UINTN) FileInfo->FileSize;
	
		FileData  = AllocatePool((UINTN) FileInfo->FileSize);
		Status = FileHandle->Read(FileHandle, &FileDataLength, FileData );
		if (EFI_ERROR(Status)) {
			Print(L"Loading file error! \n");
		}
		
		FileData[FileDataLength/2 -1]=0x0;
		Print(L"File contants: [%s]",FileData);
		
		FreePool(FileData);
		FileProtocol->Close(FileHandle);
  }
	
  if ((CurrentName) != NULL) { FreePool((CurrentName)); CurrentName = NULL; }

  return EFI_SUCCESS;
}

int
EFIAPI
main (                                         
  IN int Argc,
  IN char **Argv
  )
{
  EFI_STATUS                Status;
  EFI_HANDLE                *HandleBuffer=NULL;
  UINTN                     BufferSize=0;
  UINTN                     LoopVar;
  BOOLEAN                   Found;

  //1. We have to use some function in SE2 
  //
  // UEFI 2.0 shell interfaces (used preferentially)
  //
  Status = gBS->OpenProtocol(
    gImageHandle,
    &gEfiShellProtocolGuid,
    (VOID **)&gEfiShellProtocol,
    gImageHandle,
    NULL,
    EFI_OPEN_PROTOCOL_GET_PROTOCOL
   );
   
  if (EFI_ERROR(Status)) {
    //
    // Search for the shell protocol
    //
    Status = gBS->LocateProtocol(
      &gEfiShellProtocolGuid,
      NULL,
      (VOID **)&gEfiShellProtocol
     );
    if (EFI_ERROR(Status)) {
      gEfiShellProtocol = NULL;
     }
  }

  
  //
  //2. Look up all SimpleFileSystems in the platform
  //
  Status = gBS->LocateHandle(
    ByProtocol,
    &gEfiSimpleFileSystemProtocolGuid,
    NULL,
    &BufferSize,
    HandleBuffer);
	
  if (Status == EFI_BUFFER_TOO_SMALL) {
		HandleBuffer = AllocateZeroPool(BufferSize);
		if (HandleBuffer == NULL) {
			return (SHELL_OUT_OF_RESOURCES);
		}
		Status = gBS->LocateHandle(
			ByProtocol,
			&gEfiSimpleFileSystemProtocolGuid,
			NULL,
			&BufferSize,
			HandleBuffer);
   }

  //
  // Get the map name(s) for each one.
  //
  for ( LoopVar = 0, Found = FALSE
      ; LoopVar < (BufferSize / sizeof(EFI_HANDLE)) && HandleBuffer != NULL
      ; LoopVar ++
     ) {
	//3.Emulate every Handle which has SimpileFileSystem 
    Status = PerformSingleMappingDisplay(HandleBuffer[LoopVar]);
    if (!EFI_ERROR(Status)) {
      Found = TRUE;
    }
  }
  
  FreePool(HandleBuffer);
	
  return EFI_SUCCESS;
}

 

我是在虚拟机下实验的，运行之后打开并且读取 fsnt2:\hello.txt 的内容（内容是 www.lab-z.com123）。

特别注意的是：直接读取之后按照 CHAR16 的字符串来处理，但是读取内容没有 0x00 0x00的结尾。直接用Print 输出的时候字符串后面会有意料之外的字符。所以用下面这个语句 FileData[FileDataLength/2 -1]=0x0; 直接添加一个结尾。这也是为什么字符3被截掉的原因。

完整代码下载
OpenFSX

参考：

1. https://www.lab-z.com/esptest/ Step to UEFI (54） ----- EFI_SIMPLE_FILE_SYSTEM_PROTOCOL 写文件
2. https://www.lab-z.com/shellfsx/ Step to UEFI (36) ----- 枚举Shell下的全部盘符
3. https://www.lab-z.com/stu63/ Step to UEFI (63） ----- 常用的字符串函数(下)
4. https://www.lab-z.com/nstring/ Step to UEFI (62） ----- 常用的字符串函数(上)