Step to UEFI (54） ----- EFI_SIMPLE_FILE_SYSTEM_PROTOCOL 写文件

通常，每个UEFI系统至少有一个 ESP (EFI System Partition)分区，在这个分区上存放启动文件。EFI内置了EFI_SIMPLE_FILE_SYSTEM_PROTOCOL(简称 FileSystemIo)可以用来操作FAT文件系统【参考1】。

相关的介绍：

\MdePkg\Include\Protocol\SimpleFileSystem.h

///
/// The EFI_FILE_PROTOCOL provides file IO access to supported file systems.
/// An EFI_FILE_PROTOCOL provides access to a file's or directory's contents, 
/// and is also a reference to a location in the directory tree of the file system 
/// in which the file resides. With any given file handle, other files may be opened 
/// relative to this file's location, yielding new file handles.
///
struct _EFI_FILE_PROTOCOL {
  ///
  /// The version of the EFI_FILE_PROTOCOL interface. The version specified 
  /// by this specification is EFI_FILE_PROTOCOL_LATEST_REVISION.
  /// Future versions are required to be backward compatible to version 1.0.
  ///
  UINT64                Revision;
  EFI_FILE_OPEN         Open;
  EFI_FILE_CLOSE        Close;
  EFI_FILE_DELETE       Delete;
  EFI_FILE_READ         Read;
  EFI_FILE_WRITE        Write;
  EFI_FILE_GET_POSITION GetPosition;
  EFI_FILE_SET_POSITION SetPosition;
  EFI_FILE_GET_INFO     GetInfo;
  EFI_FILE_SET_INFO     SetInfo;
  EFI_FILE_FLUSH        Flush;
  EFI_FILE_OPEN_EX      OpenEx;
  EFI_FILE_READ_EX      ReadEx;
  EFI_FILE_WRITE_EX     WriteEx;
  EFI_FILE_FLUSH_EX     FlushEx;
};

\MdePkg\Include\Protocol\SimpleFileSystem.h

#define EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_GUID \
  { \
    0x964e5b22, 0x6459, 0x11d2, {0x8e, 0x39, 0x0, 0xa0, 0xc9, 0x69, 0x72, 0x3b } \
  }

\EdkCompatibilityPkg\Foundation\Efi\Protocol\SimpleFileSystem\SimpleFileSystem.c

EFI_GUID  gEfiSimpleFileSystemProtocolGuid = EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_GUID;

从原理上来说，先通过这个Protocol OpenVolume,即可获得FAT文件系统上的根目录句柄。目录句柄(EFI_FILE_PROTOCOL)包含了操作该目录里文件的文件操作接口。之后我们再用 Open打开这个目录，选定需要操作的文件即可写入。

\MdePkg\Include\Protocol\SimpleFileSystem.h

/**
  Writes data to a file.

  @param  This       A pointer to the EFI_FILE_PROTOCOL instance that is the file
                     handle to write data to.
  @param  BufferSize On input, the size of the Buffer. On output, the amount of data
                     actually written. In both cases, the size is measured in bytes.
  @param  Buffer     The buffer of data to write.

  @retval EFI_SUCCESS          Data was written.
  @retval EFI_UNSUPPORTED      Writes to open directory files are not supported.
  @retval EFI_NO_MEDIA         The device has no medium.
  @retval EFI_DEVICE_ERROR     The device reported an error.
  @retval EFI_DEVICE_ERROR     An attempt was made to write to a deleted file.
  @retval EFI_VOLUME_CORRUPTED The file system structures are corrupted.
  @retval EFI_WRITE_PROTECTED  The file or medium is write-protected.
  @retval EFI_ACCESS_DENIED    The file was opened read only.
  @retval EFI_VOLUME_FULL      The volume is full.

**/
typedef
EFI_STATUS
(EFIAPI *EFI_FILE_WRITE)(
  IN EFI_FILE_PROTOCOL        *This,
  IN OUT UINTN                *BufferSize,
  IN VOID                     *Buffer
  );

完整代码：

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

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

#include <Protocol/SimpleFileSystem.h>

extern EFI_BOOT_SERVICES         *gBS;
extern EFI_SYSTEM_TABLE			 *gST;


int
EFIAPI
main (                                         
  IN int Argc,
  IN char **Argv
  )
{
    EFI_STATUS          			Status;
	EFI_FILE_PROTOCOL    			*Root;
	EFI_SIMPLE_FILE_SYSTEM_PROTOCOL *SimpleFileSystem;
	UINTN	BufSize;
	CHAR16 *Textbuf = (CHAR16*) L"www.lab-z.com";
	EFI_FILE_PROTOCOL *FileHandle=0;
	
    Status = gBS->LocateProtocol(
						&gEfiSimpleFileSystemProtocolGuid, 
						NULL,
						(VOID **)&SimpleFileSystem);
						
	
    if (EFI_ERROR(Status)) {
		    Print(L"Cannot find EFI_SIMPLE_FILE_SYSTEM_PROTOCOL \r\n");
            return Status;	
	}

	Status = SimpleFileSystem->OpenVolume(SimpleFileSystem,&Root);
    if (EFI_ERROR(Status)) {
		    Print(L"OpenVolume error \r\n");
            return Status;	
	}
   
    Status = Root -> Open(Root,
			&FileHandle,
			(CHAR16 *) L"atest.txt",
			EFI_FILE_MODE_CREATE | EFI_FILE_MODE_READ | EFI_FILE_MODE_WRITE,
			0);
			
    if (EFI_ERROR(Status) || (FileHandle==0)) {
		    Print(L"Open error \r\n");
            return Status;	
	}	
	
	BufSize = StrLen (Textbuf) * 2;
	Print(L"[%d]\r\n",BufSize);		
	Print(L"[%s]\r\n",Textbuf);			
	Status = FileHandle -> Write(FileHandle, &BufSize, Textbuf);
	
	Print(L"Write Done \r\n");	
	
	Status  = FileHandle -> Close (FileHandle);
	
    return EFI_SUCCESS;
}

运行结果：

比较有意思的是，我们按照上面的程序写入之后，使用 type 文件名 来显示文件内容和我们的预期有差别，原因是Type命令默认使用　ASCII 来显内容，而我们的文件中写入的是 Unicode。使用 type -u 强制使用 Unicode即可看到我们期望的内容。

根据【参考2】的提示，我们还可以通过给TXT文件加一个头来通知当前内容格式的方法克服这个问题。

关键代码：

	UINT16  TextHeader =0xFEFF;

	BufSize = 2;
	Status = FileHandle -> Write(FileHandle, &BufSize, &TextHeader);
	
	BufSize = StrLen (Textbuf) * 2;
	Print(L"[%d]\r\n",BufSize);		
	Print(L"[%s]\r\n",Textbuf);			
	Status = FileHandle -> Write(FileHandle, &BufSize, Textbuf);

运行结果：

可以看到经过这样的处理，都可以正常显示内容了。

完整代码下载
ESPTest

参考：

1.UEFI 原理与编程 戴正华 著 P152页

2.http://www.biosren.com/thread-6541-2-1.html UEFI下使用EFI_FILE_PROTOCOL 檔案操作能多次讀寫嗎?

=============================================================

2024年9月20日

下面这个代码段能够实现将指定内存内容保存为文件，方便调试，有需要的朋友可以试试。

#include <Library/BaseMemoryLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Protocol/SimpleFileSystem.h>

extern EFI_HANDLE        			  gImageHandle;

EFI_STATUS
WriteMemoryToFile(
    IN EFI_HANDLE ImageHandle,
    IN CHAR16 *FileName,
    IN VOID *Buffer,
    IN UINTN BufferSize
)
{
    EFI_STATUS Status;
    EFI_SIMPLE_FILE_SYSTEM_PROTOCOL *SimpleFileSystem;
    EFI_FILE_PROTOCOL *Root;
    EFI_FILE_PROTOCOL *File;
    EFI_HANDLE *Handles = NULL;
    UINTN HandleCount = 0;

    // Locate all handles that support the Simple File System Protocol
    Status = gBS->LocateHandleBuffer(ByProtocol, &gEfiSimpleFileSystemProtocolGuid, NULL, &HandleCount, &Handles);
    if (EFI_ERROR(Status)) {
        Print(L"Failed to locate handles for Simple File System Protocol: %r\n", Status);
        return Status;
    }

    // Open the first Simple File System Protocol
    Status = gBS->HandleProtocol(Handles[0], &gEfiSimpleFileSystemProtocolGuid, (VOID **)&SimpleFileSystem);
    if (EFI_ERROR(Status)) {
        Print(L"Failed to open Simple File System Protocol: %r\n", Status);
        return Status;
    }

    // Open the root directory
    Status = SimpleFileSystem->OpenVolume(SimpleFileSystem, &Root);
    if (EFI_ERROR(Status)) {
        Print(L"Failed to open root directory: %r\n", Status);
        return Status;
    }

    // Create or open the file
    Status = Root->Open(Root, &File, FileName, EFI_FILE_MODE_CREATE | EFI_FILE_MODE_WRITE | EFI_FILE_MODE_READ, 0);
    if (EFI_ERROR(Status)) {
        Print(L"Failed to open or create file: %r\n", Status);
        return Status;
    }

    // Write the buffer to the file
    Status = File->Write(File, &BufferSize, Buffer);
    if (EFI_ERROR(Status)) {
        Print(L"Failed to write to file: %r\n", Status);
        File->Close(File);
        return Status;
    }

    // Close the file
    Status = File->Close(File);
    if (EFI_ERROR(Status)) {
        Print(L"Failed to close file: %r\n", Status);
        return Status;
    }

    Print(L"Memory successfully written to file: %s\n", FileName);
    return EFI_SUCCESS;
}