BIOS实战之读取文件---获取文件路径+最终读取

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接上一节，获取文件路径实际上也是获取当前这个APP的路径，怎么获取这个APP的路径，这里需要用到一个EFI_LOADED_IMAGE_PROTOCOL，原理如下：

根据当前 Application 的 ImageHandle 取得对应的 Handle。
使用 HandleProtcol 直接打开加载在Application 上面的 EFI_LOADED_IMAGE_PROTOCOL。
在这个 Protocol上有 FilePath，就是当前 Image 的 Device Path Protocol

通过引用看下面的代码一目了然：

EFI_LOADED_IMAGE_PROTOCOL *LoadedImage;Status = gBS->HandleProtocol(gImageHandle, &gEfiLoadedImageProtocolGuid,(void **)&LoadedImage);if(EFI_ERROR(Status)) {Print(L"Application path error!\n");return Status;}EFI_DEVICE_PATH_PROTOCOL  *ptFilePath;ptFilePath  = LoadedImage->FilePath;if(!ptFilePath) {Print(L"Unkown media!\n");return Status;}

ok，又到了Device Path Protocol的环节，在设备路径，找到我们放置APP的设备：

while(!IsDevicePathEnd(ptFilePath)){if(DevicePathType(ptFilePath)==MEDIA_DEVICE_PATH && DevicePathSubType(ptFilePath)==MEDIA_FILEPATH_DP){break;}ptFilePath = NextDevicePathNode(ptFilePath);    }TmpPath = ((FILEPATH_DEVICE_PATH*)ptFilePath)->PathName;

那么这个TmpPath就是app的路径了，如\xxx\xxx\xxx\xx.efi，但是我们只需要路径，不需要app的名字，那么咱们就可以通过判断‘\’来将这个app名字去掉，那么最终的函数如下：

EFI_STATUS
GetAPPFolderPathStr(CHAR16 **Path)
{EFI_STATUS                Status;EFI_DEVICE_PATH_PROTOCOL  *ptFilePath;CHAR16                    *PathName, *TmpPath;UINTN                     StrSize;Status = EFI_SUCCESS;  PathName    = NULL;EFI_LOADED_IMAGE_PROTOCOL *LoadedImage;Status = gBS->HandleProtocol(gImageHandle, &gEfiLoadedImageProtocolGuid,(void **)&LoadedImage);if(EFI_ERROR(Status)) {Print(L"Application path error!\n");return Status;}ptFilePath  = LoadedImage->FilePath;if(!ptFilePath) {Print(L"Unkown media!\n");return Status;}while(!IsDevicePathEnd(ptFilePath)){if(DevicePathType(ptFilePath)==MEDIA_DEVICE_PATH && DevicePathSubType(ptFilePath)==MEDIA_FILEPATH_DP){break;}ptFilePath = NextDevicePathNode(ptFilePath);    }TmpPath = ((FILEPATH_DEVICE_PATH*)ptFilePath)->PathName;while ((TmpPath = StrStr (TmpPath+1, L"\\")) != NULL) {PathName = TmpPath;}if(PathName != NULL){StrSize = (PathName - ((FILEPATH_DEVICE_PATH*)ptFilePath)->PathName)*sizeof(CHAR16);}else{StrSize = 2;}PathName = (CHAR16 *)AllocateZeroPool(StrSize + 2);if(PathName==NULL) {Status = EFI_OUT_OF_RESOURCES;goto ProcExit; }TmpPath = ((FILEPATH_DEVICE_PATH*)ptFilePath)->PathName;CopyMem (PathName, TmpPath, StrSize);if(PathName[0] != L'\\'){Status = EFI_UNSUPPORTED;goto ProcExit;}*Path = PathName;ProcExit:if(EFI_ERROR(Status) && PathName != NULL){FreePool(PathName);PathName = NULL; }return Status;
}

获取这个路径之后咱们还需要将文件的名字加上，这个才是最终需要的：

EFI_STATUS
GetFullPathBaseOnAPPFolder (IN       CHAR16 *FileName,IN OUT   CHAR16 **FullPath)
{EFI_STATUS  Status;CHAR16      *AppFolder;UINTN       FullPathSize;CHAR16      *AppFullPath;CHAR16      Slash = L'\\';Status      = EFI_SUCCESS;AppFolder   = NULL;AppFullPath = NULL;if(FileName == NULL || FullPath == NULL){Status = EFI_INVALID_PARAMETER;goto ProcExit;}GetAPPFolderPathStr(&AppFolder);//上个函数的返回路径if (AppFolder == NULL) {Status = EFI_OUT_OF_RESOURCES;goto ProcExit;}FullPathSize = strsize(AppFolder) + strsize(FileName);AppFullPath  = AllocateZeroPool(FullPathSize);if(AppFullPath == NULL){Status = EFI_OUT_OF_RESOURCES;goto ProcExit;}if (strsize(AppFolder) > 4) { // '\' and '\0'CopyMem (AppFullPath, AppFolder, strsize(AppFolder) - 2); // skip '\0'CopyMem (AppFullPath + strsize(AppFolder)/2 - 1, &Slash, 2);CopyMem (AppFullPath + strsize(AppFolder)/2, FileName, strsize(FileName));} else {CopyMem (AppFullPath, FileName, strsize(FileName));}*FullPath = AppFullPath;

这个AppFullPath的内容就是xxx\xx\xxx.bmp

最终的读取函数，我们就可以把上述的函数串联起来：

EFI_STATUS
ReadFile (IN     CHAR16  *FileName,IN OUT UINT8   **FileBuffer,OUT    UINTN   *FileSize
)
{EFI_STATUS  Status;CHAR16      *FullPath;// get File full pathStatus = GetFullPathBaseOnAPPFolder(FileName, &FullPath);if(EFI_ERROR(Status)) {return Status;}Status = ReadFileInFS(FullPath, FileBuffer, FileSize);FreePool (FullPath);return Status;
}

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