我正在使用GNU-EFI开发各种引导加载程序。到目前为止，我已经能够读取Boot####NVRAM 变量，所以我有一个半填充的FilePathList[]，它看起来像这样(用DevicePathToStr打印)：
HD(Part2, SigCD0400E6-54F3-49F4-81F2-65B21E8278A8)/EFIMicrosoftBootbootmgfw.efi
当传递给LoadImage时，它会失败并显示EFI_NOT_FOUND。据我了解(UEFI 文档第 3.1.2 节)，我需要在已有路径之前添加完整路径。我发现正确的路径是PciRoot(0x0)/Pci(0x1, 0x1)/Ata(0x0)，但我不确定如何根据我所拥有的以编程方式找到这条路径，以便可以对其进行前缀。
到目前为止，我拥有的代码如下，请原谅质量低下，到目前为止我一直在尝试让一些东西工作。
EFI_STATUS status;
EFI_GUID vendor = EFI_GLOBAL_VARIABLE;
UINT32 Attr;
UINTN size = 256;
UINT16 *buf = AllocateZeroPool(size);
if (buf == NULL)
Print(L"Failed to allocate buffern");
status = uefi_call_wrapper(RT->GetVariable, 5,
L"BootOrder", /*VariableName*/
&vendor, /*VendorGuid*/
&Attr, /*Attributes*/
&size, /*DataSize*/
buf /*Data*/
);
if (status != EFI_SUCCESS)
Print(L"Failed to read BootOrder (%d)n", status);
// should contain an int for the correct boot option
UINT16 bootopt = buf[0];
FreePool(buf);
CHAR16 *name = AllocateZeroPool(18); // Bootxxxx unicode
SPrint(name, 18, L"Boot%04x", bootopt);
Print(L"Next boot: %sn", name);
size = 0;
do {
buf = AllocateZeroPool(size);
if (buf == NULL)
Print(L"Failed to allocate buffern");
status = uefi_call_wrapper(RT->GetVariable, 5,
name,
&vendor,
&Attr,
&size,
buf
);
if (status == EFI_SUCCESS) break;
FreePool(buf);
// if it fails, size is set to what it needs to be
// handy that
} while(status == EFI_BUFFER_TOO_SMALL);
if (!(buf[0]&LOAD_OPTION_ACTIVE)) Print(L"BootOption not activen");
Print(L"%s: 0x%rnn", name, buf);
UINT8 *OrigFilePathList = ((UINT8*)buf) + (sizeof(UINT32) + sizeof(UINT16) + StrSize(buf+3));
UINT16 *FilePathListLength = ((UINT16*)OrigFilePathList)+2;
Print(L"&OrigFilePathList = 0x%rn", OrigFilePathList);
Print(L"sizeof(_EFI_LOAD_OPTION) = %dn", size);
Print(L"struct _EFI_LOAD_OPTION {n");
Print(L" Attributes = %dn", *(UINT32 *)(buf));
Print(L" FilePathListLength = %d,n", *FilePathListLength);
Print(L" Description = %s,n", buf+3);
Print(L" FilePathList[] = {n");
UINT16 totallength = 0;
UINT8 *FilePathList = OrigFilePathList;
for (UINT8 i = 0; i < *FilePathListLength+1; i++) {
Print(L" &FilePathList[%d] = 0x%rn", i, OrigFilePathList);
Print(L" FilePathList[%d].Type = %d ", i, *OrigFilePathList);
switch (*OrigFilePathList) {
case 0x01:
Print(L"(Hardware Device Path)n");
break;
case 0x02:
Print(L"(ACPI Device Path)n");
break;
case 0x03:
Print(L"(Messaging Device Path)n");
break;
case 0x04:
Print(L"(Media Device Path)n");
break;
case 0x05:
Print(L"(BIOS Boot Specification Device Path)n");
break;
case 0x7f:
Print(L"(End Of Hardware Device Path)n");
break;
default:
Print(L"(Unknown Device Path)n");
break;
}
Print(L" FilePathList[%d].SubType = %dn", i, *(OrigFilePathList+1));
Print(L" FilePathList[%d].Length = %dn", i, *(UINT16*)(OrigFilePathList+2));
totallength += *(UINT16*)(OrigFilePathList+2);
OrigFilePathList += *(UINT16*)(OrigFilePathList+2);
}
Print(L" }n");
Print(L" &OptionalData = 0x%rn", OrigFilePathList);
Print(L" OptionalDataLength = %dn", size-totallength);
Print(L"}n");
// The hard drive device path can be appended to the matching hardware
// device path and normal boot behavior can then be used.
// We need to locate the Type 1 FilePathList and prepend it to what we've already got
// Need to prefix PciRoot(0x0)/Pci(0x1, 0x1)/Ata(0x0)
// but automatically find it
// in theory we should be able to use the list of handles to devices that support SIMPLE_FILE_SYSTEM_PROTOCOL
// to find the right device
Print(L"%sn", DevicePathToStr((EFI_DEVICE_PATH *)FilePathList));
/* EFI_STATUS (EFIAPI *EFI_IMAGE_LOAD) (
IN BOOLEAN BootPolicy,
IN EFI_HANDLE ParentImageHandle,
IN EFI_DEVICE_PATH_PROTOCOL *DevicePath,
IN VOID *SourceBuffer OPTIONAL,
IN UINTN SourceSize,
OUT EFI_HANDLE *ImageHandle
); */
EFI_HANDLE *NextHandle = AllocateZeroPool(sizeof(EFI_HANDLE));
status = uefi_call_wrapper(BS->LoadImage, 6,
/* status = BS->LoadImage( */
TRUE, /* BootPolicy */
ImageHandle, /* ParentImageHandle */
(EFI_DEVICE_PATH *)FilePathList, /* DevicePath */
NULL, /* SourceBuffer */
0, /* SourceSize */
NextHandle /* ImageHandle */
);
if (status != EFI_SUCCESS)
Print(L"Failed to LoadImage (%d)n", status);
else
Print(L"LoadImage OKn");
我需要哪些函数和流程才能完全限定FilePathList以便它可以与LoadImage一起使用？
相信当我寻求帮助时，我会解决它。
一般的想法是使用LocateHandleBuffer查找SIMPLE_FILE_SYSTEM_PROTOCOL的所有句柄。使用这些句柄，将路径(使用DevicePathFromHandle)与我们已经拥有的路径进行比较，以找到合适的设备。LoadImage现在对我有用。
下面的示例代码(buf是GetVariable中Boot####变量的值)：
Print(L"Description = %sn", (CHAR16*)buf + 3);
EFI_DEVICE_PATH *BootX = (EFI_DEVICE_PATH*) (((UINT8*)buf) + (sizeof(UINT32) + sizeof(UINT16) + StrSize(buf+3)));
UINTN NoHandles = 0;
EFI_HANDLE *handles = NULL;
EFI_GUID SimpleFileSystemGUID = SIMPLE_FILE_SYSTEM_PROTOCOL;
status = uefi_call_wrapper(BS->LocateHandleBuffer,
5,
ByProtocol,
&SimpleFileSystemGUID,
NULL,
&NoHandles,
&handles
);
if (status != EFI_SUCCESS)
Print(L"Failed to LocateHandleBuffer (%d)n", status);
else
Print(L"LocateHandleBuffer OK (%d handles)n", NoHandles);
EFI_DEVICE_PATH *prefix;
UINTN index;
for (index = 0; index < NoHandles; index++) {
prefix = DevicePathFromHandle(handles[index]);
while(!IsDevicePathEnd(NextDevicePathNode(prefix))) prefix = NextDevicePathNode(prefix);
if(LibMatchDevicePaths(prefix, BootX)) {
break;
} else {
FreePool(prefix);
}
}
prefix = DevicePathFromHandle(handles[index]);
// prefix ends with the same node that BootX starts with
// so skip forward BootX so we can prepend prefix
BootX = NextDevicePathNode(BootX);
EFI_DEVICE_PATH *fullpath = AppendDevicePath(prefix, BootX);
Print(L"Booting: %sn", DevicePathToStr(fullpath));
/* EFI_STATUS (EFIAPI *EFI_IMAGE_LOAD) (
IN BOOLEAN BootPolicy,
IN EFI_HANDLE ParentImageHandle,
IN EFI_DEVICE_PATH_PROTOCOL *DevicePath,
IN VOID *SourceBuffer OPTIONAL,
IN UINTN SourceSize,
OUT EFI_HANDLE *ImageHandle
); */
EFI_HANDLE *NextHandle = AllocateZeroPool(sizeof(EFI_HANDLE));
status = uefi_call_wrapper(BS->LoadImage, 6,
/* status = BS->LoadImage( */
TRUE, /* BootPolicy */
ImageHandle, /* ParentImageHandle */
fullpath, /* DevicePath */
NULL, /* SourceBuffer */
0, /* SourceSize */
NextHandle /* ImageHandle */
);
if (status != EFI_SUCCESS)
Print(L"Failed to LoadImage (%d)n", status);
else
Print(L"LoadImage OKn");