在BIOS的功能完善过程中，我们经常需要调整启动顺序，比如在有UEFI shell启动项的情况下，我们需要将其放在最后，或者要将某个硬盘放在首位。
EfiBootManagerSortLoadOptionVariable (LoadOptionTypeBoot, (SORT_COMPARE)CompareBootOption);
INTN
EFIAPI
CompareBootOption (
CONST EFI_BOOT_MANAGER_LOAD_OPTION *Left,
CONST EFI_BOOT_MANAGER_LOAD_OPTION *Right
)
{
return BootOptionPriority (Left) - BootOptionPriority (Right);
}
UINTN
BootOptionPriority (
CONST EFI_BOOT_MANAGER_LOAD_OPTION *BootOption
)
{
EFI_DEVICE_PATH_PROTOCOL *DevPath;
DevPath = BootOption->FilePath;
while(!IsDevicePathEndType((void*)DevPath))
{
if ( (DevPath->Type == MESSAGING_DEVICE_PATH) && (DevPath->SubType == MSG_SATA_DP) ){
return 10;
}else if( (DevPath->Type == MESSAGING_DEVICE_PATH) && (DevPath->SubType == MSG_USB_DP) ){
return 20;
}else if((DevPath->Type == MESSAGING_DEVICE_PATH) && ((DevPath->SubType == MSG_IPv4_DP) || (DevPath->SubType == MSG_IPv6_DP))){
return 30;
}
DevPath = NextDevicePathNode((void*)DevPath);
}
//shell
if (StrCmp (BootOption->Description, L"UEFI Shell") == 0) {
return 40;
}
return 1000;
}
在调整启动顺序代码段添加上述代码就能很好的调整默认启动顺序，但是怎么让shell或者某个选项在最后呢，就需要使用到如下的代码：
VOID
EFIAPI
EfiBootManagerSetShellAsLast ()
{
EFI_STATUS Status;
EFI_BOOT_MANAGER_LOAD_OPTION *LoadOption;
UINTN LoadOptionCount;
UINTN Index, BootOrderIndex;
UINT16 *OptionOrder;
LoadOption = EfiBootManagerGetLoadOptions (&LoadOptionCount, LoadOptionTypeBoot);
//
// Create new ****Order variable
//
OptionOrder = AllocatePool (LoadOptionCount * sizeof (UINT16));
ASSERT (OptionOrder != NULL);
BootOrderIndex = 0;
for (Index = 0; Index < LoadOptionCount; Index++) {
if (StrCmp(LoadOption[Index].Description, L"UEFI Shell") != 0)
{
OptionOrder[BootOrderIndex] = (UINT16) LoadOption[Index].OptionNumber;
BootOrderIndex ++;
}else
{
OptionOrder[LoadOptionCount-1] = (UINT16) LoadOption[Index].OptionNumber;
}
}
Status = gRT->SetVariable (
mBmLoadOptionOrderName[LoadOptionTypeBoot],
&gEfiGlobalVariableGuid,
EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS | EFI_VARIABLE_NON_VOLATILE,
LoadOptionCount * sizeof (UINT16),
OptionOrder
);
//
// Changing the *Order content without increasing its size with current variable implementation shouldn't fail.
//
ASSERT_EFI_ERROR (Status);
FreePool (OptionOrder);
EfiBootManagerFreeLoadOptions (LoadOption, LoadOptionCount);
}
通过上述两者，我们就能很好的调整启动顺序了，当然有特殊的启动顺序要求也可以根据上面的逻辑进行编写。