[WIP] EVE Custom EFI App to change UEFI setings

[shjala]

The idea is to not have pre-cooked OVMF_VARS files for different UEFI settings, but to have EFI application to run and manipulate the settings to our liking before booting the guest VMs.

The EVE part is janky and hacky, I will fix that in time, right now I'm more interested to know if this is viable option or not, so @rene @eriknordmark @OhmSpectator @rucoder comments are welcomed.

This is how it works :

1. Run qemu with only option to boot into the UEFI shell and run the EFI app, this is needed because I can't trust how UEFI is creating the boot order so we need a way to guarantee that our app gets a chance to run.
2. Run the efi app, change the settings, we can feed custom config to the app as smbios OEM strings.
3. Running the efi app will change the boot order in the OVMF_VARS.fd so when EVE is launching the VM (using the OVMF_VARS cooked in 2), it will continue to boot into the UEFI shell even if there is nothing to run (no efi.img passed to qemu)
4. To fix this we run the qemu with the efi app present but this time efi app tries all the boot options until it finds an option that boots successfully.

Efi app is simple and uses gnu-efi.

[rucoder]

@shjala I do not really understand how SMBIOS custom string may affect EFI variable. Could you point me to a spec?

[shjala]

@rucoder (1/2) here I get the OEM string aka type=11,value=BlahBlah, aka BlahBlah in the smbios string table.

[shjala]

@rucoder (2/2) here I convert the smbios OEM string to the a predefined config value and then apply it based on what it is.

[shjala]

@shjala I do not really understand how SMBIOS custom string may affect EFI variable. Could you point me to a spec?

It won't, I read the SMBIOS custom string in my EFI application, if it is one of the pre-defined config values I parse it and then apply it.