Support persisting EFI vars

[g-arjones]

mkosi commit the issue has been seen with

main

Used host distribution

Ubuntu 24.04

Used target distribution

Ubuntu 24.04

Linux kernel version used

Kernel 6.12

CPU architectures issue was seen on

x86_64

Unexpected behaviour you saw

Mkosi creates a file to store EFI variables but it’s always temporary. When testing and/or debugging bootable images it’s often useful to persist them so mkosi should at least provide an option to keep the file around between multiple mkosi qemu invocations

Used mkosi config

Not relevant

mkosi output

Not relevant

[DaanDeMeyer]

I'm not necessarily against this, but can you add more detail on when this would be useful?

[g-arjones]

I can talk about my use case specifically. I'm building a custom OS image with an A/B system updater, and to fully test the whole process effectively (e.g., bootloader update scripts, efi vars updates, etc), it is important to have the efi vars persisted (especially for integration tests in CI environment).

[DaanDeMeyer]

I can talk about my use case specifically. I'm building a custom OS image with an A/B system updater, and to fully test the whole process effectively (e.g., bootloader update scripts, efi vars updates, etc), it is important to have the efi vars persisted (especially for integration tests in CI environment).

But would you ever shut down in that case? If you just reboot the variables are kept around no?

[g-arjones]

But would you ever shut down in that case? If you just reboot the variables are kept around no?

We have a few test suites, and sometimes the QEMU process is indeed restarted (as opposed to just rebooting the VM). Also, during debugging and development, QEMU has to be restarted frequently.

[DaanDeMeyer]

The annoying thing about implementing this is that with a naive implementation you can't just change FirmwareVariables= anymore and have it be picked up automatically the next time you boot the virtual machine. You'd have to explicitly remove the persisted variables first.

We have a few test suites, and sometimes the QEMU process is indeed restarted (as opposed to just rebooting the VM). Also, during debugging and development, QEMU has to be restarted frequently.

Sure but how often do you need to restart qemu with persisted efi vars during development/testing?

[g-arjones]

The annoying thing about implementing this is that with a naive implementation you can't just change FirmwareVariables= anymore and have it be picked up automatically the next time you boot the virtual machine. You'd have to explicitly remove the persisted variables first.

That makes sense to me; they could be copied as part of the build process. But I would also be fine with making FirmwareVariables and FirmwareVariablesPersisted mutually exclusive.

Sure but how often do you need to restart qemu with persisted efi vars during development/testing?

"Frequently". I don't have a number, if that's what you mean.