Adding a safeguard for UEFI/legacy config switch

[ydirson]

Currently, when the system is installed using, say, legacy boot, and a user subsequently changes to UEFI for booting a new install media, the choice to upgrade the installed system is still offered, even though it will not work, and will possibly not be detected until late post-installation phase.
Similarly, and possibly more likely, if a backup exists, which can date from before a voluntary switch from legacy to UEFI, it will be offered with similar consequences.

It should be doable to record the boot-type in /etc/xensource-inventory so we can avoid early such situations. Another option (or fallback option) could be to rely on the /etc/fstab contents to check for an /boot/efi entry.

Does it look like something that could be accepted ?

[rosslagerwall]

In an ideal world this would be possible but since it might be tricky and introduce a bunch of test edge cases, I think it is OK to block it for now.

There is existing code in the installer which checks for UEFI boot by checking for an ESP like this efi_boot = boot_part and boot_part['id'] == GPTPartitionTool.ID_EFI_BOOT so I would suggest using the same pattern.