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Zbigniew Jędrzejewski-Szmek fed0a899b2 hibernate-resume: remove kernel/image version comparison when resuming

We already had a similar check that was removed, see
8340b762e4 (*). The kernel supports loading of a
resume image from a different kernel version. This makes sense, because the
goal of "resume" is to replace the running system by a saved memory image, so
it doesn't really matter that the short-lived kernel is different.

By removing the check, we make the process more reliable: for example, the user
may select a different kernel from a list, or not have the previously running
kernel in /boot at all, etc. Requiring the exact same kernel version makes the
process more fragile for no benefit.

Similar reasoning holds for the image version: the image may be updated, and
for example an older kernel+initrd might be used, with an embedded VERSION_ID
that is not the latest. This is fine, and the check is not useful.

I left the check for ID/IMAGE_ID: we probably don't want to use the resume
image if the hibernation was done from a different installation.

(Note: why not check VERSION_ID/IMAGE_VERSION? Because of the following
scenario: a user has an installation of Fedora 35, and they upgrade to Fedora
36, which means that the os-release file on disk gets replaced and now
specifies VERSION_ID=36. But the running kernel is not replaced, and its
package is not removed because the running kernel version is never removed, so
we still have a boot entry that in initrd-release says VERSION_ID=35. Without
rebooting, the user does hibernation. When resuming, we want to resume, no
matter if one of the new entries with VERSION_ID=36 or one of the old entries
with VERSION_ID=35 is picked in the boot loader menu.

If the installation is image-based, i.e. it has IMAGE_ID+IMAGE_VERSION, the
situation is similar: after an upgrade, we may still have an boot entry from
before the upgrade. Using an older kernel+initrd to boot and switch-root into a
newer installation is supported and is rather common.

In fact, it is a rather common situation that the version reported by the boot
entry (or stored internally in the initrd-release in the initrd) does not match
the actual system on disk. Generally, this metadata is saved when the boot menu
entry is written and does not reflect subsequent upgrades. Various
distributions generally keep at least 3 kernels after a upgrade, and during an
upgrade only install one new, which means that after a major upgrade, generally
there will be at least two kernels which have mismatched version information.)

OTOH, I think it is useful to *write* all the details to the EFI var. As
discussed in https://github.com/systemd/systemd/issues/29037, we may want to
show this information in the boot loader. It is also useful for debugging.

(*) Also again discussed and verified in
https://github.com/systemd/systemd/pull/27330#discussion_r1234332080.

", ignored" is dropped, since this failure is likely to cause the following
check to fail. Better not to say anything then to say the misleading thing.

2023-10-12 12:30:12 +02:00