Re: [RFC PATCH 0/3] liveupdate: Move to feature flags for LUO and memfd ABI compatibility

On Wed, Sep 02, 2026 at 07:34:49PM -0700, Logan Odell wrote:

We're including maintainers from all subsystems that currently is or
will be expected to participate in live update to ensure alignment on
the path forward for compatibility.

Currently, Live Update Orchestrator (LUO) and its file handlers rely on
monolithic compatibility strings (such as "luo-v5" and "memfd-v1") to
validate ABI compatibility across kexec live updates. Any modification
to serialized structures requires bumping the version string, which
strictly breaks compatibility between adjacent kernels even when changes
are additive, backwards-compatible, or optional.

That was the intention, I aruged strongly that upstream does not want
to maintain a CSP matrix of endless kernel version combinations. That
is far too much work to push on maintainers. Upstream would do much
less, maybe only same-version, depending.

This RFC series transitions LUO and subsystem file handlers to use
granular feature bitmasks instead of compatibility strings. We replace
the compatibility string with a header structure that includes some
reserved space to define the features that are included after the
feature.

The compatability string is only a small part of it, you also need a
serializing ABI that can handle some random mixmash of these
features. Ie the various TLV schemes that were all proposed. What is
the plan here?

Jason