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

[Jason Gunthorpe]

On Thu, Sep 10, 2026 at 03:42:36PM -0700, Sean Christopherson wrote:
> On Thu, Sep 10, 2026, Jason Gunthorpe wrote:
> > Sean's initial email was asking for strict never-break ABI compatability
> > rules on top, and that is what I've been reacting to.
> 
> No, I was never asking for that.  I think we just have a different interpretation
> of ABI, or rather are talking about different pieces of ABI.
> 
> I am still asking for never-break serialization format compatibility, i.e. the
> more literal save/restore ABI.  I'm not asking for full backwards/forwards
> compatibility across all kernels version, i.e. the higher level "kernel" ABI.
> 
> To phrase things differently: I am a-ok if kernels are inherently incompatible
> because they fundamentally operate differently and/or support different features.
> I am not ok if we end up with incompatible kernels because the save/restore
> interfaces and payloads are poorly designed, lack abstraction, etc.  

I can more agree with this, it is mostly what I thought we'd end up
doing anyhow with version numbers and growing the structs not
replacing them.

So you still end up with a version label (string I guess?) because we
can break it from time to time, just the version should have the
feature mechanism layered under it? I'm fine with that

Jason