Re: [PATCH v2 06/10] PCI/LUO: Save and restore driver name

[Pasha Tatashin]

> > A driver that preserves state across a reboot already has an implicit
> > contract with its future self about that data's format. The GUID
> > simply makes that contract explicit and machine-checkable. It does not
> > have to be GUID, but nevertheless there has to be a specific contract.
>
> So how are you going to "version" these GUID?  I see you use "schema Vx"

Driver developer who changes a driver to support live-update.

> above, but how is that really going to work in the end?  Lots of data
> structures change underneath the base driver that it knows nothing
> about, not to mention basic things like compiler flags and the like
> (think about how we have changed things for spectre issues over the
> years...)

We are working on versioning protocol, the GUID I am suggesting is not
to protect "struct" coherency, but just to identify which driver to
bind to which device compatability.

>
> And when can you delete an old "schema"?  This feels like you are
> forcing future developers to maintain things "for forever"...

This won't be an issue because of how live update support is planned.
The support model will be phased and limited:

Initially, and for a while there will be no stability guarantees
between different kernel versions.
Eventually, we will support specific, narrow upgrade paths (e.g.,
minor-to-minor, or stable-A to stable-A+1).
Downgrades and arbitrary version jumps ("any-to-any") will not be
supported upstream. Since we only ever need to handle a well-defined
forward path, the code for old, irrelevant schemas can always be
removed. There is no "forever".

Pasha