Proposal: how to make incompatible changes

[Alexander Amelkin]

15.04.2020 02:00, Joseph Reynolds пишет:
> Proposal: how to make incompatible changes
>
> This is a proposal to add guidelines for making incompatible changes 
> to OpenBMC interfaces.  Is it okay to make incompatible changes? Yes, 
> IMHO: the project will continuously break compatibility in various 
> ways, and its users will adapt.  The main idea is to minimize churn 
> and make it easier for users to adapt.
>
> As the OpenBMC project moves forward with new releases, it will make 
> changes that necessarily break existing use cases.  My recommendations 
> are:
> - Try hard to maintain forward compatibility.  For example, maintain 
> all of the BMC's intended user interfaces.
> - Identify changes that break compatibility.  Briefly describe the use 
> case, what breaks, how a user can adapt, and cross-link technical 
> discussions (Gerrit reviews, issues, emails).
> - Work with maintainers to determine which incompatible changes get 
> merged and what documentation is needed.
> - Give users time to adapt to incompatible changes.  For example, 
> deprecate interfaces in a previous release.
> - List incompatible changes in the [release notes][] so community 
> members will know they have to adapt, and link to how to adapt.
>
>
I'd say that any incompatible change must be reflected in the interface 
version.

As far as I understand, RedFish has all the interfaces strictly 
specified and those specifications are bound to a specific RedFish 
version that is then encoded in the URL (e.g. /redfish/v1/).

Any other interface should have a similar approach. A more relaxed one, 
if we keep our own flavor of REST, could be that each interface could 
have a Version property (probably also encoded in the REST URL).

That way, any user trying to access an old interface (thus via a 
non-existant URL) would get a 404.

Internally, for inter-process dbus communication the interface version 
could be checked during compile time to prevent problems that couldn't 
be detected by compiler/linker automatically. Those problems are, for 
instance, incompatible change in the meaning of the values of a property.

Alexander.