Re: [libvirt] [PATCH 7/9] qmp: Add runnability information to query-cpu-definitions

> > > > > > > > Just FYI, on other architectures (e.g. s390x), other conditions (e.g. cpu > > > > generation) also define if a CPU model is runnable, so the pure availability of > > > > features does not mean that a cpu model is runnable. > > > > > > > > We could have runnable=false and unavailable-features being an empty list. > > > > > > Even on those cases, can't the root cause be mapped to a QOM > > > property name (e.g. "cpu-generation"), even if it's property that > > > can't be changed by the user? > > > > In the current state, no. > > But it could be implemented by s390x in the future, if it's > considered useful, right? Yes, we could fit that into read-only properties if we would ever need it (like cpu-generation you mentioned and cpu-ga-level - both will always be read-only). However we could come up with more optional fields for that in the future. (like unsupported-values or sth. like that). I actually prefer unavailable-features over runnability-blockers. > > > > > So I think for runnable=false: > > a) unavailable-features set -> can be made runnable > > b) unavailable-features not set -> cannot be made runnable > > > > would be enough. > > I understand it would be enough, but I would like to at least > define semantics that would make sense for all architectures in > case it gets implemented in the future. Would the proposal below > make sense? > Yes, I think so. However to really make good hints, upper layers would most likely need more information about the exact problem with a property - maybe something like an enum value per problematic property. (UNAVAILABLE_FEATURE, VALUE_TOO_BIG, VALUE_TOO_SMALL, UNSUPPORTED_VALUE) ...

> > > > > > We could replace this with something more generic, like: > > > > > > @runnability-blockers: List of attributes that prevent the CPU > > > model from running in the current host. > > > > > > A list of QOM property names that represent CPU model > > > attributes that prevent the CPU from running. If the QOM > > > property is read-only, that means the CPU model can never run > > > in the current host. If the property is read-write, it means > > > that it MAY be possible to run the CPU model in the current > > > host if that property is changed. > > > > > > Management software can use it as hints to suggest or choose an > > > alternative for the user, or just to generate meaningful error > > > messages explaining why the CPU model can't be used. > > > > > > (I am looking for a better name than "runnability-blockers"). > > > Not sure which approach would be better.