Eric Blake <[email protected]> writes: > On 7/30/20 10:59 AM, Daniel P. Berrangé wrote: > >>> Well, I suspect that management-layer code currently has >>> gone for "assume we're always running on Linux" and was >>> written by people who knew they were getting a Linux tid... >> >> Yes, on the libvirt side, the functionality that relies on thread_is is >> only compiled on Linux. If someone wants to use it on other OS, they'll >> have to provide an impl using their platforms equivalent of >> sched_setaffinity and friends since none of this stuff is standardized >> across OS. >> >> >>>> The PID is quite unlikely to be "an OS-specific identifier of the >>>> current thread". Shouldn't we fail instead of lie when we don't know >>>> how to compute the truth? >>> >>> Yeah, I think the default codepath is pretty bogus too. Should >>> the QMP functions have a mechanism for saying "we don't know >>> a thread-id on this platform" ? >> >> Thread_id should be optional and thus not filled in if we >> can't provide a sensible value. Unfortunately we made it >> mandatory in QMP. > > Normally, converting a mandatory output value to optional is a > back-compatibility risk (we could break apps that depended on it being > present). But if the only apps that depended on it being present are > compiled on Linux, where the member will actually be present, I think > that changing the schema to make it optional for non-Linux platforms > won't be a back-compatibility nightmare (but we will have to be > careful in our documentation).
Options for systems where don't know how to compute a system-wide thread ID: 0. Return a bogus value: the PID. This is the status quo. 1. Return a more obviously bogus value: -1. Semantic compatibility break. Should be harmless, because a QMP client relying on the thread-id being the PID would be insane. 2. Make thread-id optional, present iff we can compute a value. This is what we should have done, but we didn't, and now it's a syntactic compatibility break. Matters only if it actually breaks QMP clients. We believe the one we know shouldn't break. Preferences?
