On Tue, 10 Jun 2014 18:29:43 +0200 Paolo Bonzini <pbonz...@redhat.com> wrote:
> Il 10/06/2014 16:48, Luiz Capitulino ha scritto: > > > The s390 restart interrupt is a per-vcpu interrupt, which we really > > > don't want to inject on _all_ vcpus. OTOH, we want to inject that > > > interrupt on any vcpu - we don't care which one it is. So I'd really > > > like an "inject nmi on default cpu" option. > > > > We could define a default CPU for the command. What isn't going to work > > is to use the human monitor's "current CPU" concept (set with the cpu > > command). > > It isn't going to work, but to me it seems like a bug. Why was the NMI > command even converted to QAPI if it cannot work? It works by sending the NMI to all CPUs. That's the solution we found to avoid creating a dependency between a QMP command and HMP w/o breaking the nmi command compatibility. If this is not right, I'd have expected people to complain as I know this has been used for quite some time to generate crash dumps. All I'm suggesting is to add a new QMP command, say inject-nmi-cpu, which takes a CPU index as an argument. This solves any concern on compatibility Alex talked about, gives a chance to design the command the way we like and doesn't create a dependency between a QMP command and HMP (which would be a design flaw). The QAPI had two main motivations. Automatically generate open-coded json present in all QMP commands and decouple QMP from HMP, as the two were tight coupled in the past. Having the two decoupled is very important so that QMP doesn't depend on HMP's global garbage (good for concurrency and for allowing to have a different HMP on top of QMP). Also, we were planning having a QMP-only socket, session support and other features. Being able to build QMP w/o building the monitor would be a good milestone. Making a QMP command depend on HMP is step back for all this planning and a big de-motivator for all the hard work we put on separating the two. Again, I wonder if I'm missing something, but I see it as a very simple change to add a new command. Note that we can do whatever we want in hmp_inject_nmi(), we can use the new command with whatever semantics we like.
