On Thu, Jun 29, 2017 at 04:18:49PM -0300, Eduardo Habkost wrote: > On Thu, Jun 29, 2017 at 11:00:13AM +0800, Peter Xu wrote: > > On Thu, Jun 29, 2017 at 12:42:56AM +0200, Juan Quintela wrote: > > > Eduardo Habkost <ehabk...@redhat.com> wrote: > > > > > > > > > > > So, this is a case where a user-provided config option (-machine > > > > enforce-config-section) should trigger a different default in another > > > > class (migration.send-configuration). > > > > > > > > Also, the new default triggered by -machine has a very specific > > > > priority: > > > > > > > > * AccelClass::global_props must not override "-machine > > > > enforce-config-section=on" > > > > * MachineClass::compat_props must not override > > > > "-machine enforce-config-section=on" > > > > > > > > We must also decide in advance what should be result of: > > > > * "-machine enforce-config-section=on -global > > > > migration.send-configuration=off" > > > > * "-machine enforce-config-section=off -global > > > > migration.send-configuration=on" > > > > * "-global migration.send-configuration=off -machine > > > > enforce-config-section=off" > > > > * "-global migration.send-configuration=on -machine > > > > enforce-config-section=on" > > > > Yes, this is considered before this patch: currently > > enforce-config-section will have the highest priority in case if > > someone used both of the old & new parameters for it (considering > > "enforce-config-section" has the word "enforce" inside, it makes some > > sense). While... > > > > > > > > BOOM!!!!! > > > > > > We use old configuration or new one. > > > > ... I agree more with Juan here, that user should not really specify > > these two parameters at the same time. If the user knows the new > > parameter, he/she should know that the new one is obsoleting the old > > one. And since even for that case this patch can handle it well (will > > take -M param), I think it's okay. > > If that's the intended result, it's OK to me. But I think the > relationship between enforce-config-section and > migration.send-configuration should be documented in qemu-options.hx. > And considering that this could break silently in future code > refactoring, an automated test would be interesting (but not critical, > as setting options contradicting each other is not a common scenario). > > > > > > > > > > > > > > > I'm not sure what we should decide about these 4 cases above, but I > > > > believe it would be safer to encode that decision at the same place we > > > > handle the priority between accel/machine/user globals: > > > > register_global_properties() at vl.c. > > > > > > > > > > > > Or maybe this extra complexity is a sign that we shouldn't try to add > > > > extra magic to make -machine affect the "migration" object properties, > > > > and keep the existing machine->enforce_config_section check in the > > > > migration code? I'm not sure. > > > > > > Not sure there either. I preffer doing it in a single place, but I am > > > not the expert here. > > > > IMHO it is not necessary to introduce such a thing in > > register_global_properties(). AFAIU this is the only place where one > > machine property can collapse with a global property? And it currently > > only happens in migration codes. Actually it is well ordered, since we > > init the migration object after register_global_properties(), so > > everthing should possibly be fine. Introducing framework-level thing > > for this may only make things more complicated imho. > > True. Considering we need to keep the "overrides everything else" > semantics of enforce-config-section, your approach is not bad. > > > > > After all we can remove all these one day when we can obsolete the > > "enforce-config-section" parameter (maybe we should add one OBSOLETE > > warning when the -M parameter is used). Thanks, > > I don't think we need a warning, but a documentation update is > important, IMO.
Since the pull request has been merged already, I'll add some documentation to qemu-options.hx for this in separate patch (and I'll temporarily skip the unit test since I really think we should obsolete the old parameter one day). Thanks! -- Peter Xu
