Re: [libvirt] [Qemu-devel] CPU models and feature probing (was Re: [PATCH qom-cpu 00/16 v10] target-i386: convert CPU) features into properties

On Tue, Feb 11, 2014 at 7:25 AM, Eduardo Habkost <ehabkost(a)redhat.com&gt; wrote: > On Tue, Feb 11, 2014 at 06:31:35AM -0800, Anthony Liguori wrote: >> On Fri, Feb 7, 2014 at 2:55 AM, Paolo Bonzini <pbonzini(a)redhat.com&gt; wrote: >> > Il 07/02/2014 11:16, Eduardo Habkost ha scritto: >> > >> >> You are not alone. I remember we spent lots of time trying to convince >> >> Anthony to allow global properties and compat_props affect dynamic >> >> properties not just static properties, and static properties were a big >> >> deal due to reasons I didn't understand completely. Now I am hearing the >> >> opposite message, and I don't understand the reasons for the change of >> >> plans. I am confused. >> > >> > >> > Picture me confused as well, but at the same I think I understand the >> > reasons for the change of plans. >> >> There's no real convincing. It's just a question of code. > > I am sure there's a lot of convincing involved, even after the code is > written (in this case, 15 months after the code was written). N.B. the code you refer to doesn't "make global propeties and compat_props affect dynamic properties." It converts CPU properties to static properties which I'm pretty sure I said many times is a perfectly reasonable thing to do.

>> There are >> no defaults in classes for dynamic properties to modify. compat_props >> are a nice mechanism, making them work for all properties is a >> reasonable thing to do. > > That's exactly the opposite of what you said before[1]. But that isn't > supposed to be a problem, I understand there may be change of plans (we > should be able to change our minds). I think you're confusing a few things. You cannot make dynamic properties work with globals today. Globals change class default values and there are no class defaults for dynamic properties.[*]

There's a perfectly valid discussion to have about whether we should even have dynamic properties. It's certainly been a long time since they were introduced and they haven't made their way into all that many devices so it's reasonable to say that perhaps we'd be better off without them. I would not object to a patch series that moved properties to classes entirely provided it removed existing uses of dynamic properties and didn't just introduce yet another mechanism.

But compat properties as a concept could be made to work with dynamic properties. They would have to be evaluated after instance init. There's quite a few places they would end up touching I suspect.