Re: [Qemu-devel] [PATCH] pc: acpi: force FADT rev1 for old i440fx machine types

[Programmingkid]

> On Jul 21, 2017, at 7:40 PM, Michael S. Tsirkin <address@hidden> wrote:
> 
> On Fri, Jul 21, 2017 at 12:10:48PM +0200, Igor Mammedov wrote:
>> On Fri, 21 Jul 2017 10:49:55 +0100
>> "Daniel P. Berrange" <address@hidden> wrote:
>> 
>>> On Fri, Jul 21, 2017 at 11:32:11AM +0200, Igor Mammedov wrote:
>>>> w2k used to boot on QEMU until we bumped revision of FADT to rev3
>>>> (commit 77af8a2b hw/i386: Use Rev3 FADT (ACPI 2.0) instead of Rev1 to 
>>>> improve guest OS support.)
>>>> 
>>>> Considering that w2k is ancient and long time EOLed, leave default
>>>> rev3 but make pc-i440fx-2.9 and older machine types to force rev1
>>>> so old setups won't break (w2k could boot).  
>>> 
>>> There needs to be a machine type property added to control this
>>> feature. When provisioning new VMs, management apps need to be
>>> able to set the property explicitly - having them rely on picking
>>> particular machine type name+versions is not viable, because
>>> downstream vendors replace the machine types with their own
>>> names + versions.
>> having property doesn't really help here and we don't do it for every
>> compat tweak /ex: save_tsc_khz, linuxboot_dma_enabled/.
>> 
>> Management would not benefit much from having property vs machine version
>> as it would have to encode somewhere that for w2k it should set
>> some machine property or pick a particular machine type.
> 
> I think I'd disagree with that. If
> users might need this for compatibility with some guests,
> then it should be a property not just a machine type.
> 
> But see below - I think we rushed it for the PC anyway.
> 
>> Probably no one would worry about fixing virt-install or something
>> else for the sake of w2k and if they are going to fix it
>> it doesn't matter if they map machine type vs property.
>> 
>> Also with new machine type deprecation policy we would be able
>> easily to phase out rev1 support along with 2.9 machine,
>> but if you expose property then removing it would break
>> CLI not only for 2.9 but possible later machines if it's set there.
>> 
>> So I'm against adding properties/CLI options for unless we have to in this 
>> case,
>> and I'm not convinced that w2k deserves it.
> 
> If I have to choose, I'd say Mac OSX is way less interesting than old
> windows versions. Lots of people have software that will only run on old
> windows and there's probably good money to be had running it on new
> hardware in VMs. And PC machine is all about compatibility - we have Q35
> for new stuff.  Besides OSX uses q35 anyway I think.
> 
> So maybe the right thing to do is to
> - switch default for PC back to rev 1
> - keep default for Q35 at rev 3
> 
> No machinetype hacks.

I agree with your ideas.