Re: [Qemu-devel] [PATCH v5 1/6] machine: Convert the valid cpu types to use cpu_model

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 18 Jun 2019 10:55:16 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Tue, Jun 18, 2019 at 01:34:10PM +0200, Igor Mammedov wrote:
> > On Mon, 17 Jun 2019 13:27:00 -0300
> > Eduardo Habkost <ehabkost@redhat.com> wrote:
> >   
> > > On Mon, Jun 17, 2019 at 05:33:43PM +0200, Igor Mammedov wrote:  
> > > > On Mon, 17 Jun 2019 17:15:21 +0200
> > > > Philippe Mathieu-Daudé <philmd@redhat.com> wrote:    
> > > [...]  
> > > > > Yes. Eduardo and you should write some lines to explain this, and then
> > > > > we will follow :)    
> > > > Unfortunately I don't recall details anymore. One could check out all
> > > > implementations of class_by_name callbacks to find out current state.    
> > > 
> > > See this message for a summary of existing class_by_name quirks:
> > > 
> > >   https://www.mail-archive.com/qemu-devel@nongnu.org/msg615503.html
> > >   Date: Wed, 08 May 2019 10:34:44 +0200
> > >   Message-ID: <877eb173a3.fsf@dusky.pond.sub.org>
> > >   Subject: Re: [Qemu-devel] [PATCH 0/7] Delete 16 *_cpu_class_by_name() functions
> > > 
> > > I'm unsure about Igor's suggestion to get rid of CPU model names
> > > and use only QOM type names in external interfaces.  In either
> > > case, we can still simplify the rules rules and reduce the amount
> > > of arch-specific code.  
> > as far as we have cpu_class_by_name, we have to watch over that
> > new patches/targets won't add some custom handling/fallbac/whatnot.  
> 
> We can get rid of CPUClass::cpu_class_by_name() without changing
> the external interfaces provided by QEMU.
if you mean QMP, than it is possible to keep model there where
it already exists. Based on experiment [1](x86) I did, it's local to
affected target and doesn't pollute other code.

> I don't have a strong opinion about using only QOM types at -cpu,
> yet.  But first we need to get rid of the arch-specific CPU model
> name exceptions enumerated at the URL above (which would be very
> welcome).
One way to get rid of them is to deprecate them in favor of strict
match (no fallback/substitutions/aliases) to typename and when we
drop it make switch type based naming only.

1) I've just took a quick look at how much of duplicated/confusing
code we could get rid off if we drop cpu_class_by_name/*_cpu_list.
It amounts to >800LOC of trivial removal (not counting ppc/s390
that depend on model naming heavily and in need of some non
trivial refactoring)

> 
> > 
> > On contrary -device works just with type names for all devices,
> > applying the same to -cpu which is basically translator
> >    model->type[,-global type.foo,...]
> > would be consistent with -device and less confusing for everyone
> > (not counting significant code reduction).
> > It would certainly simplify contributing new targets as contributor
> > won't have to care about cpu model naming and do something about it.
> > 
> > This option wasn't considered before because we didn't have deprecation
> > back then, but now it opens possibility to simplify qemu and consolidate
> > naming. (we probably would be able to fold '-cpu help' into '-device help'
> > as well).
> >   
>