Re: [Qemu-devel] [PATCH 20/24] machine: drop MachineState::cpu_model

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, Jan 19, 2018 at 02:39:49PM +0100, Igor Mammedov wrote:
> On Fri, 19 Jan 2018 11:14:30 -0200
> Eduardo Habkost <ehabkost@redhat.com> wrote:
> 
> > On Fri, Jan 19, 2018 at 11:14:39AM +0100, Igor Mammedov wrote:
> > > On Thu, 18 Jan 2018 17:18:09 -0200
> > > Eduardo Habkost <ehabkost@redhat.com> wrote:
> > > 
> > > > On Thu, Jan 18, 2018 at 11:10:35AM +0100, Igor Mammedov wrote:
> > > > > On Wed, 17 Jan 2018 23:48:46 -0200
> > > > > Eduardo Habkost <ehabkost@redhat.com> wrote:
> > > > >   
> > > > > > On Wed, Jan 17, 2018 at 04:43:32PM +0100, Igor Mammedov wrote:  
> > > > > > > The last user of it was machine type 'none', which used field
> > > > > > > to create CPU id user requested it on CLI with -cpu option.
> > > [...]
> > > 
> > > > It looks like default_cpu_type is being overloaded for two
> > > > different roles: 1) specifying the default CPU type; 2) finding
> > > > the arch-specific class to be used to parse -cpu.
> > > > 
> > > > In the case of null-machine, these two roles conflict with each
> > > > other.  I believe we can find other solutions instead of this
> > > > hack that involves lying on MachineClass::default_cpu_type (and
> > > > then having to work around the lie on machine_none_init()).
> > > > 
> > > > I see multiple options: adding a new MachineClass field for that
> > > > (e.g.  resolving_cpu_type, which defaults to default_cpu_type if
> > > > NULL); moving the CPU parsing code to arch_init.c (so it could
> > > > use CPU_RESOLVING_TYPE or something similar); adding a optional
> > > > MachineClass::parse_cpu_model hook.  We could even try to get rid
> > > > of CPUClass::parse_features completely
> > > Adding hooks just for the sake on null-machine seems to be overkill,
> > > I'd go for arch_init.c but it won't work for linux-user, how about
> > > exec.c as following:
> > > 
> > > diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> > > index 93bd546..0185589 100644
> > > --- a/include/qom/cpu.h
> > > +++ b/include/qom/cpu.h
> > > @@ -661,8 +661,7 @@ ObjectClass *cpu_class_by_name(const char *typename, const char *cpu_model);
> > > [...]
> > > 
> > > diff --git a/exec.c b/exec.c
> > > index d28fc0c..4543f06 100644
> > > --- a/exec.c
> > > +++ b/exec.c
> > > @@ -817,6 +817,29 @@ void cpu_exec_realizefn(CPUState *cpu, Error **errp)
> > >  #endif
> > >  }
> > >  
> > > +const char *parse_cpu_model(const char *cpu_model)
> > > +{
> > > +    ObjectClass *oc;
> > > +    CPUClass *cc;
> > > +    gchar **model_pieces;
> > > +    const char *cpu_type;
> > > +
> > > +    model_pieces = g_strsplit(cpu_model, ",", 2);
> > > +
> > > +    oc = cpu_class_by_name(CPU_RESOLVING_TYPE, model_pieces[0]);
> > > +    if (oc == NULL) {
> > > +        error_report("unable to find CPU model '%s'", model_pieces[0]);
> > > +        g_strfreev(model_pieces);
> > > +        exit(EXIT_FAILURE);
> > > +    }
> > > +
> > > +    cpu_type = object_class_get_name(oc);
> > > +    cc = CPU_CLASS(oc);
> > > +    cc->parse_features(cpu_type, model_pieces[1], &error_fatal);
> > > +    g_strfreev(model_pieces);
> > > +    return cpu_type;
> > > +}
> > 
> > Sounds good to me.  Only two comments:
> > 
> > This looks like duplication of cpu_parse_cpu_model().  Should
> > this function body be replaced with:
> >   cpu_parse_cpu_model(CPU_RESOLVING_TYPE, cpu_model)
> it's cpu_parse_cpu_model() which is moved to exec.c
> and first typename argument is replaced by inline CPU_RESOLVING_TYPE
> 
> 
> > I would move this to arch_init.c, because that's where existing
> > target-dependent initialization code lives.
> arch_init.c doesn't fit linux-user, it has only sys emulation code
> while exec.c is used by both and still target depended so CPU_RESOLVING_TYPE
> could be used there

I don't really like adding more code to the mess that is exec.c,
but this looks like the simplest solution.

-- 
Eduardo