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

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 5 Feb 2018 11:54:01 -0200
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Mon, Feb 05, 2018 at 12:22:35PM +0100, Igor Mammedov wrote:
> > On Fri, 2 Feb 2018 16:23:26 -0200
> > Eduardo Habkost <ehabkost@redhat.com> wrote:
> >   
> > > On Thu, Feb 01, 2018 at 04:42:05PM -0800, Alistair Francis wrote:  
> > > > As cpu_type is not a user visible string let's convert the
> > > > valid_cpu_types to compare against cpu_model instead. This way we have a
> > > > user friendly string to report back.
> > > > 
> > > > Once we have a cpu_type to cpu_model conversion this patch should be
> > > > reverted and we should use cpu_type instead.
> > > > 
> > > > Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
> > > > ---
> > > > 
> > > >  hw/core/machine.c | 11 +++++------
> > > >  1 file changed, 5 insertions(+), 6 deletions(-)
> > > > 
> > > > diff --git a/hw/core/machine.c b/hw/core/machine.c
> > > > index cdc1163dc6..de5bac1c84 100644
> > > > --- a/hw/core/machine.c
> > > > +++ b/hw/core/machine.c
> > > > @@ -776,13 +776,12 @@ void machine_run_board_init(MachineState *machine)
> > > >      /* If the machine supports the valid_cpu_types check and the user
> > > >       * specified a CPU with -cpu check here that the user CPU is supported.
> > > >       */
> > > > -    if (machine_class->valid_cpu_types && machine->cpu_type) {
> > > > -        ObjectClass *class = object_class_by_name(machine->cpu_type);
> > > > +    if (machine_class->valid_cpu_types && machine->cpu_model) {
> > > >          int i;
> > > >  
> > > >          for (i = 0; machine_class->valid_cpu_types[i]; i++) {
> > > > -            if (object_class_dynamic_cast(class,
> > > > -                                          machine_class->valid_cpu_types[i])) {
> > > > +            if (!strcmp(machine->cpu_model,
> > > > +                        machine_class->valid_cpu_types[i])) {    
> > > 
> > > I would rename valid_cpu_types to valid_cpu_models to make the
> > > new semantics clearer.
> > > 
> > > Anyway, I have bad and good news:
> > > 
> > > The bad news is Igor already sent patches last week that remove
> > > MachineState::cpu_model, so this conflicts with his series.  Now
> > > parse_cpu_model() will be the only place where the original CPU model name is
> > > available, but the function needs to work on *-user too.  See:
> > > "[PATCH v3 23/25] Use cpu_create(type) instead of cpu_init(cpu_model)".
> > > 
> > > The good news is that I think we can fix this very easily if
> > > validation is done at the same place where parse_cpu_model() is
> > > called.  e.g.:
> > > 
> > >     current_machine->cpu_type = machine_class->default_cpu_type;
> > >     if (cpu_model) {
> > >         current_machine->cpu_type = parse_cpu_model(cpu_model);
> > > 
> > >         if (machine_class->valid_cpu_models) {
> > >             ObjectClass *class = object_class_by_name(machine->cpu_type);
> > >             int i;
> > > 
> > >             for (i = 0; machine_class->valid_cpu_models[i]; i++) {
> > >                 const char *valid_model = machine_class->valid_cpu_models[i];
> > >                 ObjectClass *valid_class = cpu_class_by_name(machine->cpu_type, valid_model);
> > >                 if (object_class_dynamic_cast(class,
> > >                                               object_class_get_name(valid_class))) {
> > >                      /* Valid CPU type, we're good to go */
> > >                      break;
> > >                 }
> > >             }
> > >             if (!machine_class->valid_cpu_models[i]) {
> > >                 error_report("Invalid CPU model: %s", cpu_model);
> > >                 error_printf("The valid CPU models are: %s",
> > >                              machine_class->valid_cpu_models[0]);
> > >                 for (i = 1; machine_class->valid_cpu_models[i]; i++) {
> > >                     error_printf(", %s", machine_class->valid_cpu_models[i]);
> > >                 }
> > >                 error_printf("\n");
> > >                 exit(1);
> > >             }
> > >         }
> > >     }
> > > 
> > > This can be done inside main(), or moved inside
> > > machine_run_board_init() if main() pass cpu_model as argument to
> > > the function.
> > > 
> > > On either case, I think it's a good idea to do validation and
> > > printing of error messages closer to the code that parses the
> > > command-line options.  This way we separate parsing/validation
> > > from initialization.  
> > I agree it's better like you suggest as at least it prevents
> > ms->cpu_model creeping back into boards code.
> > 
> > But I still dislike (hate) an idea of new code adding non
> > canonized cpu_model strings back in the boards code.
> > It's just a matter of time when someone would use them
> > and cpu_model parsing will creep back into boards.
> > 
> > It would be much better to if we add 
> >    char *MachineClass::cpu_name_by_type_name(char *cpu_type)
> > callback and let machines in this patchset to set it,
> > something along following lines which is not much of
> > refactoring and allows for gradual conversion:
> > 
> > diff --git a/target/arm/cpu.h b/target/arm/cpu.h
> > index 9631670..85cca84 100644
> > --- a/target/arm/cpu.h
> > +++ b/target/arm/cpu.h
> > @@ -2885,4 +2885,6 @@ static inline void *arm_get_el_change_hook_opaque(ARMCPU *cpu)
> >      return cpu->el_change_hook_opaque;
> >  }
> >  
> > +char *arm_cpu_name_by_type_name(const char *typename);
> > +
> >  #endif
> > diff --git a/hw/arm/netduino2.c b/hw/arm/netduino2.c
> > index f936017..ae6adb7 100644
> > --- a/hw/arm/netduino2.c
> > +++ b/hw/arm/netduino2.c
> > @@ -46,6 +46,7 @@ static void netduino2_machine_init(MachineClass *mc)
> >      mc->desc = "Netduino 2 Machine";
> >      mc->init = netduino2_init;
> >      mc->ignore_memory_transaction_failures = true;
> > +    mc->cpu_name_by_type_name = arm_cpu_name_by_type_name:  
> 
> I really don't want to introduce a new arch-specific hook just
> for that.  We should move CPU type lookup logic to common code
> and make it unnecessary to write new hooks.
unfortunately cpu_model (cpu name part) is target specific
and it's translation to type and back is target specific mayhem.

So I'd prefer having both back and forth functions together in
one place. And common code to call them when necessary.

We could do global cpu_name_by_type_name() instead of hook,
which I'd prefer even more but then conversion can't be done
only for one target but rather for all targets at once.
 
> I agree it would be better if we had a cpu_name_by_type_name()
> function, but I would like to have it implemented cleanly.
In some cases(targets) it can be common helper, but in other
cases it's not so.
My suggestion though allows to do gradual conversion and
avoid putting cpu_model names back in board's code (which I just manged to remove).
Once all targets converted and relevant code is isolated
we can attempt to generalize it if it's possible or at least
make of it global per target helper to get rid of
temporary machine hook.

(seeing this series reposted with cpu_model names in boards code,
it doesn't looks like author would like to implement tree-wide
generalization first)