[Qemu-devel] qdev static properties, custom setter/getter & validation (was Re: [PATCH 04/10] target-i386: convert 'hv_spinlocks' to static property)

[Eduardo Habkost]

TL;DR: I want to understand why a
  DEFINE_PROP_CUSTOM(name, type, getter_func, setter_func)
macro doesn't exist yet.


On Tue, Feb 26, 2013 at 11:38:59AM -0300, Eduardo Habkost wrote:
[...]
> > +static void x86_get_hv_spinlocks(Object *obj, Visitor *v, void *opaque,
> > +                                 const char *name, Error **errp)
> > +{
> > +    X86CPU *cpu = X86_CPU(obj);
> > +    int64_t value = cpu->env.hyperv_spinlock_attempts;
> > +
> > +    visit_type_int(v, &value, name, errp);
> > +}
> > +
> > +static void x86_set_hv_spinlocks(Object *obj, Visitor *v, void *opaque,
> > +                                 const char *name, Error **errp)
> > +{
> > +    const int64_t min = 0xFFF;
> > +    const int64_t max = UINT_MAX;
> > +    X86CPU *cpu = X86_CPU(obj);
> > +    int64_t value;
> > +
> > +    visit_type_int(v, &value, name, errp);
> > +    if (error_is_set(errp)) {
> > +        return;
> > +    }
> > +
> > +    if (value < min || value > max) {
> > +        error_setg(errp, "Property %s.%s doesn't take value %" PRId64
> > +                  " (minimum: %" PRId64 ", maximum: %" PRId64 ")",
> > +                  object_get_typename(obj), name ? name : "null",
> > +                  value, min, max);
> > +        return;
> > +    }
> > +    cpu->env.hyperv_spinlock_attempts = value;
> > +}
> > +
> > +static PropertyInfo qdev_prop_spinlocks = {
> > +    .name  = "int",
> > +    .get   = x86_get_hv_spinlocks,
> > +    .set   = x86_set_hv_spinlocks,
> > +};
> > +#define DEFINE_PROP_HV_SPINLOCKS(_n, _defval) {                            
> >     \
> > +    .name  = _n,                                                           
> >     \
> > +    .info  = &qdev_prop_spinlocks,                                         
> >     \
> > +    .qtype = QTYPE_QINT,                                                   
> >     \
> > +    .defval = _defval                                                      
> >     \
> > +}
> > +
> >  static Property cpu_x86_properties[] = {
> >      DEFINE_PROP_FAMILY("family"),
> >      DEFINE_PROP_MODEL("model"),
> > @@ -1304,6 +1348,7 @@ static Property cpu_x86_properties[] = {
> >      DEFINE_PROP_VENDOR("vendor"),
> >      DEFINE_PROP_MODEL_ID("model-id"),
> >      DEFINE_PROP_TSC_FREQ("tsc-frequency"),
> > +    DEFINE_PROP_HV_SPINLOCKS("hv-spinlocks", HYPERV_SPINLOCK_NEVER_RETRY),
> 
> I'm still bothered by how complicated it is to define a simple property
> that has a custom setter/getter.
> 
> Registering a property with a getter/setter on instance_init require
> only one line of code, why doing the same with a static property
> requires _twelve_ lines?
> 
> Are we using the static property API in a wrong or unexpected way, or
> this is really how things are supposed to work?

I was discussing this with Igor, and my main question is:

Maybe the static property API makes this really complicated on purpose
because we're supposed to validate property values on realizefn()
instead of the property setter?

> 
> 
> >      DEFINE_PROP_END_OF_LIST(),
> >  };
> >  
> > @@ -1421,6 +1466,7 @@ static void cpu_x86_parse_featurestr(X86CPU *cpu, 
> > char *features, Error **errp)
> >              } else if (!strcmp(featurestr, "hv-spinlocks")) {
> >                  char *err;
> >                  const int min = 0xFFF;
> > +                char num[32];
> >                  numvalue = strtoul(val, &err, 0);
> >                  if (!*val || *err) {
> >                      error_setg(errp, "bad numerical value %s", val);
> > @@ -1432,7 +1478,8 @@ static void cpu_x86_parse_featurestr(X86CPU *cpu, 
> > char *features, Error **errp)
> >                              min);
> >                      numvalue = min;
> >                  }
> > -                env->hyperv_spinlock_attempts = numvalue;
> > +                snprintf(num, sizeof(num), "%" PRId32, numvalue);
> > +                object_property_parse(OBJECT(cpu), num, featurestr, errp);
> >              } else {
> >                  error_setg(errp, "unrecognized feature %s", featurestr);
> >                  goto out;
> > @@ -1597,7 +1644,6 @@ static void cpu_x86_register(X86CPU *cpu, const char 
> > *name, Error **errp)
> >          def->kvm_features |= kvm_default_features;
> >      }
> >      def->ext_features |= CPUID_EXT_HYPERVISOR;
> > -    env->hyperv_spinlock_attempts = HYPERV_SPINLOCK_NEVER_RETRY;
> >  
> >      object_property_set_str(OBJECT(cpu), def->vendor, "vendor", errp);
> >      object_property_set_int(OBJECT(cpu), def->level, "level", errp);
> > -- 
> > 1.7.1
> > 
> 
> -- 
> Eduardo
> 

-- 
Eduardo