Re: [Xen-devel] [Qemu-devel] [PATCH for-3.2 v4 15/28] hw: apply accel compat properties without touching globals

[Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>]

Hi

On Tue, Nov 27, 2018 at 11:40 PM Eduardo Habkost <ehabkost@xxxxxxxxxx> wrote:
>
> On Tue, Nov 27, 2018 at 01:27:48PM +0400, Marc-André Lureau wrote:
> > Introduce object_apply_global_props() function, to apply compatibility
> > properties from a GPtrArray.
> >
> > For accel compatibility properties, apply them during
> > device_post_init(), after accel_register_compat_props() has set them.
> >
> > To populate the compatibility properties, introduce SET_COMPAT(), a
> > more generic version of SET_MACHINE_COMPAT() that can set compat
> > properties on other objects than Machine, and using GPtrArray.
> >
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>
> > ---
> >  include/hw/qdev-core.h | 13 +++++++++++++
> >  include/qom/object.h   |  3 +++
> >  include/sysemu/accel.h |  4 +---
> >  accel/accel.c          | 12 ------------
> >  hw/core/qdev.c         | 11 +++++++++++
> >  hw/xen/xen-common.c    | 38 +++++++++++++++++++-------------------
> >  qom/object.c           | 25 +++++++++++++++++++++++++
> >  vl.c                   |  2 +-
> >  8 files changed, 73 insertions(+), 35 deletions(-)
> >
> > diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> > index a24d0dd566..82afd3c50d 100644
> > --- a/include/hw/qdev-core.h
> > +++ b/include/hw/qdev-core.h
> > @@ -267,6 +267,19 @@ typedef struct GlobalProperty {
> >      Error **errp;
> >  } GlobalProperty;
> >
> > +#define SET_COMPAT(S, COMPAT)                                       \
> > +    do {                                                            \
> > +        int i;                                                      \
> > +        static GlobalProperty props[] = {                           \
> > +            COMPAT                                                  \
> > +        };                                                          \
> > +        for (i = 0; i < G_N_ELEMENTS(props); i++) {                 \
> > +            g_ptr_array_add((S)->compat_props, (void *)&props[i]);  \
> > +        }                                                           \
> > +    } while (0)
>
> I think this macro would be an acceptable alternative to the
> existing SET_MACHINE_COMPAT macro trickery, but:
>
> > +
> > +void accel_register_compat_props(const GPtrArray *props);
> [...]
> > @@ -185,7 +183,9 @@ static void xen_accel_class_init(ObjectClass *oc, void 
> > *data)
> >      ac->init_machine = xen_init;
> >      ac->setup_post = xen_setup_post;
> >      ac->allowed = &xen_allowed;
> > -    ac->global_props = xen_compat_props;
> > +    ac->compat_props = g_ptr_array_new();
> > +
> > +    SET_COMPAT(ac, XEN_COMPAT);
>
> I think this is a step backwards.  I like us to be able to
> register compat properties without macro magic.  The existence of
> SET_MACHINE_COMPAT is a bug and not a feature.
>
> If you really want to use GPtrArray instead of a simple
> GlobalProperty* field (I'm not sure I understand the reasoning
> behind the choice to use GPtrArray), what about:

Except in the Xen case, It needs to register multiple GlobalProperty*,
not necessarily from contiguous in memory. That's why we have an array
of ptr.

>
> static GPtrArray *build_compat_props_array(GlobalProperty *props)
> {
>     GlobalProperty *p = props;
>     GPtrArray *array = g_ptr_array_new();
>     while (p->driver) {
>         g_ptr_array_add(array, (void *)p);
>     }
>     return array;
> }
>
>
> static void xen_accel_class_init(ObjectClass *oc, void *data)
> {
>     ...
>     ac->compat_props = build_compat_props_array(xen_compat_props);

If we would register from one place, that would be fine.

We could replace the macro by a function, then we would have to
declare the GlobalProperty arrays manually basically.

> }
>
>
>
> >  }
> >
> >  #define TYPE_XEN_ACCEL ACCEL_CLASS_NAME("xen")
> > diff --git a/qom/object.c b/qom/object.c
> > index 17921c0a71..dbdab0aead 100644
> > --- a/qom/object.c
> > +++ b/qom/object.c
> > @@ -370,6 +370,31 @@ static void object_post_init_with_type(Object *obj, 
> > TypeImpl *ti)
> >      }
> >  }
> >
> > +void object_apply_global_props(Object *obj, const GPtrArray *props, Error 
> > **errp)
> > +{
> > +    Error *err = NULL;
> > +    int i;
> > +
> > +    if (!props) {
> > +        return;
> > +    }
> > +
> > +    for (i = 0; i < props->len; i++) {
> > +        GlobalProperty *p = g_ptr_array_index(props, i);
> > +
> > +        if (object_dynamic_cast(obj, p->driver) == NULL) {
> > +            continue;
> > +        }
> > +        p->used = true;
> > +        object_property_parse(obj, p->value, p->property, &err);
> > +        if (err != NULL) {
> > +            error_prepend(&err, "can't apply global %s.%s=%s: ",
> > +                          p->driver, p->property, p->value);
> > +            error_propagate(errp, err);
> > +        }
> > +    }
> > +}
> > +
> >  static void object_initialize_with_type(void *data, size_t size, TypeImpl 
> > *type)
> >  {
> >      Object *obj = data;
> > diff --git a/vl.c b/vl.c
> > index fa25d1ae2d..c06e94271c 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -2963,7 +2963,7 @@ static void user_register_global_props(void)
> >   */
> >  static void register_global_properties(MachineState *ms)
> >  {
> > -    accel_register_compat_props(ms->accelerator);
> > +    
> > accel_register_compat_props(ACCEL_GET_CLASS(ms->accelerator)->compat_props);
> >      machine_register_compat_props(ms);
> >      user_register_global_props();
> >  }
> > --
> > 2.20.0.rc1
> >
> >
>
> --
> Eduardo

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