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

[Eduardo Habkost <ehabkost@xxxxxxxxxx>]

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:

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);
}



>  }
>  
>  #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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