[v2,1/7] qom: add object_property_add_alias()

Sometimes an object needs to present a property which is actually on
another object, or it needs to provide an alias name for an existing
property.

Examples:
  a.foo -> b.foo
  a.old_name -> a.new_name

The new object_property_add_alias() API allows objects to alias a
property on the same object or another object.  The source and target
names can be different.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
v2:
 * Explain refcount handling in doc comment [Paolo]
 * Fix "property" duplicate typo [Peter Crosthwaite]
 * Add "the same object or" to clarify commit description [Igor]
---
 include/qom/object.h | 20 ++++++++++++++++++++
 qom/object.c         | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)

On Fri, May 23, 2014 at 1:40 AM, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> Sometimes an object needs to present a property which is actually on
> another object, or it needs to provide an alias name for an existing
> property.
>
> Examples:
>   a.foo -> b.foo
>   a.old_name -> a.new_name
>
> The new object_property_add_alias() API allows objects to alias a
> property on the same object or another object.  The source and target
> names can be different.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>

> ---
> v2:
>  * Explain refcount handling in doc comment [Paolo]
>  * Fix "property" duplicate typo [Peter Crosthwaite]
>  * Add "the same object or" to clarify commit description [Igor]
> ---
>  include/qom/object.h | 20 ++++++++++++++++++++
>  qom/object.c         | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 72 insertions(+)
>
> diff --git a/include/qom/object.h b/include/qom/object.h
> index a641dcd..854a0d5 100644
> --- a/include/qom/object.h
> +++ b/include/qom/object.h
> @@ -1203,6 +1203,26 @@ void object_property_add_uint64_ptr(Object *obj, const char *name,
>                                      const uint64_t *v, Error **Errp);
>
>  /**
> + * object_property_add_alias:
> + * @obj: the object to add a property to
> + * @name: the name of the property
> + * @target_obj: the object to forward property access to
> + * @target_name: the name of the property on the forwarded object
> + * @errp: if an error occurs, a pointer to an area to store the error
> + *
> + * Add an alias for a property on an object.  This function will add a property
> + * of the same type as the forwarded property.
> + *
> + * The caller must ensure that <code>@target_obj</code> stays alive as long as
> + * this property exists.  In the case of a child object or an alias on the same
> + * object this will be the case.  For aliases to other objects the caller is
> + * responsible for taking a reference.
> + */
> +void object_property_add_alias(Object *obj, const char *name,
> +                               Object *target_obj, const char *target_name,
> +                               Error **errp);
> +
> +/**
>   * object_child_foreach:
>   * @obj: the object whose children will be navigated
>   * @fn: the iterator function to be called
> diff --git a/qom/object.c b/qom/object.c
> index e42b254..ff50f37 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -1515,6 +1515,58 @@ void object_property_add_uint64_ptr(Object *obj, const char *name,
>                          NULL, NULL, (void *)v, errp);
>  }
>
> +typedef struct
> +{
> +    Object *target_obj;
> +    const char *target_name;
> +} AliasProperty;
> +
> +static void property_get_alias(Object *obj, struct Visitor *v, void *opaque,
> +                               const char *name, Error **errp)
> +{
> +    AliasProperty *prop = opaque;
> +
> +    object_property_get(prop->target_obj, v, prop->target_name, errp);
> +}
> +
> +static void property_set_alias(Object *obj, struct Visitor *v, void *opaque,
> +                               const char *name, Error **errp)
> +{
> +    AliasProperty *prop = opaque;
> +
> +    object_property_set(prop->target_obj, v, prop->target_name, errp);
> +}
> +
> +static void property_release_alias(Object *obj, const char *name, void *opaque)
> +{
> +    AliasProperty *prop = opaque;
> +
> +    g_free(prop);
> +}
> +
> +void object_property_add_alias(Object *obj, const char *name,
> +                               Object *target_obj, const char *target_name,
> +                               Error **errp)
> +{
> +    AliasProperty *prop;
> +    ObjectProperty *target_prop;
> +
> +    target_prop = object_property_find(target_obj, target_name, errp);
> +    if (!target_prop) {
> +        return;
> +    }
> +
> +    prop = g_malloc(sizeof(*prop));
> +    prop->target_obj = target_obj;
> +    prop->target_name = target_name;
> +
> +    object_property_add(obj, name, target_prop->type,
> +                        property_get_alias,
> +                        property_set_alias,
> +                        property_release_alias,
> +                        prop, errp);
> +}
> +
>  static void object_instance_init(Object *obj)
>  {
>      object_property_add_str(obj, "type", qdev_get_type, NULL, NULL);
> --
> 1.9.0
>
>