Re: [Qemu-devel] [PATCH 2/9] qom: add object_property_add_unnamed_child

[Stefan Hajnoczi <stefanha@redhat.com>]

On Mon, May 06, 2013 at 01:48:34PM -0500, mdroth wrote:
> On Mon, May 06, 2013 at 09:44:13AM +0200, Paolo Bonzini wrote:
> > Il 03/05/2013 18:03, Michael Roth ha scritto:
> > > This interface allows us to add a child property without specifying a
> > > name. Instead, a unique name is created and passed back after adding
> > > the property.
> > > 
> > > Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
> > > ---
> > >  include/qom/object.h |   16 ++++++++++++++++
> > >  qom/object.c         |   25 +++++++++++++++++++++++++
> > >  2 files changed, 41 insertions(+)
> > > 
> > > diff --git a/include/qom/object.h b/include/qom/object.h
> > > index 86f1e2e..ca0fce8 100644
> > > --- a/include/qom/object.h
> > > +++ b/include/qom/object.h
> > > @@ -1041,6 +1041,22 @@ void object_property_add_child(Object *obj, const char *name,
> > >                                 Object *child, struct Error **errp);
> > >  
> > >  /**
> > > + * object_property_add_unnamed_child:
> > > + *
> > > + * @obj: the object to add a property to
> > > + * @name: the name of the property
> > > + * @child: the child object
> > > + * @errp: if an error occurs, a pointer to an area to store the area
> > > + *
> > > + * Same as object_property_add_child, but will allocate a unique name to
> > > + * identify the child property.
> > > + *
> > > + * Returns: The name assigned to the child property, or NULL on failure.
> > > + */
> > > +char *object_property_add_unnamed_child(Object *obj, Object *child,
> > > +                                        struct Error **errp);
> > > +
> > > +/**
> > >   * object_property_add_link:
> > >   * @obj: the object to add a property to
> > >   * @name: the name of the property
> > > diff --git a/qom/object.c b/qom/object.c
> > > index c932f64..229a9a7 100644
> > > --- a/qom/object.c
> > > +++ b/qom/object.c
> > > @@ -926,6 +926,31 @@ static void object_finalize_child_property(Object *obj, const char *name,
> > >      object_unref(child);
> > >  }
> > >  
> > > +char *object_property_add_unnamed_child(Object *obj, Object *child, Error **errp)
> > > +{
> > > +    int idx = 0;
> > > +    bool next_idx_found = false;
> > > +    char name[64];
> > > +    ObjectProperty *prop;
> > > +
> > > +    while (!next_idx_found) {
> > > +        sprintf(name, "unnamed[%d]", idx);
> > > +        QTAILQ_FOREACH(prop, &obj->properties, node) {
> > > +            if (strcmp(name, prop->name) == 0) {
> > > +                idx++;
> > > +                break;
> > > +            }
> > > +        }
> > > +        if (!prop) {
> > > +            next_idx_found = true;
> > > +        }
> > > +    }
> > > +
> > > +    object_property_add_child(obj, name, child, errp);
> > > +
> > > +    return error_is_set(errp) ? NULL : g_strdup(name);
> > > +}
> > 
> > This is O(n^3) for adding N children.  O(n^2) would be not-that-great
> > but fine; can you take the occasion to convert the properties list to a
> > hashtable?
> 
> Sure, I'll look into it.

Given that we already have the child pointer, perhaps just use the
uintptr_t child memory address as a unique name.  It's guaranteed to be
unique unless you add the same child twice.

Stefan