Re: [Qemu-devel] [PATCH 1/2] object: Add can_be_deleted callback to TypeInfo and TypeImpl

[Igor Mammedov]

On Thu, 26 Mar 2015 11:07:27 +0100
Andreas Färber <address@hidden> wrote:

> Am 26.03.2015 um 11:05 schrieb Igor Mammedov:
> > On Wed, 25 Mar 2015 23:47:46 +0800
> > Lin Ma <address@hidden> wrote:
> >> 在 2015年03月23日 21:30, Igor Mammedov 写道:
> >>> On Mon, 23 Mar 2015 14:13:07 +0100
> >>> Andreas Färber <address@hidden> wrote:
> >>>> Am 23.03.2015 um 13:06 schrieb Paolo Bonzini:
> >>>>> On 23/03/2015 11:36, Peter Crosthwaite wrote:
> >>>>>> I don't think TypeInfo is the right place for this. You can however
> >>>>>> define function hooks for Object in ObjectClass. See the unparent
> >>>>>> field of ObjectClass for a precedent.
> >>>> Agree.
> >>>>
> >>>>> In this case, the right place could be UserCreatable.
> >>>> Maybe, not so familiar with that interface myself. Does object_del allow
> >>>> to delete non-UserCreatable objects? Then it wouldn't help much.
> >>> object_del() works only with /objects children, and so far the only way
> >>> that child placed there is via object_add() which requires a new object
> >>> to have TYPE_USER_CREATABLE interface.
> >>> I'd go this way rather than overhaul object_unparent() in this case.
> >> What about these changes?
> >> 1. Add a callback function named 'ObjectCanBeDeleted *can_be_deleted' to 
> >> struct ObjectClass in object.h
> >> 2. Call the function in qmp_object_del of qmp.c, says:
> >>      ObjectClass *obj_class = object_get_class(obj);
> >>          if (obj_class->can_be_deleted)
> >>              if (!obj_class->can_be_deleted(obj))
> >>                  error out
> >>
> >> 3. Then implement can_be_deleted callback in backends, says:
> >>      static bool host_memory_backend_can_be_deleted(Object *obj) {......}
> >>
> >>      static void host_memory_backend_class_init(ObjectClass *oc, void 
> >> *data) {
> >>          ......
> >>          oc->can_be_deleted = host_memory_backend_can_be_deleted;
> >>      }
> > 
> > all backends currently implement TYPE_USER_CREATABLE interface,
> > so I'd rather extend UserCreatableClass with:
> > 
> >      bool can_be_deleted(UserCreatable *uc)
> > 
> > callback, which backends could implement if needed.
> 
> As for the implementation, could we simply look at Object::ref field?
What value of ref, one would use to decide if deletion is possible?

In generic case object can have ref > 1 but still be eligible for deleting
via object-del.

> 
> Regards,
> Andreas
>