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From: Eric Blake <eblake@redhat.com>
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Date: Thu, 28 Apr 2016 09:44:26 -0600
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Subject: Re: [Qemu-devel] [PATCH v15 22/23] qapi: Simplify semantics of
 visit_next_list()
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To: qemu-devel@nongnu.org
Cc: Alexander Graf <agraf@suse.de>, David Gibson <david@gibson.dropbear.id.au>, "open list:sPAPR" <qemu-ppc@nongnu.org>, armbru@redhat.com, Michael Roth <mdroth@linux.vnet.ibm.com>

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On 04/27/2016 06:01 PM, Eric Blake wrote:
> The semantics of the list visit are somewhat baroque, with the
> following pseudocode when FooList is used:
>=20

>=20
> We can greatly simplify things by hoisting the special case
> into the start() routine, and flipping the order in the loop
> to visit before advance:
>=20
> start(head)
> for (tail =3D *head; tail; tail =3D next(tail)) {
>     visit(&tail->value)
> }
>=20

> +++ b/qapi/qapi-visit-core.c
> @@ -48,15 +48,17 @@ void visit_end_struct(Visitor *v)
>      v->end_struct(v);
>  }
>=20
> -void visit_start_list(Visitor *v, const char *name, Error **errp)
> +void visit_start_list(Visitor *v, const char *name, GenericList **list=
,
> +                      size_t size, Error **errp)
>  {
> -    v->start_list(v, name, errp);
> +    assert(!list || size >=3D sizeof(GenericList));
> +    v->start_list(v, name, list, size, errp);
>  }

As mentioned in 02/23, this would be a good place to assert that:

if (v->type =3D=3D VISITOR_INPUT) {
    assert(!(err && *list));
}

of course, that means declaring a local 'err'.

--=20
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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