Subject: Re: [patch net-next v2] tools: ynl: introduce option to process unknown attributes or types

From: Jakub Kicinski <[email-masked]>
Date: Mon, 16 Oct 2023 17:59:03 -0700

On Mon, 16 Oct 2023 13:02:22 +0200 Jiri Pirko wrote:
> +class FakeSpecAttr:
> +    def __init__(self, name):
> +        self.dict = {"name": name, "type": None}
> +        self.is_multi = False
> +
> +    def __getitem__(self, key):
> +        return self.dict[key]
> +
> +    def __contains__(self, key):
> +        return key in self.dict

Why the new class? Why not attach the NlAttr object directly?

I have an idea knocking about in my head to support "polymorphic"
nests (nests where decoding depends on value of another attr,
link rtnl link attrs or tc object attrs). The way I'm thinking 
about doing it is to return NlAttr / struct nla_attr back to the user.
And let the users call a sub-parser of choice by hand.

So returning a raw NlAttr appeals to me more.

> +                if not self.process_unknown:
> +                    raise Exception(f'Unknown {attr_spec["type"]} with name {attr_spec["name"]}')
> +                if attr._type & Netlink.NLA_F_NESTED:
> +                    subdict = self._decode(NlAttrs(attr.raw), None)
> +                    decoded = subdict
> +                else:
> +                    decoded = attr.as_bin()

Again, I wouldn't descend at all.