netdev - Re: [xdp-hints] Re: [RFC bpf-next v2 06/14] xdp: Carry over xdp metadata into skb context

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Date:   Thu, 10 Nov 2022 15:58:22 -0800
From:   Martin KaFai Lau <martin.lau@...ux.dev>
To:     Stanislav Fomichev <sdf@...gle.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        song@...nel.org, yhs@...com, john.fastabend@...il.com,
        kpsingh@...nel.org, haoluo@...gle.com, jolsa@...nel.org,
        David Ahern <dsahern@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Anatoly Burakov <anatoly.burakov@...el.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [xdp-hints] Re: [RFC bpf-next v2 06/14] xdp: Carry over xdp
 metadata into skb context

On 11/10/22 10:52 AM, Stanislav Fomichev wrote:
>>> Oh, that seems even better than returning it from
>>> bpf_xdp_metadata_export_to_skb.
>>> bpf_xdp_metadata_export_to_skb can return true/false and the rest goes
>>> via default verifier ctx resolution mechanism..
>>> (returning ptr from a kfunc seems to be a bit complicated right now)

What is the complication in returning ptr from a kfunc?  I want to see if it can 
be solved because it will be an easier API to use instead of calling another 
kfunc to get the ptr.

>> See my response to John in the other thread about mixing stable UAPI (in
>> xdp_md) and unstable BTF structures in the xdp_md struct: I think this
>> is confusing and would prefer a kfunc.

hmm... right, it will be one of the first considering the current __bpf_md_ptr() 
usages are only exposing another struct in uapi, eg. __bpf_md_ptr(struct 
bpf_sock *, sk).

A kfunc will also be fine.