netdev - Re: [bpf-next,v3] bpf: cpumap: report queue_index to xdp_rxq

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Message-ID: <dcad6dc7-b152-4511-becf-9e7721996f6a@kernel.org>
Date: Wed, 14 Jan 2026 14:30:07 +0100
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Toke Høiland-Jørgensen <toke@...hat.com>,
 Sai Aung Hlyan Htet <saiaunghlyanhtet2003@...il.com>
Cc: bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org,
 Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Subject: Re: [bpf-next,v3] bpf: cpumap: report queue_index to xdp_rxq_info




On 14/01/2026 13.33, Toke Høiland-Jørgensen wrote:
> Sai Aung Hlyan Htet <saiaunghlyanhtet2003@...il.com> writes:
> 
>> On Wed, Jan 14, 2026 at 8:39 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>>
>>> Yeah, this has been discussed as well :)
>>>
>>> See:
>>> https://netdevconf.info/0x19/sessions/talk/traits-rich-packet-metadata.html
>>>
>>> Which has since evolved a bit to these series:
>>>
>>> https://lore.kernel.org/r/20260105-skb-meta-safeproof-netdevs-rx-only-v2-0-a21e679b5afa@cloudflare.com
>>>
>>> https://lore.kernel.org/r/20260110-skb-meta-fixup-skb_metadata_set-calls-v1-0-1047878ed1b0@cloudflare.com
>>>

Above links are about 100% user defined metadata, that the kernel itself
have no structural knowledge about.

The RX queue_index (as you wrote in desc[1]) is something that gets lost
when XDP-redirecting. The series in [0] is about transferring
properties/info that got lost due to XDP-redirect. Lost info that the
SKB could be populated with.

  [0] 
https://lore.kernel.org/all/175146824674.1421237.18351246421763677468.stgit@firesoul/
  - Subj: "[V2 0/7] xdp: Allow BPF to set RX hints for XDP_REDIRECTed 
packets"

  [1] 
https://lore.kernel.org/all/20260114060430.1287640-1-saiaunghlyanhtet2003@gmail.com/


>>> (Also, please don't top-post on the mailing lists)
>>>

Please read Networking subsystem (netdev) process[2]:
  [2] https://kernel.org/doc/html/latest/process/maintainer-netdev.html


>> Thanks for the pointers. It is really great to see this series. One
>> question: Would adding queue_index to the packet traits KV store be
>> a useful follow-up once the core infrastructure lands?
> 
> Possibly? Depends on where things land, I suppose. I'd advise following
> the discussion on the list until it does :)
> 

Hmm, the "original" RX queue_index isn't super interesting to CPUMAP.
You patch doesn't transfer this lost information to the SKB.

Information that got lost in the XDP-redirect and which is needed for
the SKB is RX-hash, hardware VLAN (not inlined in pkts) and RX-
timestamp. As implemented in [0].

--Jesper