linux-kernel - Re: [PATCH RFC 0/4] Add XDP RX queue index metadata via kfuncs

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Message-ID: <f103da72-0973-4a45-af81-ec1537422433@gmail.com>
Date: Wed, 24 Sep 2025 11:40:26 +0100
From: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, donald.hunter@...il.com, andrew+netdev@...n.ch,
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 david.hunter.linux@...il.com, skhan@...uxfoundation.org, horms@...nel.org,
 sdf@...ichev.me, netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org, linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH RFC 0/4] Add XDP RX queue index metadata via kfuncs

On 9/23/25 9:45 PM, Stanislav Fomichev wrote:
> On 09/23, Mehdi Ben Hadj Khelifa wrote:
>> ---
>> Mehdi Ben Hadj Khelifa (4):
>>    netlink: specs: Add XDP RX queue index to XDP metadata
>>    net: xdp: Add xmo_rx_queue_index callback
>>    uapi: netdev: Add XDP RX queue index metadata flags
>>    net: veth: Implement RX queue index XDP hint
>>
>>   Documentation/netlink/specs/netdev.yaml |  5 +++++
>>   drivers/net/veth.c                      | 12 ++++++++++++
>>   include/net/xdp.h                       |  5 +++++
>>   include/uapi/linux/netdev.h             |  3 +++
>>   net/core/xdp.c                          | 15 +++++++++++++++
>>   tools/include/uapi/linux/netdev.h       |  3 +++
>>   6 files changed, 43 insertions(+)
>>   ---
>>   base-commit: 07e27ad16399afcd693be20211b0dfae63e0615f
>>   this is the commit of tag: v6.17-rc7 on the mainline.
>>   This patch series is intended to make a base for setting
>>   queue_index in the xdp_rxq_info struct in bpf/cpumap.c to
>>   the right index. Although that part I still didn't figure
>>   out yet,I m searching for my guidance to do that as well
>>   as for the correctness of the patches in this series.

> But why do you need a kfunc getter? You can already get rxq index
> via xdp_md rx_queue_index.

Hi Stanislav, When i was looking at the available information or recent
similar patches to populate the queue_index in xdp_rxq_info inside of
the cpu map of an ebpf program to run xdp. i stumbled upon this: 
https://lkml.rescloud.iu.edu/2506.1/02808.html

which suggests that in order to that, a struct called "xdp_rx_meta" 
should be the route to do that. In my navigation of code i only found
the closest thing to that is xdp_rx_metadata which is an enum. I tried 
to follow was done for other metadata there like timestamp in order to 
see if that gets me closer to do that. which was stupid with the 
information that i have now but for my lack of experience (this is my 
first patch) i tried to reason with the code.So yeah, since xdp_md is 
the structure for transfering metadata to ebpf programs that use xdp. 
it's useless to have a kfunc to expose queue_index since it's already 
present there. But how would one try to populate the queue_index in 
xdp_rxq_info in cpu_map_bpf_prog_run_xdp()? Any sort of hints or guides 
would be much appreciated.
Thank you for your time.

Best Regards,
Mehdi Ben Hadj Khelifa