linux-kernel - Re: [PATCH bpf-next v2] bpf/cpumap.c: Remove unnecessary TODO comment

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Message-ID: <4c849c04-6647-432c-807c-5fa7afa7fb47@gmail.com>
Date: Tue, 21 Oct 2025 12:13:52 +0100
From: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
To: Jesper Dangaard Brouer <hawk@...nel.org>, ast@...nel.org,
 daniel@...earbox.net, davem@...emloft.net, kuba@...nel.org,
 john.fastabend@...il.com, sdf@...ichev.me, andrii@...nel.org,
 martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
 yonghong.song@...ux.dev, kpsingh@...nel.org, haoluo@...gle.com,
 jolsa@...nel.org
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org, skhan@...uxfoundation.org,
 david.hunter.linux@...il.com, khalid@...nel.org,
 linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH bpf-next v2] bpf/cpumap.c: Remove unnecessary TODO comment

On 10/21/25 10:37 AM, Jesper Dangaard Brouer wrote:
> 
> 
> On 20/10/2025 19.02, Mehdi Ben Hadj Khelifa wrote:
>> After discussion with bpf maintainers[1], queue_index could
>> be propagated to the remote XDP program by the xdp_md struct[2]
>> which makes this todo a misguide for future effort.
>>
>> [1]:https://lore.kernel.org/all/87y0q23j2w.fsf@cloudflare.com/
>> [2]:https://docs.ebpf.io/linux/helper-function/bpf_xdp_adjust_meta/
>>
>> Signed-off-by: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
>> ---
>> Changelog:
>>
>> Changes from v1:
>>
>> -Added a comment to clarify that RX queue_index is lost after the frame
>> redirection.
>>
>> Link:https://lore.kernel.org/bpf/d9819687-5b0d-4bfa-9aec- 
>> aef71b847383@...il.com/T/#mcb6a0315f174d02db3c9bc4fa556cc939c87a706
>>   kernel/bpf/cpumap.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
>> index 703e5df1f4ef..6856a4a67840 100644
>> --- a/kernel/bpf/cpumap.c
>> +++ b/kernel/bpf/cpumap.c
>> @@ -195,7 +195,10 @@ static int cpu_map_bpf_prog_run_xdp(struct 
>> bpf_cpu_map_entry *rcpu,
>>           rxq.dev = xdpf->dev_rx;
>>           rxq.mem.type = xdpf->mem_type;
>> -        /* TODO: report queue_index to xdp_rxq_info */
>> +        /* The NIC RX queue_index is lost after the frame redirection
>> +         * but in case of need, it can be passed as a custom XDP
>> +         * metadata via xdp_md struct to the remote XDP program
> 
> Argh, saying XDP metadata is accessed via the xdp_md struct is just wrong.
> 
Ack, I didn't clarify that XDP metadata should be propagated via the 
bpf_xdp_adjust_meta like mentionned in the link[2]... Maybe I was 
thinking more in the technical side that xdp_md->data_meta would hold 
the value internally... I will send a v3 with appropriate changes.
Thanks for the review.

Best Regards,
Mehdi Ben Hadj Khelifa
> Nacked-by: Jesper Dangaard Brouer <hawk@...nel.org>
> 
>> +         */
>>           xdp_convert_frame_to_buff(xdpf, &xdp);
>