Re: [PATCH net] net: stmmac: set XDP metadata length on the page_pool RX path

[Nicolai Buchwitz <nb@tipi-net.de>]

Hi Lorenzo

On 2.11.2026 12:46, Lorenzo Bianconi wrote:
> stmmac_rx() initializes the XDP buffer with the metadata area valid, so
> an XDP program can reserve metadata with bpf_xdp_adjust_meta() and 
> write
> it in [xdp->data_meta, xdp->data), for example to export the RX 
> hardware
> timestamp obtained from the metadata kfunc. When such a frame is passed
> to the stack, the skb is built in place around the same page with
> napi_build_skb(), but skb_metadata_set() is never called.
> 
> napi_build_skb() clears skb_shared_info up to dataref, which includes
> meta_len, so skb_metadata_len() stays zero. The stack and TC BPF then 
> see
> an empty metadata range even though the bytes are present in the skb
> headroom. The AF_XDP zero-copy path already records the length in
> stmmac_construct_skb_zc().
> 
> Record the metadata length after reserving the headroom and adding the
> frame data. No copy is needed because the skb is built over the buffer 
> the
> XDP program wrote to. With the length recorded, the software VLAN
> stripping path can move the metadata together with the MAC header, as 
> it
> already does for zero-copy frames.
> 
> Fixes: e3f9c3e34840 ("net: stmmac: add Rx HWTS metadata to XDP receive 
> pkt")
> Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@oss.qualcomm.com>
> ---

> [...]

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>

Thanks,
Nicolai