Re: [PATCH bpf-next 01/15] xdp: reserve an skb core extension area after the xdp_frame

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 11/10/26 04:56, Tianyi Gao wrote:
> Reserve the skb core extension area in the headroom, right after the
> xdp_frame. An XDP program stores RX metadata there for the skb that is
> built later.
> 
> The area begins with a header, struct xdp_skb_ext. It records the offset
> of each entry and the end of the last entry, in 4-byte units.
> bpf_xdp_adjust_head(), bpf_xdp_adjust_meta() and bpf_xdp_pull_data() use
> xdp_skb_ext_end() as their lower bound, so packet data and metadata
> cannot overwrite the entries.
> 
> The XDP_FLAGS_HAS_SKB_EXT flag indicates that the header is valid. Most
> drivers reuse the xdp_buff between packets, so xdp_prepare_buff() clears
> it. With BPF_F_TEST_XDP_LIVE_FRAMES, reset_ctx() restores the flags
> before each run, and ctx_was_changed() compares them.
> 
> Suggested-by: Jesper Dangaard Brouer <hawk@kernel.org>
> Link: https://lore.kernel.org/all/1d5521eb-84fc-4417-a3f5-6366694d160a@kernel.org/
> Signed-off-by: Tianyi Gao <tianyi@cloudflare.com>
> ---
>   include/net/xdp.h  | 45 +++++++++++++++++++++++++++++++++++++++++++++
>   net/bpf/test_run.c |  4 +++-
>   net/core/filter.c  |  8 +++-----
>   3 files changed, 51 insertions(+), 6 deletions(-)
> 
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 07231adfb5f8..c888353425d4 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -81,6 +81,9 @@ enum xdp_buff_flags {
>   	 * XDP program is not attached.
>   	 */
>   	XDP_FLAGS_FRAGS_UNREADABLE	= BIT(2),
> +	XDP_FLAGS_HAS_SKB_EXT		= BIT(3), /* skb core extension header
> +						   * is valid
> +						   */

This can be on 1-line (80 chars) of you change the comment to be:
  /* skb core ext hdr valid */

>   };
The rest looks good to me.

Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>