netdev - Re: [PATCH v7 bpf-next 10/14] bpf: add new frame

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Date:   Fri, 19 Mar 2021 21:42:55 -0600
From:   David Ahern <dsahern@...il.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     lorenzo.bianconi@...hat.com, davem@...emloft.net, kuba@...nel.org,
        ast@...nel.org, daniel@...earbox.net, shayagr@...zon.com,
        john.fastabend@...il.com, dsahern@...nel.org, brouer@...hat.com,
        echaudro@...hat.com, jasowang@...hat.com,
        alexander.duyck@...il.com, saeed@...nel.org,
        maciej.fijalkowski@...el.com, sameehj@...zon.com
Subject: Re: [PATCH v7 bpf-next 10/14] bpf: add new frame_length field to the
 XDP ctx

On 3/19/21 3:47 PM, Lorenzo Bianconi wrote:
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 19cd6642e087..e47d9e8da547 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -75,6 +75,10 @@ struct xdp_buff {
>  	struct xdp_txq_info *txq;
>  	u32 frame_sz:31; /* frame size to deduce data_hard_end/reserved tailroom*/
>  	u32 mb:1; /* xdp non-linear buffer */
> +	u32 frame_length; /* Total frame length across all buffers. Only needs
> +			   * to be updated by helper functions, as it will be
> +			   * initialized at XDP program start.
> +			   */
>  };
>  
>  static __always_inline void

If you do another version of this set ...

I think you only need 17-bits for the frame length (size is always <=
128kB). It would be helpful for extensions to xdp if you annotated how
many bits are really needed here.