Subject: Re: [PATCH v2 net-next 1/4] bpf: xdp: Allow head adjustment in XDP prog

From: Jesper Dangaard Brouer <[email-masked]>
Date: Mon, 5 Dec 2016 08:35:33 +0100

On Sat, 3 Dec 2016 19:17:23 -0800 Martin KaFai Lau <[email-masked]> wrote:

> This patch allows XDP prog to extend/remove the packet
> data at the head (like adding or removing header).  It is
> done by adding a new XDP helper bpf_xdp_adjust_head().
> 
> It also renames bpf_helper_changes_skb_data() to
> bpf_helper_changes_pkt_data() to better reflect
> that XDP prog does not work on skb.
> 
> Acked-by: Alexei Starovoitov <[email-masked]>
> Signed-off-by: Martin KaFai Lau <[email-masked]>
> ---
[...]
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 56b43587d200..ccef948cf58a 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2234,7 +2234,34 @@ static const struct bpf_func_proto bpf_skb_change_head_proto = {
>  	.arg3_type	= ARG_ANYTHING,
>  };
>  
> -bool bpf_helper_changes_skb_data(void *func)
> +BPF_CALL_2(bpf_xdp_adjust_head, struct xdp_buff *, xdp, int, offset)
> +{
> +	/* Both mlx4 and mlx5 driver align each packet to PAGE_SIZE when
> +	 * XDP prog is set.
> +	 * If the above is not true for the other drivers to support
> +	 * bpf_xdp_adjust_head, struct xdp_buff can be extended.
> +	 */
> +	unsigned long addr = (unsigned long)xdp->data & PAGE_MASK;
> +	void *data_hard_start = (void *)addr;
> +	void *data = xdp->data + offset;
> +
> +	if (unlikely(data < data_hard_start || data > xdp->data_end - ETH_HLEN))
> +		return -EINVAL;
> +
> +	xdp->data = data;
> +
> +	return 0;
> +}

Thanks for adjusting this, I like Daniel's suggestion.

For this patch:

Acked-by: Jesper Dangaard Brouer <[email-masked]>

As it still looks like 3/4 need some adjustments based on Saeed's
comments.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer