netdev - Re: [PATCH RFC v2] net: xdp: allow for layer 3 packets in generic skb handler

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Message-ID: <58760713-438f-a332-77ab-e5c34f0f61b6@gmail.com>
Date:   Mon, 27 Apr 2020 08:45:28 -0600
From:   David Ahern <dsahern@...il.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>, netdev@...r.kernel.org
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH RFC v2] net: xdp: allow for layer 3 packets in generic skb
 handler

On 4/27/20 4:22 AM, Jason A. Donenfeld wrote:
> @@ -4544,6 +4544,13 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
>  	 * header.
>  	 */
>  	mac_len = skb->data - skb_mac_header(skb);
> +	if (!mac_len) {
> +		add_eth_hdr = true;
> +		mac_len = sizeof(struct ethhdr);
> +		*((struct ethhdr *)skb_push(skb, mac_len)) = (struct ethhdr) {
> +			.h_proto = skb->protocol
> +		};

please use a temp variable and explicit setting of the fields; that is
not pleasant to read and can not be more performant than a more direct

                eth_zero_addr(eth->h_source);
                eth_zero_addr(eth->h_dest);
                eth->h_proto = skb->protocol;