Re: [PATCH net-next v5 09/14] ip_tunnel: add drop reasons to the transmit path

[Ido Schimmel]

On Wed, Sep 30, 2026 at 09:39:05PM +0300, Anton Danilov wrote:
> @@ -636,6 +641,12 @@ enum skb_drop_reason {
>  	SKB_DROP_REASON_TUNNEL_OLD_SEQ,
>  	/** @SKB_DROP_REASON_GRE_CSUM: GRE checksum error */
>  	SKB_DROP_REASON_GRE_CSUM,
> +	/**
> +	 * @SKB_DROP_REASON_TUNNEL_ENCAP: failed to build the encapsulation
> +	 * header of a tunnel, e.g. an unknown or unregistered encapsulation
> +	 * type.
> +	 */
> +	SKB_DROP_REASON_TUNNEL_ENCAP,
>  	/**
>  	 * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
>  	 * shouldn't be used as a real 'reason' - only for tracing code gen

[...]

> @@ -620,8 +623,10 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev,
>  	if (!tunnel_hlen)
>  		tunnel_hlen = ip_encap_hlen(&tun_info->encap);
>  
> -	if (ip_tunnel_encap(skb, &tun_info->encap, &proto, &fl4) < 0)
> +	if (ip_tunnel_encap(skb, &tun_info->encap, &proto, &fl4) < 0) {
> +		reason = SKB_DROP_REASON_TUNNEL_ENCAP;

This will also cover the -ENOMEM from the callbacks, where
SKB_DROP_REASON_NOMEM is more appropriate. Better to change
ip_tunnel_encap() to return the appropriate drop reason like you did
with gre_parse_header().

>  		goto tx_error;
> +	}
>  
>  	use_cache = ip_tunnel_dst_cache_usable(skb, tun_info);
>  	if (use_cache)