Subject: Re: [PATCH v3 net-next 3/6] net: Add SW fallback infrastructure for offloaded sockets

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Mon, 18 Dec 2017 17:18:27 -0200

On Mon, Dec 18, 2017 at 01:10:30PM +0200, Ilya Lesokhin wrote:
> Offloaded sockets rely on the netdev to transform the transmitted
> packets before sending them over the network.
> When a packet from an offloaded socket is looped back or
> rerouted to a different device we need to detect it and
> do the transformation in software
> 
> Signed-off-by: Ilya Lesokhin <[email-masked]>
> Signed-off-by: Boris Pismenny <[email-masked]>
> ---
>  include/net/sock.h | 17 +++++++++++++++++
>  net/core/dev.c     |  4 ++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 9a9047268d37..5397307603ec 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -479,6 +479,9 @@ struct sock {
>  	void			(*sk_error_report)(struct sock *sk);
>  	int			(*sk_backlog_rcv)(struct sock *sk,
>  						  struct sk_buff *skb);
> +	struct sk_buff*		(*sk_offload_check)(struct sock *sk,
> +						    struct net_device *dev,
> +						    struct sk_buff *skb);
>  	void                    (*sk_destruct)(struct sock *sk);
>  	struct sock_reuseport __rcu	*sk_reuseport_cb;
>  	struct rcu_head		sk_rcu;
> @@ -2324,6 +2327,20 @@ static inline bool sk_fullsock(const struct sock *sk)
>  	return (1 << sk->sk_state) & ~(TCPF_TIME_WAIT | TCPF_NEW_SYN_RECV);
>  }
>  
> +/* Checks if this SKB belongs to an HW offloaded socket
> + * and whether any SW fallbacks are required based on dev.
> + */
> +static inline struct sk_buff *skb_offload_check(struct sk_buff *skb,
> +						struct net_device *dev)
> +{
> +	struct sock *sk = skb->sk;
> +
> +	if (sk && sk_fullsock(sk) && sk->sk_offload_check)

Isn't this going to hurt the fast path, checking for sk fields here?

> +		skb = sk->sk_offload_check(sk, dev, skb);
> +
> +	return skb;
> +}
> +
>  /* This helper checks if a socket is a LISTEN or NEW_SYN_RECV
>   * SYNACK messages can be attached to either ones (depending on SYNCOOKIE)
>   */
> diff --git a/net/core/dev.c b/net/core/dev.c
> index b0eee49a2489..6a78d9046674 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3051,6 +3051,10 @@ static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device
>  	if (unlikely(!skb))
>  		goto out_null;
>  
> +	skb = skb_offload_check(skb, dev);
> +	if (!skb)
> +		goto out_null;
> +
>  	if (netif_needs_gso(skb, features)) {
>  		struct sk_buff *segs;
>  
> -- 
> 2.15.0.317.g14c63a9
>