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Date:   Mon, 25 Apr 2022 12:07:24 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Cong Wang <xiyou.wangcong@gmail.com>
Cc:     netdev@vger.kernel.org, Cong Wang <cong.wang@bytedance.com>,
        Eric Dumazet <edumazet@google.com>,
        John Fastabend <john.fastabend@gmail.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Jakub Sitnicki <jakub@cloudflare.com>
Subject: Re: [Patch bpf-next v1 1/4] tcp: introduce tcp_read_skb()
Message-ID: <20220425120724.32af0cc3@kernel.org>
In-Reply-To: <20220410161042.183540-2-xiyou.wangcong@gmail.com>
References: <20220410161042.183540-1-xiyou.wangcong@gmail.com>
        <20220410161042.183540-2-xiyou.wangcong@gmail.com>
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On Sun, 10 Apr 2022 09:10:39 -0700 Cong Wang wrote:
> +int tcp_read_skb(struct sock *sk, read_descriptor_t *desc,
> +		 sk_read_actor_t recv_actor)
> +{
> +	struct sk_buff *skb;
> +	struct tcp_sock *tp =3D tcp_sk(sk);
> +	u32 seq =3D tp->copied_seq;
> +	u32 offset;
> +	int copied =3D 0;
> +
> +	if (sk->sk_state =3D=3D TCP_LISTEN)
> +		return -ENOTCONN;
> +	while ((skb =3D tcp_recv_skb(sk, seq, &offset, true)) !=3D NULL) {
> +		if (offset < skb->len) {
> +			int used;
> +			size_t len;
> +
> +			len =3D skb->len - offset;
> +			used =3D recv_actor(desc, skb, offset, len);
> +			if (used <=3D 0) {
> +				if (!copied)
> +					copied =3D used;
> +				break;
> +			}
> +			if (WARN_ON_ONCE(used > len))
> +				used =3D len;
> +			seq +=3D used;
> +			copied +=3D used;
> +			offset +=3D used;
> +
> +			if (offset !=3D skb->len)
> +				continue;
> +		}
> +		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
> +			kfree_skb(skb);
> +			++seq;
> +			break;
> +		}
> +		kfree_skb(skb);
> +		if (!desc->count)
> +			break;
> +		WRITE_ONCE(tp->copied_seq, seq);
> +	}
> +	WRITE_ONCE(tp->copied_seq, seq);
> +
> +	tcp_rcv_space_adjust(sk);
> +
> +	/* Clean up data we have read: This will do ACK frames. */
> +	if (copied > 0)
> +		tcp_cleanup_rbuf(sk, copied);
> +
> +	return copied;
> +}
> +EXPORT_SYMBOL(tcp_read_skb);

I started prototyping a similar patch for TLS a while back but I have
two functions - one to get the skb and another to consume it. I thought
that's better for TLS, otherwise skbs stuck in the middle layer are not
counted towards the rbuf. Any thoughts on structuring the API that way?
I guess we can refactor that later, since TLS TCP-only we don't need
proto_ops plumbing there.

Overall =F0=9F=91=8D for adding such API.