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Date: Mon, 2 May 2022 17:02:07 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
Cong Wang <cong.wang@...edance.com>,
John Fastabend <john.fastabend@...il.com>,
Daniel Borkmann <daniel@...earbox.net>,
Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: [Patch bpf-next v2 1/4] tcp: introduce tcp_read_skb()
On Mon, May 2, 2022 at 11:24 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> From: Cong Wang <cong.wang@...edance.com>
>
> This patch inroduces tcp_read_skb() based on tcp_read_sock(),
> a preparation for the next patch which actually introduces
> a new sock ops.
>
> TCP is special here, because it has tcp_read_sock() which is
> mainly used by splice(). tcp_read_sock() supports partial read
> and arbitrary offset, neither of them is needed for sockmap.
>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: John Fastabend <john.fastabend@...il.com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Jakub Sitnicki <jakub@...udflare.com>
> Signed-off-by: Cong Wang <cong.wang@...edance.com>
> ---
> include/net/tcp.h | 2 ++
> net/ipv4/tcp.c | 63 +++++++++++++++++++++++++++++++++++++++++------
> 2 files changed, 57 insertions(+), 8 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 94a52ad1101c..ab7516e5cc56 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -667,6 +667,8 @@ void tcp_get_info(struct sock *, struct tcp_info *);
> /* Read 'sendfile()'-style from a TCP socket */
> int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
> sk_read_actor_t recv_actor);
> +int tcp_read_skb(struct sock *sk, read_descriptor_t *desc,
> + sk_read_actor_t recv_actor);
>
> void tcp_initialize_rcv_mss(struct sock *sk);
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index db55af9eb37b..8d48126e3694 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1600,7 +1600,7 @@ static void tcp_eat_recv_skb(struct sock *sk, struct sk_buff *skb)
> __kfree_skb(skb);
> }
>
> -static struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off)
> +static struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off, bool unlink)
> {
> struct sk_buff *skb;
> u32 offset;
> @@ -1613,6 +1613,8 @@ static struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off)
> }
> if (offset < skb->len || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)) {
> *off = offset;
> + if (unlink)
> + __skb_unlink(skb, &sk->sk_receive_queue);
Why adding this @unlink parameter ?
This makes your patch more invasive than needed.
Can not this unlink happen from your new helper instead ? See [3] later.
> return skb;
> }
> /* This looks weird, but this can happen if TCP collapsing
> @@ -1646,7 +1648,7 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
>
> if (sk->sk_state == TCP_LISTEN)
> return -ENOTCONN;
> - while ((skb = tcp_recv_skb(sk, seq, &offset)) != NULL) {
> + while ((skb = tcp_recv_skb(sk, seq, &offset, false)) != NULL) {
> if (offset < skb->len) {
> int used;
> size_t len;
> @@ -1677,7 +1679,7 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
> * getting here: tcp_collapse might have deleted it
> * while aggregating skbs from the socket queue.
> */
> - skb = tcp_recv_skb(sk, seq - 1, &offset);
> + skb = tcp_recv_skb(sk, seq - 1, &offset, false);
> if (!skb)
> break;
> /* TCP coalescing might have appended data to the skb.
> @@ -1702,13 +1704,58 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
>
> /* Clean up data we have read: This will do ACK frames. */
> if (copied > 0) {
> - tcp_recv_skb(sk, seq, &offset);
> + tcp_recv_skb(sk, seq, &offset, false);
> tcp_cleanup_rbuf(sk, copied);
> }
> return copied;
> }
> EXPORT_SYMBOL(tcp_read_sock);
>
> +int tcp_read_skb(struct sock *sk, read_descriptor_t *desc,
> + sk_read_actor_t recv_actor)
> +{
> + struct tcp_sock *tp = tcp_sk(sk);
> + u32 seq = tp->copied_seq;
> + struct sk_buff *skb;
> + int copied = 0;
> + u32 offset;
> +
> + if (sk->sk_state == TCP_LISTEN)
> + return -ENOTCONN;
> +
> + while ((skb = tcp_recv_skb(sk, seq, &offset, true)) != NULL) {
[3]
The unlink from sk->sk_receive_queue could happen here.
> + int used = recv_actor(desc, skb, 0, skb->len);
> +
> + if (used <= 0) {
> + if (!copied)
> + copied = used;
> + break;
> + }
> + seq += used;
> + copied += used;
> +
> + if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
> + kfree_skb(skb);
[1]
The two kfree_skb() ([1] & [2]) should be a consume_skb() ?
> + ++seq;
> + break;
> + }
> + kfree_skb(skb);
[2]
> + 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);
> +
> int tcp_peek_len(struct socket *sock)
> {
> return tcp_inq(sock->sk);
> @@ -1890,7 +1937,7 @@ static int receive_fallback_to_copy(struct sock *sk,
> struct sk_buff *skb;
> u32 offset;
>
> - skb = tcp_recv_skb(sk, tcp_sk(sk)->copied_seq, &offset);
> + skb = tcp_recv_skb(sk, tcp_sk(sk)->copied_seq, &offset, false);
> if (skb)
> tcp_zerocopy_set_hint_for_skb(sk, zc, skb, offset);
> }
> @@ -1937,7 +1984,7 @@ static int tcp_zc_handle_leftover(struct tcp_zerocopy_receive *zc,
> if (skb) {
> offset = *seq - TCP_SKB_CB(skb)->seq;
> } else {
> - skb = tcp_recv_skb(sk, *seq, &offset);
> + skb = tcp_recv_skb(sk, *seq, &offset, false);
> if (TCP_SKB_CB(skb)->has_rxtstamp) {
> tcp_update_recv_tstamps(skb, tss);
> zc->msg_flags |= TCP_CMSG_TS;
> @@ -2130,7 +2177,7 @@ static int tcp_zerocopy_receive(struct sock *sk,
> skb = skb->next;
> offset = seq - TCP_SKB_CB(skb)->seq;
> } else {
> - skb = tcp_recv_skb(sk, seq, &offset);
> + skb = tcp_recv_skb(sk, seq, &offset, false);
> }
>
> if (TCP_SKB_CB(skb)->has_rxtstamp) {
> @@ -2186,7 +2233,7 @@ static int tcp_zerocopy_receive(struct sock *sk,
> tcp_rcv_space_adjust(sk);
>
> /* Clean up data we have read: This will do ACK frames. */
> - tcp_recv_skb(sk, seq, &offset);
> + tcp_recv_skb(sk, seq, &offset, false);
> tcp_cleanup_rbuf(sk, length + copylen);
> ret = 0;
> if (length == zc->length)
> --
> 2.32.0
>
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