netdev - Re: [Patch bpf-next v6 08/12] udp: implement ->read

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Date:   Wed, 24 Mar 2021 13:04:58 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, duanxiongchun@...edance.com,
        Dongdong Wang <wangdongdong.6@...edance.com>,
        Jiang Wang <jiang.wang@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [Patch bpf-next v6 08/12] udp: implement ->read_sock() for sockmap

On Mon, Mar 22, 2021 at 11:31 PM Yunsheng Lin <linyunsheng@...wei.com> wrote:
>
> On 2021/3/23 8:38, Cong Wang wrote:
> > From: Cong Wang <cong.wang@...edance.com>
> >
> > This is similar to tcp_read_sock(), except we do not need
> > to worry about connections, we just need to retrieve skb
> > from UDP receive queue.
> >
> > Cc: John Fastabend <john.fastabend@...il.com>
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > Cc: Jakub Sitnicki <jakub@...udflare.com>
> > Cc: Lorenz Bauer <lmb@...udflare.com>
> > Signed-off-by: Cong Wang <cong.wang@...edance.com>
> > ---
> >  include/net/udp.h   |  2 ++
> >  net/ipv4/af_inet.c  |  1 +
> >  net/ipv4/udp.c      | 35 +++++++++++++++++++++++++++++++++++
> >  net/ipv6/af_inet6.c |  1 +
> >  4 files changed, 39 insertions(+)
> >
> > diff --git a/include/net/udp.h b/include/net/udp.h
> > index df7cc1edc200..347b62a753c3 100644
> > --- a/include/net/udp.h
> > +++ b/include/net/udp.h
> > @@ -329,6 +329,8 @@ struct sock *__udp6_lib_lookup(struct net *net,
> >                              struct sk_buff *skb);
> >  struct sock *udp6_lib_lookup_skb(const struct sk_buff *skb,
> >                                __be16 sport, __be16 dport);
> > +int udp_read_sock(struct sock *sk, read_descriptor_t *desc,
> > +               sk_read_actor_t recv_actor);
> >
> >  /* UDP uses skb->dev_scratch to cache as much information as possible and avoid
> >   * possibly multiple cache miss on dequeue()
> > diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> > index 1355e6c0d567..f17870ee558b 100644
> > --- a/net/ipv4/af_inet.c
> > +++ b/net/ipv4/af_inet.c
> > @@ -1070,6 +1070,7 @@ const struct proto_ops inet_dgram_ops = {
> >       .setsockopt        = sock_common_setsockopt,
> >       .getsockopt        = sock_common_getsockopt,
> >       .sendmsg           = inet_sendmsg,
> > +     .read_sock         = udp_read_sock,
> >       .recvmsg           = inet_recvmsg,
> >       .mmap              = sock_no_mmap,
> >       .sendpage          = inet_sendpage,
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index 38952aaee3a1..a0adee3b1af4 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -1782,6 +1782,41 @@ struct sk_buff *__skb_recv_udp(struct sock *sk, unsigned int flags,
> >  }
> >  EXPORT_SYMBOL(__skb_recv_udp);
> >
> > +int udp_read_sock(struct sock *sk, read_descriptor_t *desc,
> > +               sk_read_actor_t recv_actor)
> > +{
> > +     int copied = 0;
> > +
> > +     while (1) {
> > +             int offset = 0, err;
> > +             struct sk_buff *skb;
> > +
> > +             skb = __skb_recv_udp(sk, 0, 1, &offset, &err);
> > +             if (!skb)
> > +                     break;
>
> Does above error handling need the below additional handling?
> It seems __skb_recv_udp() will return the error by parameter "err",
> if "copied == 0", does it need to return the error?

Not for skmsg case, because the return value is just unused:

static void sk_psock_verdict_data_ready(struct sock *sk)
{
        struct socket *sock = sk->sk_socket;
        read_descriptor_t desc;

        if (unlikely(!sock || !sock->ops || !sock->ops->read_sock))
                return;

        desc.arg.data = sk;
        desc.error = 0;
        desc.count = 1;

        sock->ops->read_sock(sk, &desc, sk_psock_verdict_recv);
}

Thanks.