netdev - Re: [Patch bpf-next 08/19] udp: implement ->read

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Date:   Mon, 8 Feb 2021 17:35:22 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        duanxiongchun@...edance.com,
        Dongdong Wang <wangdongdong.6@...edance.com>,
        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>
Subject: Re: [Patch bpf-next 08/19] udp: implement ->read_sock() for sockmap

On Mon, Feb 8, 2021 at 1:48 AM Lorenz Bauer <lmb@...udflare.com> wrote:
>
> On Wed, 3 Feb 2021 at 04:17, Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > From: Cong Wang <cong.wang@...edance.com>
> >
> > 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     | 34 ++++++++++++++++++++++++++++++++++
> >  3 files changed, 37 insertions(+)
> >
> > diff --git a/include/net/udp.h b/include/net/udp.h
> > index 13f9354dbd3e..b6b75cabf4e4 100644
> > --- a/include/net/udp.h
> > +++ b/include/net/udp.h
> > @@ -327,6 +327,8 @@ 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 d184d9379a92..4a4c6d3d2786 100644
> > --- a/net/ipv4/af_inet.c
> > +++ b/net/ipv4/af_inet.c
> > @@ -1072,6 +1072,7 @@ const struct proto_ops inet_dgram_ops = {
> >         .getsockopt        = sock_common_getsockopt,
> >         .sendmsg           = inet_sendmsg,
> >         .sendmsg_locked    = udp_sendmsg_locked,
> > +       .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 635e1e8b2968..6dffbcec0b51 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -1792,6 +1792,40 @@ 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)
> > +{
> > +       struct sk_buff *skb;
> > +       int copied = 0, err;
> > +
> > +       while (1) {
> > +               int offset = 0;
> > +
> > +               skb = __skb_recv_udp(sk, 0, 1, &offset, &err);
>
> Seems like err isn't used outside of the loop, is that on purpose? If
> yes, how about moving the declaration of err to be with offset. Maybe
> rename to ignored?

It should be moved inside the loop.

>
> > +               if (!skb)
> > +                       break;
> > +               if (offset < skb->len) {
> > +                       int used;
> > +                       size_t len;
> > +
> > +                       len = skb->len - offset;
> > +                       used = recv_actor(desc, skb, offset, len);
> > +                       if (used <= 0) {
> > +                               if (!copied)
> > +                                       copied = used;
> > +                               break;
> > +                       } else if (used <= len) {
>
> In which case can used be > len?

I think in splice() case it could return a larger value than 'len', but
UDP does not support splice() even after this patchset. I can change
it to 'else', or just leave it as it is, in case we will add splice() support in
the future.

Thanks.