netdev - Re: [Patch bpf-next v3 02/10] af_unix: implement ->read

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Message-ID: <CAM_iQpVS9BL_NPPX3L=8ka9nn1WtyYb9VMP0MU6gKi70WvdPbQ@mail.gmail.com>
Date:   Thu, 6 May 2021 18:00:28 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jakub Sitnicki <jakub@...udflare.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Jiang Wang <jiang.wang@...edance.com>,
        Xiongchun Duan <duanxiongchun@...edance.com>,
        Dongdong Wang <wangdongdong.6@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [Patch bpf-next v3 02/10] af_unix: implement ->read_sock() for sockmap

On Wed, May 5, 2021 at 10:14 AM Jakub Sitnicki <jakub@...udflare.com> wrote:
>
> On Mon, Apr 26, 2021 at 04:49 AM CEST, Cong Wang wrote:
> > From: Cong Wang <cong.wang@...edance.com>
> >
> > Implement ->read_sock() for AF_UNIX datagram socket, it is
> > pretty much similar to udp_read_sock().
> >
> > 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>
> > ---
> >  net/unix/af_unix.c | 38 ++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 38 insertions(+)
> >
> > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> > index 5a31307ceb76..f4dc22db371d 100644
> > --- a/net/unix/af_unix.c
> > +++ b/net/unix/af_unix.c
> > @@ -661,6 +661,8 @@ static ssize_t unix_stream_splice_read(struct socket *,  loff_t *ppos,
> >                                      unsigned int flags);
> >  static int unix_dgram_sendmsg(struct socket *, struct msghdr *, size_t);
> >  static int unix_dgram_recvmsg(struct socket *, struct msghdr *, size_t, int);
> > +static int unix_read_sock(struct sock *sk, read_descriptor_t *desc,
> > +                       sk_read_actor_t recv_actor);
> >  static int unix_dgram_connect(struct socket *, struct sockaddr *,
> >                             int, int);
> >  static int unix_seqpacket_sendmsg(struct socket *, struct msghdr *, size_t);
> > @@ -738,6 +740,7 @@ static const struct proto_ops unix_dgram_ops = {
> >       .listen =       sock_no_listen,
> >       .shutdown =     unix_shutdown,
> >       .sendmsg =      unix_dgram_sendmsg,
> > +     .read_sock =    unix_read_sock,
> >       .recvmsg =      unix_dgram_recvmsg,
> >       .mmap =         sock_no_mmap,
> >       .sendpage =     sock_no_sendpage,
> > @@ -2183,6 +2186,41 @@ static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
> >       return err;
> >  }
> >
> > +static int unix_read_sock(struct sock *sk, read_descriptor_t *desc,
> > +                       sk_read_actor_t recv_actor)
> > +{
> > +     int copied = 0;
> > +
> > +     while (1) {
> > +             struct unix_sock *u = unix_sk(sk);
> > +             struct sk_buff *skb;
> > +             int used, err;
> > +
> > +             mutex_lock(&u->iolock);
> > +             skb = skb_recv_datagram(sk, 0, 1, &err);
> > +             if (!skb) {
> > +                     mutex_unlock(&u->iolock);
> > +                     return err;
> > +             }
> > +
> > +             used = recv_actor(desc, skb, 0, skb->len);
> > +             if (used <= 0) {
> > +                     if (!copied)
> > +                             copied = used;
> > +                     mutex_unlock(&u->iolock);
> > +                     break;
> > +             } else if (used <= skb->len) {
> > +                     copied += used;
> > +             }
> > +             mutex_unlock(&u->iolock);
>
> Do we need hold the mutex for recv_actor to process the skb?

Hm, it does look like we can just release it after dequeuing the
skb. Let me double check.

Thanks.