netdev - Re: [PATCH] net: pass back data left in socket after receive

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Message-ID: <CANn89iLQLKc6rUaA8k9rTerXP3yhb0seQS4_K7WGVz1nDGKJ3g@mail.gmail.com>
Date:   Thu, 28 Apr 2022 15:37:08 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Paolo Abeni <pabeni@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: pass back data left in socket after receive

On Thu, Apr 28, 2022 at 3:18 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Wed, 27 Apr 2022 13:49:34 -0600 Jens Axboe wrote:
> > This is currently done for CMSG_INQ, add an ability to do so via struct
> > msghdr as well and have CMSG_INQ use that too. If the caller sets
> > msghdr->msg_get_inq, then we'll pass back the hint in msghdr->msg_inq.
> >
> > Rearrange struct msghdr a bit so we can add this member while shrinking
> > it at the same time. On a 64-bit build, it was 96 bytes before this
> > change and 88 bytes afterwards.
> >
> > Signed-off-by: Jens Axboe <axboe@...nel.dk>
>
> LGTM, but I said that once before..  Eric?

For some reason I have not received this patch to my primary email address.

This looks good, but needs to be rebased for net-next, see below ?

Also, maybe the title should reflect that it is really a TCP patch.

>
> FWIW the io_uring patch that uses it is here:
> https://git.kernel.dk/cgit/linux-block/commit/?h=io_uring-flags2
>
> > diff --git a/include/linux/socket.h b/include/linux/socket.h
> > index 6f85f5d957ef..12085c9a8544 100644
> > --- a/include/linux/socket.h
> > +++ b/include/linux/socket.h
> > @@ -50,6 +50,9 @@ struct linger {
> >  struct msghdr {
> >       void            *msg_name;      /* ptr to socket address structure */
> >       int             msg_namelen;    /* size of socket address structure */
> > +
> > +     int             msg_inq;        /* output, data left in socket */
> > +
> >       struct iov_iter msg_iter;       /* data */
> >
> >       /*
> > @@ -62,8 +65,9 @@ struct msghdr {
> >               void __user     *msg_control_user;
> >       };
> >       bool            msg_control_is_user : 1;
> > -     __kernel_size_t msg_controllen; /* ancillary data buffer length */
> > +     bool            msg_get_inq : 1;/* return INQ after receive */
> >       unsigned int    msg_flags;      /* flags on received message */
> > +     __kernel_size_t msg_controllen; /* ancillary data buffer length */
> >       struct kiocb    *msg_iocb;      /* ptr to iocb for async requests */
> >  };
> >
> > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > index cf18fbcbf123..78d79e26fb4d 100644
> > --- a/net/ipv4/tcp.c
> > +++ b/net/ipv4/tcp.c
> > @@ -2335,8 +2335,10 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len,
> >       if (sk->sk_state == TCP_LISTEN)
> >               goto out;
> >
> > -     if (tp->recvmsg_inq)
> > +     if (tp->recvmsg_inq) {
> >               *cmsg_flags = TCP_CMSG_INQ;
> > +             msg->msg_get_inq = 1;
> > +     }
> >       timeo = sock_rcvtimeo(sk, nonblock);
> >
> >       /* Urgent data needs to be handled specially. */
> > @@ -2559,7 +2561,7 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len,
> >  int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
> >               int flags, int *addr_len)
> >  {
> > -     int cmsg_flags = 0, ret, inq;
> > +     int cmsg_flags = 0, ret;
> >       struct scm_timestamping_internal tss;
> >
> >       if (unlikely(flags & MSG_ERRQUEUE))
> > @@ -2576,12 +2578,14 @@ int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
> >       release_sock(sk);
> >       sk_defer_free_flush(sk);

sk_defer_free_flush() has been removed in net-next.

> >
> > -     if (cmsg_flags && ret >= 0) {
> > +     if ((cmsg_flags || msg->msg_get_inq) && ret >= 0) {
> >               if (cmsg_flags & TCP_CMSG_TS)
> >                       tcp_recv_timestamp(msg, sk, &tss);
> > +             if (msg->msg_get_inq)
> > +                     msg->msg_inq = tcp_inq_hint(sk);
> >               if (cmsg_flags & TCP_CMSG_INQ) {
> > -                     inq = tcp_inq_hint(sk);
> > -                     put_cmsg(msg, SOL_TCP, TCP_CM_INQ, sizeof(inq), &inq);
> > +                     put_cmsg(msg, SOL_TCP, TCP_CM_INQ, sizeof(msg->msg_inq),
> > +                              &msg->msg_inq);
> >               }
> >       }
> >       return ret;
> >
>