netdev - Re: [PATCH net-next v3 07/14] net-timestamp: add a new triggered point to set sk_tsflags

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Message-ID: <CAL+tcoCBxTUU9mPUTC=9LmGLsrUrjVDVk-982M-TjewSW-hjzQ@mail.gmail.com>
Date: Tue, 29 Oct 2024 09:23:20 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, dsahern@...nel.org, willemb@...gle.com, ast@...nel.org, 
	daniel@...earbox.net, andrii@...nel.org, martin.lau@...ux.dev, 
	eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev, 
	john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me, 
	haoluo@...gle.com, jolsa@...nel.org, shuah@...nel.org, ykolal@...com, 
	bpf@...r.kernel.org, netdev@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v3 07/14] net-timestamp: add a new triggered
 point to set sk_tsflags_bpf in UDP layer

On Tue, Oct 29, 2024 at 9:07 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> Jason Xing wrote:
> > From: Jason Xing <kernelxing@...cent.com>
> >
> > This patch behaves like how cmsg feature works, that is to say,
> > check and set on each call of udp_sendmsg before passing sk_tsflags_bpf
> > to cork tsflags.
> >
> > Signed-off-by: Jason Xing <kernelxing@...cent.com>
> > ---
> >  include/net/sock.h             | 1 +
> >  include/uapi/linux/bpf.h       | 3 +++
> >  net/core/skbuff.c              | 2 +-
> >  net/ipv4/udp.c                 | 1 +
> >  tools/include/uapi/linux/bpf.h | 3 +++
> >  5 files changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/net/sock.h b/include/net/sock.h
> > index 062f405c744e..cf7fea456455 100644
> > --- a/include/net/sock.h
> > +++ b/include/net/sock.h
> > @@ -2828,6 +2828,7 @@ static inline bool sk_listener_or_tw(const struct sock *sk)
> >  }
> >
> >  void sock_enable_timestamp(struct sock *sk, enum sock_flags flag);
> > +void timestamp_call_bpf(struct sock *sk, int op, u32 nargs, u32 *args);
> >  int sock_recv_errqueue(struct sock *sk, struct msghdr *msg, int len, int level,
> >                      int type);
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 6fc3bd12b650..055ffa7c965c 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -7028,6 +7028,9 @@ enum {
> >                                        * feature is on. It indicates the
> >                                        * recorded timestamp.
> >                                        */
> > +     BPF_SOCK_OPS_TS_UDP_SND_CB,     /* Called when every udp_sendmsg
> > +                                      * syscall is triggered
> > +                                      */
> >  };
> >
> >  /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index 8b2a79c0fe1c..0b571306f7ea 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -5622,7 +5622,7 @@ static void skb_tstamp_tx_output(struct sk_buff *orig_skb,
> >       __skb_complete_tx_timestamp(skb, sk, tstype, opt_stats);
> >  }
> >
> > -static void timestamp_call_bpf(struct sock *sk, int op, u32 nargs, u32 *args)
> > +void timestamp_call_bpf(struct sock *sk, int op, u32 nargs, u32 *args)
> >  {
> >       struct bpf_sock_ops_kern sock_ops;
> >
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index 9a20af41e272..e768421abc37 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -1264,6 +1264,7 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
> >       if (!corkreq) {
> >               struct inet_cork cork;
> >
> > +             timestamp_call_bpf(sk, BPF_SOCK_OPS_TS_UDP_SND_CB, 0, NULL);
> >               skb = ip_make_skb(sk, fl4, getfrag, msg, ulen,
> >                                 sizeof(struct udphdr), &ipc, &rt,
> >                                 &cork, msg->msg_flags);
> > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> > index 6fc3bd12b650..055ffa7c965c 100644
> > --- a/tools/include/uapi/linux/bpf.h
> > +++ b/tools/include/uapi/linux/bpf.h
> > @@ -7028,6 +7028,9 @@ enum {
> >                                        * feature is on. It indicates the
> >                                        * recorded timestamp.
> >                                        */
> > +     BPF_SOCK_OPS_TS_UDP_SND_CB,     /* Called when every udp_sendmsg
> > +                                      * syscall is triggered
> > +                                      */
>
> If adding a timestamp as close to syscall entry as possible, give it a
> generic name, not specific to UDP.

Good suggestion, then it will also solve the remaining issue for TCP type:
__when__ we should record the user timestamp which exists in the
application SO_TIMESTAMPING feature.

>
> And please explain in the commit message the reason for a new
> timestamp recording point: with existing timestamping the application
> can call clock_gettime before (and optionally after) the send call.
> An admin using BPF does not have this option, so needs this as part of
> the BPF timestamping API.

Will revise this part. Thanks for your description!

Thanks,
Jason