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Message-ID: <CAL+tcoAid3eSbnu-h8PR9o-_pr4bOdsKAxsT=WT-d_GD91pVuQ@mail.gmail.com>
Date: Tue, 29 Oct 2024 11:12:13 +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 9:33 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> Jason Xing wrote:
> > 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!
>
> Actually, I may have misunderstood the intention of this new hook.
>
> I thought it was to record an additional timestamp.
I planned to do it after this series. For now, without the new hook,
it will not work for UDP type.
>
> But it is (also?) to program skb_shared_info.tx_flags based on
> instructions parsed from cmsg in __sock_cmsg_send.
I'm not sure if I grasp the key point you said.
For UDP, skb_shared_info.tx_flags will finally be initialized in
__ip_append_data() based on cork->tx_flags.
cork->tx_flags is computed by sock_tx_timestamp() based on
ipc->sockc.tsflags if cmsg feature is turned on.
__sock_tx_timestamp() uses "flags |= xxx" to initialize the
cork->tx_flags, so that the cork->tx_flags will not be completely
overridden by either the cmsg method or bpf program, that is to say,
the cork->tx_flags can combine both of them.
Then another key point is that we do the check to see which one
actually works in sk_tstamp_tx_flags() by testing sk->sk_tsflags or
sk->sk_tsflags_bpf in patch [2/14]. It guarantees that.
Thanks,
Jason
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