On Wed, Oct 9, 2024 at 2:56 AM Willem de Bruijn
<willemdebruijn.kernel@xxxxxxxxx> wrote:
>
> Jason Xing wrote:
> > From: Jason Xing <kernelxing@xxxxxxxxxxx>
> >
> > We can set OPT_ID|OPT_ID_TCP before we initialize the last skb
> > from each sendmsg. We only set the socket once like how we use
> > setsockopt() with OPT_ID|OPT_ID_TCP flags.
> >
> > Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx>
> > ---
> > net/core/skbuff.c | 16 +++++++++++++---
> > net/ipv4/tcp.c | 19 +++++++++++++++----
> > 2 files changed, 28 insertions(+), 7 deletions(-)
> >
>
> > @@ -491,10 +491,21 @@ static u32 bpf_tcp_tx_timestamp(struct sock *sk)
> > if (!(flags & SOF_TIMESTAMPING_TX_RECORD_MASK))
> > return 0;
> >
> > + /* We require users to set both OPT_ID and OPT_ID_TCP flags
> > + * together here, or else the key might be inaccurate.
> > + */
> > + if (flags & SOF_TIMESTAMPING_OPT_ID &&
> > + flags & SOF_TIMESTAMPING_OPT_ID_TCP &&
> > + !(sk->sk_tsflags & (SOF_TIMESTAMPING_OPT_ID | SOF_TIMESTAMPING_OPT_ID_TCP))) {
> > + atomic_set(&sk->sk_tskey, (tcp_sk(sk)->write_seq - copied));
> > + sk->sk_tsflags |= (SOF_TIMESTAMPING_OPT_ID | SOF_TIMESTAMPING_OPT_ID_TCP);
>
> So user and BPF admin conflict on both sk_tsflags and sktskey?
>
> I think BPF resetting this key, or incrementing it, may break user
> expectations.
Yes, when it comes to OPT_ID and OPT_ID_TCP, conflict could happen.
The reason why I don't use it like BPF_SOCK_OPS_TS_SCHED_OPT_CB flags
(which is set along with each last skb) is that OPT_ID logic is a
little bit complex. If we want to avoid touching sk_tsflags field in
struct sock, we have to re-implement a similiar logic as you've
already done in these years.
Now, this patch is easier but as you said it may "break" users... But
I wonder if we can give the bpf program the first priority like what
TCP_BPF_RTO_MIN does. TCP_BPF_RTO_MIN can override icsk_rto_min field
in struct inet_connection_sock.
Thanks,
Jason
