netdev - Re: [PATCH v15 net-next 10/14] tcp: accecn: AccECN option

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Message-ID: <CANn89iKyU-r93MWukKRh4qPmEgLwSNKudOp_xQ2A6YpaWoUJFw@mail.gmail.com>
Date: Thu, 21 Aug 2025 10:46:26 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: "Chia-Yu Chang (Nokia)" <chia-yu.chang@...ia-bell-labs.com>, Neal Cardwell <ncardwell@...gle.com>
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Subject: Re: [PATCH v15 net-next 10/14] tcp: accecn: AccECN option

On Thu, Aug 21, 2025 at 7:58 AM Chia-Yu Chang (Nokia)
<chia-yu.chang@...ia-bell-labs.com> wrote:
>
> > -----Original Message-----
> > From: Eric Dumazet <edumazet@...gle.com>
> > Sent: Thursday, August 21, 2025 2:30 PM
> > To: Chia-Yu Chang (Nokia) <chia-yu.chang@...ia-bell-labs.com>
> > Cc: pabeni@...hat.com; linux-doc@...r.kernel.org; corbet@....net; horms@...nel.org; dsahern@...nel.org; kuniyu@...zon.com; bpf@...r.kernel.org; netdev@...r.kernel.org; dave.taht@...il.com; jhs@...atatu.com; kuba@...nel.org; stephen@...workplumber.org; xiyou.wangcong@...il.com; jiri@...nulli.us; davem@...emloft.net; andrew+netdev@...n.ch; donald.hunter@...il.com; ast@...erby.net; liuhangbin@...il.com; shuah@...nel.org; linux-kselftest@...r.kernel.org; ij@...nel.org; ncardwell@...gle.com; Koen De Schepper (Nokia) <koen.de_schepper@...ia-bell-labs.com>; g.white@...lelabs.com; ingemar.s.johansson@...csson.com; mirja.kuehlewind@...csson.com; cheshire@...le.com; rs.ietf@....at; Jason_Livingood@...cast.com; vidhi_goel@...le.com
> > Subject: Re: [PATCH v15 net-next 10/14] tcp: accecn: AccECN option
> >
> >
> > CAUTION: This is an external email. Please be very careful when clicking links or opening attachments. See the URL nok.it/ext for additional information.
> >
> >
> >
> > On Fri, Aug 15, 2025 at 1:40 AM <chia-yu.chang@...ia-bell-labs.com> wrote:
> [...]
> > >  /* Used for make_synack to form the ACE flags */ diff --git
> > > a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h index
> > > bdac8c42fa82..53e0e85b52be 100644
> > > --- a/include/uapi/linux/tcp.h
> > > +++ b/include/uapi/linux/tcp.h
> > > @@ -316,6 +316,13 @@ struct tcp_info {
> > >                                          * in milliseconds, including any
> > >                                          * unfinished recovery.
> > >                                          */
> > > +       __u32   tcpi_received_ce;    /* # of CE marks received */
> > > +       __u32   tcpi_delivered_e1_bytes;  /* Accurate ECN byte counters */
> > > +       __u32   tcpi_delivered_e0_bytes;
> > > +       __u32   tcpi_delivered_ce_bytes;
> > > +       __u32   tcpi_received_e1_bytes;
> > > +       __u32   tcpi_received_e0_bytes;
> > > +       __u32   tcpi_received_ce_bytes;
> > >  };
> > >
> >
> > We do not add more fields to tcp_info, unless added fields are a multiple of 64 bits.
> >
> > Otherwise a hole is added and can not be recovered.
>
> Hi Eric,
>
> Thanks for the feedback.
>
> Then, would it make sense to add __u32 reserved; here or this is not an option?
>

I would prefer we take the opportunity to export a 32bit field right
there, instead of a hole.

A reserved field makes it difficult for ss commands to know if a new
kernel is using it for a different purpose.

Neal, any idea of what would be useful ?

I was thinking lately of sk_err_soft, but I am not yet convinced.