netdev - RE: [PATCH v9 net-next 13/15] tcp: accecn: add tcpi_ecn_mode and tcpi_option2 in tcp

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Message-ID:
 <PAXPR07MB7984BA30924000787013DD26A389A@PAXPR07MB7984.eurprd07.prod.outlook.com>
Date: Tue, 20 Jan 2026 11:37:41 +0000
From: "Chia-Yu Chang (Nokia)" <chia-yu.chang@...ia-bell-labs.com>
To: Eric Dumazet <edumazet@...gle.com>
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Subject: RE: [PATCH v9 net-next 13/15] tcp: accecn: add tcpi_ecn_mode and
 tcpi_option2 in tcp_info

> -----Original Message-----
> From: Eric Dumazet <edumazet@...gle.com> 
> Sent: Tuesday, January 20, 2026 12:18 PM
> To: Chia-Yu Chang (Nokia) <chia-yu.chang@...ia-bell-labs.com>
> Cc: pabeni@...hat.com; parav@...dia.com; linux-doc@...r.kernel.org; corbet@....net; horms@...nel.org; dsahern@...nel.org; kuniyu@...gle.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 <cheshire@...le.com>; rs.ietf@....at; Jason_Livingood@...cast.com; Vidhi Goel <vidhi_goel@...le.com>
> Subject: Re: [PATCH v9 net-next 13/15] tcp: accecn: add tcpi_ecn_mode and tcpi_option2 in tcp_info
> 
> 
> 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 Mon, Jan 19, 2026 at 7:59 PM <chia-yu.chang@...ia-bell-labs.com> wrote:
> >
> > From: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> >
> > Add 2-bit tcpi_ecn_mode feild within tcp_info to indicate which ECN 
> > mode is negotiated: ECN_MODE_DISABLED, ECN_MODE_RFC3168, 
> > ECN_MODE_ACCECN, or ECN_MODE_PENDING. This is done by utilizing 
> > available bits from tcpi_accecn_opt_seen (reduced from 16 bits to 2 
> > bits) and tcpi_accecn_fail_mode (reduced from 16 bits to 4 bits).
> >
> > Also, an extra 24-bit tcpi_options2 field is identified to represent 
> > newer options and connection features, as all 8 bits of tcpi_options 
> > field have been used.
> >
> > Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> > Co-developed-by: Neal Cardwell <ncardwell@...gle.com>
> > Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> 
> Are you sure Neal Cardwell really is ok with this patch, saw it and gave his SOB ?
> 
> > ---
> 
> >  struct tcp_info {
> >         __u8    tcpi_state;
> >         __u8    tcpi_ca_state;
> > @@ -316,15 +334,17 @@ struct tcp_info {
> >                                          * in milliseconds, including any
> >                                          * unfinished recovery.
> >                                          */
> > -       __u32   tcpi_received_ce;    /* # of CE marks received */
> > +       __u32   tcpi_ecn_mode:2,
> > +               tcpi_accecn_opt_seen:2,
> > +               tcpi_accecn_fail_mode:4,
> > +               tcpi_options2:24;
> > +       __u32   tcpi_received_ce;    /* # of CE marked segments 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;
> > -       __u16   tcpi_accecn_fail_mode;
> > -       __u16   tcpi_accecn_opt_seen;
> >  };
> 
> tcp_info is ABI.
> 
> We can not add/remove fields in the middle.
> 
> You must add fields at the end of it only.

Sure, I will update this is the next version and submit new corresponding patch to packetdrill (after this patch is accepted.)

Chia-Yu