> -----Original Message----- > From: Paolo Abeni <[email protected]> > Sent: Tuesday, November 18, 2025 1:02 PM > To: Chia-Yu Chang (Nokia) <[email protected]>; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; Koen De Schepper (Nokia) > <[email protected]>; [email protected]; > [email protected]; [email protected]; cheshire > <[email protected]>; [email protected]; [email protected]; Vidhi Goel > <[email protected]> > Subject: Re: [PATCH v6 net-next 03/14] net: update commnets for > SKB_GSO_TCP_ECN and SKB_GSO_TCP_ACCECN > > > 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. > > > > Note: typo in the subj > > On 11/14/25 8:13 AM, [email protected] wrote: > > From: Chia-Yu Chang <[email protected]> > > > > No functional changes. > > Some real commit message is needed. > > > > > Co-developed-by: Ilpo Järvinen <[email protected]> > > Signed-off-by: Ilpo Järvinen <[email protected]> > > Signed-off-by: Chia-Yu Chang <[email protected]> > > > > --- > > v6: > > - Update comments. > > --- > > include/linux/skbuff.h | 14 +++++++++++++- > > 1 file changed, 13 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index > > ff90281ddf90..e09455cee8e3 100644 > > --- a/include/linux/skbuff.h > > +++ b/include/linux/skbuff.h > > @@ -671,7 +671,13 @@ enum { > > /* This indicates the skb is from an untrusted source. */ > > SKB_GSO_DODGY = 1 << 1, > > > > - /* This indicates the tcp segment has CWR set. */ > > + /* For Tx, this indicates the first TCP segment has CWR set, and any > > + * subsequent segment in the same skb has CWR cleared. This is not > > + * used on Rx except for virtio_net. However, because the connection > > + * to which the segment belongs is not tracked to use RFC3168 or > > + * Accurate ECN, and using RFC3168 ECN offload may corrupt AccECN > > + * signal of AccECN segments. Therefore, this cannot be used on Rx. > > Stating both that is used by virtio_net and can not be used in the RX path is > a bit confusing. Random Contributor may be tempted from removing ECN support > from virtio_net > > Please state explicitly: > - why it makes sense to use this in virtio_net > - this must not be used in the RX path _outside_ the virtio net driver > > something alike: > > /* For Tx, this indicates the first TCP segment has CWR set, and any > * subsequent segment in the same skb has CWR cleared. However, because > * the connection to which the segment belongs is not tracked to use > * RFC3168 or Accurate ECN, and using RFC3168 ECN offload may corrupt > * AccECN signal of AccECN segments. Therefore, this cannot be used on > * Rx outside the virtio_net driver. Such exception exist due to > * <reason> > */ > > /P Hi Paolo and Ilpo,
I was thinking to totally remove ECN from Rx path, and add the comments only in AccECN, like below: Because we could use SKB_GSO_TCP_ACCECN in Rx to explicitly tell latter GSO Tx in a forwarding case that do NOT clean CWR flag. What do you think? /* For Tx, this indicates the first TCP segment has CWR set, and any * subsequent segment in the same skb has CWR cleared. However, because * the connection to which the segment belongs is not tracked to use * RFC3168 or Accurate ECN, and using RFC3168 ECN offload may corrupt * ACE signal of AccECN segments. Therefore, this cannot be used on Rx. */ SKB_GSO_TCP_ECN = 1 << 2, [...] /* For TX, this indicates the TCP segment uses the CWR flag as part of * ACE signal, and the CWR flag is not modified in the skb. For RX, any * CWR flagged segment must use SKB_GSO_TCP_ACCECN to ensure CWR flag * is not cleared by any RFC3168 ECN offload, and thus keeping ACE * signal of AccECN segments. This is particularly used for Rx of * virtio_net driver in order to tell latter GSO Tx in a forwarding * scenario that it is NOT ok to clean CWR flag from the 2nd segment. */ SKB_GSO_TCP_ACCECN = 1 << 19, Chia-Yu
