RE: [PATCH v10 1/2] virtio-net: Fix ECN feature descriptions

Hi,

> From: [email protected] <chia-yu.chang@nokia-bell-
> labs.com>
> 
> From: Chia-Yu Chang <[email protected]>
> 
> Clarify that the VIRTIO_NET_HDR_GSO_ECN gso_type flag does not mean that
> TCP has IP-ECN set; instead, it identifies that the TCP CWR flag is set and will
> be cleared from the second segment of an aggregated segment.
>
Above text is seems to be clarified only in commit message, not in the spec changes below.
Can you please add it in the actual spec wording, including requirements?

> This is used to offload the TCP CWR flag in a way that is compatible with
> RFC3168 ECN but is problematic for non-RFC3168 use of the TCP CWR flag.
> 
> Foe detailed requirements, please refer to IETF RFC3168:

[..]

> Signed-off-by: Chia-Yu Chang <[email protected]>
> ---
>  device-types/net/description.tex | 35 +++++++++++++++++---------------
>  introduction.tex                 |  3 +++
>  2 files changed, 22 insertions(+), 16 deletions(-)
> 
> diff --git a/device-types/net/description.tex b/device-
> types/net/description.tex
> index da9ff17..0da8f9f 100644
> --- a/device-types/net/description.tex
> +++ b/device-types/net/description.tex
> @@ -54,7 +54,9 @@ \subsection{Feature bits}\label{sec:Device Types /
> Network Device / Feature bits
> 
>  \item[VIRTIO_NET_F_GUEST_TSO6 (8)] Driver can receive TSOv6.
> 
> -\item[VIRTIO_NET_F_GUEST_ECN (9)] Driver can receive TSO with ECN.
> +\item[VIRTIO_NET_F_GUEST_ECN (9)] Driver can receive TSO with the CWR
> flag set
> +    and follow the requirements of the CWR bit described in
> +    ``Section 6.1.2. The TCP Sender'' of \hyperref[intro:rfc3168]{[RFC3168]}.
> 
>  \item[VIRTIO_NET_F_GUEST_UFO (10)] Driver can receive UFO.
> 
> @@ -62,7 +64,9 @@ \subsection{Feature bits}\label{sec:Device Types /
> Network Device / Feature bits
> 
>  \item[VIRTIO_NET_F_HOST_TSO6 (12)] Device can receive TSOv6.
> 
> -\item[VIRTIO_NET_F_HOST_ECN (13)] Device can receive TSO with ECN.
> +\item[VIRTIO_NET_F_HOST_ECN (13)] Device can receive TSO with the CWR
> flag set
> +    and follow the requirements of the CWR bit described in
> +    ``Section 6.1.2. The TCP Sender'' of \hyperref[intro:rfc3168]{[RFC3168]}.
> 
>  \item[VIRTIO_NET_F_HOST_UFO (14)] Device can receive UFO.
> 
> @@ -729,9 +733,10 @@ \subsubsection{Packet
> Transmission}\label{sec:Device Types / Network Device / De
>      header (ie. MSS).
> 
>    \item If the driver negotiated the VIRTIO_NET_F_HOST_ECN feature,
> -    the VIRTIO_NET_HDR_GSO_ECN bit in \field{gso_type}
> -    indicates that the TCP packet has the ECN bit set\footnote{This case is not
> handled by some older hardware, so is called out
> -specifically in the protocol.}.
> +    the VIRTIO_NET_HDR_GSO_ECN bit in \field{gso_type} indicates that the
> TCP packet
> +    has the CWR flag set and follows the requirements of the CWR flag
> described in
> +    ``Section 6.1.2. The TCP Sender'' of \hyperref[intro:rfc3168]{[RFC3168]}.
> +    \footnote{This case is not handled by some older hardware, so is called
> out specifically in the protocol.}.
>     \end{itemize}
> 
>  \item If the driver negotiated the VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO
> feature and the @@ -828,10 +833,9 @@ \subsubsection{Packet
> Transmission}\label{sec:Device Types / Network Device / De  \field{gso_type}
> to VIRTIO_NET_HDR_GSO_UDP_L4.
> 
>  The driver SHOULD NOT send to the device TCP packets requiring
> segmentation offload -which have the Explicit Congestion Notification bit set,
> unless the -VIRTIO_NET_F_HOST_ECN feature is negotiated, in which case the
> -driver MUST set the VIRTIO_NET_HDR_GSO_ECN bit in -\field{gso_type}.
> +which need to follow the CWR flag requirements described in ``Section 6.1.2.
> The TCP Sender''
> +of \hyperref[intro:rfc3168]{[RFC3168]}, unless the
> +VIRTIO_NET_F_HOST_ECN feature is negotiated, in which case the driver
> MUST set the VIRTIO_NET_HDR_GSO_ECN bit in \field{gso_type}.
> 
>  If VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO is negotiated, the driver MAY set
>  VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV4 bit or the
> VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV6 bit @@ -1168,9 +1172,9 @@
> \subsubsection{Processing of Incoming Packets}\label{sec:Device Types /
> Network  \end{enumerate}
> 
>  Additionally, VIRTIO_NET_F_GUEST_CSUM, TSO4, TSO6, UDP, UDP_TUNNEL -
> and ECN features enable receive checksum, large receive offload and ECN -
> support which are the input equivalents of the transmit checksum, -transmit
> segmentation offloading and ECN features, as described
> +and ECN features enable receive checksum, large receive offload and
> +RFC3168 ECN support which are the input equivalents of the transmit
> +checksum, transmit segmentation offloading and RFC3168 ECN features, as
> +described
>  in \ref{sec:Device Types / Network Device / Device Operation /  Packet
> Transmission}:
>  \begin{enumerate}
> @@ -1273,10 +1277,9 @@ \subsubsection{Processing of Incoming
> Packets}\label{sec:Device Types / Network  the
> VIRTIO_NET_HDR_F_UDP_TUNNEL_CSUM bit in \field{flags}.
> 
>  The device SHOULD NOT send to the driver TCP packets requiring
> segmentation offload -which have the Explicit Congestion Notification bit set,
> unless the -VIRTIO_NET_F_GUEST_ECN feature is negotiated, in which case
> the -device MUST set the VIRTIO_NET_HDR_GSO_ECN bit in -\field{gso_type}.
> +which need to follow the CWR flag requirements described in ``Section 6.1.2.
> The TCP Sender''
> +of \hyperref[intro:rfc3168]{[RFC3168]}, unless the
> +VIRTIO_NET_F_GUEST_ECN feature is negotiated, in which case the device
> MUST set the VIRTIO_NET_HDR_GSO_ECN bit in \field{gso_type}.
> 
>  If VIRTIO_NET_F_OUT_NET_HEADER has been negotiated, the device MAY
> set the \field{outer_nh_offset} to nonzero value to indicate outer network
> header offset, diff --git a/introduction.tex b/introduction.tex index
> 80aa67a..1c4cb33 100644
> --- a/introduction.tex
> +++ b/introduction.tex
> @@ -180,6 +180,9 @@ \section{Normative References}\label{sec:Normative
> References}
>      Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words",
> BCP
>      14, RFC 8174, DOI 10.17487/RFC8174, May 2017
> 
> \newline\url{https://nam11.safelinks.protection.outlook.com/?url=http%3A%
> 2F%2Fwww.ietf.org%2Frfc%2Frfc8174.txt&data=05%7C02%7Cparav%40nvidia.
> com%7Cc6ffebfc748f4772784708dddb2a50c9%7C43083d15727340c1b7db39e
> fd9ccc17a%7C0%7C0%7C638907696998232587%7CUnknown%7CTWFpbGZsb
> 3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkF
> OIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=jRjpor%2FkXifPfp
> t7IFBo5JNF4%2FlE8pBsw7CMT4wS%2FRo%3D&reserved=0}\\
> +	\phantomsection\label{intro:rfc3168}\textbf{[RFC3168]} &
> +    S. Floyd., ``The Addition of Explicit Congestion Notification (ECN) to IP'',
> September 2001.
> +
> +\newline\url{https://nam11.safelinks.protection.outlook.com/?url=http%3
> +A%2F%2Fwww.ietf.org%2Frfc%2Frfc3168.txt&data=05%7C02%7Cparav%40nv
> idia.c
> +om%7Cc6ffebfc748f4772784708dddb2a50c9%7C43083d15727340c1b7db39e
> fd9ccc17
> +a%7C0%7C0%7C638907696998249586%7CUnknown%7CTWFpbGZsb3d8eyJ
> FbXB0eU1hcGki
> +OnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIj
> oyfQ%
> +3D%3D%7C0%7C%7C%7C&sdata=q7NaQPhNzVlOz0bGZVTw5ZYWFcq412q8J
> 57YHxTpkMs%3D
> +&reserved=0}\\
>  \end{longtable}
> 
>  \section{Non-Normative References}
> --
> 2.34.1
>