Re: [virtio-comment] [PATCH] virtio-net: define USO feature

["Michael S. Tsirkin" <mst@redhat.com>]

On Sat, Apr 10, 2021 at 12:27:15PM +0300, Yuri Benditovich wrote:
> Fixes: https://github.com/oasis-tcs/virtio-spec/issues/104
> 
> Unlike UFO (fragmenting the packet) the USO splits large UDP packet
> to several segments when each of these smaller packets has UDP
> header. In Linux see SKB_GSO_UDP_L4.
> 
> Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>


looks good to me.

> ---
>  content.tex | 31 ++++++++++++++++++++-----------
>  1 file changed, 20 insertions(+), 11 deletions(-)
> 
> diff --git a/content.tex b/content.tex
> index e536fd4..2708386 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -2964,6 +2964,8 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits
>  \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control
>      channel.
>  
> +\item[VIRTIO_NET_F_HOST_USO (56)] Device can receive USO.
> +

USO packets maybe?

>  \item[VIRTIO_NET_F_HASH_REPORT(57)] Device can report per-packet hash
>      value and a type of calculated hash.
>  
> @@ -2998,6 +3000,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device
>  \item[VIRTIO_NET_F_HOST_TSO6] Requires VIRTIO_NET_F_CSUM.
>  \item[VIRTIO_NET_F_HOST_ECN] Requires VIRTIO_NET_F_HOST_TSO4 or VIRTIO_NET_F_HOST_TSO6.
>  \item[VIRTIO_NET_F_HOST_UFO] Requires VIRTIO_NET_F_CSUM.
> +\item[VIRTIO_NET_F_HOST_USO] Requires VIRTIO_NET_F_CSUM.
>  
>  \item[VIRTIO_NET_F_CTRL_RX] Requires VIRTIO_NET_F_CTRL_VQ.
>  \item[VIRTIO_NET_F_CTRL_VLAN] Requires VIRTIO_NET_F_CTRL_VQ.
> @@ -3200,10 +3203,10 @@ \subsection{Device Initialization}\label{sec:Device Types / Network Device / Dev
>  \item A performant driver would indicate that it will generate checksumless
>    packets by negotating the VIRTIO_NET_F_CSUM feature.
>  
> -\item If that feature is negotiated, a driver can use TCP or UDP
> -  segmentation offload by negotiating the VIRTIO_NET_F_HOST_TSO4 (IPv4
> -  TCP), VIRTIO_NET_F_HOST_TSO6 (IPv6 TCP) and VIRTIO_NET_F_HOST_UFO
> -  (UDP fragmentation) features.
> +\item If that feature is negotiated, a driver can use TCP segmentation or UDP
> +  segmentation/fragmentation offload by negotiating the VIRTIO_NET_F_HOST_TSO4 (IPv4
> +  TCP), VIRTIO_NET_F_HOST_TSO6 (IPv6 TCP), VIRTIO_NET_F_HOST_UFO
> +  (UDP fragmentation) and VIRTIO_NET_F_HOST_USO (UDP segmentation) features.
>  
>  \item The converse features are also available: a driver can save
>    the virtual device some work by negotiating these features.\note{For example, a network packet transported between two guests on
> @@ -3242,6 +3245,7 @@ \subsection{Device Operation}\label{sec:Device Types / Network Device / Device O
>  #define VIRTIO_NET_HDR_GSO_TCPV4       1
>  #define VIRTIO_NET_HDR_GSO_UDP         3
>  #define VIRTIO_NET_HDR_GSO_TCPV6       4
> +#define VIRTIO_NET_HDR_GSO_UDP_L4      5
>  #define VIRTIO_NET_HDR_GSO_ECN      0x80
>          u8 gso_type;
>          le16 hdr_len;
> @@ -3312,9 +3316,9 @@ \subsubsection{Packet Transmission}\label{sec:Device Types / Network Device / De
>  \end{note}
>  
>  \item If the driver negotiated
> -  VIRTIO_NET_F_HOST_TSO4, TSO6 or UFO, and the packet requires
> -  TCP segmentation or UDP fragmentation, then \field{gso_type}
> -  is set to VIRTIO_NET_HDR_GSO_TCPV4, TCPV6 or UDP.
> +  VIRTIO_NET_F_HOST_TSO4, TSO6, USO or UFO, and the packet requires
> +  TCP segmentation, UDP segmentation or fragmentation, then \field{gso_type}
> +  is set to VIRTIO_NET_HDR_GSO_TCPV4, TCPV6, UDP_L4 or UDP.
>    (Otherwise, it is set to VIRTIO_NET_HDR_GSO_NONE). In this
>    case, packets larger than 1514 bytes can be transmitted: the
>    metadata indicates how to replicate the packet header to cut it
> @@ -3372,9 +3376,14 @@ \subsubsection{Packet Transmission}\label{sec:Device Types / Network Device / De
>  
>  If VIRTIO_NET_F_HOST_UFO is negotiated, the driver MAY set
>  \field{gso_type} to VIRTIO_NET_HDR_GSO_UDP to request UDP
> -segmentation, otherwise the driver MUST NOT set
> +fragmentation, otherwise the driver MUST NOT set
>  \field{gso_type} to VIRTIO_NET_HDR_GSO_UDP.

This is actually a bugfix. Could you split this to a separate patch
so we can track this as a defect?

>  
> +If VIRTIO_NET_F_HOST_USO is negotiated, the driver MAY set
> +\field{gso_type} to VIRTIO_NET_HDR_GSO_UDP_L4 to request UDP
> +segmentation, otherwise the driver MUST NOT set
> +\field{gso_type} to VIRTIO_NET_HDR_GSO_UDP_L4.


How about adding the text from the commit log here (no need
to mention linux) so people are not confused which is which.
E.g.:
 Unlike UFO (fragmenting the packet) the USO splits large UDP packet
 to several segments when each of these smaller packets has UDP
 header.


> +
>  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
> @@ -3398,7 +3407,7 @@ \subsubsection{Packet Transmission}\label{sec:Device Types / Network Device / De
>  	packet;
>  \end{enumerate}
>  
> -If none of the VIRTIO_NET_F_HOST_TSO4, TSO6 or UFO options have
> +If none of the VIRTIO_NET_F_HOST_TSO4, TSO6, USO or UFO options have
>  been negotiated, the driver MUST set \field{gso_type} to
>  VIRTIO_NET_HDR_GSO_NONE.
>  
> @@ -3407,7 +3416,7 @@ \subsubsection{Packet Transmission}\label{sec:Device Types / Network Device / De
>  \field{flags} and MUST set \field{gso_size} to indicate the
>  desired MSS.
>  
> -If one of the VIRTIO_NET_F_HOST_TSO4, TSO6 or UFO options have
> +If one of the VIRTIO_NET_F_HOST_TSO4, TSO6, USO or UFO options have
>  been negotiated:
>  \begin{itemize}
>  \item If the VIRTIO_NET_F_GUEST_HDRLEN feature has been negotiated,
> @@ -3434,7 +3443,7 @@ \subsubsection{Packet Transmission}\label{sec:Device Types / Network Device / De
>  If VIRTIO_NET_HDR_F_NEEDS_CSUM bit in \field{flags} is not set, the
>  device MUST NOT use the \field{csum_start} and \field{csum_offset}.
>  
> -If one of the VIRTIO_NET_F_HOST_TSO4, TSO6 or UFO options have
> +If one of the VIRTIO_NET_F_HOST_TSO4, TSO6, USO or UFO options have
>  been negotiated:
>  \begin{itemize}
>  \item If the VIRTIO_NET_F_GUEST_HDRLEN feature has been negotiated,
> -- 
> 2.25.1
> 
> 
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