[virtio-dev] Re: [PATCH v7] virtio_net: support split header

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

On Tue, Aug 16, 2022 at 05:34:55PM +0800, Heng Qi wrote:
> From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> 
> The purpose of this feature is to split the header and the payload of
> the packet.
> 
> |                    receive buffer                                    |
> |                       0th descriptor             | 1th descriptor    |
> | virtnet hdr | mac | ip hdr | tcp hdr|<-- hold -->|   payload         |
> 
> We can use a buffer plus a separate page when allocating the receive
> buffer. In this way, we can ensure that all payloads can be
> independently in a page, which is very beneficial for the zerocopy
> implemented by the upper layer.
> 
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
> Reviewed-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>

OK so really VIRTIO_NET_F_MRG_RXBUF and !VIRTIO_NET_F_MRG_RXBUF
are completely different in their behaviour.

Which is really important for you? I would suggest we first
try to get that one case right, later the other one.





> ---
> v7:
> 	1. Fix some presentation issues.
> 	2. Use "split transport header". @Jason Wang
> 	3. Clarify some paragraphs. @Cornelia Huck
> 	4. determine the device what to do if it does not perform header split on a packet.
> 
> v6:
> 	1. Fix some syntax issues. @Cornelia Huck
> 	2. Clarify some paragraphs. @Cornelia Huck
> 	3. Determine the device what to do if it does not perform header split on a packet.
> 
> v5:
> 	1. Determine when hdr_len is credible in the process of rx
> 	2. Clean up the use of buffers and descriptors
> 	3. Clarify the meaning of used lenght if the first descriptor is skipped in the case of merge
> 
> v4:
> 	1. fix typo @Cornelia Huck @Jason Wang
> 	2. do not split header for IP fragmentation packet. @Jason Wang
> 
> v3:
> 	1. Fix some syntax issues
> 	2. Fix some terminology issues
> 	3. It is not unified with ip alignment, so ip alignment is not included
> 	4. Make it clear that the device must support four types, in the case of successful negotiation.
> 
>  conformance.tex |   2 ++
>  content.tex     | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 104 insertions(+)
> 
> diff --git a/conformance.tex b/conformance.tex
> index 2b86fc6..4e2b82e 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -150,6 +150,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Offloads State Configuration / Setting Offloads State}
>  \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) }
>  \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing}
> +\item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Split Transport Header}
>  \end{itemize}
>  
>  \conformance{\subsection}{Block Driver Conformance}\label{sec:Conformance / Driver Conformance / Block Driver Conformance}
> @@ -415,6 +416,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Automatic receive steering in multiqueue mode}
>  \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) / RSS processing}
>  \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing}
> +\item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Split Transport Header}
>  \end{itemize}
>  
>  \conformance{\subsection}{Block Device Conformance}\label{sec:Conformance / Device Conformance / Block Device Conformance}
> diff --git a/content.tex b/content.tex
> index e863709..5676da9 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -3084,6 +3084,9 @@ \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_SPLIT_TRANSPORT_HEADER (52)] Device supports splitting
> +    the transport header and the payload.
> +
>  \item[VIRTIO_NET_F_NOTF_COAL(53)] Device supports notifications coalescing.
>  
>  \item[VIRTIO_NET_F_GUEST_USO4 (54)] Driver can receive USOv4 packets.
> @@ -3140,6 +3143,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device
>  \item[VIRTIO_NET_F_NOTF_COAL] Requires VIRTIO_NET_F_CTRL_VQ.
>  \item[VIRTIO_NET_F_RSC_EXT] Requires VIRTIO_NET_F_HOST_TSO4 or VIRTIO_NET_F_HOST_TSO6.
>  \item[VIRTIO_NET_F_RSS] Requires VIRTIO_NET_F_CTRL_VQ.
> +\item[VIRTIO_NET_F_SPLIT_TRANSPORT_HEADER] Requires VIRTIO_NET_F_CTRL_VQ.
>  \end{description}
>  
>  \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network Device / Feature bits / Legacy Interface: Feature bits}
> @@ -3371,6 +3375,7 @@ \subsection{Device Operation}\label{sec:Device Types / Network Device / Device O
>  #define VIRTIO_NET_HDR_F_NEEDS_CSUM    1
>  #define VIRTIO_NET_HDR_F_DATA_VALID    2
>  #define VIRTIO_NET_HDR_F_RSC_INFO      4
> +#define VIRTIO_NET_HDR_F_SPLIT_TRANSPORT_HEADER  8
>          u8 flags;
>  #define VIRTIO_NET_HDR_GSO_NONE        0
>  #define VIRTIO_NET_HDR_GSO_TCPV4       1
> @@ -3823,6 +3828,11 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network
>  been negotiated, the driver MAY use \field{hdr_len} only as a hint about the
>  transport header size.
>  The driver MUST NOT rely on \field{hdr_len} to be correct.
> +
> +If the VIRTIO_NET_HDR_F_SPLIT_TRANSPORT_HEADER bit in \field{flags} is set,
> +the driver SHOULD treat the \field{hdr_len} as the length of the transport header
> +inside the first descriptor.
> +
>  \begin{note}
>  This is due to various bugs in implementations.
>  \end{note}
> @@ -4483,6 +4493,98 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
>  according to the native endian of the guest rather than
>  (necessarily when not using the legacy interface) little-endian.
>  
> +\paragraph{Split Transport Header}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Split Transport Header}
> +
> +If the VIRTIO_NET_F_SPLIT_TRANSPORT_HEADER feature is negotiated,
> +the device supports splitting the transport header and the payload.
> +The transport header and the payload will be separated into different
> +descriptors.
> +
> +\subparagraph{Split Transport Header}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Split Transport Header / Setting Split Transport Header}
> +
> +To configure the split transport header, the following layout structure and definitions
> +are used:
> +
> +\begin{lstlisting}
> +struct virtio_net_split_transport_header_config {
> +#define VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_TCP4     (1 << 0)
> +#define VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_TCP6     (1 << 1)
> +#define VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_UDP4     (1 << 2)
> +#define VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_UDP6     (1 << 3)
> +    le64 type;
> +};
> +
> +#define VIRTIO_NET_CTRL_SPLIT_TRANSPORT_HEADER       6
> + #define VIRTIO_NET_CTRL_SPLIT_TRANSPORT_HEADER_SET   0
> +\end{lstlisting}
> +
> +The class VIRTIO_NET_CTRL_SPLIT_TRANSPORT_HEADER has one command:
> +VIRTIO_NET_CTRL_SPLIT_TRANSPORT_HEADER_SET applies the new split transport header configuration.
> +
> +The driver can enable or disable split transport header for different protocols by
> +setting or clearing corresponding bits in \field{type}.
> +
> +\begin{itemize}
> +    \item VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_TCP4: split after ipv4 tcp header
> +    \item VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_TCP6: split after ipv6 tcp header
> +    \item VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_UDP4: split after ipv4 udp header
> +    \item VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_UDP6: split after ipv6 udp header
> +\end{itemize}
> +
> +\devicenormative{\subparagraph}{Setting Split Transport Header}{Device Types / Network Device / Device Operation / Control Virtqueue / Split Transport Header}
> +
> +A device MUST initialize \field{type} to 0, and MUST set it to 0
> +upon device reset.
> +
> +If VIRTIO_NET_F_SPLIT_TRANSPORT_HEADER is negotiated, the device MUST support
> +VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_TCP4, VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_TCP6,
> +VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_UDP4, VIRTIO_NET_SPLIT_TRANSPORT_HEADER_TYPE_UDP6.
> +
> +A device MUST NOT split the transport header if it encounters any of the following cases:
> +\begin{itemize}
> +    \item the device does not recognize the protocol of the packet.
> +    \item the packet is an IP fragmentation.
> +    \item \field{type} does not include the protocol of the packet.
> +    \item the buffer consists of only one descriptor.
> +    \item the total size of the virtio net header and the transport header exceeds
> +        the size of the first descriptor.
> +    \item when VIRTIO_NET_F_MRG_RXBUF is not negotiated and the size of the
> +        payload exceeds the size of the descriptor chain starting from the 2nd
> +        descriptor.
> +\end{itemize}
> +
> +If the header is split by the device, the VIRTIO_NET_HDR_F_SPLIT_TRANSPORT_HEADER bit
> +in \field{flags} MUST be set. The transport header MUST be on the first
> +descriptor, following the virtio net header. The payload MUST start from the
> +second descriptor. The device MUST set \field{hdr_len} of structure
> +virtio_net_hdr to the length of the transport header.
> +
> +If all of the following applies:
> +\begin{itemize}
> +    \item the header is split by the device.
> +    \item VIRTIO_NET_F_MRG_RXBUF has been negotiated.
> +    \item the received packet is spread over multiple buffers.
> +\end {itemize}
> +then if the device uses the buffers after the 1st buffer, and the buffer
> +consists of multiple descriptors, the device MUST skip the first descriptor,
> +because the first descriptor is used to carry the transport header.
> +The used length still reports the number of bytes it has written to memory.
> +
> +If VIRTIO_NET_F_SPLIT_TRANSPORT_HEADER is negotiated, but the device does not split the
> +virtio net header and the transport header, and the buffer consists of at least two
> +descriptors, the device MUST start with the first descriptor to store the packet, and
> +MUST NOT set the VIRTIO_NET_HDR_F_SPLIT_TRANSPORT_HEADER bit in \field{flags}.
> +
> +\drivernormative{\subparagraph}{Setting Split Transport Header}{Device Types / Network Device / Device Operation / Control Virtqueue / Split Transport Header}
> +
> +If the VIRTIO_NET_HDR_F_SPLIT_TRANSPORT_HEADER bit in \field{flags} is set, the driver
> +MUST treat the contents of \field{hdr_len} as the length of the transport header
> +inside the first descriptor.
> +
> +If the split transport header is enabled, the buffers submitted to receiveq by the
> +driver MUST be composed of at least two descriptors.
> +When the buffer consists of two descriptors, the length of the first
> +descriptor MUST be greater than the one of the virtio net header.
>  
>  \paragraph{Notifications Coalescing}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing}
>  
> -- 
> 1.8.3.1


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