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Subject: Re: [PATCH v7] virtio_net: support split header
On Fri, Sep 02, 2022 at 02:21:04PM +0800, Jason Wang wrote:On Tue, Aug 16, 2022 at 5:35 PM Heng Qi <hengqi@linux.alibaba.com> 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> --- 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.Nit: type is a field of the command, not something belongs to the device. (though an implementation should record the types internally). maybe it's better to say A device MUST disable header splitting upon reset and initialization?I don't know what that will mean, either. just what are you trying to say here?
This states that if the VIRTIO_NET_F_SPLIT_TRANSPORT_HEADER feature is negotiated and the driver does not use the VIRTIO_NET_CTRL_SPLIT_TRANSPORT_HEADER command to tell the device which protocol types to split, the device must disable header splitting upon reset and initialization. I will take the Jason' suggestion in the next version.
+ +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."The splitting of the specific transport protocol is not enabled via VIRTIO_NET_CTRL_SPLIT_TRANSPORT_HEADER_SET?"+ \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"the following buffers"?+consists of multiple descriptors, the device MUST skip the first descriptor,"skip the first descriptor of the following buffers"?+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}.Is this intended to describe what happens if the device doesn't split the header? If yes, I wonder if it's better to just drop this. (Duplicated with message framing part?)Jason maybe you understand what is going on here? The use of descriptors here in the device description just confuses me to the point where I don't understand what is going on. Devices should ever only deal with buffers and offsets within buffers.
When VIRTIO_NET_F_SPLIT_TRANSPORT_HEADER is negotiated,
the driver requires that the buffers submitted to receiveq
MUST be composed of at least two descriptors,
which means that each buffer the device gets is a descriptor chain,
even if the device does not split the header for some packets.
To store packet in the descriptor chain without header splitting
by the device, the device MUST start with the first descriptor of
the descriptor chain to store the packet, and MUST NOT set the
VIRTIO_NET_HDR_F_SPLIT_TRANSPORT_HEADER bit in \field{flags}.
Thanks.
+ +\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 headerI'd change "MUST" to "SHOULD" as the driver needs to validate the hdr_len before trying to use it.+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.Similarly, should we use "SHOULD" here. Or maybe we can see, if the driver want the device to split the header, it MUST .... Thanks\paragraph{Notifications Coalescing}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing} -- 1.8.3.1
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