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Subject: Re: [PATCH v2] virtio_net: support split header
On Sat, May 07, 2022 at 03:15:33PM +0800, Xuan Zhuo wrote: > 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> Okay, but I don't think this covers all possible use-cases. If we are doing this let's try to address alignment requirements too. > --- > conformance.tex | 2 ++ > content.tex | 72 +++++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 74 insertions(+) > > diff --git a/conformance.tex b/conformance.tex > index 663e7c3..6f561fb 100644 > --- a/conformance.tex > +++ b/conformance.tex > @@ -149,6 +149,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets} > \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Automatic receive steering in multiqueue mode} > \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 / Split Header} > \end{itemize} > > \conformance{\subsection}{Block Driver Conformance}\label{sec:Conformance / Driver Conformance / Block Driver Conformance} > @@ -411,6 +412,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets} > \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Gratuitous Packet Sending} > \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 / Split 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 060bdab..3340402 100644 > --- a/content.tex > +++ b/content.tex > @@ -3092,6 +3092,9 @@ \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_HEADER (55)] Device supports to split the header and > + the payload. > + > \item[VIRTIO_NET_F_HOST_USO (56)] Device can receive USO packets. Unlike UFO > (fragmenting the packet) the USO splits large UDP packet > to several segments when each of these smaller packets has UDP header. > @@ -3139,6 +3142,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device > \item[VIRTIO_NET_F_CTRL_MAC_ADDR] 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_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} > @@ -3370,6 +3374,7 @@ \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_HEADER 8 > u8 flags; > #define VIRTIO_NET_HDR_GSO_NONE 0 > #define VIRTIO_NET_HDR_GSO_TCPV4 1 > @@ -4471,6 +4476,73 @@ \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 Header}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Split Header} > + > +If the VIRTIO_NET_F_SPLIT_HEADER feature is negotiated, > +the device supports to split the header and the payload. > +The header and payload will be separated into different buffers. > + > +\subparagraph{Split Header}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Split Header / Setting Split Header} > + > +To configure the split header, the following layout structure and definitions > +are used: > + > +\begin{lstlisting} > +struct virtio_net_split_header_config { > +#define VIRTIO_NET_SPLIT_HEADER_TYPE_TCPv4 1 > +#define VIRTIO_NET_SPLIT_HEADER_TYPE_TCPv6 2 > +#define VIRTIO_NET_SPLIT_HEADER_TYPE_UDPv4 4 > +#define VIRTIO_NET_SPLIT_HEADER_TYPE_UDPv6 8 > + le64 type; > +}; > + how do we know what types does device support? > +#define VIRTIO_NET_CTRL_SPLIT_HEADER 6 > + #define VIRTIO_NET_CTRL_SPLIT_HEADER_SET 0 > +\end{lstlisting} > + > +The class VIRTIO_NET_CTRL_SPLIT_HEADER has one command: > +VIRTIO_NET_CTRL_SPLIT_HEADER_SET applies the new split header configuration. > + > +\field{type} passed as command data is a bitmask, bits set define > +packet types to split header, bits cleared - split header to be disabled. > + > +The header contains the struct virtio_net_hdr and the header of the package. > +Such as \field{VIRTIO_NET_SPLIT_HEADER_TYPE_TCPv4} specified header contains > +virtio_net_hdr, MAC header, IPv4 header (including IPv4 options), TCP header > +(include TCP options). The back part is the payload. > + > +\devicenormative{\subparagraph}{Setting Split Header}{Device Types / Network Device / Device Operation / Control Virtqueue / Split Header} > + > +Split header MUST be disabled after device initialization. > + > +A device MUST NOT perform split header in the following cases: > +\begin{itemize} > + \item device does not recognize protocol of the packet. > + \item \field{type} does not include the protocol of the packet. > + \item the packet is a IP fragmentation. > + \item the receive buffer consists of only one descriptor. > + \item the header exceeds the size of the 0th descriptor. > + \item If VIRTIO_NET_F_MRG_RXBUF is not negotiated and the size of the > + payload is greater than the total size of the 1th\ldots Nth descriptor. > +\end{itemize} > + > +If the split header completed, then the \field{flags} of virtnet hdr MUST > +contains VIRTIO_NET_HDR_F_SPLIT_HEADER. The header MUST is on the buffer of the > +0th descriptor, and the payload MUST starts from the buffer of the 1th descriptor. > +The device MUST set \field{hdr_len} of virtnet hdr. > + > +If VIRTIO_NET_F_MRG_RXBUF is negotiated and the device is to use multiple > +receive buffers, each subsequent receive buffer MUST skip the 0th descriptor. > + > +\drivernormative{\subparagraph}{Setting Split Header}{Device Types / Network Device / Device Operation / Control Virtqueue / Split Header} > + > +If VIRTIO_NET_HDR_F_SPLIT_HEADER bit in \field{flags} is set, the driver MUST > +believe \field{hdr_len}, the length of the header in the 0th descriptor is equal > +to the length of struct virtio_net_hdr plus \field{hdr_len}. > + > +If the split header function is enable, the buffers submitted by the driver > +SHOULD at least be composed of two descriptors. The buffer specified by the 0th > +descriptor SHOULD be able to accommodate the header. > I am not sure I understand what all this is saying. Lots of this is ungrammatical. Also - I do not understand what do you mean believe, or 0th descriptor. Also pls formulate in terms of buffers not descriptors. Thanks! > \subsubsection{Legacy Interface: Framing Requirements}\label{sec:Device > Types / Network Device / Legacy Interface: Framing Requirements} > -- > 2.31.0
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