On Mon, 25 Jul 2022 13:04:09 +0200, Cornelia Huck <[email protected]> wrote:
> On Wed, Jul 20 2022, Xuan Zhuo <[email protected]> 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 <[email protected]>
> > Reviewed-by: Heng Qi <[email protected]>
> > Reviewed-by: Kangjie Xu <[email protected]>
> > ---
> > 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 | 97 +++++++++++++++++++++++++++++++++++++++++++++++--
> > 2 files changed, 96 insertions(+), 3 deletions(-)
>
> (...)
>
> > @@ -3786,7 +3791,8 @@ \subsubsection{Processing of Incoming
> > Packets}\label{sec:Device Types / Network
> > not set VIRTIO_NET_HDR_F_RSC_INFO bit in \field{flags}.
> >
> > If one of the VIRTIO_NET_F_GUEST_TSO4, TSO6 or UFO options have
> > -been negotiated, the device SHOULD set \field{hdr_len} to a value
> > +been negotiated and the VIRTIO_NET_HDR_F_SPLIT_HEADER bit in \field{flags}
> > +is not set, the device SHOULD set \field{hdr_len} to a value
> > not less than the length of the headers, including the transport
> > header.
>
> One thing I find a bit hard to figure out is what hdr_len is supposed to
> look like if the SPLIT_HEADER flag is actually on. It is explained in
> the split header section, but I feel like the reader is left a bit
> hanging here.
>
> Not sure how to solve this; maybe simply add a pointer to the split
> header specification below?
OK, I will try.
>
> (...)
>
> > +A device MUST NOT split the header encounter any of the following cases:
>
> Maybe "A device MUST NOT split the header if it encounters any of the
> following cases"?
Will fix.
>
> > +\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 protocol 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_HEADER bit
> > +in \field{flags} MUST be set. The protocol 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 protocol header.
> > +
> > +If the header is split by the device, VIRTIO_NET_F_MRG_RXBUF is negotiated,
> > +and the received packet is spread over multiple buffers, when the device
> > uses a
> > +buffer other than the first, if the buffer consists of multiple
> > descriptors, the
> > +device MUST skip the first descriptor, because the first descriptor is
> > used to
> > +carry the protocol header. The used length still reports the number of
> > bytes it
> > +has written to memory.
>
> Personally, I find this paragraph hard to follow... maybe something like
> the following:
>
> "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 split over multiple buffers,
> \item the device uses a buffer other than the first, [*]
> \item the buffer consists of multiple descriptors
> \end {itemize}
> the device MUST skip the first descriptor, because the first descriptor
> is used to carry the protocol header. The used length still reports the
> number of bytes it has written to memory."
Will fix.
>
> Although I'm not quite sure what [*] means, the first of what?
I mean:
the device uses a buffer other than the first buffer.
I will fix it in next version.
Thanks.
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