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Subject: Re: [virtio-comment] [PATCH v3] virtio-net: Add support for correct hdr_len field.
Cornelia could you pls post a fixup for the missing articles?
On Sun, Nov 17, 2019 at 06:24:46AM +0000, Vitaly Mireyno wrote:
> Fixes: https://github.com/oasis-tcs/virtio-spec/issues/57
>
> >-----Original Message-----
> >From: virtio-comment@lists.oasis-open.org <virtio-comment@lists.oasis-
> >open.org> On Behalf Of Vitaly Mireyno
> >Sent: Tuesday, 5 November, 2019 17:26
> >To: virtio-comment@lists.oasis-open.org
> >Cc: Michael S. Tsirkin <mst@redhat.com>; Jason Wang
> ><jasowang@redhat.com>
> >Subject: [EXT] [virtio-comment] [PATCH v3] virtio-net: Add support for correct
> >hdr_len field.
> >
> >Incorporated more v1 comments
> >
> >Changes from v2:
> > * Added device implementation note for using hdr_len
> >
> >Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com>
> >---
> > content.tex | 56 +++++++++++++++++++++++++++++++++++++++++++-----
> >-----
> > 1 file changed, 46 insertions(+), 10 deletions(-)
> >
> >diff --git a/content.tex b/content.tex
> >index b1ea9b9..5d3f865 100644
> >--- a/content.tex
> >+++ b/content.tex
> >@@ -2811,6 +2811,9 @@ \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_GUEST_HDRLEN(59)] Driver can provide the exact
> >\field{hdr_len}
> >+ value. Device benefits from knowing the exact header length.
> >+
> > \item[VIRTIO_NET_F_RSC_EXT(61)] Device can process duplicated ACKs
> > and report number of coalesced segments and duplicated ACKs
> >
> >@@ -3095,12 +3098,21 @@ \subsubsection{Packet
> >Transmission}\label{sec:Device Types / Network Device / De
> > into smaller packets. The other gso fields are set:
> >
> > \begin{itemize}
> >- \item \field{hdr_len} is a hint to the device as to how much of the header
> >+ \item If the VIRTIO_NET_F_GUEST_HDRLEN feature has been negotiated,
> >+ \field{hdr_len} indicates the header length that needs to be replicated
> >+ for each packet. It's a number of bytes from beginning of the packet
> >+ to beginning of the transport payload.
> >+ Otherwise, if the VIRTIO_NET_F_GUEST_HDRLEN feature has not been
> >negotiated,
> >+ \field{hdr_len} is a hint to the device as to how much of the
> >+ header
> > needs to be kept to copy into each packet, usually set to the
> > length of the headers, including the transport header\footnote{Due to
> >various bugs in implementations, this field is not useful as a guarantee of the
> >transport header size.
> > }.
> >
> >+ \begin{note}
> >+ Some devices benefit from knowledge of the exact header length.
> >+ \end{note}
> >+
> > \item \field{gso_size} is the maximum size of each packet beyond that
> > header (ie. MSS).
> >
> >@@ -3173,9 +3185,20 @@ \subsubsection{Packet
> >Transmission}\label{sec:Device Types / Network Device / De desired MSS.
> >
> > If one of the VIRTIO_NET_F_HOST_TSO4, TSO6 or UFO options have -been
> >negotiated, the driver SHOULD set \field{hdr_len} to a value -not less than the
> >length of the headers, including the transport -header.
> >+been negotiated:
> >+\begin{itemize}
> >+\item If the VIRTIO_NET_F_GUEST_HDRLEN feature has been negotiated,
> >+ the driver MUST set \field{hdr_len} to a value equal to the length
> >+ of the headers, including the transport header.
> >+
> >+\item If the VIRTIO_NET_F_GUEST_HDRLEN feature has not been
> >negotiated,
> >+ the driver SHOULD set \field{hdr_len} to a value
> >+ not less than the length of the headers, including the transport
> >+ header.
> >+\end{itemize}
> >+
> >+The driver SHOULD accept the VIRTIO_NET_F_GUEST_HDRLEN feature if it
> >+has been offered, and if it's able to provide the exact header length.
> >
> > The driver MUST NOT set the VIRTIO_NET_HDR_F_DATA_VALID and
> >VIRTIO_NET_HDR_F_RSC_INFO bits in \field{flags}.
> >@@ -3187,12 +3210,25 @@ \subsubsection{Packet
> >Transmission}\label{sec:Device Types / Network Device / De 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 -been
> >negotiated, the device MAY use \field{hdr_len} only as a hint about the -
> >transport header size.
> >-The device MUST NOT rely on \field{hdr_len} to be correct.
> >-\begin{note}
> >-This is due to various bugs in implementations.
> >-\end{note}
> >+been negotiated:
> >+\begin{itemize}
> >+\item If the VIRTIO_NET_F_GUEST_HDRLEN feature has been negotiated,
> >+ the device MAY use \field{hdr_len} as the transport header size.
> >+
> >+ \begin{note}
> >+ Caution should be taken by the implementation so as to prevent
> >+ malicious driver from attacking the device by setting incorrect hdr_len.
> >+ \end{note}
> >+
> >+\item If the VIRTIO_NET_F_GUEST_HDRLEN feature has not been
> >negotiated,
> >+ the device MAY use \field{hdr_len} only as a hint about the
> >+ transport header size.
> >+ The device MUST NOT rely on \field{hdr_len} to be correct.
> >+
> >+ \begin{note}
> >+ This is due to various bugs in implementations.
> >+ \end{note}
> >+\end{itemize}
> >
> > If VIRTIO_NET_HDR_F_NEEDS_CSUM is not set, the device MUST NOT rely
> >on the packet checksum being correct.
> >--
> >
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