[PATCH] virtio-net: define feature of per-packet RSS hash delivery

[Yuri Benditovich <yuri.benditovich@daynix.com>]

Fixes: https://github.com/oasis-tcs/virtio-spec/issues/66
Conditional extending of virtio header structure to deliver
packet's hash and hash type used for calculation.

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
---
 content.tex | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/content.tex b/content.tex
index 01be7df..44975e4 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_HASH_REPORT(58)] Device can report per-packet hash value
+    and a type of calculated hash
+
 \item[VIRTIO_NET_F_RSS(60)] Device supports RSS (receive-side scaling)
     with Toeplitz hash calculation and configurable hash parameters for receive steering
 
@@ -2844,6 +2847,8 @@ \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_HASH_REPORT] Requires VIRTIO_NET_F_RSS.
+
 \end{description}
 
 \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network Device / Feature bits / Legacy Interface: Feature bits}
@@ -3071,6 +3076,8 @@ \subsection{Device Operation}\label{sec:Device Types / Network Device / Device O
         le16 csum_start;
         le16 csum_offset;
         le16 num_buffers;
+        le32 hash_value; (Only if VIRTIO_NET_F_HASH_REPORT negotiated)
+        le16 hash_type; (Only if VIRTIO_NET_F_HASH_REPORT negotiated)
 };
 \end{lstlisting}
 
@@ -3330,6 +3337,15 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network
   set: if so, device has validated the packet checksum.
   In case of multiple encapsulated protocols, one level of checksums
   has been validated.
+\item If VIRTIO_NET_F_HASH_REPORT was negotiated and a device has calculated
+  a hash for the packet, \field{hash_value} contains calculated hash value and
+  \field{hash_type} contains exact hash type.
+
+  If the hash was not calculated, \field{hash_type} contains zero.
+
+  For defined hash types and their meaning, see \ref{sec:Device Types / Network Device / Device configuration layout / RSS}.
+
+  For the procedure of hash calculation, see \ref{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) / RSS hash types}.
 \end{enumerate}
 
 Additionally, VIRTIO_NET_F_GUEST_CSUM, TSO4, TSO6, UDP and ECN
@@ -3909,6 +3925,14 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
 \item Else skip IPv6 extension headers and calculate the hash as defined above for IPv6 packet without extension headers
 \end{itemize}
 
+If VIRTIO_NET_F_HASH_REPORT was negotiated, the device reports calculated hash information in fields of virtio_net_hdr as follows:
+
+Exact hash type is populated in \field{hash_type}
+
+Hash value is populated in \field{hash_value}
+
+If, due to any reason, the device did not calculate the hash, it sets \field{hash_type} to zero.
+
 \drivernormative{\subparagraph}{Setting RSS parameters}{Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) }
 
 A driver MUST NOT send the VIRTIO_NET_CTRL_MQ_RSS_CONFIG command if the feature VIRTIO_NET_F_RSS has not been negotiated.
-- 
2.17.2