[virtio-comment] content: Declare virtio-net legacy feature bits 41-42

These bits are in use by current Windows production driver
for virtio-net. If virtio-net device uses one of them
the driver will not function. Reserving these bits for
virtio-net device until current production driver reaches EOL.

Fixes: https://github.com/oasis-tcs/virtio-spec/issues/21

Signed-off-by: Yuri Benditovich <>
---
 content.tex | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/content.tex b/content.tex
index be18234..6484491 100644
--- a/content.tex
+++ b/content.tex
@@ -2552,13 +2552,13 @@ Some networking feature bits require other networking feature bits
 
 \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network Device / Feature bits / Legacy Interface: Feature bits}
 \begin{description}
-\item[VIRTIO_NET_F_GSO (6)] Device handles packets with any GSO type.
+\item[VIRTIO_NET_F_GSO (6)] Device handles packets with any GSO type. This was supposed to indicate segmentation offload support, but
+upon further investigation it became clear that multiple bits were needed.
+\item[VIRTIO_NET_F_GUEST_RSC4 (41)] Device coalesces TCPIP v4 packets. This was implemented by hypervisor patch for certification
+purposes and current Windows driver depends on it. It will not function if virtio-net device reports this feature.
+\item[VIRTIO_NET_F_GUEST_RSC6 (42)] Device coalesces TCPIP v6 packets. Similar to VIRTIO_NET_F_GUEST_RSC4.
 \end{description}
 
-This was supposed to indicate segmentation offload support, but
-upon further investigation it became clear that multiple bits
-were needed.
-
 \subsection{Device configuration layout}\label{sec:Device Types / Network Device / Device configuration layout}
 \label{sec:Device Types / Block Device / Feature bits / Device configuration layout}
 
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2.17.0