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-rw-r--r--content.tex20
1 files changed, 14 insertions, 6 deletions
diff --git a/content.tex b/content.tex
index 51a00b2..ef28bdb 100644
--- a/content.tex
+++ b/content.tex
@@ -3561,10 +3561,13 @@ Processing incoming packets involves:
this packet is spread over (including this one): this will
always be 1 if VIRTIO_NET_F_MRG_RXBUF was not negotiated.
This allows receipt of large packets without having to allocate large
- buffers. In this case, there will be at least \field{num_buffers} in
- the used ring, and the device chains them together to form a
- single packet. The other buffers will not begin with a struct
- virtio_net_hdr.
+ buffers: a packet that does not fit in a single buffer can flow
+ over to the next buffer, and so on. In this case, there will be
+ at least \field{num_buffers} in the used ring, and the device
+ chains them together to form a single packet in a way similar to
+ how it would store it in a single buffer spread over multiple
+ descriptors.
+ The other buffers will not begin with a struct virtio_net_hdr.
\item If
\field{num_buffers} is one, then the entire packet will be
@@ -3605,10 +3608,15 @@ If VIRTIO_NET_F_MRG_RXBUF has not been negotiated, the device MUST set
\field{num_buffers} to 1.
If VIRTIO_NET_F_MRG_RXBUF has been negotiated, the device MUST set
-\field{num_buffers} to indicate the number of descriptors
+\field{num_buffers} to indicate the number of buffers
the packet (including the header) is spread over.
-The device MUST use all descriptors used by a single receive
+If a receive packet is spread over multiple buffers, the device
+MUST use all buffers but the last (i.e. the first $num_buffers -
+1$ buffers) completely up to the full length of each buffer
+supplied by the driver.
+
+The device MUST use all buffers used by a single receive
packet together, by atomically incrementing \field{idx} in the
used ring by the \field{num_buffers} value.