[PATCH v2 03/11] transport-fabircs: introduce Segment Descriptor Definition

[zhenwei pi <pizhenwei@bytedance.com>]

Introduce segment descriptor to describe the Virtio device buffer
segments.

Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
---
 transport-fabrics.tex | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/transport-fabrics.tex b/transport-fabrics.tex
index 26b0192..b88acfd 100644
--- a/transport-fabrics.tex
+++ b/transport-fabrics.tex
@@ -45,3 +45,46 @@ \subsection{Virtio Qualified Name}\label{sec:Virtio Transport Options / Virtio O
 \item The string is null terminated.
 \item There is no strict style limitation.
 \end{itemize}
+
+\subsection{Transmission Protocol}\label{sec:Virtio Transport Options / Virtio Over Fabrics / Transmission Protocol}
+This section defines transmission protocol for Virtio Over Fabrics. All the
+fields use little endian format.
+
+\subsubsection{Segment Descriptor Definition}\label{sec:Virtio Transport Options / Virtio Over Fabrics / Transmission Protocol / Segment Descriptor Definition}
+Virtio Over Fabrics uses the following structure to describe data segment:
+
+\begin{lstlisting}
+struct virtio_of_vring_desc {
+        le64 addr;
+        le32 length;
+        /* This marks the unique ID within a command, no limitation among inflight commands */
+        le16 id;
+        /* This marks a buffer as keyed transmission (otherwise stream transmission) */
+#define VIRTIO_OF_DESC_F_KEYED     1
+        /* This marks a buffer as device write-only (otherwise device read-only). */
+#define VIRTIO_OF_DESC_F_WRITE     2
+        le16 flags;
+        le32 key;
+};
+\end{lstlisting}
+
+The structure virtio_of_vring_desc is used for both keyed transmission
+(i.e. RDMA) and stream transmission(i.e. TCP). The fields is described as follows:
+
+\begin{tabular}{ |l|l|l| }
+\hline
+Field & keyed transmission & stream transmission \\
+\hline \hline
+addr & Start address of remote memory buffer & Start address within the stream buffer \\
+\hline
+length & The length of remote memory buffer & The length of buffer within the stream \\
+\hline
+id & The ID of this descriptor & The ID of this descriptor \\
+\hline
+flags & both keyed transmission and stream transmission supported & stream transmission only \\
+\hline
+key & Key of the remote Memory Region & Ignore \\
+\hline
+\end{tabular}
+
+Depending on the opcode, a Command contains zero or more structure virtio_of_vring_desc.
-- 
2.25.1