doc: document the Pseudo-encoding of LED state

Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Message-id: 1366867752-11578-5-git-send-email-lilei@linux.vnet.ibm.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

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+VNC LED state Pseudo-encoding
+=============================
+
+Introduction
+------------
+
+This document describes the Pseudo-encoding of LED state for RFB which
+is the protocol used in VNC as reference link below:
+
+http://tigervnc.svn.sourceforge.net/viewvc/tigervnc/rfbproto/rfbproto.rst?content-type=text/plain
+
+When accessing a guest by console through VNC, there might be mismatch
+between the lock keys notification LED on the computer running the VNC
+client session and the current status of the lock keys on the guest
+machine.
+
+To solve this problem it attempts to add LED state Pseudo-encoding
+extension to VNC protocol to deal with setting LED state.
+
+Pseudo-encoding
+---------------
+
+This Pseudo-encoding requested by client declares to server that it supports
+LED state extensions to the protocol.
+
+The Pseudo-encoding number for LED state defined as:
+
+======= ===============================================================
+Number  Name
+======= ===============================================================
+-261    'LED state Pseudo-encoding'
+======= ===============================================================
+
+LED state Pseudo-encoding
+--------------------------
+
+The LED state Pseudo-encoding describes the encoding of LED state which
+consists of 3 bits, from left to right each bit represents the Caps, Num,
+and Scroll lock key respectively. '1' indicates that the LED should be
+on and '0' should be off.
+
+Some example encodings for it as following:
+
+======= ===============================================================
+Code    Description
+======= ===============================================================
+100     CapsLock is on, NumLock and ScrollLock are off
+010     NumLock is on, CapsLock and ScrollLock are off
+111     CapsLock, NumLock and ScrollLock are on
+======= ===============================================================