doc: add socket console backend for virtio-console

add new console backend of socket for virtio-console

Signed-off-by: Gao Junhao <junhao.gao@intel.com>

doc/developer-guides/hld/virtio-console.rst

@@ -72,7 +72,7 @@ device model: STDIO, TTY, PTY and regular file.
 The device model configuration command syntax for virtio-console is::
 
    virtio-console,[@]stdio|tty|pty|file:portname[=portpath]\
-      [,[@]stdio|tty|pty|file:portname[=portpath]]
+      [,[@]stdio|tty|pty|file:portname[=portpath][:socket_type]]
 
 -  Preceding with ``@`` marks the port as a console port, otherwise it is a
    normal virtio serial port
@@ -86,6 +86,9 @@ The device model configuration command syntax for virtio-console is::
    (e.g., by ``sleep 2d`` command), and will not read input from stdin before it
    is used by virtio-console to redirect guest output.
 
+-  When virtio-console socket_type is appointed to client, please make sure
+   server VM(socket_type is appointed to server) has started.
+
 -  Claiming multiple virtio serial ports as consoles is supported,
    however the guest Linux OS will only use one of them, through the
    ``console=hvcN`` kernel parameter. For example, the following command
@@ -129,18 +132,22 @@ PTY
    after ``acrn-dm`` is launched (``/dev/pts/0`` may be different,
    depending on your use case):
 
-   .. code-block: console
+   .. code-block:: console
 
         virt-console backend redirected to /dev/pts/0
 
 #. Use a terminal emulator, such as minicom or screen, to connect to the
-   tty node::
+   tty node:
 
-     minicom -D /dev/pts/0
+   .. code-block:: console
 
-   or ::
+        # minicom -D /dev/pts/0
  
-     screen /dev/pts/0
+   or :
+
+   .. code-block:: console
+
+        # screen /dev/pts/0
 
 TTY
 ===
@@ -149,24 +156,32 @@ TTY
 
    - If you're connected to your device over the network via ssh, use
      the linux ``tty`` command, and it will report the node (may be
-     different in your use case)::
+     different in your use case):
+
+     .. code-block:: console
 
          /dev/pts/0
-        sleep 2d
+         # sleep 2d
  
    - If you do not have network access to your device, use screen
-     to create a new tty::
+     to create a new tty:
 
-        screen
+     .. code-block:: console
-        tty
 
-     you will see (depending on your use case)::
+         # screen
+         # tty
+
+     you will see (depending on your use case):
+
+     .. code-block:: console
 
          /dev/pts/0
 
-     Prevent the tty from responding by sleeping::
+     Prevent the tty from responding by sleeping:
 
-        sleep 2d
+     .. code-block:: console
+
+         # sleep 2d
 
      and detach the tty by pressing :kbd:`CTRL-A` :kbd:`d`.
 
@@ -180,10 +195,12 @@ TTY
         console=hvc0
 
 #. Go back to the previous tty.  For example, if you're using
-   ``screen``, use::
+   ``screen``, use:
 
-      screen -ls
+   .. code-block:: console
-      screen -r <pid_of_your_tty>
+
+        # screen -ls
+        # screen -r <pid_of_your_tty>
 
 FILE
 ====
@@ -198,3 +215,39 @@ The File backend only supports console output to a file (no input).
 #. Add the console parameter to the guest OS kernel command line::
 
         console=hvc0
+
+SOCKET
+======
+
+The virtio-console socket-type can be set as socket server or client. Device model will
+create an unix domain socket if appointed the socket_type as server, then server VM or
+another user VM can bind and listen for communication requirement. If appointed to
+client, please make sure the socket server is ready prior to launch device model.
+
+1. Add a pci slot to the device model (``acrn-dm``) command line, adjusting
+   the ``</path/to/file.sock>`` to your use case in the VM1 configuration::
+
+        -s n,virtio-console,socket:socket_file_name=</path/to/file.sock>:server
+
+#. Add a pci slot to the device model (``acrn-dm``) command line, adjusting
+   the ``</path/to/file.sock>`` to your use case in the VM2 configuration::
+
+        -s n,virtio-console,socket:socket_file_name=</path/to/file.sock>:client
+
+#. Login to VM1, connect to the virtual port(vport1p0, 1 is decided
+   by front-end driver):
+
+   .. code-block:: console
+
+        # minicom -D /dev/vport1p0
+
+#. Login to VM2, connect to the virtual port(vport3p0, 3 is decided
+   by front-end driver):
+
+   .. code-block:: console
+
+        # minicom -D /dev/vport3p0
+
+#. Input into minicom window of VM1 or VM2, the minicom window of VM1
+   will indicate the input from VM2, the minicom window of VM2 will
+   indicate the input from VM1.