Update vhost-device-console

Add a new "network" backend with which the device can work with multiple
QEMU guests. For each guest a new localhost server is created and the user
can connect and execute command into the guest by running:

    host# nc 127.0.0.1 12345

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>

staging/vhost-device-console/Cargo.toml

@@ -16,6 +16,8 @@ xen = ["vm-memory/xen", "vhost/xen", "vhost-user-backend/xen"]
 
 [dependencies]
 console = "0.15.7"
+crossterm = "0.27.0"
+nix = "0.21.1"
 queues = "1.0.2"
 clap = { version = "4.4",  features = ["derive"] }
 env_logger = "0.10"

staging/vhost-device-console/README.md

@@ -1,8 +1,30 @@
 # vhost-device-console - Console emulation backend daemon
 
+## Description
+
+This program is a vhost-user backend that emulates a VirtIO Console device.
+The device's binary takes as parameter a socket, a socket number which is the
+number of connections, commonly used across all vhost-devices to communicate
+with the vhost-user frontend devices, and the backend type "nested" or
+"network".
+
+By using the "nested" backend, vhost-device-console, as soon as, the guest
+is booted, will print the login prompt into the same terminal and gives
+the ability to insert characters or certain keys as in a regular
+terminal.
+
+By using "network" backend, vhost-device-console, as soon as the guests
+is booted, creates a local server in the given localhost port, and gives
+the chance to connect on them and interact with the guests.
+
+This program is tested with QEMU's `vhost-user-device-pci` device.
+Examples' section below.
+
+This program is a vhost-user backend that emulates a VirtIO Console device.
+
 ## Synopsis
 ```text
-vhost-device-can --socket-path=<SOCKET_PATH>
+vhost-device-console --socket-path=<SOCKET_PATH>
 ```
 
 ## Options
@@ -15,37 +37,31 @@ vhost-device-can --socket-path=<SOCKET_PATH>
 
 .. option:: -s, --socket-path=PATH
 
-  Location of vhost-user Unix domain sockets
+  Location of vhost-user Unix domain sockets, this path will be suffixed with
+  0,1,2..socket_count-1.
 
+.. option:: -p, --tcp-port=PORT_NUMBER
 
-## Description
+ The localhost's port to be used for each guest, this part will be increased with
+ 0,1,2..socket_count-1.
 
-This program is a vhost-user backend that emulates a VirtIO Console device.
-The device's binary takes as parameter a socket which is commonly used 
-across all vhost-devices to communicate with the vhost-user frontend device.
+-- option:: -b, --backend=network|nested
 
-This program is tested with QEMU's `vhost-user-device-pci` device and
-Virtio-loopback's `-device vhost-user-can`.
-Examples' section below.
-
-This program is a vhost-user backend that emulates a VirtIO Console device.
+  The backend type vhost-device-console will use.
+  Note: The nested backend can be used only when socket_count equals 1.
 
 ## Limitations
 
-This device is still work-in-progress (WIP). Currently the device works
-only with one guest at the time (no multi-guest support).
-
-## Next steps
-
-Next development steps are:
-1) Enable multi-guest support
-2) Update the restart process of the device
+This device is still work-in-progress (WIP). The current version has been tested
+with VIRTIO_CONSOLE_F_MULTIPORT, but only for one console.
 
 ## Features
 
-The current device gives access to a QEMU guest by providing a login prompt.
-This prompt appears as soon as the guest is fully booted and gives the ability
-to user run command as a in regular terminal.
+The current device gives access to multiple QEMU guest by providing a login prompt
+either by connecting to a localhost server port (network backend) or by creating an
+nested command prompt in the current terminal (nested backend). This prompt appears
+as soon as the guest is fully booted and gives the ability to user run command as a
+in regular terminal.
 
 ## Examples
 
@@ -62,8 +78,11 @@ For testing the device the required dependencies are:
 
 The daemon should be started first:
 ```shell
-host# vhost-device-can --socket-path=can.sock --can-in="can0" --can-out="can1"
+host# vhost-device-console --socket-path=console.sock --socket-count=1 \
+                           --tcp-port=12345 --backend=network
 ```
+>Note: In case the backend is "nested" there is no need to provide
+       "--socket-count" and "--tcp-port" parameters.
 
 The QEMU invocation needs to create a chardev socket the device can
 use to communicate as well as share the guests memory over a memfd.
@@ -96,6 +115,14 @@ host# qemu-system
     ...
 ```
 
+Eventually, the user can connect to the console by running:
+```test
+host# nc 127.0.0.1 12345
+```
+
+>Note: In case the backend is "nested" a nested terminal will be shown into
+       vhost-device-console terminal space.
+
 ## License
 
 This project is licensed under either of