feat: vsock support for remote console access

Having a remote console access can be helpful for different reasons,
e.g. an easy way to have multiple terminals, not using a serial which
can be slow to print a lot of text, etc.

With this new support, a user can simply use vng like before, and add
the new --vsock option:

  vng --vsock (...)

Then in another terminal, it can connect to the existing VM:

  vng --vsock-connect

Advanced users can set a different CID with --vsock-cid, useful when
multiple VMs are started in parallel.

It is also possible to change the command that is executed when
connected inside the VM. By default, 'bash -i' is used, but it is
possible to pass something else, e.g.

  vng --vsock byobu

Or zsh, fish, tmux, etc. Or a script, for example to set env vars, change dir
and set other dimensions, etc., e.g. starting the VM with:

  $ vng --vsock "${PWD}/console.sh"

... and connecting to it from another terminal with:

  $ read -r rows columns <<< "$(stty size)"
  $ cat <<-EOF > console.sh
	#! /bin/bash
	stty rows ${rows} columns ${columns}
	cd "\${virtme_chdir}"
	HOME=${HOME}
	byobu
    EOF
  $ chmod +x console.sh
  $ vng --vsock-connect

Note: on my side, 'bash' is a bit weird: I cannot see the command I'm
typing. I didn't try to find a solution for a too long time as I'm
usually not using bash.

Regarding the kernel config, two new config are now required: VSOCKETS
and VIRTIO_VSOCKETS. They seem light enough.

While at it, fixed a typo in the README file with the --network option.

Link: #151
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

Author: matttbe

README.md

@@ -345,6 +345,33 @@ Examples
    # vmlinux available in the system.
 ```
 
+ - Connect to a simple remote shell:
+```
+   # Start the vng instance with vsock support:
+   $ vng --vsock
+
+   # In a separate terminal run the following command to connect to a remote shell:
+   $ vng --vsock-connect
+```
+
+ - Connect to a remote shell with proper dimensions, env vars, and using 'Fish':
+```
+   # Start the vng instance with vsock support:
+   $ vng --vsock "${PWD}/console.sh"
+
+   # In a separate terminal run the following commands:
+   $ read -r rows columns <<< "$(stty size)"
+   $ cat <<-EOF > console.sh
+         #! /bin/bash
+         stty rows ${rows} columns ${columns}
+         cd "\${virtme_chdir}"
+         HOME=${HOME}
+         fish  # use use zsh, tmux, byobu, screen, etc.
+     EOF
+   $ chmod +x console.sh
+   $ vng --vsock-connect
+```
+
  - Run virtme-ng inside a docker container:
 ```
    $ docker run -it --privileged ubuntu:23.10 /bin/bash
@@ -449,7 +476,7 @@ Troubleshooting
   $ groups | grep "kvm\|libvirt"
 ```
 
- - When using `--net bridge` to create a bridged network in the guest you
+ - When using `--network bridge` to create a bridged network in the guest you
    may get the following error:
 ```
   ...

virtme/commands/configkernel.py

@@ -159,6 +159,9 @@ def arg_fail(message):
     "CONFIG_ZONE_DEVICE=y",
     "CONFIG_FUSE_FS=y",
     "CONFIG_VIRTIO_FS=y",
+    "##: vsock support",
+    "CONFIG_VSOCKETS=y",
+    "CONFIG_VIRTIO_VSOCKETS=y",
 ]
 
 _GENERIC_CONFIG_OPTIONAL = [

virtme/commands/run.py

@@ -130,6 +130,25 @@ def make_parser() -> argparse.ArgumentParser:
         help="The MAC address to assign to the NIC interface, e.g. 52:54:00:12:34:56. "
         + "The last octet will be incremented for the next network devices.",
     )
+    g.add_argument(
+        "--vsock",
+        action="store",
+        default=None,
+        help="Enable a VSock to communicate from the host to the device and "
+        + "execute the specified command.",
+    )
+    g.add_argument(
+        "--vsock-cid",
+        action="store",
+        type=int,
+        default=3,
+        help="CID for the VSock.",
+    )
+    g.add_argument(
+        "--vsock-connect",
+        action="store_true",
+        help="Connect to a VM using VSock.",
+    )
     g.add_argument(
         "--balloon",
         action="store_true",
@@ -847,6 +866,13 @@ def is_subpath(path, potential_parent):
 def do_it() -> int:
     args = _ARGPARSER.parse_args()
 
+    if args.vsock_connect:
+        tty = os.ttyname(sys.stdin.fileno())
+        command = ['socat', f'file:{tty},raw,echo=0',
+                   f'VSOCK-CONNECT:{args.vsock_cid}:1024']
+        os.execvp('socat', command)
+        sys.exit(0)
+
     arch = architectures.get(args.arch)
     is_native = args.arch == platform.machine()
 
@@ -1383,6 +1409,10 @@ def get_net_mac(index):
             ]
         )
 
+    if args.vsock:
+        kernelargs.extend([f"virtme.vsockexec=`{args.vsock}`"])
+        qemuargs.extend(["-device", "vhost-vsock-pci,guest-cid=%d" % args.vsock_cid])
+
     if args.pwd:
         rel_pwd = os.path.relpath(os.getcwd(), args.root)
         if rel_pwd.startswith(".."):

virtme/guest/virtme-init

@@ -275,6 +275,12 @@ if cat /proc/cmdline |grep -q -E '(^| )virtme.snapd($| )'; then
     fi
 fi
 
+vsock_exec=$(sed -ne "s/.*virtme.vsockexec=\`\(.*\)\`.*/\1/p" /proc/cmdline)
+if [[ -n "${vsock_exec}" ]]; then
+    socat "VSOCK-LISTEN:1024,reuseaddr,fork" \
+          "EXEC:\"${vsock_exec}\",pty,stderr,setsid,sigint,sane,echo=0" &
+fi
+
 user_cmd=$(sed -ne "s/.*virtme.exec=\`\(.*\)\`.*/\1/p" /proc/cmdline)
 if [[ -n "${user_cmd}" ]]; then
     if [[ ! -e "/dev/virtio-ports/virtme.stdin" ||

virtme_ng/run.py

@@ -359,6 +359,28 @@ def make_parser():
         + "The last octet will be incremented for the next network devices.",
     )
 
+    parser.add_argument(
+        "--vsock",
+        action="store",
+        const="bash -i",
+        nargs="?",
+        help="Enable a VSock to communicate from the host to the device. "
+        + "An argument can be optionally specify to start a different shell.",
+    )
+
+    parser.add_argument(
+        "--vsock-cid",
+        action="store",
+        type=int,
+        help="CID for the VSock.",
+    )
+
+    parser.add_argument(
+        "--vsock-connect",
+        action="store_true",
+        help="Connect to a VM using VSock.",
+    )
+
     parser.add_argument(
         "--disk",
         "-D",
@@ -947,6 +969,24 @@ def _get_virtme_net_mac_address(self, args):
         else:
             self.virtme_param["net_mac_address"] = ""
 
+    def _get_virtme_vsock(self, args):
+        if args.vsock is not None:
+            self.virtme_param["vsock"] = "--vsock '" + args.vsock + "'"
+        else:
+            self.virtme_param["vsock"] = ""
+
+    def _get_virtme_vsock_cid(self, args):
+        if args.vsock_cid is not None:
+            self.virtme_param["vsock_cid"] = "--vsock-cid " + str(args.vsock_cid)
+        else:
+            self.virtme_param["vsock_cid"] = ""
+
+    def _get_virtme_vsock_connect(self, args):
+        if args.vsock_connect:
+            self.virtme_param["vsock_connect"] = "--vsock-connect"
+        else:
+            self.virtme_param["vsock_connect"] = ""
+
     def _get_virtme_disk(self, args):
         if args.disk is not None:
             disk_str = ""
@@ -1102,6 +1142,9 @@ def run(self, args):
         self._get_virtme_mods(args)
         self._get_virtme_network(args)
         self._get_virtme_net_mac_address(args)
+        self._get_virtme_vsock(args)
+        self._get_virtme_vsock_cid(args)
+        self._get_virtme_vsock_connect(args)
         self._get_virtme_disk(args)
         self._get_virtme_sound(args)
         self._get_virtme_disable_microvm(args)
@@ -1141,6 +1184,9 @@ def run(self, args):
             + f'{self.virtme_param["mods"]} '
             + f'{self.virtme_param["network"]} '
             + f'{self.virtme_param["net_mac_address"]} '
+            + f'{self.virtme_param["vsock"]} '
+            + f'{self.virtme_param["vsock_cid"]} '
+            + f'{self.virtme_param["vsock_connect"]} '
             + f'{self.virtme_param["disk"]} '
             + f'{self.virtme_param["sound"]} '
             + f'{self.virtme_param["disable_microvm"]} '