vsock: connect: generate helper script

Directly connecting to the remote shell using socat launching 'bash'
remotely doesn't give a nice user experience: env vars like $HOME are
not propagated, the terminal size is set to 80x24, the command that is
typed is not visible, the directory is not the one picked with --cwd,
etc.

To give a better user experience, the '--vsock-connect' option is now
creating a script that is setting up the missing pieces. This script is
executed when the VM is launched with '--vsock' without any arguments.

Note that it is required to pass info from the host, when launching
'--vsock-connect', to the VM, e.g. for the terminal size. This is done
via the script that is executed once connected to the vsock inside the
VM. The VM needs access to this script, and the host needs to be able to
modify it. Such script is then created in /tmp/virtme-vsock/<CID>.sh on
both the host and the VM. If the whole filesystem is mounted (default),
this file will be accessible from the VM. If not, a mount point will be
added to access the parent directory from the VM.

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

Author: matttbe

README.md

@@ -354,24 +354,6 @@ Examples
    $ 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

virtme/commands/run.py

@@ -133,13 +133,16 @@ def make_parser() -> argparse.ArgumentParser:
     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.",
+        nargs="?",
+        metavar="COMMAND",
+        const="",
+        help="Enable a VSock to communicate from the host to the device. "
+        + "An argument can be optionally specify to start a different command.",
     )
     g.add_argument(
         "--vsock-cid",
         action="store",
+        metavar="CID",
         type=int,
         default=3,
         help="CID for the VSock.",
@@ -866,7 +869,27 @@ def is_subpath(path, potential_parent):
 def do_it() -> int:
     args = _ARGPARSER.parse_args()
 
+    vsock_script_path = os.path.join(tempfile.gettempdir(), "virtme-vsock",
+                                     f"{args.vsock_cid}.sh")
+
     if args.vsock_connect:
+        # Note: we could accept arguments passed to --vsock-connect to run a
+        # specific command, and return, without requiring an interactive tty.
+        try:
+            (cols, rows) = os.get_terminal_size()
+        except OSError:
+            cols, rows = (80, 24)
+
+        with open(vsock_script_path, 'w', encoding="utf-8") as file:
+            print((
+                '#! /bin/bash\n'
+                f'stty rows {rows} cols {cols} iutf8 echo\n'
+                'HOME=$(getent passwd ${virtme_user:-root} | cut -d: -f6)\n'
+                'cd ${virtme_chdir:+"${virtme_chdir}"}\n'
+                'exec su ${virtme_user:-root}'
+            ), file=file)
+        os.chmod(vsock_script_path, 0o755)
+
         tty = os.ttyname(sys.stdin.fileno())
         command = ['socat', f'file:{tty},raw,echo=0',
                    f'VSOCK-CONNECT:{args.vsock_cid}:1024']
@@ -1409,8 +1432,34 @@ def get_net_mac(index):
             ]
         )
 
-    if args.vsock:
-        kernelargs.extend([f"virtme.vsockexec=`{args.vsock}`"])
+    def cleanup_vsock_script():
+        os.unlink(vsock_script_path)
+
+    if args.vsock is not None:
+        if os.path.exists(vsock_script_path):
+            arg_fail("vsock: '%s' file exists: " % vsock_script_path
+                     + "another VM is running with the same --vsock-cid? "
+                     + "If not, remove this file.")
+
+        # create an empty file that can be populated later on
+        vsock_script_dir = os.path.dirname(vsock_script_path)
+        os.makedirs(vsock_script_dir, exist_ok=True)
+        open(vsock_script_path, 'w', encoding="utf-8").close()
+        atexit.register(cleanup_vsock_script)
+
+        if args.vsock:
+            vsock_exec = args.vsock
+        else:
+            vsock_exec = vsock_script_path
+            if args.root != "/":
+                virtfs_config = VirtFSConfig(
+                    path=vsock_script_dir,
+                    mount_tag="virtme.vsockmount",
+                )
+                export_virtfs(qemu, arch, qemuargs, virtfs_config)
+                kernelargs.append("virtme_vsockmount=%s" % vsock_script_dir)
+
+        kernelargs.extend([f"virtme.vsockexec=`{vsock_exec}`"])
         qemuargs.extend(["-device", "vhost-vsock-pci,guest-cid=%d" % args.vsock_cid])
 
     if args.pwd:

virtme/guest/virtme-init

@@ -277,6 +277,10 @@ fi
 
 vsock_exec=$(sed -ne "s/.*virtme.vsockexec=\`\(.*\)\`.*/\1/p" /proc/cmdline)
 if [[ -n "${vsock_exec}" ]]; then
+    if [[ -n "${virtme_vsockmount}" ]]; then
+        mkdir -p "${virtme_vsockmount}"
+        mount -t 9p -o version=9p2000.L,trans=virtio,access=any "virtme.vsockmount" "${virtme_vsockmount}"
+    fi
     socat "VSOCK-LISTEN:1024,reuseaddr,fork" \
           "EXEC:\"${vsock_exec}\",pty,stderr,setsid,sigint,sane,echo=0" &
 fi

virtme_ng/run.py

@@ -362,15 +362,17 @@ def make_parser():
     parser.add_argument(
         "--vsock",
         action="store",
-        const="bash -i",
         nargs="?",
+        metavar="COMMAND",
+        const="",
         help="Enable a VSock to communicate from the host to the device. "
-        + "An argument can be optionally specify to start a different shell.",
+        + "An argument can be optionally specify to start a different command.",
     )
 
     parser.add_argument(
         "--vsock-cid",
         action="store",
+        metavar="CID",
         type=int,
         help="CID for the VSock.",
     )