virtme-ng: channel the return code of a command to the host

Send the return code of the command executed inside the guest to the
host.

This allows to run commands inside a guest and give users the impression
that they are running on the host.

Examples:

  $ vng -r -- true && echo OK || echo ERROR: $?
  OK
  $ vng -r -- false && echo OK || echo ERROR: $?
  ERROR: 1
  $ vng -r -- exit 22 && echo OK || echo ERROR: $?
  ERROR: 22

This feature is particularly useful for automation/CI, since it easily
allows to check the return code of a script executed inside virtme-ng as
if it was running directly on the host.

This fixes issue #48.

Signed-off-by: Andrea Righi <[email protected]>

virtme/commands/run.py

@@ -1054,7 +1054,24 @@ def do_it() -> int:
                 ]
             )
 
-    def do_script(shellcmd: str, show_boot_console=False) -> None:
+    ret_path = None
+
+    def cleanup_script_retcode():
+        os.unlink(ret_path)
+
+    def fetch_script_retcode():
+        if ret_path is None:
+            return None
+        try:
+            with open(ret_path, 'r', encoding="utf-8") as file:
+                number_str = file.read().strip()
+                if number_str.isdigit():
+                    return int(number_str)
+                return None
+        except FileNotFoundError:
+            return None
+
+    def do_script(shellcmd: str, ret_path=None, show_boot_console=False) -> None:
         if args.graphics is None:
             # Turn off default I/O
             qemuargs.extend(arch.qemu_nodisplay_args())
@@ -1106,6 +1123,13 @@ def do_script(shellcmd: str, show_boot_console=False) -> None:
             ["-device", "virtserialport,name=virtme.dev_stderr,chardev=dev_stderr"]
         )
 
+        # Create a virtio serial device to channel the retcode of the script
+        # executed in the guest to the host.
+        if ret_path is not None:
+            qemuargs.extend(["-chardev", f"file,id=ret,path={ret_path}"])
+            qemuargs.extend(["-device", arch.virtio_dev_type("serial")])
+            qemuargs.extend(["-device", "virtserialport,name=virtme.ret,chardev=ret"])
+
         # Scripts shouldn't reboot
         qemuargs.extend(["-no-reboot"])
 
@@ -1141,7 +1165,9 @@ def do_script(shellcmd: str, show_boot_console=False) -> None:
         args.script_sh = args.graphics
 
     if args.script_sh is not None:
-        do_script(args.script_sh, show_boot_console=args.show_boot_console)
+        _, ret_path = tempfile.mkstemp(prefix="virtme_ret")
+        atexit.register(cleanup_script_retcode)
+        do_script(args.script_sh, ret_path=ret_path, show_boot_console=args.show_boot_console)
 
     if args.script_exec is not None:
         do_script(
@@ -1305,7 +1331,11 @@ def do_script(shellcmd: str, show_boot_console=False) -> None:
         if pid:
             try:
                 pid, status = os.waitpid(pid, 0)
+                ret = fetch_script_retcode()
+                if ret is not None:
+                    return ret
                 return status
+
             except KeyboardInterrupt:
                 sys.stderr.write("Interrupted.")
                 sys.exit(1)

virtme/guest/virtme-init

@@ -260,6 +260,11 @@ if [[ -n "${user_cmd}" ]]; then
             /dev/virtio-ports/virtme.stderr     \
             /dev/virtio-ports/virtme.dev_stdout \
             /dev/virtio-ports/virtme.dev_stderr
+
+        if [ -e /dev/virtio-ports/virtme.ret ]; then
+            chown ${virtme_user}                \
+                /dev/virtio-ports/virtme.ret
+        fi
     fi
 
     # Fix /dev/stdout and /dev/stderr.
@@ -289,7 +294,13 @@ if [[ -n "${user_cmd}" ]]; then
         else
             setsid bash /tmp/.virtme-script </dev/virtio-ports/virtme.stdin >/dev/virtio-ports/virtme.stdout 2>/dev/virtio-ports/virtme.stderr
         fi
-        log "script returned $?"
+	ret=$?
+        log "script returned {$ret}"
+
+        # Channel exit code to the host.
+        if [ -e /dev/virtio-ports/virtme.ret ]; then
+            echo ${ret} > /dev/virtio-ports/virtme.ret
+        fi
 
         # Hmm.  We should expose the return value somehow.
         sync

virtme_ng/run.py

@@ -1102,8 +1102,7 @@ def clean(kern_source, args):
 
 def run(kern_source, args):
     """Run the kernel."""
-    kern_source.run(args)
-    return True
+    return kern_source.run(args)
 
 
 @spinner_decorator(message="🐞 generating memory dump")
@@ -1137,12 +1136,17 @@ def do_it() -> int:
             if not args.skip_config:
                 config(kern_source, args)
                 if args.kconfig:
-                    return
+                    return 0
             make(kern_source, args)
         else:
-            run(kern_source, args)
+            try:
+                run(kern_source, args)
+                return 0
+            except CalledProcessError as exc:
+                return exc.returncode
     except CalledProcessError as exc:
         raise SilentError() from exc
+    return 0
 
 
 def main() -> int: