Re: [PATCH 1/2] python/qemu: Add set_qmp_monitor() to QEMUMachine

[Cleber Rosa <crosa@redhat.com>]

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On Tue, Nov 12, 2019 at 08:58:00AM -0500, Wainer dos Santos Moschetta wrote:
> The QEMUMachine VM has a monitor setup on which an QMP
> connection is always attempted on _post_launch() (executed
> by launch()). In case the QEMU process immediatly exits
> then the qmp.accept() (used to establish the connection) stalls
> until it reaches timeout and consequently an exception raises.
> 
> That behavior is undesirable when, for instance, it needs to
> gather information from the QEMU binary ($ qemu -cpu list) or a
> test which launches the VM expecting its failure.
> 
> This patch adds the set_qmp_monitor() method to QEMUMachine that
> allows turn off the creation of the monitor machinery on VM launch.
> 
> Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
> ---
>  python/qemu/machine.py | 68 ++++++++++++++++++++++++++++--------------
>  1 file changed, 45 insertions(+), 23 deletions(-)
> 
> diff --git a/python/qemu/machine.py b/python/qemu/machine.py
> index a4631d6934..04ee86e1ba 100644
> --- a/python/qemu/machine.py
> +++ b/python/qemu/machine.py
> @@ -104,6 +104,7 @@ class QEMUMachine(object):
>          self._events = []
>          self._iolog = None
>          self._socket_scm_helper = socket_scm_helper
> +        self._qmp_set = True   # Enable QMP monitor by default.
>          self._qmp = None
>          self._qemu_full_args = None
>          self._test_dir = test_dir
> @@ -228,15 +229,16 @@ class QEMUMachine(object):
>                  self._iolog = iolog.read()
>  
>      def _base_args(self):
> -        if isinstance(self._monitor_address, tuple):
> -            moncdev = "socket,id=mon,host=%s,port=%s" % (
> +        args = ['-display', 'none', '-vga', 'none']
> +        if self._qmp_set:
> +            if isinstance(self._monitor_address, tuple):
> +                moncdev = "socket,id=mon,host=%s,port=%s" % (
>                  self._monitor_address[0],
>                  self._monitor_address[1])
> -        else:
> -            moncdev = 'socket,id=mon,path=%s' % self._vm_monitor
> -        args = ['-chardev', moncdev,
> -                '-mon', 'chardev=mon,mode=control',
> -                '-display', 'none', '-vga', 'none']
> +            else:
> +                moncdev = 'socket,id=mon,path=%s' % self._vm_monitor
> +            args.extend(['-chardev', moncdev, '-mon',
> +                         'chardev=mon,mode=control'])
>          if self._machine is not None:
>              args.extend(['-machine', self._machine])
>          if self._console_set:
> @@ -255,20 +257,21 @@ class QEMUMachine(object):
>  
>      def _pre_launch(self):
>          self._temp_dir = tempfile.mkdtemp(dir=self._test_dir)
> -        if self._monitor_address is not None:
> -            self._vm_monitor = self._monitor_address
> -        else:
> -            self._vm_monitor = os.path.join(self._sock_dir,
> -                                            self._name + "-monitor.sock")
> -            self._remove_files.append(self._vm_monitor)
>          self._qemu_log_path = os.path.join(self._temp_dir, self._name + ".log")
>          self._qemu_log_file = open(self._qemu_log_path, 'wb')
>  
> -        self._qmp = qmp.QEMUMonitorProtocol(self._vm_monitor,
> -                                            server=True)
> +        if self._qmp_set:
> +            if self._monitor_address is not None:
> +                self._vm_monitor = self._monitor_address
> +            else:
> +                self._vm_monitor = os.path.join(self._sock_dir,
> +                                                self._name + "-monitor.sock")
> +                self._remove_files.append(self._vm_monitor)
> +            self._qmp = qmp.QEMUMonitorProtocol(self._vm_monitor, server=True)
>  
>      def _post_launch(self):
> -        self._qmp.accept()
> +        if self._qmp:
> +            self._qmp.accept()
>  
>      def _post_shutdown(self):
>          if self._qemu_log_file is not None:
> @@ -330,7 +333,8 @@ class QEMUMachine(object):
>          Wait for the VM to power off
>          """
>          self._popen.wait()
> -        self._qmp.close()
> +        if self._qmp:
> +            self._qmp.close()
>          self._load_io_log()
>          self._post_shutdown()
>  
> @@ -346,12 +350,13 @@ class QEMUMachine(object):
>              self._console_socket = None
>  
>          if self.is_running():
> -            try:
> -                if not has_quit:
> -                    self._qmp.cmd('quit')
> -                self._qmp.close()
> -            except:
> -                self._popen.kill()
> +            if self._qmp:
> +                try:
> +                    if not has_quit:
> +                        self._qmp.cmd('quit')
> +                    self._qmp.close()
> +                except:
> +                    self._popen.kill()
>              self._popen.wait()
>  
>          self._load_io_log()
> @@ -368,6 +373,23 @@ class QEMUMachine(object):
>  
>          self._launched = False
>  
> +    def set_qmp_monitor(self, disabled=False, monitor_address=None):
> +        """
> +        Set the QMP monitor.
> +
> +        @param disabled: if True, qmp monitor options will be removed from the
> +                         base arguments of the resulting QEMU command line.

I personally tend avoid double negatives as long as I'm aware of them.
Wouldn't "enabled=True" be more straightforward?  Just my personal
preference though.

> +        @param monitor_address: address for the QMP monitor.

Do you have a use case for passing the monitor address here too, in
addition to also being available as a parameter to __init__()?  In the
next patch, I don't see it being used (or here for that matter).

> +        @note: call this function before launch().
> +        """
> +        if disabled:
> +            self._qmp_set = False
> +            self._qmp = None
> +        else:
> +            self._qmp_set = True
> +            if monitor_address:
> +                self._monitor_address = monitor_address
> +
>      def qmp(self, cmd, conv_keys=True, **args):
>          """
>          Invoke a QMP command and return the response dict
> -- 
> 2.18.1
> 

Other than those comments, it LGTM.

- Cleber.

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