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

[Wainer dos Santos Moschetta]

On 12/10/19 3:17 AM, Cleber Rosa wrote:
> 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 <address@hidden>
> > ---
> >   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.

I don't have a strong opinion about double negatives. So I'm fine with 
use 'enabled' instead. Besides make you happier. ;)

> > +        @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).

I thought it would be useful in case an acceptance test needs to set the 
monitor address. And because avocado_qemu transparently creates the 
QEMUMachine instance, the test doesn't have access to the constructor. 
But no, I don't have a concrete case. I'm just being overcareful, so I 
don't mind to remove that parameter.

Good catch. Thanks!

- Wainer

> > +        @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.