scripts/qemu.py: introduce set_console() method

The set_console() method is intended to ease higher level use cases
that require a console device.

The amount of intelligence is limited on purpose, requiring either the
device type explicitly, or the existence of a machine (pattern)
definition.

Because of the console device type selection criteria (by machine
type), users should also be able to define that.  It'll then be used
for both '-machine' and for the console device type selection.

Users of the set_console() method will certainly be interested in
accessing the console device, and for that a console_socket property
has been added.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Message-Id: <20180530184156.15634-5-crosa@redhat.com>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

scripts/qemu.py

@@ -17,19 +17,41 @@ import logging
 import os
 import subprocess
 import qmp.qmp
+import re
 import shutil
+import socket
 import tempfile
 
 
 LOG = logging.getLogger(__name__)
 
 
+#: Maps machine types to the preferred console device types
+CONSOLE_DEV_TYPES = {
+    r'^clipper$': 'isa-serial',
+    r'^malta': 'isa-serial',
+    r'^(pc.*|q35.*|isapc)$': 'isa-serial',
+    r'^(40p|powernv|prep)$': 'isa-serial',
+    r'^pseries.*': 'spapr-vty',
+    r'^s390-ccw-virtio.*': 'sclpconsole',
+    }
+
+
 class QEMUMachineError(Exception):
     """
     Exception called when an error in QEMUMachine happens.
     """
 
 
+class QEMUMachineAddDeviceError(QEMUMachineError):
+    """
+    Exception raised when a request to add a device can not be fulfilled
+
+    The failures are caused by limitations, lack of information or conflicting
+    requests on the QEMUMachine methods.  This exception does not represent
+    failures reported by the QEMU binary itself.
+    """
+
 class MonitorResponseError(qmp.qmp.QMPError):
     '''
     Represents erroneous QMP monitor reply
@@ -91,6 +113,10 @@ class QEMUMachine(object):
         self._test_dir = test_dir
         self._temp_dir = None
         self._launched = False
+        self._machine = None
+        self._console_device_type = None
+        self._console_address = None
+        self._console_socket = None
 
         # just in case logging wasn't configured by the main script:
         logging.basicConfig()
@@ -175,9 +201,19 @@ class QEMUMachine(object):
                 self._monitor_address[1])
         else:
             moncdev = 'socket,id=mon,path=%s' % self._vm_monitor
-        return ['-chardev', moncdev,
+        args = ['-chardev', moncdev,
                 '-mon', 'chardev=mon,mode=control',
                 '-display', 'none', '-vga', 'none']
+        if self._machine is not None:
+            args.extend(['-machine', self._machine])
+        if self._console_device_type is not None:
+            self._console_address = os.path.join(self._temp_dir,
+                                                 self._name + "-console.sock")
+            chardev = ('socket,id=console,path=%s,server,nowait' %
+                       self._console_address)
+            device = '%s,chardev=console' % self._console_device_type
+            args.extend(['-chardev', chardev, '-device', device])
+        return args
 
     def _pre_launch(self):
         self._temp_dir = tempfile.mkdtemp(dir=self._test_dir)
@@ -202,6 +238,10 @@ class QEMUMachine(object):
 
         self._qemu_log_path = None
 
+        if self._console_socket is not None:
+            self._console_socket.close()
+            self._console_socket = None
+
         if self._temp_dir is not None:
             shutil.rmtree(self._temp_dir)
             self._temp_dir = None
@@ -365,3 +405,58 @@ class QEMUMachine(object):
         Adds to the list of extra arguments to be given to the QEMU binary
         '''
         self._args.extend(args)
+
+    def set_machine(self, machine_type):
+        '''
+        Sets the machine type
+
+        If set, the machine type will be added to the base arguments
+        of the resulting QEMU command line.
+        '''
+        self._machine = machine_type
+
+    def set_console(self, device_type=None):
+        '''
+        Sets the device type for a console device
+
+        If set, the console device and a backing character device will
+        be added to the base arguments of the resulting QEMU command
+        line.
+
+        This is a convenience method that will either use the provided
+        device type, of if not given, it will used the device type set
+        on CONSOLE_DEV_TYPES.
+
+        The actual setting of command line arguments will be be done at
+        machine launch time, as it depends on the temporary directory
+        to be created.
+
+        @param device_type: the device type, such as "isa-serial"
+        @raises: QEMUMachineAddDeviceError if the device type is not given
+                 and can not be determined.
+        '''
+        if device_type is None:
+            if self._machine is None:
+                raise QEMUMachineAddDeviceError("Can not add a console device:"
+                                                " QEMU instance without a "
+                                                "defined machine type")
+            for regex, device in CONSOLE_DEV_TYPES.items():
+                if re.match(regex, self._machine):
+                    device_type = device
+                    break
+            if device_type is None:
+                raise QEMUMachineAddDeviceError("Can not add a console device:"
+                                                " no matching console device "
+                                                "type definition")
+        self._console_device_type = device_type
+
+    @property
+    def console_socket(self):
+        """
+        Returns a socket connected to the console
+        """
+        if self._console_socket is None:
+            self._console_socket = socket.socket(socket.AF_UNIX,
+                                                 socket.SOCK_STREAM)
+            self._console_socket.connect(self._console_address)
+        return self._console_socket