target: Implement target runner classes

Add support for launching emulated targets on QEMU. The base class
``TargetRunner`` has groundwork for target runners like
``QEMUTargetRunner``.

``TargetRunner`` is a contextmanager which starts runner process (e.g.,
QEMU), makes sure the target is accessible over SSH (if
``connect=True``), and terminates the runner process once it's done.

The other newly introduced ``QEMUTargetRunner`` class:
- performs sanity checks to ensure QEMU executable, kernel, and initrd
  images exist,
- builds QEMU parameters properly,
- creates ``Target`` object,
- and lets ``TargetRunner`` manage the QEMU instance.

Also add a new test case in ``tests/test_target.py`` to ensure devlib
can run a QEMU target and execute some basic commands on it.

While we are in neighborhood, fix a typo in ``Target.setup()``.

Signed-off-by: Metin Kaya <metin.kaya@arm.com>

tests/target_configs.yaml.example

@@ -15,3 +15,16 @@ LocalLinuxTarget:
     connection_settings:
       unrooted: True
 
+QEMUTargetRunner:
+  entry-0:
+    qemu_settings:
+      kernel_image: '/path/to/devlib/tools/buildroot/buildroot-v2023.11.1-aarch64/output/images/Image'
+
+  entry-1:
+    connection_settings:
+      port : 8023
+
+    qemu_settings:
+      kernel_image: '/path/to/devlib/tools/buildroot/buildroot-v2023.11.1-x86_64/output/images/bzImage'
+      arch: 'x86_64'
+      cmdline: 'console=ttyS0'

tests/test_target.py

@@ -20,7 +20,7 @@ import os
 from pprint import pp
 import pytest
 
-from devlib import AndroidTarget, LinuxTarget, LocalLinuxTarget
+from devlib import AndroidTarget, LinuxTarget, LocalLinuxTarget, QEMUTargetRunner
 from devlib.utils.android import AdbConnection
 from devlib.utils.misc import load_struct_from_yaml
 
@@ -44,32 +44,49 @@ def build_targets():
                 connection_settings=entry['connection_settings'],
                 conn_cls=lambda **kwargs: AdbConnection(adb_as_root=True, **kwargs),
             )
-            targets.append(a_target)
+            targets.append((a_target, None))
 
     if target_configs.get('LinuxTarget') is not None:
         print('> Linux targets:')
         for entry in target_configs['LinuxTarget'].values():
             pp(entry)
             l_target = LinuxTarget(connection_settings=entry['connection_settings'])
-            targets.append(l_target)
+            targets.append((l_target, None))
 
     if target_configs.get('LocalLinuxTarget') is not None:
         print('> LocalLinux targets:')
         for entry in target_configs['LocalLinuxTarget'].values():
             pp(entry)
             ll_target = LocalLinuxTarget(connection_settings=entry['connection_settings'])
-            targets.append(ll_target)
+            targets.append((ll_target, None))
+
+    if target_configs.get('QEMUTargetRunner') is not None:
+        print('> QEMU target runners:')
+        for entry in target_configs['QEMUTargetRunner'].values():
+            pp(entry)
+            qemu_settings = entry.get('qemu_settings') and entry['qemu_settings']
+            connection_settings = entry.get(
+                'connection_settings') and entry['connection_settings']
+
+            qemu_runner = QEMUTargetRunner(
+                qemu_settings=qemu_settings,
+                connection_settings=connection_settings,
+            )
+            targets.append((qemu_runner.target, qemu_runner))
 
     return targets
 
 
-@pytest.mark.parametrize("target", build_targets())
-def test_read_multiline_values(target):
+@pytest.mark.parametrize("target, target_runner", build_targets())
+def test_read_multiline_values(target, target_runner):
     """
     Test Target.read_tree_values_flat()
 
     :param target: Type of target per :class:`Target` based classes.
     :type target: Target
+
+    :param target_runner: Target runner object to terminate target (if necessary).
+    :type target: TargetRunner
     """
 
     data = {
@@ -96,4 +113,8 @@ def test_read_multiline_values(target):
     print(f'Removing {target.working_directory}...')
     target.remove(target.working_directory)
 
+    if target_runner is not None:
+        print('Terminating target runner...')
+        target_runner.terminate()
+
     assert {k: v.strip() for k, v in data.items()} == result