lxd: Setup image and target arch for cross-compilation

snapcraft/_options.py

@@ -233,6 +233,10 @@ def _set_machine(self, target_deb_arch):
         self.__machine_info = _ARCH_TRANSLATIONS[self.__target_machine]
 
 
+def _get_deb_arch(machine):
+    return _ARCH_TRANSLATIONS[machine].get('deb', None)
+
+
 def _find_machine(deb_arch):
     for machine in _ARCH_TRANSLATIONS:
         if _ARCH_TRANSLATIONS[machine].get('deb', '') == deb_arch:

snapcraft/internal/lxd.py

@@ -24,9 +24,11 @@
 from time import sleep
 
 import petname
+import yaml
 
 from snapcraft.internal.errors import SnapcraftEnvironmentError
 from snapcraft.internal import common
+from snapcraft._options import _get_deb_arch
 
 logger = logging.getLogger(__name__)
 
@@ -52,6 +54,19 @@ def __init__(self, *, output, source, project_options,
             remote = _get_default_remote()
         _verify_remote(remote)
         self._container_name = '{}:snapcraft-{}'.format(remote, container_name)
+        # Use the server architecture to avoid emulation overhead
+        kernel = self._get_remote_info()['environment']['kernel_architecture']
+        deb_arch = _get_deb_arch(kernel)
+        if not deb_arch:
+            raise SnapcraftEnvironmentError(
+                'Unrecognized server architecture {}'.format(kernel))
+        self._host_arch = deb_arch
+        self._image = 'ubuntu:xenial/{}'.format(deb_arch)
+
+    def _get_remote_info(self):
+        remote = self._container_name.split(':')[0]
+        return yaml.load(check_output([
+            'lxc', 'info', '{}:'.format(remote)]).decode())
 
     def _push_file(self, src, dst):
         check_call(['lxc', 'file', 'push',
@@ -68,9 +83,7 @@ def _container_run(self, cmd):
 
     def _ensure_container(self):
         check_call([
-            'lxc', 'launch', '-e',
-            'ubuntu:xenial/{}'.format(self._project_options.deb_arch),
-            self._container_name])
+            'lxc', 'launch', '-e', self._image, self._container_name])
         check_call([
             'lxc', 'config', 'set', self._container_name,
             'environment.SNAPCRAFT_SETUP_CORE', '1'])
@@ -94,6 +107,8 @@ def execute(self, step='snap', args=None):
             command = ['snapcraft', step]
             if step == 'snap':
                 command += ['--output', self._snap_output]
+            if self._host_arch != self._project_options.deb_arch:
+                command += ['--target-arch', self._project_options.deb_arch]
             if args:
                 command += args
             try:
@@ -166,9 +181,7 @@ def _get_container_status(self):
     def _ensure_container(self):
         if not self._get_container_status():
             check_call([
-                'lxc', 'init',
-                'ubuntu:xenial/{}'.format(self._project_options.deb_arch),
-                self._container_name])
+                'lxc', 'init', self._image, self._container_name])
             check_call([
                 'lxc', 'config', 'set', self._container_name,
                 'environment.SNAPCRAFT_SETUP_CORE', '1'])

snapcraft/tests/fixture_setup.py

@@ -394,6 +394,11 @@ def call_effect(*args, **kwargs):
                 return 'local'.encode('utf-8')
         elif args[0] == ['lxc', 'list', 'my-remote:'] and fail_on_remote:
             raise CalledProcessError(returncode=255, cmd=args[0])
+        elif args[0][:2] == ['lxc', 'info']:
+            return '''
+                environment:
+                  kernel_architecture: x86_64
+                '''.encode('utf-8')
         elif args[0][:3] == ['lxc', 'list', '--format=json']:
             return '''
                 [{"name": "snapcraft-snap-test",

snapcraft/tests/test_lxd.py

@@ -33,33 +33,40 @@
 class LXDTestCase(tests.TestCase):
 
     scenarios = [
-        ('local', dict(remote='local')),
-        ('remote', dict(remote='my-remote')),
+        ('local', dict(remote='local', target_arch=None)),
+        ('remote', dict(remote='my-remote', target_arch=None)),
+        ('cross', dict(remote='local', target_arch='armhf')),
     ]
 
     @patch('petname.Generate')
-    def test_cleanbuild(self, mock_pet):
+    @patch('platform.machine')
+    @patch('platform.architecture')
+    def test_cleanbuild(self, mock_arch, mock_machine, mock_pet):
         fake_lxd = tests.fixture_setup.FakeLXD()
         self.useFixture(fake_lxd)
         fake_logger = fixtures.FakeLogger(level=logging.INFO)
         self.useFixture(fake_logger)
 
         mock_pet.return_value = 'my-pet'
-
-        project_options = ProjectOptions()
+        mock_arch.return_value = ('64bit', 'ELF')
+        mock_machine.return_value = 'x86_64'
+        project_options = ProjectOptions(target_deb_arch=self.target_arch)
         metadata = {'name': 'project'}
         project_folder = 'build_project'
         lxd.Cleanbuilder(output='snap.snap', source='project.tar',
                          metadata=metadata, remote=self.remote,
                          project_options=project_options).execute()
-        expected_arch = project_options.deb_arch
-
-        self.assertEqual(
-            'Setting up container with project assets\n'
-            'Waiting for a network connection...\n'
-            'Network connection established\n'
-            'Retrieved snap.snap\n',
-            fake_logger.output)
+        expected_arch = 'amd64'
+
+        self.assertIn('Setting up container with project assets\n'
+                      'Waiting for a network connection...\n'
+                      'Network connection established\n'
+                      'Retrieved snap.snap\n', fake_logger.output)
+        args = []
+        if self.target_arch:
+            self.assertIn('Setting target machine to \'{}\'\n'.format(
+                          self.target_arch), fake_logger.output)
+            args += ['--target-arch', self.target_arch]
 
         container_name = '{}:snapcraft-my-pet'.format(self.remote)
         fake_lxd.check_call_mock.assert_has_calls([
@@ -90,7 +97,7 @@ def test_cleanbuild(self, mock_pet):
                   'apt-get', 'install', 'snapcraft', '-y']),
             call(['lxc', 'exec', container_name,
                   '--env', 'HOME=/{}'.format(project_folder), '--',
-                  'snapcraft', 'snap', '--output', 'snap.snap']),
+                  'snapcraft', 'snap', '--output', 'snap.snap', *args]),
             call(['lxc', 'file', 'pull',
                   '{}/{}/snap.snap'.format(container_name, project_folder),
                   'snap.snap']),