Add shm_size extension to provide --shm-size argument

setup.py

@@ -62,6 +62,7 @@
             'privileged = rocker.extensions:Privileged',
             'pulse = rocker.extensions:PulseAudio',
             'rmw = rocker.rmw_extension:RMW',
+            'shm_size = rocker.extensions:ShmSize',
             'ssh = rocker.ssh_extension:Ssh',
             'ulimit = rocker.ulimit_extension:Ulimit',
             'user = rocker.extensions:User',

src/rocker/extensions.py

@@ -468,3 +468,27 @@ def register_arguments(parser, defaults):
             default=defaults.get(GroupAdd.get_name(), None),
             action='append',
             help="Add additional groups to join.")
+
+class ShmSize(RockerExtension):
+    @staticmethod
+    def get_name():
+        return 'shm_size'
+
+    def __init__(self):
+        self.name = ShmSize.get_name()
+
+    def get_preamble(self, cliargs):
+        return ''
+
+    def get_docker_args(self, cliargs):
+        args = ''
+        shm_size = cliargs.get('shm_size', None)
+        if shm_size:
+            args += f' --shm-size {shm_size} '
+        return args
+
+    @staticmethod
+    def register_arguments(parser, defaults={}):
+        parser.add_argument('--shm-size',
+                            default=defaults.get('shm_size', None),
+                            help="Set the size of the shared memory for the container (e.g., 512m, 1g).")

test/test_extension.py

@@ -617,3 +617,35 @@ def test_group_add_extension(self):
         args = p.get_docker_args(mock_cliargs)
         self.assertIn('--group-add sudo', args)
         self.assertIn('--group-add docker', args)
+
+class ShmSizeExtensionTest(unittest.TestCase):
+
+    def setUp(self):
+        # Work around interference between empy Interpreter
+        # stdout proxy and test runner. empy installs a proxy on stdout
+        # to be able to capture the information.
+        # And the test runner creates a new stdout object for each test.
+        # This breaks empy as it assumes that the proxy has persistent
+        # between instances of the Interpreter class
+        # empy will error with the exception
+        # "em.Error: interpreter stdout proxy lost"
+        em.Interpreter._wasProxyInstalled = False
+
+    @pytest.mark.docker
+    def test_shm_size_extension(self):
+        plugins = list_plugins()
+        shm_size_plugin = plugins['shm_size']
+        self.assertEqual(shm_size_plugin.get_name(), 'shm_size')
+
+        p = shm_size_plugin()
+        self.assertTrue(plugin_load_parser_correctly(shm_size_plugin))
+
+        mock_cliargs = {}
+        self.assertEqual(p.get_snippet(mock_cliargs), '')
+        self.assertEqual(p.get_preamble(mock_cliargs), '')
+        args = p.get_docker_args(mock_cliargs)
+        self.assertNotIn('--shm-size', args)
+
+        mock_cliargs = {'shm_size': '12g'}
+        args = p.get_docker_args(mock_cliargs)
+        self.assertIn('--shm-size 12g', args)