Check if process' cmdline is "space separarated"

According to proc man page process arguments in /proc/{pid}/cmdline
should be separated with '\0' char and that char was used in
neutron.agent.linux.utils.get_cmdline_from_pid function.

Recently in fullstack tests it was noticed that sometimes it may
happend that those arguments are separated with space char and this
caused failed test because async_process.AsyncProcess() was not able
to check that process is really active.

This patch adds attempt to split cmdline arguments with space in case
when split with '\0' returns only 1 element.

Change-Id: I35d4c0e2cf56fc3ff15cf307aaf11a8ad8489e1f
Closes-Bug: #1820870

neutron/agent/linux/utils.py

@@ -324,7 +324,20 @@ def get_cmdline_from_pid(pid):
     if not process_is_running(pid):
         return []
     with open('/proc/%s/cmdline' % pid, 'r') as f:
-        return f.readline().split('\0')[:-1]
+        cmdline = f.readline()
+        cmdline_args = cmdline.split('\0')[:-1]
+
+        # NOTE(slaweq): sometimes it may happen that values in
+        # /proc/{pid}/cmdline are separated by space instead of NUL char,
+        # in such case we would have everything in one element of cmdline_args
+        # list and it would not match to expected cmd so we need to try to
+        # split it by spaces
+        if len(cmdline_args) == 1:
+            cmdline_args = cmdline_args[0].split(' ')
+
+        LOG.debug("Found cmdline %s for rocess with PID %s.",
+                  cmdline_args, pid)
+        return cmdline_args
 
 
 def cmd_matches_expected(cmd, expected_cmd):

neutron/tests/unit/agent/linux/test_utils.py

@@ -27,6 +27,7 @@ import oslo_i18n
 from neutron.agent.linux import utils
 from neutron.tests import base
 from neutron.tests.common import helpers
+from neutron.tests import tools
 
 
 _marker = object()
@@ -294,6 +295,43 @@ class TestKillProcess(base.BaseTestCase):
         self._test_kill_process('1', kill_signal=signal.SIGTERM)
 
 
+class TestGetCmdlineFromPid(base.BaseTestCase):
+
+    def setUp(self):
+        super(TestGetCmdlineFromPid, self).setUp()
+        self.pid = 34
+        self.process_is_running_mock = mock.patch.object(
+            utils, "process_is_running").start()
+
+    def _test_cmdline(self, process, expected_cmd):
+        self.process_is_running_mock.return_value = True
+        mock_open = self.useFixture(
+            tools.OpenFixture('/proc/%s/cmdline' % self.pid, process)
+        ).mock_open
+        cmdline = utils.get_cmdline_from_pid(self.pid)
+        mock_open.assert_called_once_with('/proc/%s/cmdline' % self.pid, 'r')
+        self.assertEqual(expected_cmd, cmdline)
+
+    def test_cmdline_separated_with_null_char(self):
+        process_cmd = "python3\0test-binary\0test option\0"
+        expected_cmdline = ["python3", "test-binary", "test option"]
+        self._test_cmdline(process_cmd, expected_cmdline)
+
+    def test_cmdline_separated_with_space_char(self):
+        process_cmd = "python3 test-binary test option\0"
+        expected_cmdline = ["python3", "test-binary", "test", "option"]
+        self._test_cmdline(process_cmd, expected_cmdline)
+
+    def test_no_process_running(self):
+        self.process_is_running_mock.return_value = False
+        mock_open = self.useFixture(
+            tools.OpenFixture('/proc/%s/cmdline' % self.pid)
+        ).mock_open
+        cmdline = utils.get_cmdline_from_pid(self.pid)
+        mock_open.assert_not_called()
+        self.assertEqual([], cmdline)
+
+
 class TestFindChildPids(base.BaseTestCase):
 
     def test_returns_empty_list_for_exit_code_1(self):