Always check cmd which does not exist

In daemon mode, if run a cmd which does not exist,
it will raise an Exception. But when we install the
cmd later and run cmd, it still raise an Exception.
The only work around right now is to restart the
daemon, with this change, we can avoid restarting
the daemon

Closes-Bug: #1663216
Change-Id: I6f6ff540ed103f0fec329d6264bdac26493c8fad

oslo_rootwrap/filters.py

@@ -39,7 +39,6 @@ class CommandFilter(object):
         exec_dirs = exec_dirs or []
         if self.real_exec is not None:
             return self.real_exec
-        self.real_exec = ""
         if os.path.isabs(self.exec_path):
             if os.access(self.exec_path, os.X_OK):
                 self.real_exec = self.exec_path

oslo_rootwrap/tests/test_functional.py

@@ -18,6 +18,7 @@ import io
 import logging
 import os
 import pwd
+import shutil
 import signal
 import sys
 import threading
@@ -44,6 +45,7 @@ class _FunctionalBase(object):
         super(_FunctionalBase, self).setUp()
         tmpdir = self.useFixture(fixtures.TempDir()).path
         self.config_file = os.path.join(tmpdir, 'rootwrap.conf')
+        self.later_cmd = os.path.join(tmpdir, 'later_install_cmd')
         filters_dir = os.path.join(tmpdir, 'filters.d')
         filters_file = os.path.join(tmpdir, 'filters.d', 'test.filters')
         os.mkdir(filters_dir)
@@ -58,7 +60,8 @@ cat: CommandFilter, /bin/cat, root
 sh: CommandFilter, /bin/sh, root
 id: CommandFilter, /usr/bin/id, nobody
 unknown_cmd: CommandFilter, /unknown/unknown_cmd, root
-""")
+later_install_cmd: CommandFilter, %s, root
+""" % self.later_cmd)
 
     def _test_run_once(self, expect_byte=True):
         code, out, err = self.execute(['echo', 'teststr'])
@@ -192,6 +195,15 @@ class RootwrapDaemonTest(_FunctionalBase, testtools.TestCase):
     def test_run_with_stdin(self):
         self._test_run_with_stdin(expect_byte=False)
 
+    def test_run_with_later_install_cmd(self):
+        code, out, err = self.execute(['later_install_cmd'])
+        self.assertEqual(cmd.RC_NOEXECFOUND, code)
+        # Install cmd and try again
+        shutil.copy('/bin/echo', self.later_cmd)
+        code, out, err = self.execute(['later_install_cmd'])
+        # Expect successfully run the cmd
+        self.assertEqual(0, code)
+
     def test_daemon_ressurection(self):
         # Let the client start a daemon
         self.execute(['cat'])