Fix race in check and access of /dev/disk/by-path/

If udev deletes the directory between the check and access then we have
an exception thrown. Instead of checking, just list the directory and
handle the exception in case it doesn't exist.

Co-Authored-By: Jordan Pittier <jordan.pittier@scality.com>
Change-Id: I52143923d2407b3d43eccf5d3c51526a92d1e3c5
Closes-Bug: 1478473

os_brick/initiator/host_driver.py

@@ -13,6 +13,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import errno
 import os
 
 
@@ -20,10 +21,15 @@ class HostDriver(object):
 
     def get_all_block_devices(self):
         """Get the list of all block devices seen in /dev/disk/by-path/."""
-        files = []
         dir = "/dev/disk/by-path/"
-        if os.path.isdir(dir):
+        try:
             files = os.listdir(dir)
+        except OSError as e:
+            if e.errno == errno.ENOENT:
+                files = []
+            else:
+                raise
+
         devices = []
         for file in files:
             devices.append(dir + file)

os_brick/tests/initiator/test_connector.py

@@ -193,22 +193,6 @@ class ConnectorTestCase(base.TestCase):
             self.assertFalse(self.connector.check_valid_device('/dev'))
 
 
-class HostDriverTestCase(base.TestCase):
-
-    def setUp(self):
-        super(HostDriverTestCase, self).setUp()
-        self.devlist = ['device1', 'device2']
-        mock.patch.object(os.path, 'isdir', return_value=True).start()
-        mock.patch.object(os, 'listdir', return_value=self.devlist).start()
-        self.addCleanup(mock.patch.stopall)
-
-    def test_host_driver(self):
-        expected = ['/dev/disk/by-path/' + dev for dev in self.devlist]
-        driver = host_driver.HostDriver()
-        actual = driver.get_all_block_devices()
-        self.assertEqual(expected, actual)
-
-
 class ISCSIConnectorTestCase(ConnectorTestCase):
 
     def setUp(self):

os_brick/tests/initiator/test_host_driver.py

@@ -0,0 +1,47 @@
+# Copyright (c) 2015 Scality
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import errno
+
+import mock
+
+from os_brick.initiator import host_driver
+from os_brick.tests import base
+
+
+class HostDriverTestCase(base.TestCase):
+
+    def test_get_all_block_devices(self):
+        fake_dev = ['device1', 'device2']
+        expected = ['/dev/disk/by-path/' + dev for dev in fake_dev]
+
+        driver = host_driver.HostDriver()
+        with mock.patch('os.listdir', return_value=fake_dev):
+            actual = driver.get_all_block_devices()
+
+        self.assertEqual(expected, actual)
+
+    def test_get_all_block_devices_when_oserror_is_enoent(self):
+        driver = host_driver.HostDriver()
+        oserror = OSError(errno.ENOENT, "")
+        with mock.patch('os.listdir', side_effect=oserror):
+            block_devices = driver.get_all_block_devices()
+
+        self.assertEqual([], block_devices)
+
+    def test_get_all_block_devices_when_oserror_is_not_enoent(self):
+        driver = host_driver.HostDriver()
+        oserror = OSError(errno.ENOMEM, "")
+        with mock.patch('os.listdir', side_effect=oserror):
+            self.assertRaises(OSError, driver.get_all_block_devices)