Make mount_check option usable in containerized environments

The ismount_raw method does not work inside containers if disks are
mounted on the hostsystem and only mountpoints are exposed inside the
containers. In this case the inode and device checks fail, making this
option unusable.

Mounting devices into the containers would solve this. However, this
would require that all processes that require access to a device are
running inside the same container, which counteracts the container
concept.

This patch adds the possiblity to place stubfiles named ".ismount" into
the root directory of any device, and Swift assumes a given device to be
mounted if that file exists. This should be transparent to existing
clusters.

Change-Id: I9d9fc0a4447a8c5dd39ca60b274c119af6b4c28f

swift/common/utils.py

@@ -3583,6 +3583,12 @@ def ismount_raw(path):
         # path/.. is the same i-node as path
         return True
 
+    # Device and inode checks are not properly working inside containerized
+    # environments, therefore using a workaround to check if there is a
+    # stubfile placed by an operator
+    if os.path.isfile(os.path.join(path, ".ismount")):
+        return True
+
     return False
 
 

test/unit/common/test_utils.py

@@ -3300,6 +3300,16 @@ cluster_dfw1 = http://dfw1.host/v1/
         finally:
             shutil.rmtree(tmpdir)
 
+    def test_ismount_successes_stubfile(self):
+        tmpdir = mkdtemp()
+        fname = os.path.join(tmpdir, ".ismount")
+        try:
+            with open(fname, "w") as stubfile:
+                stubfile.write("")
+            self.assertTrue(utils.ismount(tmpdir))
+        finally:
+            shutil.rmtree(tmpdir)
+
     def test_parse_content_type(self):
         self.assertEqual(utils.parse_content_type('text/plain'),
                          ('text/plain', []))