Relax mount point name checking.

In general, Linux does not care about what a mount point is named as
long as it is a vaild directory name (no / or null characters).
However, that is too relaxed for swift, which will pass that mount
point name around as part of url path construction all over the
place.  To make sure that the mount point name was sane from that POV,
Swift was using isalnum to verify that the mount point name was sane,
which is overly restrictive.

This patch replaces that test with a test that verifies that the name
has no characters that need to be URL encoded.

The specific use case this enables is allowing mount points to be
named according to the UUID of the filesystem that is being mounted,
which will make Swift more robust in the face of device name instability.

Change-Id: I4d49b21c1783e97c16d3f394c2171f1f80eea058

swift/common/constraints.py

@@ -14,6 +14,7 @@
 # limitations under the License.
 
 import os
+import urllib
 from ConfigParser import ConfigParser, NoSectionError, NoOptionError, \
     RawConfigParser
 
@@ -159,7 +160,7 @@ def check_mount(root, drive):
     :param drive: drive name to be checked
     :returns: True if it is a valid mounted device, False otherwise
     """
-    if not drive.isalnum():
+    if not (urllib.quote_plus(drive) == drive):
         return False
     path = os.path.join(root, drive)
     return os.path.exists(path) and os.path.ismount(path)

test/unit/common/test_constraints.py

@@ -173,6 +173,11 @@ class TestConstraints(unittest.TestCase):
         self.assertFalse(constraints.check_mount('', ''))
         constraints.os = MockTrue()  # mock os module
         self.assertTrue(constraints.check_mount('/srv', '1'))
+        self.assertTrue(constraints.check_mount('/srv', 'foo-bar'))
+        self.assertTrue(constraints.check_mount('/srv', '003ed03c-242a-4b2f-bee9-395f801d1699'))
+        self.assertFalse(constraints.check_mount('/srv', 'foo bar'))
+        self.assertFalse(constraints.check_mount('/srv', 'foo/bar'))
+        self.assertFalse(constraints.check_mount('/srv', 'foo?bar'))
         reload(constraints)  # put it back
 
     def test_check_float(self):