Read mounts from /proc/mounts instead of running mount

When creating multiple concurrent volumes, there's a lock
that prevents mount from returning quickly. Reading /proc/mounts
is way faster.

Change-Id: If31d120955eb216823a55005fdd3d24870aa6b9a
Closes-Bug: #1856889
(cherry picked from commit f240960847)

os_brick/remotefs/remotefs.py

@@ -81,16 +81,19 @@ class RemoteFsClient(executor.Executor):
                             self._get_hash_str(device_name))
 
     def _read_mounts(self):
-        (out, _err) = self._execute('mount', check_exit_code=0)
-        lines = out.split('\n')
-        mounts = {}
-        for line in lines:
-            tokens = line.split()
-            if 2 < len(tokens):
-                device = tokens[0]
-                mnt_point = tokens[2]
-                mounts[mnt_point] = device
-        return mounts
+        """Returns a dict of mounts and their mountpoint
+
+        Format reference:
+        http://man7.org/linux/man-pages/man5/fstab.5.html
+        """
+        with open("/proc/mounts", "r") as mounts:
+            # Remove empty lines and split lines by whitespace
+            lines = [l.split() for l in mounts.read().splitlines()
+                     if l.strip()]
+
+            # Return {mountpoint: mountdevice}.  Fields 2nd and 1st as per
+            # http://man7.org/linux/man-pages/man5/fstab.5.html
+            return {line[1]: line[0] for line in lines if line[0] != '#'}
 
     def mount(self, share, flags=None):
         """Mount given share."""

os_brick/tests/remotefs/test_remotefs.py

@@ -59,15 +59,17 @@ class RemoteFsClientTestCase(base.TestCase):
         self.mock_execute.assert_has_calls(calls)
 
     def test_read_mounts(self):
-        mounts = """device1 on mnt_point1
-                    device2 on mnt_point2 type ext4 opts"""
-        with mock.patch.object(priv_rootwrap, 'execute',
-                               return_value=[mounts, '']):
+        mounts = """device1 mnt_point1 ext4 rw,seclabel,relatime 0 0
+                    device2 mnt_point2 ext4 rw,seclabel,relatime 0 0"""
+        mockopen = mock.mock_open(read_data=mounts)
+        mockopen.return_value.__iter__ = lambda self: iter(self.readline, '')
+        with mock.patch.object(six.moves.builtins, "open", mockopen,
+                               create=True):
             client = remotefs.RemoteFsClient("cifs", root_helper='true',
                                              smbfs_mount_point_base='/mnt')
             ret = client._read_mounts()
-            self.assertEqual(ret, {'mnt_point1': 'device1',
-                                   'mnt_point2': 'device2'})
+        self.assertEqual(ret, {'mnt_point1': 'device1',
+                               'mnt_point2': 'device2'})
 
     @mock.patch.object(priv_rootwrap, 'execute')
     @mock.patch.object(remotefs.RemoteFsClient, '_do_mount')