block_device: remove cmp_mount_order

This comparator is buggy, and orders differently on python 3.13

 $ python3.14 ./test.py
 [('/', 'fake_name'), ('/var/log', 'fake_log'), ('/boot', 'fake_boot'), ('/var', 'fake_name')]

 $ python3.10 ./test.py
 [('/', 'fake_name'), ('/var', 'fake_name'), ('/var/log', 'fake_log'), ('/boot', 'fake_boot')]

It is saying that if it's not equal, or doesn't start with the same
prefix, it is bigger.  Hence "/boot > /var" but also "/var > /boot"
which confuses things.

I really think what we want here is to ensure that parents mount
before children.  So string comparision is fine?  "/var < /var/log <
/var/log/foo"?

Replace it with that

Change-Id: Ieac277c90b13bdb8b2c651b17fa4617ac4c1b845
Signed-off-by: Ian Wienand <iwienand@redhat.com>

diskimage_builder/block_device/level3/mount.py

@@ -12,7 +12,6 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-import functools
 import logging
 import os
 import time
@@ -137,30 +136,6 @@ class MountPointNode(NodeBase):
         self.umount()
 
 
-def cmp_mount_order(this, other):
-    """Sort comparision function for mount-point sorting
-
-    See if ``this`` comes before ``other`` in mount-order list.  In
-    words: if the other mount-point has us as it's parent, we come
-    before it (are less than it). e.g. ``/var < /var/log <
-    /var/log/foo``
-
-    :param this: tuple of mount_point, node name
-    :param other: tuple of mount_point, node name
-    :returns int: cmp value
-
-    """
-    # sort is only based on the mount_point.
-    this, _ = this
-    other, _ = other
-    if this == other:
-        return 0
-    if other.startswith(this):
-        return -1
-    else:
-        return 1
-
-
 class Mount(PluginBase):
     def __init__(self, config, defaults, state):
         super(Mount, self).__init__()
@@ -185,7 +160,10 @@ class Mount(PluginBase):
                 "Mount point [%s] specified more than once"
                 % self.node.mount_point)
         sorted_mount_points.append((self.node.mount_point, self.node.name))
-        sorted_mount_points.sort(key=functools.cmp_to_key(cmp_mount_order))
+        # Sort by mount point so hierarchy is in shortest to longest, such
+        # that parents mount before children; e.g.
+        #  /var < /var/log
+        sorted_mount_points.sort(key=lambda x: x[0])
         # Save the state if it's new (otherwise this is idempotent update)
         state['sorted_mount_points'] = sorted_mount_points
         logger.debug("Ordered mounts now: %s", sorted_mount_points)

diskimage_builder/block_device/tests/test_mount_order.py

@@ -10,7 +10,6 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-import functools
 import logging
 import os
 from unittest import mock
@@ -20,37 +19,11 @@ import diskimage_builder.block_device.tests.test_config as tc
 from diskimage_builder.block_device.config import config_tree_to_graph
 from diskimage_builder.block_device.config import create_graph
 from diskimage_builder.block_device.level2.mkfs import FilesystemNode
-from diskimage_builder.block_device.level3.mount import cmp_mount_order
 from diskimage_builder.block_device.level3.mount import MountPointNode
-from diskimage_builder.block_device.tests.test_base import TestBase
 
 logger = logging.getLogger(__name__)
 
 
-class TestMountComparator(TestBase):
-
-    def test_mount_comparator(self):
-        # This tests cmp_mount_order to ensure it sorts in the
-        # expected order.  The comparator takes a tuple of
-        # (mount_point, node_name) but we can ignore the name
-        partitions = [
-            ('/var/log', 'fake_log'),
-            ('/boot', 'fake_boot'),
-            ('/', 'fake_name'),
-            ('/var', 'fake_name')]
-        partitions.sort(key=functools.cmp_to_key(cmp_mount_order))
-
-        res = list(x[0] for x in partitions)
-
-        # "/" must be first
-        self.assertEqual(res[0], '/')
-
-        # /var before /var/log
-        var_pos = res.index('/var')
-        var_log_pos = res.index('/var/log')
-        self.assertGreater(var_log_pos, var_pos)
-
-
 class TestMountOrder(tc.TestGraphGeneration):
 
     def _exec_sudo_log(*args, **kwargs):