Detect kernel version before swap file creation

cloudinit/config/cc_mounts.py

@@ -65,7 +65,7 @@
 from string import whitespace
 
 import logging
-import os.path
+import os
 import re
 
 from cloudinit import type_utils
@@ -263,7 +263,8 @@ def create_swap(fname, size, method):
 
     fstype = util.get_mount_info(swap_dir)[1]
 
-    if fstype in ("xfs", "btrfs"):
+    if (fstype == "xfs" and
+            util.kernel_version() < (4, 18)) or fstype == "btrfs":
         create_swap(fname, size, "dd")
     else:
         try:

cloudinit/util.py

@@ -68,6 +68,11 @@
                    ['lxc-is-container'])
 
 
+@lru_cache()
+def kernel_version():
+    return tuple(map(int, os.uname().release.split('.')[:2]))
+
+
 @lru_cache()
 def get_dpkg_architecture(target=None):
     """Return the sanitized string output by `dpkg --print-architecture`.

tests/unittests/test_handler/test_handler_mounts.py

@@ -7,6 +7,8 @@
 
 from cloudinit.tests import helpers as test_helpers
 
+from cloudinit import util
+
 
 class TestSanitizeDevname(test_helpers.FilesystemMockingTestCase):
 
@@ -183,6 +185,56 @@ def device_name_to_device(self, path):
 
         return dev
 
+    @mock.patch('cloudinit.util.kernel_version')
+    @mock.patch('cloudinit.util.get_mount_info')
+    def test_swap_creation_method(self, m_kernel_version, m_get_mount_info):
+        log = mock.MagicMock()
+        m_kernel_version.return_value = (3, 18)
+        m_get_mount_info.return_value = ["", "xfs"]
+        fstab = '/swap.img swap swap defaults 0 0\n'
+
+        with open(cc_mounts.FSTAB_PATH, 'w') as fd:
+            fd.write(fstab)
+        cc = {'swap': ['filename: /swap.img', 'size: 512', 'maxsize: 512']}
+        cc_mounts.handle(None, cc, self.mock_cloud, self.mock_log, [])
+
+        swap_log = 'Creating swapfile in /swap.img on fstype xfs using dd'
+        util.multi_log('{0}\n'.format(swap_log), log=log)
+        self.assertEqual((mock.ANY, swap_log), log.log.call_args[0])
+
+        m_kernel_version.reset_mock()
+        m_get_mount_info.reset_mock()
+
+        m_kernel_version.return_value = (4, 20)
+        m_get_mount_info.return_value = ["", "btrfs"]
+        fstab = '/swap2.img swap swap defaults 0 0\n'
+
+        with open(cc_mounts.FSTAB_PATH, 'w') as fd:
+            fd.write(fstab)
+        cc = {'swap': ['filename: /swap2.img', 'size: 512', 'maxsize: 512']}
+        cc_mounts.handle(None, cc, self.mock_cloud, self.mock_log, [])
+
+        swap_log = 'Creating swapfile in /swap.img on fstype btrfs using dd'
+        util.multi_log('{0}\n'.format(swap_log), log=log)
+        self.assertEqual((mock.ANY, swap_log), log.log.call_args[0])
+
+        m_kernel_version.reset_mock()
+        m_get_mount_info.reset_mock()
+
+        m_kernel_version.return_value = (4, 20)
+        m_get_mount_info.return_value = ["", "ext4"]
+        fstab = '/swap3.img swap swap defaults 0 0\n'
+
+        with open(cc_mounts.FSTAB_PATH, 'w') as fd:
+            fd.write(fstab)
+        cc = {'swap': ['filename: /swap3.img', 'size: 512', 'maxsize: 512']}
+        cc_mounts.handle(None, cc, self.mock_cloud, self.mock_log, [])
+
+        swap_log = 'Creating swapfile in /swap.img on fstype btrfs using' \
+                   ' fallocate'
+        util.multi_log('{0}\n'.format(swap_log), log=log)
+        self.assertEqual((mock.ANY, swap_log), log.log.call_args[0])
+
     def test_swap_integrity(self):
         '''Ensure that the swap file is correctly created and can
         swapon successfully. Fixing the corner case of:

tests/unittests/test_util.py

@@ -956,6 +956,12 @@ def test_get_proc_ppid(self):
         self.assertEqual(my_ppid, util.get_proc_ppid(my_pid))
 
 
+@mock.patch('os.uname')
+def test_kernel_version(m_uname):
+    m_uname().release = '5.6.19-300.fc32.x86_64'
+    assert util.kernel_version() == (5, 6)
+
+
 @mock.patch('cloudinit.subp.subp')
 def test_find_devs_with_openbsd(m_subp):
     m_subp.return_value = (