cc_mounts: check if mount -a on no-change fstab path

Under some circumstances, cc_disk_setup may reformat volumes which
already appear in /etc/fstab (e.g. Azure ephemeral drive is reformatted
from NTFS to ext4 after service-heal). Normally, cc_mounts only calls
mount -a if it altered /etc/fstab. With this change cc_mounts will read
/proc/mounts and verify if configured mounts are already mounted and if
not raise flag to request a mount -a.  This handles the case where no
changes to fstab occur but a mount -a is required due to change in
underlying device which prevented the .mount unit from running until
after disk was reformatted.

LP: #1825596

2 files changed, 40 insertions, 1 deletions

diff --git a/cloudinit/config/cc_mounts.py b/cloudinit/config/cc_mounts.py
index 339baba9..123ffb84 100644
--- a/cloudinit/config/cc_mounts.py
+++ b/cloudinit/config/cc_mounts.py
@@ -439,6 +439,7 @@ def handle(_name, cfg, cloud, log, _args):
 
     cc_lines = []
     needswap = False
+    need_mount_all = False
     dirs = []
     for line in actlist:
         # write 'comment' in the fs_mntops, entry,  claiming this
@@ -449,11 +450,18 @@ def handle(_name, cfg, cloud, log, _args):
             dirs.append(line[1])
         cc_lines.append('\t'.join(line))
 
+    mount_points = [v['mountpoint'] for k, v in util.mounts().items()
+                    if 'mountpoint' in v]
     for d in dirs:
         try:
             util.ensure_dir(d)
         except Exception:
             util.logexc(log, "Failed to make '%s' config-mount", d)
+        # dirs is list of directories on which a volume should be mounted.
+        # If any of them does not already show up in the list of current
+        # mount points, we will definitely need to do mount -a.
+        if not need_mount_all and d not in mount_points:
+            need_mount_all = True
 
     sadds = [WS.sub(" ", n) for n in cc_lines]
     sdrops = [WS.sub(" ", n) for n in fstab_removed]
@@ -473,6 +481,9 @@ def handle(_name, cfg, cloud, log, _args):
         log.debug("No changes to /etc/fstab made.")
     else:
         log.debug("Changes to fstab: %s", sops)
+        need_mount_all = True
+
+    if need_mount_all:
         activate_cmds.append(["mount", "-a"])
         if uses_systemd:
             activate_cmds.append(["systemctl", "daemon-reload"])
diff --git a/tests/unittests/test_handler/test_handler_mounts.py b/tests/unittests/test_handler/test_handler_mounts.py
index 8fea6c2a..0fb160be 100644
--- a/tests/unittests/test_handler/test_handler_mounts.py
+++ b/tests/unittests/test_handler/test_handler_mounts.py
@@ -154,7 +154,15 @@ class TestFstabHandling(test_helpers.FilesystemMockingTestCase):
                        return_value=True)
 
         self.add_patch('cloudinit.config.cc_mounts.util.subp',
-                       'mock_util_subp')
+                       'm_util_subp')
+
+        self.add_patch('cloudinit.config.cc_mounts.util.mounts',
+                       'mock_util_mounts',
+                       return_value={
+                           '/dev/sda1': {'fstype': 'ext4',
+                                         'mountpoint': '/',
+                                         'opts': 'rw,relatime,discard'
+                                         }})
 
         self.mock_cloud = mock.Mock()
         self.mock_log = mock.Mock()
@@ -230,4 +238,24 @@ class TestFstabHandling(test_helpers.FilesystemMockingTestCase):
             fstab_new_content = fd.read()
             self.assertEqual(fstab_expected_content, fstab_new_content)
 
+    def test_no_change_fstab_sets_needs_mount_all(self):
+        '''verify unchanged fstab entries are mounted if not call mount -a'''
+        fstab_original_content = (
+            'LABEL=cloudimg-rootfs / ext4 defaults 0 0\n'
+            'LABEL=UEFI /boot/efi vfat defaults 0 0\n'
+            '/dev/vdb /mnt auto defaults,noexec,comment=cloudconfig 0 2\n'
+        )
+        fstab_expected_content = fstab_original_content
+        cc = {'mounts': [
+                 ['/dev/vdb', '/mnt', 'auto', 'defaults,noexec']]}
+        with open(cc_mounts.FSTAB_PATH, 'w') as fd:
+            fd.write(fstab_original_content)
+        with open(cc_mounts.FSTAB_PATH, 'r') as fd:
+            fstab_new_content = fd.read()
+            self.assertEqual(fstab_expected_content, fstab_new_content)
+        cc_mounts.handle(None, cc, self.mock_cloud, self.mock_log, [])
+        self.m_util_subp.assert_has_calls([
+            mock.call(['mount', '-a']),
+            mock.call(['systemctl', 'daemon-reload'])])
+
 # vi: ts=4 expandtab