resizefs: Fix regression when system booted with root=PARTUUID=

A recent cleanup of the resizefs module broke resizing when a system was
booted with root=PARTUUID=<uuid> and the device /dev/root does not exist.
This path is exposed with the Ubuntu 16.04 but not with Ubuntu 17.10. A
recreate exists under bug 1684869.

LP: #1725067

2 files changed, 70 insertions, 64 deletions

diff --git a/cloudinit/config/cc_resizefs.py b/cloudinit/config/cc_resizefs.py
index f774baa3..0d282e63 100644
--- a/cloudinit/config/cc_resizefs.py
+++ b/cloudinit/config/cc_resizefs.py
@@ -145,25 +145,6 @@ RESIZE_FS_PRECHECK_CMDS = {
 }
 
 
-def rootdev_from_cmdline(cmdline):
-    found = None
-    for tok in cmdline.split():
-        if tok.startswith("root="):
-            found = tok[5:]
-            break
-    if found is None:
-        return None
-
-    if found.startswith("/dev/"):
-        return found
-    if found.startswith("LABEL="):
-        return "/dev/disk/by-label/" + found[len("LABEL="):]
-    if found.startswith("UUID="):
-        return "/dev/disk/by-uuid/" + found[len("UUID="):]
-
-    return "/dev/" + found
-
-
 def can_skip_resize(fs_type, resize_what, devpth):
     fstype_lc = fs_type.lower()
     for i, func in RESIZE_FS_PRECHECK_CMDS.items():
@@ -172,14 +153,15 @@ def can_skip_resize(fs_type, resize_what, devpth):
     return False
 
 
-def is_device_path_writable_block(devpath, info, log):
-    """Return True if devpath is a writable block device.
+def maybe_get_writable_device_path(devpath, info, log):
+    """Return updated devpath if the devpath is a writable block device.
 
-    @param devpath: Path to the root device we want to resize.
+    @param devpath: Requested path to the root device we want to resize.
     @param info: String representing information about the requested device.
     @param log: Logger to which logs will be added upon error.
 
-    @returns Boolean True if block device is writable
+    @returns devpath or updated devpath per kernel commandline if the device
+        path is a writable block device, returns None otherwise.
     """
     container = util.is_container()
 
@@ -189,12 +171,12 @@ def is_device_path_writable_block(devpath, info, log):
         devpath = util.rootdev_from_cmdline(util.get_cmdline())
         if devpath is None:
             log.warn("Unable to find device '/dev/root'")
-            return False
+            return None
         log.debug("Converted /dev/root to '%s' per kernel cmdline", devpath)
 
     if devpath == 'overlayroot':
         log.debug("Not attempting to resize devpath '%s': %s", devpath, info)
-        return False
+        return None
 
     try:
         statret = os.stat(devpath)
@@ -207,7 +189,7 @@ def is_device_path_writable_block(devpath, info, log):
                      devpath, info)
         else:
             raise exc
-        return False
+        return None
 
     if not stat.S_ISBLK(statret.st_mode) and not stat.S_ISCHR(statret.st_mode):
         if container:
@@ -216,8 +198,8 @@ def is_device_path_writable_block(devpath, info, log):
         else:
             log.warn("device '%s' not a block device. cannot resize: %s" %
                      (devpath, info))
-        return False
-    return True
+        return None
+    return devpath  # The writable block devpath
 
 
 def handle(name, cfg, _cloud, log, args):
@@ -242,8 +224,9 @@ def handle(name, cfg, _cloud, log, args):
     info = "dev=%s mnt_point=%s path=%s" % (devpth, mount_point, resize_what)
     log.debug("resize_info: %s" % info)
 
-    if not is_device_path_writable_block(devpth, info, log):
-        return
+    devpth = maybe_get_writable_device_path(devpth, info, log)
+    if not devpth:
+        return  # devpath was not a writable block device
 
     resizer = None
     if can_skip_resize(fs_type, resize_what, devpth):
diff --git a/tests/unittests/test_handler/test_handler_resizefs.py b/tests/unittests/test_handler/test_handler_resizefs.py
index 3e5d436c..29d5574d 100644
--- a/tests/unittests/test_handler/test_handler_resizefs.py
+++ b/tests/unittests/test_handler/test_handler_resizefs.py
@@ -1,9 +1,9 @@
 # This file is part of cloud-init. See LICENSE file for license information.
 
 from cloudinit.config.cc_resizefs import (
-    can_skip_resize, handle, is_device_path_writable_block,
-    rootdev_from_cmdline)
+    can_skip_resize, handle, maybe_get_writable_device_path)
 
+from collections import namedtuple
 import logging
 import textwrap
 
@@ -138,47 +138,48 @@ class TestRootDevFromCmdline(CiTestCase):
         invalid_cases = [
             'BOOT_IMAGE=/adsf asdfa werasef  root adf', 'BOOT_IMAGE=/adsf', '']
         for case in invalid_cases:
-            self.assertIsNone(rootdev_from_cmdline(case))
+            self.assertIsNone(util.rootdev_from_cmdline(case))
 
     def test_rootdev_from_cmdline_with_root_startswith_dev(self):
         """Return the cmdline root when the path starts with /dev."""
         self.assertEqual(
-            '/dev/this', rootdev_from_cmdline('asdf root=/dev/this'))
+            '/dev/this', util.rootdev_from_cmdline('asdf root=/dev/this'))
 
     def test_rootdev_from_cmdline_with_root_without_dev_prefix(self):
         """Add /dev prefix to cmdline root when the path lacks the prefix."""
-        self.assertEqual('/dev/this', rootdev_from_cmdline('asdf root=this'))
+        self.assertEqual(
+            '/dev/this', util.rootdev_from_cmdline('asdf root=this'))
 
     def test_rootdev_from_cmdline_with_root_with_label(self):
         """When cmdline root contains a LABEL, our root is disk/by-label."""
         self.assertEqual(
             '/dev/disk/by-label/unique',
-            rootdev_from_cmdline('asdf root=LABEL=unique'))
+            util.rootdev_from_cmdline('asdf root=LABEL=unique'))
 
     def test_rootdev_from_cmdline_with_root_with_uuid(self):
         """When cmdline root contains a UUID, our root is disk/by-uuid."""
         self.assertEqual(
             '/dev/disk/by-uuid/adsfdsaf-adsf',
-            rootdev_from_cmdline('asdf root=UUID=adsfdsaf-adsf'))
+            util.rootdev_from_cmdline('asdf root=UUID=adsfdsaf-adsf'))
 
 
-class TestIsDevicePathWritableBlock(CiTestCase):
+class TestMaybeGetDevicePathAsWritableBlock(CiTestCase):
 
     with_logs = True
 
-    def test_is_device_path_writable_block_false_on_overlayroot(self):
+    def test_maybe_get_writable_device_path_none_on_overlayroot(self):
         """When devpath is overlayroot (on MAAS), is_dev_writable is False."""
         info = 'does not matter'
-        is_writable = wrap_and_call(
+        devpath = wrap_and_call(
             'cloudinit.config.cc_resizefs.util',
             {'is_container': {'return_value': False}},
-            is_device_path_writable_block, 'overlayroot', info, LOG)
-        self.assertFalse(is_writable)
+            maybe_get_writable_device_path, 'overlayroot', info, LOG)
+        self.assertIsNone(devpath)
         self.assertIn(
             "Not attempting to resize devpath 'overlayroot'",
             self.logs.getvalue())
 
-    def test_is_device_path_writable_block_warns_missing_cmdline_root(self):
+    def test_maybe_get_writable_device_path_warns_missing_cmdline_root(self):
         """When root does not exist isn't in the cmdline, log warning."""
         info = 'does not matter'
 
@@ -190,43 +191,43 @@ class TestIsDevicePathWritableBlock(CiTestCase):
         exists_mock_path = 'cloudinit.config.cc_resizefs.os.path.exists'
         with mock.patch(exists_mock_path) as m_exists:
             m_exists.return_value = False
-            is_writable = wrap_and_call(
+            devpath = wrap_and_call(
                 'cloudinit.config.cc_resizefs.util',
                 {'is_container': {'return_value': False},
                  'get_mount_info': {'side_effect': fake_mount_info},
                  'get_cmdline': {'return_value': 'BOOT_IMAGE=/vmlinuz.efi'}},
-                is_device_path_writable_block, '/dev/root', info, LOG)
-        self.assertFalse(is_writable)
+                maybe_get_writable_device_path, '/dev/root', info, LOG)
+        self.assertIsNone(devpath)
         logs = self.logs.getvalue()
         self.assertIn("WARNING: Unable to find device '/dev/root'", logs)
 
-    def test_is_device_path_writable_block_does_not_exist(self):
+    def test_maybe_get_writable_device_path_does_not_exist(self):
         """When devpath does not exist, a warning is logged."""
         info = 'dev=/I/dont/exist mnt_point=/ path=/dev/none'
-        is_writable = wrap_and_call(
+        devpath = wrap_and_call(
             'cloudinit.config.cc_resizefs.util',
             {'is_container': {'return_value': False}},
-            is_device_path_writable_block, '/I/dont/exist', info, LOG)
-        self.assertFalse(is_writable)
+            maybe_get_writable_device_path, '/I/dont/exist', info, LOG)
+        self.assertIsNone(devpath)
         self.assertIn(
             "WARNING: Device '/I/dont/exist' did not exist."
             ' cannot resize: %s' % info,
             self.logs.getvalue())
 
-    def test_is_device_path_writable_block_does_not_exist_in_container(self):
+    def test_maybe_get_writable_device_path_does_not_exist_in_container(self):
         """When devpath does not exist in a container, log a debug message."""
         info = 'dev=/I/dont/exist mnt_point=/ path=/dev/none'
-        is_writable = wrap_and_call(
+        devpath = wrap_and_call(
             'cloudinit.config.cc_resizefs.util',
             {'is_container': {'return_value': True}},
-            is_device_path_writable_block, '/I/dont/exist', info, LOG)
-        self.assertFalse(is_writable)
+            maybe_get_writable_device_path, '/I/dont/exist', info, LOG)
+        self.assertIsNone(devpath)
         self.assertIn(
             "DEBUG: Device '/I/dont/exist' did not exist in container."
             ' cannot resize: %s' % info,
             self.logs.getvalue())
 
-    def test_is_device_path_writable_block_raises_oserror(self):
+    def test_maybe_get_writable_device_path_raises_oserror(self):
         """When unexpected OSError is raises by os.stat it is reraised."""
         info = 'dev=/I/dont/exist mnt_point=/ path=/dev/none'
         with self.assertRaises(OSError) as context_manager:
@@ -234,41 +235,63 @@ class TestIsDevicePathWritableBlock(CiTestCase):
                 'cloudinit.config.cc_resizefs',
                 {'util.is_container': {'return_value': True},
                  'os.stat': {'side_effect': OSError('Something unexpected')}},
-                is_device_path_writable_block, '/I/dont/exist', info, LOG)
+                maybe_get_writable_device_path, '/I/dont/exist', info, LOG)
         self.assertEqual(
             'Something unexpected', str(context_manager.exception))
 
-    def test_is_device_path_writable_block_non_block(self):
+    def test_maybe_get_writable_device_path_non_block(self):
         """When device is not a block device, emit warning return False."""
         fake_devpath = self.tmp_path('dev/readwrite')
         util.write_file(fake_devpath, '', mode=0o600)  # read-write
         info = 'dev=/dev/root mnt_point=/ path={0}'.format(fake_devpath)
 
-        is_writable = wrap_and_call(
+        devpath = wrap_and_call(
             'cloudinit.config.cc_resizefs.util',
             {'is_container': {'return_value': False}},
-            is_device_path_writable_block, fake_devpath, info, LOG)
-        self.assertFalse(is_writable)
+            maybe_get_writable_device_path, fake_devpath, info, LOG)
+        self.assertIsNone(devpath)
         self.assertIn(
             "WARNING: device '{0}' not a block device. cannot resize".format(
                 fake_devpath),
             self.logs.getvalue())
 
-    def test_is_device_path_writable_block_non_block_on_container(self):
+    def test_maybe_get_writable_device_path_non_block_on_container(self):
         """When device is non-block device in container, emit debug log."""
         fake_devpath = self.tmp_path('dev/readwrite')
         util.write_file(fake_devpath, '', mode=0o600)  # read-write
         info = 'dev=/dev/root mnt_point=/ path={0}'.format(fake_devpath)
 
-        is_writable = wrap_and_call(
+        devpath = wrap_and_call(
             'cloudinit.config.cc_resizefs.util',
             {'is_container': {'return_value': True}},
-            is_device_path_writable_block, fake_devpath, info, LOG)
-        self.assertFalse(is_writable)
+            maybe_get_writable_device_path, fake_devpath, info, LOG)
+        self.assertIsNone(devpath)
         self.assertIn(
             "DEBUG: device '{0}' not a block device in container."
             ' cannot resize'.format(fake_devpath),
             self.logs.getvalue())
 
+    def test_maybe_get_writable_device_path_returns_cmdline_root(self):
+        """When root device is UUID in kernel commandline, update devpath."""
+        # XXX Long-term we want to use FilesystemMocking test to avoid
+        # touching os.stat.
+        FakeStat = namedtuple(
+            'FakeStat', ['st_mode', 'st_size', 'st_mtime'])  # minimal def.
+        info = 'dev=/dev/root mnt_point=/ path=/does/not/matter'
+        devpath = wrap_and_call(
+            'cloudinit.config.cc_resizefs',
+            {'util.get_cmdline': {'return_value': 'asdf root=UUID=my-uuid'},
+             'util.is_container': False,
+             'os.path.exists': False,  # /dev/root doesn't exist
+             'os.stat': {
+                 'return_value': FakeStat(25008, 0, 1)}  # char block device
+             },
+            maybe_get_writable_device_path, '/dev/root', info, LOG)
+        self.assertEqual('/dev/disk/by-uuid/my-uuid', devpath)
+        self.assertIn(
+            "DEBUG: Converted /dev/root to '/dev/disk/by-uuid/my-uuid'"
+            " per kernel cmdline",
+            self.logs.getvalue())
+
 
 # vi: ts=4 expandtab