Only use gpart if it is the BSD gpart (#131)

Currently, cloud-init will happily try to run `gpart` on Linux even
though on most distributions this a different tool [1]. Extend the
availability check to make sure the `gpart` present is really the BSD
variant, to avoid accidental execution.

Also add a pointer to the docs, so that people do not try to install
gpart on Linux in the expectation it will work with this module.

[1] https://github.com/baruch/gpart

2 files changed, 44 insertions, 11 deletions

diff --git a/cloudinit/config/cc_growpart.py b/cloudinit/config/cc_growpart.py
index aa9716e7..1b512a06 100644
--- a/cloudinit/config/cc_growpart.py
+++ b/cloudinit/config/cc_growpart.py
@@ -22,11 +22,11 @@ mountpoint in the filesystem or a path to the block device in ``/dev``.
 
 The utility to use for resizing can be selected using the ``mode`` config key.
 If ``mode`` key is set to ``auto``, then any available utility (either
-``growpart`` or ``gpart``) will be used. If neither utility is available, no
-error will be raised. If ``mode`` is set to ``growpart``, then the ``growpart``
-utility will be used. If this utility is not available on the system, this will
-result in an error. If ``mode`` is set to ``off`` or ``false``, then
-``cc_growpart`` will take no action.
+``growpart`` or BSD ``gpart``) will be used. If neither utility is available,
+no error will be raised. If ``mode`` is set to ``growpart``, then the
+``growpart`` utility will be used. If this utility is not available on the
+system, this will result in an error. If ``mode`` is set to ``off`` or
+``false``, then ``cc_growpart`` will take no action.
 
 There is some functionality overlap between this module and the ``growroot``
 functionality of ``cloud-initramfs-tools``. However, there are some situations
@@ -132,7 +132,7 @@ class ResizeGrowPart(object):
 
         try:
             (out, _err) = util.subp(["growpart", "--help"], env=myenv)
-            if re.search(r"--update\s+", out, re.DOTALL):
+            if re.search(r"--update\s+", out):
                 return True
 
         except util.ProcessExecutionError:
@@ -161,9 +161,17 @@ class ResizeGrowPart(object):
 
 class ResizeGpart(object):
     def available(self):
-        if not util.which('gpart'):
-            return False
-        return True
+        myenv = os.environ.copy()
+        myenv['LANG'] = 'C'
+
+        try:
+            (_out, err) = util.subp(["gpart", "help"], env=myenv, rcs=[0, 1])
+            if re.search(r"gpart recover ", err):
+                return True
+
+        except util.ProcessExecutionError:
+            pass
+        return False
 
     def resize(self, diskdev, partnum, partdev):
         """
diff --git a/tests/unittests/test_handler/test_handler_growpart.py b/tests/unittests/test_handler/test_handler_growpart.py
index a3e46351..1f39ebe7 100644
--- a/tests/unittests/test_handler/test_handler_growpart.py
+++ b/tests/unittests/test_handler/test_handler_growpart.py
@@ -52,6 +52,18 @@ growpart disk partition
       Resize partition 1 on /dev/sda
 """
 
+HELP_GPART = """
+usage: gpart add -t type [-a alignment] [-b start] <SNIP> geom
+       gpart backup geom
+       gpart bootcode [-b bootcode] [-p partcode -i index] [-f flags] geom
+<SNIP>
+       gpart resize -i index [-a alignment] [-s size] [-f flags] geom
+       gpart restore [-lF] [-f flags] provider [...]
+       gpart recover [-f flags] geom
+       gpart help
+<SNIP>
+"""
+
 
 class TestDisabled(unittest.TestCase):
     def setUp(self):
@@ -97,8 +109,9 @@ class TestConfig(TestCase):
             self.handle(self.name, config, self.cloud_init, self.log,
                         self.args)
 
-            mockobj.assert_called_once_with(
-                ['growpart', '--help'], env={'LANG': 'C'})
+            mockobj.assert_has_calls([
+                mock.call(['growpart', '--help'], env={'LANG': 'C'}),
+                mock.call(['gpart', 'help'], env={'LANG': 'C'}, rcs=[0, 1])])
 
     @mock.patch.dict("os.environ", clear=True)
     def test_no_resizers_mode_growpart_is_exception(self):
@@ -124,6 +137,18 @@ class TestConfig(TestCase):
             mockobj.assert_called_once_with(
                 ['growpart', '--help'], env={'LANG': 'C'})
 
+    @mock.patch.dict("os.environ", clear=True)
+    def test_mode_auto_falls_back_to_gpart(self):
+        with mock.patch.object(
+                util, 'subp',
+                return_value=("", HELP_GPART)) as mockobj:
+            ret = cc_growpart.resizer_factory(mode="auto")
+            self.assertIsInstance(ret, cc_growpart.ResizeGpart)
+
+            mockobj.assert_has_calls([
+                mock.call(['growpart', '--help'], env={'LANG': 'C'}),
+                mock.call(['gpart', 'help'], env={'LANG': 'C'}, rcs=[0, 1])])
+
     def test_handle_with_no_growpart_entry(self):
         # if no 'growpart' entry in config, then mode=auto should be used