Fix detection of already initialised lxc storage pool

The related bug was caused because the charm did not detect when
the lxc storage had already been set up using the `lxc storage`
command which is used in the 3.x series, rather than the old way
with the 2.x series.

Also fixes issue on xenial where linux-image-extra-* has been renamed to
linux-modules-extra-* from from -4.4.0-145-generic onwards.  Otherwise,
the install fails on xenial.

Change-Id: If8bdad6f5641ee21fc7860dceeb4c3facbaecc76
Closes-Bug: #1825393

hooks/lxd_utils.py

@@ -188,8 +188,12 @@ def get_block_devices():
 
 def configure_lxd_block():
     '''Configure a block device for use by LXD for containers'''
-    log('Configuring LXD container storage')
-    if filesystem_mounted('/var/lib/lxd'):
+    log('Configuring LXD container storage if not configured')
+    # determine if the lxd block has already been configured
+    if has_storage(LXD_POOL):
+        log("LXD storage pool {} already configured".format(LXD_POOL))
+        return
+    elif filesystem_mounted('/var/lib/lxd'):
         log('/var/lib/lxd already configured, skipping')
         return
 
@@ -308,9 +312,20 @@ def config_zfs(dev):
     check_call(cmd)
 
 
-def has_storage():
+def has_storage(search_for_pool=None):
     try:
-        check_call(['lxc', 'storage', 'list'])
+        pools = (check_output(['lxc', 'storage', 'list'])
+                 .decode('utf-8')
+                 .splitlines())
+        if search_for_pool is not None:
+            for pool in pools:
+                try:
+                    name = pool.split(' ')[1]
+                    if search_for_pool == name:
+                        return True
+                except IndexError:
+                    pass
+            return False
         return True
     except subprocess.CalledProcessError:
         return False
@@ -476,8 +491,12 @@ def configure_lxd_host():
 
             # Configure live migration
             if cmp_ubuntu_release == 'xenial':
-                apt_install('linux-image-extra-%s' % os.uname()[2],
-                            fatal=True)
+                uname = os.uname()[2]
+                if uname > '4.4.0-122-generic':
+                    pkg = "linux-modules-extra-{}"
+                else:
+                    pkg = "linux-image-extra-{}"
+                apt_install(pkg.format(uname), fatal=True)
 
             if cmp_ubuntu_release >= 'xenial':
                 modprobe('netlink_diag')

tox.ini

@@ -87,5 +87,5 @@ commands =
     bundletester -vl DEBUG -r json -o func-results.json --test-pattern "dev-*" --no-destroy
 
 [flake8]
-ignore = E402,E226
+ignore = E402,E226,W504
 exclude = */charmhelpers

unit_tests/test_lxd_utils.py

@@ -14,6 +14,7 @@
 
 """Tests for hooks.lxd_utils."""
 import mock
+import textwrap
 
 import lxd_utils
 import testing
@@ -238,3 +239,52 @@ class TestConfigureUIDGID(testing.CharmTestCase):
                 mock.call('ubuntu:165536:65536\n')
             ])
         self.service_restart.assert_called_with('lxd')
+
+
+class MyProcessError(Exception):
+    pass
+
+
+class TestHasStorage(testing.CharmTestCase):
+    """Tests for hooks.lxd_utils.has_storage"""
+
+    TO_PATCH = [
+        'check_output',
+    ]
+
+    def setUp(self):
+        super(TestHasStorage, self).setUp(lxd_utils, self.TO_PATCH)
+
+    def test_has_storage_default(self):
+        self.check_output.return_value = b""
+        self.assertTrue(lxd_utils.has_storage())
+
+    @mock.patch('subprocess.CalledProcessError', new=MyProcessError)
+    def test_has_storage_default_error(self):
+        def raise_error(*args, **kwargs):
+            raise MyProcessError()
+
+        self.check_output.side_effect = raise_error
+        self.assertFalse(lxd_utils.has_storage())
+
+    def test_has_storage_by_pool(self):
+        self.check_output.return_value = textwrap.dedent(
+            b"""
+            +---------+-------------+--------+--------------------------------+---------+
+            |  NAME   | DESCRIPTION | DRIVER |             SOURCE             | USED BY |
+            +---------+-------------+--------+--------------------------------+---------+
+            | default |             | btrfs  | /var/lib/lxd/disks/default.img | 1       |
+            +---------+-------------+--------+--------------------------------+---------+
+            """)  # NOQA W501
+        self.assertTrue(lxd_utils.has_storage('default'))
+
+    def test_has_storage_missing_pool(self):
+        self.check_output.return_value = textwrap.dedent(
+            b"""
+            +---------+-------------+--------+--------------------------------+---------+
+            |  NAME   | DESCRIPTION | DRIVER |             SOURCE             | USED BY |
+            +---------+-------------+--------+--------------------------------+---------+
+            | default |             | btrfs  | /var/lib/lxd/disks/default.img | 1       |
+            +---------+-------------+--------+--------------------------------+---------+
+            """)  # NOQA W501
+        self.assertFalse(lxd_utils.has_storage('btrfs'))