Azure: mount default provisioning iso before try device listing (#870)

With a few exceptions, Azure VM deployments receive provisioning
metadata through the provisioning iso presented as a cdrom device
(/dev/sr0). The existing code attempts to find this device by calling
blkid to find all devices that have either type iso9660 or udf. This
can be very expensive if the VM has a lot of disks. This commit will
attempt to mount the default iso location first and only tries to use
blkid to locate the iso location if the default mounting location fails

2 files changed, 160 insertions, 138 deletions

diff --git a/cloudinit/sources/DataSourceAzure.py b/cloudinit/sources/DataSourceAzure.py
index dcdf9f8f..2e7bfbe3 100755
--- a/cloudinit/sources/DataSourceAzure.py
+++ b/cloudinit/sources/DataSourceAzure.py
@@ -76,7 +76,7 @@ REPROVISION_NIC_ATTACH_MARKER_FILE = "/var/lib/cloud/data/wait_for_nic_attach"
 REPROVISION_NIC_DETACHED_MARKER_FILE = "/var/lib/cloud/data/nic_detached"
 REPORTED_READY_MARKER_FILE = "/var/lib/cloud/data/reported_ready"
 AGENT_SEED_DIR = '/var/lib/waagent'
-
+DEFAULT_PROVISIONING_ISO_DEV = '/dev/sr0'
 
 # In the event where the IMDS primary server is not
 # available, it takes 1s to fallback to the secondary one
@@ -428,148 +428,142 @@ class DataSourceAzure(sources.DataSource):
         # it determines the value of ret. More specifically, the first one in
         # the candidate list determines the path to take in order to get the
         # metadata we need.
-        candidates = [self.seed_dir]
+        reprovision = False
+        ovf_is_accessible = True
+        reprovision_after_nic_attach = False
+        metadata_source = None
+        ret = None
         if os.path.isfile(REPROVISION_MARKER_FILE):
-            candidates.insert(0, "IMDS")
+            reprovision = True
+            metadata_source = "IMDS"
             report_diagnostic_event("Reprovision marker file already present "
                                     "before crawling Azure metadata: %s" %
                                     REPROVISION_MARKER_FILE,
                                     logger_func=LOG.debug)
         elif os.path.isfile(REPROVISION_NIC_ATTACH_MARKER_FILE):
-            candidates.insert(0, "NIC_ATTACH_MARKER_PRESENT")
+            reprovision_after_nic_attach = True
+            metadata_source = "NIC_ATTACH_MARKER_PRESENT"
             report_diagnostic_event("Reprovision nic attach marker file "
                                     "already present before crawling Azure "
                                     "metadata: %s" %
                                     REPROVISION_NIC_ATTACH_MARKER_FILE,
                                     logger_func=LOG.debug)
-        candidates.extend(list_possible_azure_ds_devs())
-        if ddir:
-            candidates.append(ddir)
-
-        found = None
-        reprovision = False
-        ovf_is_accessible = True
-        reprovision_after_nic_attach = False
-        for cdev in candidates:
-            try:
-                LOG.debug("cdev: %s", cdev)
-                if cdev == "IMDS":
-                    ret = None
-                    reprovision = True
-                elif cdev == "NIC_ATTACH_MARKER_PRESENT":
-                    ret = None
-                    reprovision_after_nic_attach = True
-                elif cdev.startswith("/dev/"):
-                    if util.is_FreeBSD():
-                        ret = util.mount_cb(cdev, load_azure_ds_dir,
-                                            mtype="udf")
+        else:
+            for src in list_possible_azure_ds(self.seed_dir, ddir):
+                try:
+                    if src.startswith("/dev/"):
+                        if util.is_FreeBSD():
+                            ret = util.mount_cb(src, load_azure_ds_dir,
+                                                mtype="udf")
+                        else:
+                            ret = util.mount_cb(src, load_azure_ds_dir)
+                        # save the device for ejection later
+                        self.iso_dev = src
+                        ovf_is_accessible = True
                     else:
-                        ret = util.mount_cb(cdev, load_azure_ds_dir)
-                else:
-                    ret = load_azure_ds_dir(cdev)
-
-            except NonAzureDataSource:
-                report_diagnostic_event(
-                    "Did not find Azure data source in %s" % cdev,
-                    logger_func=LOG.debug)
-                continue
-            except BrokenAzureDataSource as exc:
-                msg = 'BrokenAzureDataSource: %s' % exc
-                report_diagnostic_event(msg, logger_func=LOG.error)
-                raise sources.InvalidMetaDataException(msg)
-            except util.MountFailedError:
-                report_diagnostic_event(
-                    '%s was not mountable' % cdev, logger_func=LOG.debug)
-                cdev = 'IMDS'
-                ovf_is_accessible = False
-                empty_md = {'local-hostname': ''}
-                empty_cfg = dict(
-                    system_info=dict(
-                        default_user=dict(
-                            name=''
+                        ret = load_azure_ds_dir(src)
+                    metadata_source = src
+                    break
+                except NonAzureDataSource:
+                    report_diagnostic_event(
+                        "Did not find Azure data source in %s" % src,
+                        logger_func=LOG.debug)
+                    continue
+                except util.MountFailedError:
+                    report_diagnostic_event(
+                        '%s was not mountable' % src,
+                        logger_func=LOG.debug)
+                    ovf_is_accessible = False
+                    empty_md = {'local-hostname': ''}
+                    empty_cfg = dict(
+                        system_info=dict(
+                            default_user=dict(
+                                name=''
+                            )
                         )
                     )
-                )
-                ret = (empty_md, '', empty_cfg, {})
-
-            report_diagnostic_event("Found provisioning metadata in %s" % cdev,
-                                    logger_func=LOG.debug)
-
-            # save the iso device for ejection before reporting ready
-            if cdev.startswith("/dev"):
-                self.iso_dev = cdev
-
-            perform_reprovision = reprovision or self._should_reprovision(ret)
-            perform_reprovision_after_nic_attach = (
-                reprovision_after_nic_attach or
-                self._should_reprovision_after_nic_attach(ret))
-
-            if perform_reprovision or perform_reprovision_after_nic_attach:
-                if util.is_FreeBSD():
-                    msg = "Free BSD is not supported for PPS VMs"
+                    ret = (empty_md, '', empty_cfg, {})
+                    metadata_source = 'IMDS'
+                    continue
+                except BrokenAzureDataSource as exc:
+                    msg = 'BrokenAzureDataSource: %s' % exc
                     report_diagnostic_event(msg, logger_func=LOG.error)
                     raise sources.InvalidMetaDataException(msg)
-                if perform_reprovision_after_nic_attach:
-                    self._wait_for_all_nics_ready()
-                ret = self._reprovision()
 
-            imds_md = self.get_imds_data_with_api_fallback(
-                self.fallback_interface,
-                retries=10
-            )
-            if not imds_md and not ovf_is_accessible:
-                msg = 'No OVF or IMDS available'
-                report_diagnostic_event(msg)
+        report_diagnostic_event(
+            "Found provisioning metadata in %s" % metadata_source,
+            logger_func=LOG.debug)
+
+        perform_reprovision = reprovision or self._should_reprovision(ret)
+        perform_reprovision_after_nic_attach = (
+            reprovision_after_nic_attach or
+            self._should_reprovision_after_nic_attach(ret))
+
+        if perform_reprovision or perform_reprovision_after_nic_attach:
+            if util.is_FreeBSD():
+                msg = "Free BSD is not supported for PPS VMs"
+                report_diagnostic_event(msg, logger_func=LOG.error)
                 raise sources.InvalidMetaDataException(msg)
-            (md, userdata_raw, cfg, files) = ret
-            self.seed = cdev
-            crawled_data.update({
-                'cfg': cfg,
-                'files': files,
-                'metadata': util.mergemanydict(
-                    [md, {'imds': imds_md}]),
-                'userdata_raw': userdata_raw})
-            imds_username = _username_from_imds(imds_md)
-            imds_hostname = _hostname_from_imds(imds_md)
-            imds_disable_password = _disable_password_from_imds(imds_md)
-            if imds_username:
-                LOG.debug('Username retrieved from IMDS: %s', imds_username)
-                cfg['system_info']['default_user']['name'] = imds_username
-            if imds_hostname:
-                LOG.debug('Hostname retrieved from IMDS: %s', imds_hostname)
-                crawled_data['metadata']['local-hostname'] = imds_hostname
-            if imds_disable_password:
-                LOG.debug(
-                    'Disable password retrieved from IMDS: %s',
-                    imds_disable_password
-                )
-                crawled_data['metadata']['disable_password'] = imds_disable_password  # noqa: E501
-
-            # only use userdata from imds if OVF did not provide custom data
-            # userdata provided by IMDS is always base64 encoded
-            if not userdata_raw:
-                imds_userdata = _userdata_from_imds(imds_md)
-                if imds_userdata:
-                    LOG.debug("Retrieved userdata from IMDS")
-                    try:
-                        crawled_data['userdata_raw'] = base64.b64decode(
-                            ''.join(imds_userdata.split()))
-                    except Exception:
-                        report_diagnostic_event(
-                            "Bad userdata in IMDS",
-                            logger_func=LOG.warning)
-            found = cdev
+            if perform_reprovision_after_nic_attach:
+                self._wait_for_all_nics_ready()
+            ret = self._reprovision()
 
-            report_diagnostic_event(
-                'found datasource in %s' % cdev, logger_func=LOG.debug)
-            break
+        imds_md = self.get_imds_data_with_api_fallback(
+            self.fallback_interface,
+            retries=10
+        )
+        if not imds_md and not ovf_is_accessible:
+            msg = 'No OVF or IMDS available'
+            report_diagnostic_event(msg)
+            raise sources.InvalidMetaDataException(msg)
+        (md, userdata_raw, cfg, files) = ret
+        self.seed = metadata_source
+        crawled_data.update({
+            'cfg': cfg,
+            'files': files,
+            'metadata': util.mergemanydict(
+                [md, {'imds': imds_md}]),
+            'userdata_raw': userdata_raw})
+        imds_username = _username_from_imds(imds_md)
+        imds_hostname = _hostname_from_imds(imds_md)
+        imds_disable_password = _disable_password_from_imds(imds_md)
+        if imds_username:
+            LOG.debug('Username retrieved from IMDS: %s', imds_username)
+            cfg['system_info']['default_user']['name'] = imds_username
+        if imds_hostname:
+            LOG.debug('Hostname retrieved from IMDS: %s', imds_hostname)
+            crawled_data['metadata']['local-hostname'] = imds_hostname
+        if imds_disable_password:
+            LOG.debug(
+                'Disable password retrieved from IMDS: %s',
+                imds_disable_password
+            )
+            crawled_data['metadata']['disable_password'] = imds_disable_password  # noqa: E501
+
+        # only use userdata from imds if OVF did not provide custom data
+        # userdata provided by IMDS is always base64 encoded
+        if not userdata_raw:
+            imds_userdata = _userdata_from_imds(imds_md)
+            if imds_userdata:
+                LOG.debug("Retrieved userdata from IMDS")
+                try:
+                    crawled_data['userdata_raw'] = base64.b64decode(
+                        ''.join(imds_userdata.split()))
+                except Exception:
+                    report_diagnostic_event(
+                        "Bad userdata in IMDS",
+                        logger_func=LOG.warning)
 
-        if not found:
+        if not metadata_source:
             msg = 'No Azure metadata found'
             report_diagnostic_event(msg, logger_func=LOG.error)
             raise sources.InvalidMetaDataException(msg)
+        else:
+            report_diagnostic_event(
+                'found datasource in %s' % metadata_source,
+                logger_func=LOG.debug)
 
-        if found == ddir:
+        if metadata_source == ddir:
             report_diagnostic_event(
                 "using files cached in %s" % ddir, logger_func=LOG.debug)
 
@@ -2084,18 +2078,18 @@ def _get_random_seed(source=PLATFORM_ENTROPY_SOURCE):
 
 
 @azure_ds_telemetry_reporter
-def list_possible_azure_ds_devs():
-    devlist = []
+def list_possible_azure_ds(seed, cache_dir):
+    yield seed
+    yield DEFAULT_PROVISIONING_ISO_DEV
     if util.is_FreeBSD():
         cdrom_dev = "/dev/cd0"
         if _check_freebsd_cdrom(cdrom_dev):
-            return [cdrom_dev]
+            yield cdrom_dev
     else:
         for fstype in ("iso9660", "udf"):
-            devlist.extend(util.find_devs_with("TYPE=%s" % fstype))
-
-    devlist.sort(reverse=True)
-    return devlist
+            yield from util.find_devs_with("TYPE=%s" % fstype)
+    if cache_dir:
+        yield cache_dir
 
 
 @azure_ds_telemetry_reporter
diff --git a/tests/unittests/test_datasource/test_azure.py b/tests/unittests/test_datasource/test_azure.py
index 54e06119..3bf8fdb2 100644
--- a/tests/unittests/test_datasource/test_azure.py
+++ b/tests/unittests/test_datasource/test_azure.py
@@ -635,15 +635,20 @@ scbus-1 on xpt0 bus 0
     def _get_ds(self, data, agent_command=None, distro='ubuntu',
                 apply_network=None, instance_id=None):
 
-        def dsdevs():
-            return data.get('dsdevs', [])
-
         def _wait_for_files(flist, _maxwait=None, _naplen=None):
             data['waited'] = flist
             return []
 
+        def _load_possible_azure_ds(seed_dir, cache_dir):
+            yield seed_dir
+            yield dsaz.DEFAULT_PROVISIONING_ISO_DEV
+            yield from data.get('dsdevs', [])
+            if cache_dir:
+                yield cache_dir
+
+        seed_dir = os.path.join(self.paths.seed_dir, "azure")
         if data.get('ovfcontent') is not None:
-            populate_dir(os.path.join(self.paths.seed_dir, "azure"),
+            populate_dir(seed_dir,
                          {'ovf-env.xml': data['ovfcontent']})
 
         dsaz.BUILTIN_DS_CONFIG['data_dir'] = self.waagent_d
@@ -654,6 +659,8 @@ scbus-1 on xpt0 bus 0
         self.m_report_failure_to_fabric = mock.MagicMock(autospec=True)
         self.m_ephemeral_dhcpv4 = mock.MagicMock()
         self.m_ephemeral_dhcpv4_with_reporting = mock.MagicMock()
+        self.m_list_possible_azure_ds = mock.MagicMock(
+            side_effect=_load_possible_azure_ds)
 
         if instance_id:
             self.instance_id = instance_id
@@ -667,7 +674,8 @@ scbus-1 on xpt0 bus 0
                 return '7783-7084-3265-9085-8269-3286-77'
 
         self.apply_patches([
-            (dsaz, 'list_possible_azure_ds_devs', dsdevs),
+            (dsaz, 'list_possible_azure_ds',
+                self.m_list_possible_azure_ds),
             (dsaz, 'perform_hostname_bounce', mock.MagicMock()),
             (dsaz, 'get_hostname', mock.MagicMock()),
             (dsaz, 'set_hostname', mock.MagicMock()),
@@ -844,9 +852,14 @@ scbus-1 on xpt0 bus 0
         """When a device path is used, present that in subplatform."""
         data = {'sys_cfg': {}, 'dsdevs': ['/dev/cd0']}
         dsrc = self._get_ds(data)
+        # DSAzure will attempt to mount /dev/sr0 first, which should
+        # fail with mount error since the list of devices doesn't have
+        # /dev/sr0
         with mock.patch(MOCKPATH + 'util.mount_cb') as m_mount_cb:
-            m_mount_cb.return_value = (
-                {'local-hostname': 'me'}, 'ud', {'cfg': ''}, {})
+            m_mount_cb.side_effect = [
+                MountFailedError("fail"),
+                ({'local-hostname': 'me'}, 'ud', {'cfg': ''}, {})
+            ]
             self.assertTrue(dsrc.get_data())
         self.assertEqual(dsrc.userdata_raw, 'ud')
         self.assertEqual(dsrc.metadata['local-hostname'], 'me')
@@ -1608,12 +1621,19 @@ scbus-1 on xpt0 bus 0
 
     @mock.patch(MOCKPATH + 'util.is_FreeBSD')
     @mock.patch(MOCKPATH + '_check_freebsd_cdrom')
-    def test_list_possible_azure_ds_devs(self, m_check_fbsd_cdrom,
-                                         m_is_FreeBSD):
+    def test_list_possible_azure_ds(self, m_check_fbsd_cdrom,
+                                    m_is_FreeBSD):
         """On FreeBSD, possible devs should show /dev/cd0."""
         m_is_FreeBSD.return_value = True
         m_check_fbsd_cdrom.return_value = True
-        self.assertEqual(dsaz.list_possible_azure_ds_devs(), ['/dev/cd0'])
+        possible_ds = []
+        for src in dsaz.list_possible_azure_ds(
+                "seed_dir", "cache_dir"):
+            possible_ds.append(src)
+        self.assertEqual(possible_ds, ["seed_dir",
+                                       dsaz.DEFAULT_PROVISIONING_ISO_DEV,
+                                       "/dev/cd0",
+                                       "cache_dir"])
         self.assertEqual(
             [mock.call("/dev/cd0")], m_check_fbsd_cdrom.call_args_list)
 
@@ -1967,11 +1987,19 @@ class TestAzureBounce(CiTestCase):
     with_logs = True
 
     def mock_out_azure_moving_parts(self):
+
+        def _load_possible_azure_ds(seed_dir, cache_dir):
+            yield seed_dir
+            yield dsaz.DEFAULT_PROVISIONING_ISO_DEV
+            if cache_dir:
+                yield cache_dir
+
         self.patches.enter_context(
             mock.patch.object(dsaz.util, 'wait_for_files'))
         self.patches.enter_context(
-            mock.patch.object(dsaz, 'list_possible_azure_ds_devs',
-                              mock.MagicMock(return_value=[])))
+            mock.patch.object(
+                dsaz, 'list_possible_azure_ds',
+                mock.MagicMock(side_effect=_load_possible_azure_ds)))
         self.patches.enter_context(
             mock.patch.object(dsaz, 'get_metadata_from_fabric',
                               mock.MagicMock(return_value={})))