Add ability to manage fallback network config on PhotonOS (#941)

Currently cloud-init generates fallback network config on various
scenarios.

For example:
1. When no DS found
2. There is no 'network' info given in DS metadata.
3. If a DS gives a network config once and upon reboot if DS doesn't
   give any network info, previously set network data will be
   overridden.

A newly introduced key in cloud.cfg.tmpl can be used to control this
behavior on PhotonOS.

Also, if OS comes with a set of default network files(configs), like in
PhotonOS, cloud-init should not overwrite them by default.

This change also includes some nitpicking changes of reorganizing few
config variables.

Signed-off-by: Shreenidhi Shedi <sshedi@vmware.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/cloudinit/distros/photon.py b/cloudinit/distros/photon.py
index 3ef5dd40..61e270c0 100644
--- a/cloudinit/distros/photon.py
+++ b/cloudinit/distros/photon.py
@@ -5,6 +5,7 @@
 #
 # This file is part of cloud-init. See LICENSE file for license information.
 
+from cloudinit import net
 from cloudinit import util
 from cloudinit import subp
 from cloudinit import distros
@@ -54,6 +55,20 @@ class Distro(distros.Distro):
             util.logexc(LOG, 'Command %s failed', cmd)
             return False, None, None
 
+    def generate_fallback_config(self):
+        key = 'disable_fallback_netcfg'
+        disable_fallback_netcfg = self._cfg.get(key, True)
+        LOG.debug('%s value is: %s', key, disable_fallback_netcfg)
+
+        if not disable_fallback_netcfg:
+            return net.generate_fallback_config()
+
+        LOG.info(
+            'Skipping generate_fallback_config. Rely on PhotonOS default '
+            'network config'
+        )
+        return None
+
     def apply_locale(self, locale, out_fn=None):
         # This has a dependancy on glibc-i18n, user need to manually install it
         # and enable the option in cloud.cfg