stages: allow data sources to override network config source order

Currently, if a platform provides any network configuration via the
"cmdline" method (i.e. network-data=... on the kernel command line,
ip=... on the kernel command line, or iBFT config via /run/net-*.conf),
the value of the data source's network_config property is completely
ignored.

This means that on platforms that use iSCSI boot (such as Oracle Compute
Infrastructure), there is no way for the data source to configure any
network interfaces other than those that have already been configured by
the initramfs.

This change allows data sources to specify the order in which network
configuration sources are considered.  Data sources that opt to use this
mechanism will be expected to consume the command line network data and
integrate it themselves.

(The generic merging of network configuration sources was considered,
but we concluded that the single use case we have presently (a) didn't
warrant the increased complexity, and (b) didn't give us a broad enough
view to be sure that our generic implementation would be sufficiently
generic.  This change in no way precludes a merging strategy in future.)

1 files changed, 28 insertions, 9 deletions

diff --git a/cloudinit/stages.py b/cloudinit/stages.py
index 5f9d47b9..6bcda2d1 100644
--- a/cloudinit/stages.py
+++ b/cloudinit/stages.py
@@ -24,6 +24,7 @@ from cloudinit.handlers.shell_script import ShellScriptPartHandler
 from cloudinit.handlers.upstart_job import UpstartJobPartHandler
 
 from cloudinit.event import EventType
+from cloudinit.sources import NetworkConfigSource
 
 from cloudinit import cloud
 from cloudinit import config
@@ -630,19 +631,37 @@ class Init(object):
         if os.path.exists(disable_file):
             return (None, disable_file)
 
-        cmdline_cfg = ('cmdline', cmdline.read_kernel_cmdline_config())
-        dscfg = ('ds', None)
+        available_cfgs = {
+            NetworkConfigSource.cmdline: cmdline.read_kernel_cmdline_config(),
+            NetworkConfigSource.ds: None,
+            NetworkConfigSource.system_cfg: self.cfg.get('network'),
+        }
+
         if self.datasource and hasattr(self.datasource, 'network_config'):
-            dscfg = ('ds', self.datasource.network_config)
-        sys_cfg = ('system_cfg', self.cfg.get('network'))
+            available_cfgs[NetworkConfigSource.ds] = (
+                self.datasource.network_config)
 
-        for loc, ncfg in (cmdline_cfg, sys_cfg, dscfg):
+        if self.datasource:
+            order = self.datasource.network_config_sources
+        else:
+            order = sources.DataSource.network_config_sources
+        for cfg_source in order:
+            if not hasattr(NetworkConfigSource, cfg_source):
+                LOG.warning('data source specifies an invalid network'
+                            ' cfg_source: %s', cfg_source)
+                continue
+            if cfg_source not in available_cfgs:
+                LOG.warning('data source specifies an unavailable network'
+                            ' cfg_source: %s', cfg_source)
+                continue
+            ncfg = available_cfgs[cfg_source]
             if net.is_disabled_cfg(ncfg):
-                LOG.debug("network config disabled by %s", loc)
-                return (None, loc)
+                LOG.debug("network config disabled by %s", cfg_source)
+                return (None, cfg_source)
             if ncfg:
-                return (ncfg, loc)
-        return (self.distro.generate_fallback_config(), "fallback")
+                return (ncfg, cfg_source)
+        return (self.distro.generate_fallback_config(),
+                NetworkConfigSource.fallback)
 
     def _apply_netcfg_names(self, netcfg):
         try: