DataSourceOracle: configure secondary NICs on Virtual Machines

Oracle Cloud Infrastructure's Instance Metadata Service provides network
configuration information for non-primary NICs.  This commit introduces
support, on Virtual Machines[0], for fetching that network metadata,
converting it to v1 network-config[1] and combining it into the network
configuration generated for the primary interface.

By default, this behaviour is not enabled.  Configuring the Oracle
datasource to `configure_secondary_nics` enables it:

    datasource:
      Oracle:
        configure_secondary_nics: true

Failures to fetch and generate secondary NIC configuration will log a
warning, but otherwise will not affect boot.

[0] The expected use of the IMDS-provided network configuration is
    substantially different on Bare Metal Machines, so support for that
    will be addressed separately.
[1] This is v1 config, because cloudinit.net.cmdline generates v1 config
    and we need to integrate the secondary NICs into that configuration.

1 files changed, 24 insertions, 1 deletions

diff --git a/doc/rtd/topics/datasources/oracle.rst b/doc/rtd/topics/datasources/oracle.rst
index f2383cee..98c4657c 100644
--- a/doc/rtd/topics/datasources/oracle.rst
+++ b/doc/rtd/topics/datasources/oracle.rst
@@ -8,7 +8,7 @@ This datasource reads metadata, vendor-data and user-data from
 
 Oracle Platform
 ---------------
-OCI provides bare metal and virtual machines.  In both cases, 
+OCI provides bare metal and virtual machines.  In both cases,
 the platform identifies itself via DMI data in the chassis asset tag
 with the string 'OracleCloud.com'.
 
@@ -22,5 +22,28 @@ Cloud-init has a specific datasource for Oracle in order to:
     implementation.
 
 
+Configuration
+-------------
+
+The following configuration can be set for the datasource in system
+configuration (in ``/etc/cloud/cloud.cfg`` or ``/etc/cloud/cloud.cfg.d/``).
+
+The settings that may be configured are:
+
+* **configure_secondary_nics**: A boolean, defaulting to False.  If set
+  to True on an OCI Virtual Machine, cloud-init will fetch networking
+  metadata from Oracle's IMDS and use it to configure the non-primary
+  network interface controllers in the system.  If set to True on an
+  OCI Bare Metal Machine, it will have no effect (though this may
+  change in the future).
+
+An example configuration with the default values is provided below:
+
+.. sourcecode:: yaml
+
+  datasource:
+   Oracle:
+    configure_secondary_nics: false
+
 .. _Oracle Compute Infrastructure: https://cloud.oracle.com/
 .. vi: textwidth=78