spec: add capabilityArgs for adding additional info in result.

SPEC.md

@@ -160,7 +160,7 @@ Network configuration in JSON format must be streamed to the plugin through stdi
 
 Note that IPAM plugins should return an abbreviated `Result` structure as described in [IP Allocation](#ip-allocation).
 
-Plugins must indicate success with a return code of zero and the following JSON printed to stdout in the case of the ADD command. The `ips` and `dns` items should be the same output as was returned by the IPAM plugin (see [IP Allocation](#ip-allocation) for details) except that the plugin should fill in the `interface` indexes appropriately, which are missing from IPAM plugin output since IPAM plugins should be unaware of interfaces.
+Plugins must indicate success with a return code of zero and the following JSON printed to stdout in the case of the ADD command. The `ips`, `dns` and `capabilityArgs` items should be the same output as was returned by the IPAM plugin (see [IP Allocation](#ip-allocation) for details) except that the plugin should fill in the `interface` indexes appropriately, which are missing from IPAM plugin output since IPAM plugins should be unaware of interfaces.
 
 ```
 {
@@ -193,6 +193,10 @@ Plugins must indicate success with a return code of zero and the following JSON
     "domain": <name-of-local-domain>                         (optional)
     "search": <list-of-additional-search-domains>            (optional)
     "options": <list-of-options>                             (optional)
+  },
+  "capabilityArgs": {                                        (optional)
+    "<name-of-the-arg>": <value-of-the-arg>                  (optional)
+    ...
   }
 }
 ```
@@ -216,6 +220,9 @@ See the [Routes well-known structure](#routes) section for more information.
 The `dns` field contains a dictionary consisting of common DNS information.
 See the [DNS well-known structure](#dns) section for more information.
 
+The `capabilityArgs` field contains a dictionary which carries additional plugin execution information.
+See the [CapabilityArgs well-known structure](#capabilityArgs) section for more information.
+
 The specification does not declare how this information must be processed by CNI consumers.
 Examples include generating an `/etc/resolv.conf` file to be injected into the container filesystem or running a DNS forwarder on the host.
 
@@ -674,6 +681,10 @@ Success must be indicated by a zero return code and the following JSON being pri
     "search": <list-of-search-domains>              (optional)
     "options": <list-of-options>                    (optional)
   }
+  "capabilityArgs": {                               (optional)
+    "<name-of-the-arg>": <value-of-the-arg>         (optional)
+    ...
+  }
 }
 ```
 
@@ -690,6 +701,9 @@ See the [Routes well-known structure](#routes) section for more information.
 The `dns` field contains a dictionary consisting of common DNS information.
 See the [DNS well-known structure](#dns) section for more information.
 
+The `capabilityArgs` field contains a dictionary which carries additional plugin execution information.
+See the [CapabilityArgs well-known structure](#capabilityArgs) section for more information.
+
 Errors and logs are communicated in the same way as the CNI plugin. See [CNI Plugin Result](#result) section for details.
 
 IPAM plugin examples:
@@ -763,7 +777,19 @@ The `dns` field contains a dictionary consisting of common DNS information.
 - `search` (list of strings): list of priority ordered search domains for short hostname lookups. Will be preferred over `domain` by most resolvers.
 - `options` (list of strings): list of options that can be passed to the resolver.
   See [CNI Plugin Result](#result) section for more information.
-
+
+#### CapabilityArgs
+
+```
+  "capabilityArgs": {
+    "<name-of-the-arg>": <value-of-the-arg>             (optional)
+    ...
+  }
+```
+
+The `capabilityArgs` field contains a dictionary which carries additional plugin execution information.
+For the each item of `capabilityArgs`, both the key and value are string type. If `capabilityArgs` is set, it could be passed through the chain, and the downstream plugins could consume this additional information.
+
 ## Well-known Error Codes
 
 Error codes 1-99 must not be used other than as specified here.