NMSA: Add ability to read 'live' values

This allows us to have a true picture of the system for the
operational datastore, separate from the config datastore.

2 files changed, 53 insertions, 6 deletions

diff --git a/doc/network.rst b/doc/network.rst
index 37c67b7..7291249 100644
--- a/doc/network.rst
+++ b/doc/network.rst
@@ -179,7 +179,7 @@ Parameters
 ----------
 
 For manipulating parameters in the section `Data model definition`_,
-three methods exist.
+four methods exist.
 
 
 ``get_param(iface, parameter)``
@@ -189,6 +189,16 @@ Retrieve the parameter for the specified interface.  If the parameter is
 not set for the specified interface, ``None`` will be returned.
 
 
+``curr_param(iface, parameter)``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Retrieve the current, live value for the parameter for the specified
+interface.  If the parameter is not set for the specified interface,
+``None`` will be returned.  The value returned from ``curr_param`` may
+differ from ``get_param`` if a network administrator has changed the
+value externally, or if the system configuration store is malfunctioning.
+
+
 ``set_param(iface, parameter, value)``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/ncserver/module/nms_ifupdownng.py b/ncserver/module/nms_ifupdownng.py
index 1b71051..5a06f47 100644
--- a/ncserver/module/nms_ifupdownng.py
+++ b/ncserver/module/nms_ifupdownng.py
@@ -12,6 +12,7 @@ SPDX-License-Identifier: NCSA
 
 import ipaddress
 import logging
+import pathlib
 import socket
 import subprocess
 import yaml
@@ -162,6 +163,11 @@ def _remove_one(iface: str, key: str):
             return
 
 
+def _iface_path(iface: str) -> pathlib.Path:
+    """Retrieve the system device path for the specified interface."""
+    return pathlib.Path("/sys/class/net/" + iface)
+
+
 #############################
 #    P A R A M E T E R S    #
 #############################
@@ -187,6 +193,16 @@ def get_auto(iface: str, _):
     return _find_one(iface, 'auto')
 
 
+def live_enabled(iface: str, _):
+    """Determine if the interface is enabled or not."""
+    statepath = _iface_path(iface) / "operstate"
+    if statepath.exists():
+        with open(statepath, 'r') as state_file:
+            return state_file.read().strip() == "up"
+
+    return False
+
+
 def set_auto(iface: str, _, value: bool):
     """Set the auto flag for the specified interface."""
     _replace_one(iface, 'auto', value)
@@ -198,9 +214,9 @@ def unset_auto(iface: str, _):
 
 
 _PARAMETERS = {
-    # "name": (getter, setter, unsetter)
-    "description": (get_desc, set_desc, unset_desc),
-    "enabled": (get_auto, set_auto, unset_auto)
+    # "name": (getter, live getter, setter, unsetter)
+    "description": (get_desc, get_desc, set_desc, unset_desc),
+    "enabled": (get_auto, live_enabled, set_auto, unset_auto)
 }
 """Describes all supported parameters and their methods."""
 
@@ -267,6 +283,27 @@ def get_param(iface: str, parameter: str):
     return _PARAMETERS[parameter][0](iface, parameter)
 
 
+def curr_param(iface: str, parameter: str):
+    """Retrieve the current parameter value for the specified interface."""
+    _load_config()
+
+    # XXX how do we want to handle interfaces that are missing from /e/n/i
+    # but are still present in the system?
+    if iface not in _CONFIG.keys():
+        LOGGER.warning(
+            _("requested parameter %s for non-existent interface %s"),
+            parameter, iface
+        )
+        return None
+
+    if parameter not in _PARAMETERS.keys():
+        LOGGER.error(_("requested non-existent parameter %s for interface %s"),
+                     parameter, iface)
+        return None
+
+    return _PARAMETERS[parameter][1](iface, parameter)
+
+
 def set_param(iface: str, parameter: str, value):
     """Set the parameter for the specified interface."""
     _load_config()
@@ -282,7 +319,7 @@ def set_param(iface: str, parameter: str, value):
     if iface not in _CONFIG.keys():
         _CONFIG[iface] = list()
 
-    _PARAMETERS[parameter][1](iface, parameter, value)
+    _PARAMETERS[parameter][2](iface, parameter, value)
 
 
 def unset_param(iface: str, parameter: str):
@@ -303,7 +340,7 @@ def unset_param(iface: str, parameter: str):
         )
         return
 
-    _PARAMETERS[parameter][2](iface, parameter)
+    _PARAMETERS[parameter][3](iface, parameter)
 
 
 def list_addresses(iface: str) -> list: