Add user guide for 'vppcfg dump' command

docs/user-guide.md

@@ -108,6 +108,14 @@ fully valid!
 
 ### vppcfg dump
 
+The purpose of the **dump** module is to connect to the VPP dataplane, and retrieve its
+state, printing most information found in the INFO logs. Although it does contact VPP, it
+will perform *readonly* operations and never manipulate state in the dataplane, so it
+should be safe to run.
+
+There are no flags to the dump command. It will return 0 if the connection to VPP was
+established and its state successfully dumped to the logs, and non-zero otherwise.
+
 ### vppcfg plan
 
 ### vppcfg apply

vpp/vppapi.py

@@ -270,7 +270,6 @@ class VPPApi():
 class VPPApiDumper(VPPApi):
     def __init__(self, address='/run/vpp/api.sock', clientname='vppcfg'):
         VPPApi.__init__(self, address, clientname)
-        self.readconfig()
 
     def dump(self):
         self.dump_phys()
@@ -328,7 +327,7 @@ class VPPApiDumper(VPPApi):
                 lcp = self.cache['lcps'][iface.sw_if_index]
                 tap_name = self.cache['interfaces'][lcp.host_sw_if_index].interface_name
                 tap_idx = lcp.host_sw_if_index
-                self.logger.info("  TAP: %s (tap=%s idx=%d)" % (lcp.host_if_name, tap_name, tap_idx))
+                self.logger.info("  LCP: %s (tap=%s idx=%d netns=%s)" % (lcp.host_if_name, tap_name, tap_idx, lcp.namespace))
         
             if len(self.cache['interface_addresses'][iface.sw_if_index])>0:
                 self.logger.info("  L3: %s" % ' '.join(self.cache['interface_addresses'][iface.sw_if_index]))

vppcfg

@@ -65,6 +65,9 @@ def main():
 
     if args.command=="dump":
         d = VPPApiDumper()
+        if not d.readconfig():
+            logging.error("Could not retrieve config from VPP")
+            sys.exit(-7)
         d.dump()
         sys.exit(0)