[libvirt] Python setInterfaceParameters function broken

[Brian Rak]

I've been trying to use domain.setInterfaceParameters, and I'm finding 
it's throwing the mysterious error:

libvirt.libvirtError: argument unsupported: parameter '' not supported

Enabling debug mode in libvirt reveals this:

2014-03-17 18:41:33.780+0000: 16927: debug : 
virDomainSetInterfaceParameters:8001 : dom=0x7f2ecc0009b0, (VM: 
name=SRVID8736, uuid=5121c1d6-19aa-4494-b6a7-09af270f24da), 
device=vnet0, params=0x7f2ecc0011f0, nparams=6, flags=0
2014-03-17 18:41:33.780+0000: 16927: debug : 
virDomainSetInterfaceParameters:8002 : params[""]=(uint)0
2014-03-17 18:41:33.780+0000: 16927: debug : 
virDomainSetInterfaceParameters:8002 : params[""]=(uint)64000
2014-03-17 18:41:33.780+0000: 16927: debug : 
virDomainSetInterfaceParameters:8002 : params[""]=(uint)10
2014-03-17 18:41:33.780+0000: 16927: debug : 
virDomainSetInterfaceParameters:8002 : params[""]=(uint)64000
2014-03-17 18:41:33.780+0000: 16927: debug : 
virDomainSetInterfaceParameters:8002 : params[""]=(uint)0
2014-03-17 18:41:33.780+0000: 16927: debug : 
virDomainSetInterfaceParameters:8002 : params[""]=(uint)0
(irreverent lines trimmed)

Which ultimately led me to setPyVirTypedParameter lines 200-202. These 
don't seem to work properly.  I added some debugging:

         strncpy(temp->field, keystr, sizeof(*temp->field) - 1);
         temp->field[sizeof(*temp->field) - 1] = '\0';
         DEBUG("current key name in: %s, out: %s field size: %i\n", 
keystr, temp->field, sizeof(*temp->field) - 1);
         temp->type = params[i].type;

which was displaying:

current key name in: outbound.peak, out:  field size: 0
current key name in: inbound.peak, out:  field size: 0
current key name in: inbound.burst, out:  field size: 0
current key name in: inbound.average, out:  field size: 0
current key name in: outbound.average, out:  field size: 0
current key name in: outbound.burst, out:  field size: 0

I am not good enough in C to determine what exactly the correct fix is 
here.  It seems like nothing that used this function could have ever 
worked.  My trivial patch was:

--- a/python27-libvirt/libvirt-python-1.2.2/libvirt-override.c
+++ b/python27-libvirt/libvirt-python-1.2.2/libvirt-override.c
@@ -197,8 +197,8 @@ setPyVirTypedParameter(PyObject *info,
              goto cleanup;
          }

-        strncpy(temp->field, keystr, sizeof(*temp->field) - 1);
-        temp->field[sizeof(*temp->field) - 1] = '\0';
+        strncpy(temp->field, keystr, VIR_TYPED_PARAM_FIELD_LENGTH - 1);
+        temp->field[VIR_TYPED_PARAM_FIELD_LENGTH - 1] = '\0';
          temp->type = params[i].type;
          VIR_FREE(keystr);

I am not sure if this is the best approach here.  This change definitely 
fixes the issue, and allows setInterfaceParameters to actually execute 
successfully.  I am not comfortable enough with my understanding of the 
issue to actually submit this as a patch though.  Is this something that 
someone else can take a look at or fix?

My trivial test script that was showing the issue:

import libvirt

conn = libvirt.open(None)
if conn == None:
         print 'Failed to connect';
         sys.exit(1)

for id in conn.listDomainsID():
         dom = conn.lookupByID(id)
         if dom == None:
                 continue

         params = dom.interfaceParameters('vnet0', 0)
         print params
         dom.setInterfaceParameters('vnet0', params, 0)