tools/kvm_stat: Exempt time-based counters

The new counters halt_poll_success_ns and halt_poll_fail_ns do not count
events. Instead they provide a time, and mess up our statistics. Therefore,
we should exclude them.
Removal is currently implemented with an exempt list. If more counters like
these appear, we can think about a more general rule like excluding all
fields name "*_ns", in case that's a standing convention.
Signed-off-by: Stefan Raspl <raspl@linux.ibm.com>
Tested-and-reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <20201208210829.101324-1-raspl@linux.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/kvm/kvm_stat/kvm_stat

@@ -742,7 +742,11 @@ class DebugfsProvider(Provider):
         The fields are all available KVM debugfs files
 
         """
-        return self.walkdir(PATH_DEBUGFS_KVM)[2]
+        exempt_list = ['halt_poll_fail_ns', 'halt_poll_success_ns']
+        fields = [field for field in self.walkdir(PATH_DEBUGFS_KVM)[2]
+                  if field not in exempt_list]
+
+        return fields
 
     def update_fields(self, fields_filter):
         """Refresh fields, applying fields_filter"""