[ovs-dev] [PATCH] ofproto-dpif: Always un-wildcard fields that are being set.

[Ben Pfaff]

On Fri, Aug 02, 2013 at 10:53:40PM -0700, Justin Pettit wrote:
> > In the case where we do emit a "set" action, we un-wildcard not just the
> > single field but all the fields that have to be set in the datapath in
> > one go.  Is that necessary here?  My initial thought is "no" but I want
> > to make sure that you have also considered that.
> 
> I think we need to do that, since we're overwriting all those fields.
> Isn't it essentially the same issue that unless we un-wildcard it,
> we'll overwrite other header fields regardless of their value based on
> too loose a megaflow?

Here is my logic.

For OFPACT_SET_VLAN_VID, we need to un-wildcard the VID and CFI bits
because we want the datapath actions to be correct regardless of the
VLAN in the microflow we're actually looking at.  Another way to look at
it: if we do not un-wildcard it, then the datapath actions we emit could
be different depending on whether the VLAN being set is the VLAN in the
microflow for which we're generating actions.

On the other hand, again for OFPACT_SET_VLAN_VID, I do not think the
same argument applies to the PCP bits.  The PCP bits in the microflow
for which we're generating action do not affect whether we generate a
datapath action to set the VLAN tag.  If we don't emit such an action,
no problem.  If we do emit such an action, then commit_vlan_action()
will ensure that we un-wildcard the whole VLAN tag.

Does that make sense?

Thanks,

Ben.