[ovs-dev] [non-NORMAL learning 3/3] vswitchd: Only re-learn from flows that output to OFPP_NORMAL.

[Jesse Gross]

On Wed, Aug 4, 2010 at 10:27 AM, Ben Pfaff <blp at nicira.com> wrote:

>     COVERAGE_INC(bridge_process_flow);
> -    return process_flow(br, flow, packet, actions, tags, nf_output_iface);
> +
> +    retval = process_flow(br, flow, packet, actions, tags,
> nf_output_iface);
> +    if (*tags == 0) {
> +        /* Ensure that '*tags' is nonzero, so
> bridge_account_flow_ofhook_cb()
> +         * knows that it should use this flow to update the learning
> table. */
> +        *tags = tag_arbitrary_1bit();
> +    }
>

Every flow that is interesting to learn from later on will already have a
tag set on it.  mac_learning_lookup_tag() will add a tag for every flow
except two categories: inadmissible flows and flows that are on non-learning
vlans.  Both of these types of flows will be ignored later on when we update
the table.  Put it another way: if we didn't run it through the MAC learning
code on flow setup, it probably isn't something that we want to run through
later on.

1 bit tags seem like a weird hack to me that breaks the abstraction of the
tag class (what if we decided that tags should be 1 bit?) and generally
pollutes the tag space with unrelated information.  If we really want to
store this information separately, I would just add a bool to the rule in
ofproto.  After all, if we didn't create the flow using the normal action,
it probably isn't very useful to call the account_flow callback at all.
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