These macros caused trouble if datapath-protocol.h was included before
openflow.h. Later references to the icmp_type and icmp_code members of
struct ovs_key_icmp caused compiler errors, because the macros caused them
to try to refer to nonexistent tp_src and tp_dst members in those
structures.
There are a few loose ends here. First, learning actions cause too much
flow revalidation. Upcoming commits will fix that problem. The following
additional issues have not yet been addressed:
* Resource limits: nothing yet limits the maximum number of flows that
can be learned. It is possible to exhaust all system memory.
* Age reporting: there is no way to find out how soon a learned table
entry is due to be evicted.
To try this action out, here's a recipe for a very simple-minded MAC
learning switch. It uses a 10-second MAC expiration time to make it easier
to see what's going on:
ovs-vsctl del-controller br0
ovs-ofctl del-flows br0
ovs-ofctl add-flow br0 "table=0 actions=learn(table=1, hard_timeout=10, \
NXM_OF_VLAN_TCI[0..11], NXM_OF_ETH_DST[]=NXM_OF_ETH_SRC[], \
output:NXM_OF_IN_PORT[]), resubmit(,1)"
ovs-ofctl add-flow br0 "table=1 priority=0 actions=flood"
You can then dump the MAC learning table with:
ovs-ofctl dump-flows br0 table=1
OVS already has a fairly good set of functions for working with fields that
are known at compile time, but support for working with fields that are
known only at runtime is fairly limited (and fairly unneeded). However,
with NXM identifiers becoming more and more widely used throughout Nicira
extensions, it's becoming corresponding more and more common to need to
refer to fields at runtime. This new library represents a first attempt
at a systematic approach for doing so.
