- * struct pad nl hdr total
- * ------ --- ------ -----
- * OVS_KEY_ATTR_PRIORITY 4 -- 4 8
- * OVS_KEY_ATTR_TUN_ID 8 -- 4 12
- * OVS_KEY_ATTR_IN_PORT 4 -- 4 8
- * OVS_KEY_ATTR_ETHERNET 12 -- 4 16
- * OVS_KEY_ATTR_8021Q 4 -- 4 8
- * OVS_KEY_ATTR_ETHERTYPE 2 2 4 8
- * OVS_KEY_ATTR_IPV6 40 -- 4 44
- * OVS_KEY_ATTR_ICMPV6 2 2 4 8
- * OVS_KEY_ATTR_ND 28 -- 4 32
- * -------------------------------------------------
- * total 144
+ * OVS doesn't insist that ovs-vswitchd and the datapath have exactly the same
+ * idea of a flow, so therefore this value isn't necessarily an upper bound on
+ * the length of a flow key that the datapath can pass to ovs-vswitchd.
+ *
+ * The longest nlattr-formatted flow key appended by odp_flow_key_from_flow()
+ * would be:
+ *
+ * struct pad nl hdr total
+ * ------ --- ------ -----
+ * OVS_KEY_ATTR_PRIORITY 4 -- 4 8
+ * OVS_KEY_ATTR_TUNNEL 0 -- 4 4
+ * - OVS_TUNNEL_KEY_ATTR_ID 8 -- 4 12
+ * - OVS_TUNNEL_KEY_ATTR_IPV4_SRC 4 -- 4 8
+ * - OVS_TUNNEL_KEY_ATTR_IPV4_DST 4 -- 4 8
+ * - OVS_TUNNEL_KEY_ATTR_TOS 1 3 4 8
+ * - OVS_TUNNEL_KEY_ATTR_TTL 1 3 4 8
+ * - OVS_TUNNEL_KEY_ATTR_DONT_FRAGMENT 0 -- 4 4
+ * - OVS_TUNNEL_KEY_ATTR_CSUM 0 -- 4 4
+ * OVS_KEY_ATTR_IN_PORT 4 -- 4 8
+ * OVS_KEY_ATTR_SKB_MARK 4 -- 4 8
+ * OVS_KEY_ATTR_ETHERNET 12 -- 4 16
+ * OVS_KEY_ATTR_ETHERTYPE 2 2 4 8 (outer VLAN ethertype)
+ * OVS_KEY_ATTR_8021Q 4 -- 4 8
+ * OVS_KEY_ATTR_ENCAP 0 -- 4 4 (VLAN encapsulation)
+ * OVS_KEY_ATTR_ETHERTYPE 2 2 4 8 (inner VLAN ethertype)
+ * OVS_KEY_ATTR_IPV6 40 -- 4 44
+ * OVS_KEY_ATTR_ICMPV6 2 2 4 8
+ * OVS_KEY_ATTR_ND 28 -- 4 32
+ * ----------------------------------------------------------
+ * total 208
+ *
+ * We include some slack space in case the calculation isn't quite right or we
+ * add another field and forget to adjust this value.