+#define FLOW_N_REGS 4
+BUILD_ASSERT_DECL(FLOW_N_REGS <= NXM_NX_MAX_REGS);
+
+/* Used for struct flow's dl_type member for frames that have no Ethernet
+ * type, that is, pure 802.2 frames. */
+#define FLOW_DL_TYPE_NONE 0x5ff
+
+struct flow {
+ ovs_be64 tun_id; /* Encapsulating tunnel ID. */
+ uint32_t regs[FLOW_N_REGS]; /* Registers. */
+ ovs_be32 nw_src; /* IP source address. */
+ ovs_be32 nw_dst; /* IP destination address. */
+ uint16_t in_port; /* Input switch port. */
+ ovs_be16 vlan_tci; /* If 802.1Q, TCI | VLAN_CFI; otherwise 0. */
+ ovs_be16 dl_type; /* Ethernet frame type. */
+ ovs_be16 tp_src; /* TCP/UDP source port. */
+ ovs_be16 tp_dst; /* TCP/UDP destination port. */
+ uint8_t dl_src[6]; /* Ethernet source address. */
+ uint8_t dl_dst[6]; /* Ethernet destination address. */
+ uint8_t nw_proto; /* IP protocol or low 8 bits of ARP opcode. */
+ uint8_t nw_tos; /* IP ToS (DSCP field, 6 bits). */
+};
+
+/* Assert that there are FLOW_SIG_SIZE bytes of significant data in "struct
+ * flow", followed by FLOW_PAD_SIZE bytes of padding. */
+#define FLOW_SIG_SIZE (40 + FLOW_N_REGS * 4)
+#define FLOW_PAD_SIZE 0
+BUILD_ASSERT_DECL(offsetof(struct flow, nw_tos) == FLOW_SIG_SIZE - 1);
+BUILD_ASSERT_DECL(sizeof(((struct flow *)0)->nw_tos) == 1);
+BUILD_ASSERT_DECL(sizeof(struct flow) == FLOW_SIG_SIZE + FLOW_PAD_SIZE);