Openvswitch原理与代码分析(6)：用户态流表flow table的操作

当内核无法查找到流表项的时候，则会通过upcall来调用用户态ovs-vswtichd中的flow table。

会调用ofproto-dpif-upcall.c中的udpif_upcall_handler函数。

1. static
   void *
2. udpif_upcall_handler(void *arg)
3. {
4.     struct handler *handler = arg;
5.     struct udpif *udpif = handler->udpif;
6.  
7.     while (!latch_is_set(&handler->udpif->exit_latch)) {
8.         if (recv_upcalls(handler)) {
9.             poll_immediate_wake();
10.         } else {
11.             dpif_recv_wait(udpif->dpif, handler->handler_id);
12.             latch_wait(&udpif->exit_latch);
13.         }
14.         poll_block();
15.     }
16.  
17.     return NULL;
18. }

 

会调用static size_t recv_upcalls(struct handler *handler)

在这个函数里面

(1) 首先读取upcall调用static int upcall_receive(struct upcall *upcall, const struct dpif_backer *backer, const struct dp_packet *packet, enum dpif_upcall_type type, const struct nlattr *userdata, const struct flow *flow, const unsigned int mru, const ovs_u128 *ufid, const unsigned pmd_id)

(2) 其次提取包头调用void flow_extract(struct dp_packet *packet, struct flow *flow)，提取出的flow如下：

1. struct flow {
2.     /* Metadata */
3.     struct flow_tnl tunnel; /* Encapsulating tunnel parameters. */
4.     ovs_be64 metadata; /* OpenFlow Metadata. */
5.     uint32_t regs[FLOW_N_REGS]; /* Registers. */
6.     uint32_t skb_priority; /* Packet priority for QoS. */
7.     uint32_t pkt_mark; /* Packet mark. */
8.     uint32_t dp_hash; /* Datapath computed hash value. The exact
9.                                  * computation is opaque to the user space. */
10.     union flow_in_port in_port; /* Input port.*/
11.     uint32_t recirc_id; /* Must be exact match. */
12.     uint16_t ct_state; /* Connection tracking state. */
13.     uint16_t ct_zone; /* Connection tracking zone. */
14.     uint32_t ct_mark; /* Connection mark.*/
15.     uint8_t pad1[4]; /* Pad to 64 bits. */
16.     ovs_u128 ct_label; /* Connection label. */
17.     uint32_t conj_id; /* Conjunction ID. */
18.     ofp_port_t actset_output; /* Output port in action set. */
19.     uint8_t pad2[2]; /* Pad to 64 bits. */
20.  
21.     /* L2, Order the same as in the Ethernet header! (64-bit aligned) */
22.     struct eth_addr dl_dst; /* Ethernet destination address. */
23.     struct eth_addr dl_src; /* Ethernet source address. */
24.     ovs_be16 dl_type; /* Ethernet frame type. */
25.     ovs_be16 vlan_tci; /* If 802.1Q, TCI | VLAN_CFI; otherwise 0. */
26.     ovs_be32 mpls_lse[ROUND_UP(FLOW_MAX_MPLS_LABELS, 2)]; /* MPLS label stack
27.                                                              (with padding). */
28.     /* L3 (64-bit aligned) */
29.     ovs_be32 nw_src; /* IPv4 source address. */
30.     ovs_be32 nw_dst; /* IPv4 destination address. */
31.     struct
    in6_addr ipv6_src; /* IPv6 source address. */
32.     struct
    in6_addr ipv6_dst; /* IPv6 destination address. */
33.     ovs_be32 ipv6_label; /* IPv6 flow label. */
34.     uint8_t nw_frag; /* FLOW_FRAG_* flags. */
35.     uint8_t nw_tos; /* IP ToS (including DSCP and ECN). */
36.     uint8_t nw_ttl; /* IP TTL/Hop Limit. */
37.     uint8_t nw_proto; /* IP protocol or low 8 bits of ARP opcode. */
38.     struct
    in6_addr nd_target; /* IPv6 neighbor discovery (ND) target. */
39.     struct eth_addr arp_sha; /* ARP/ND source hardware address. */
40.     struct eth_addr arp_tha; /* ARP/ND target hardware address. */
41.     ovs_be16 tcp_flags; /* TCP flags. With L3 to avoid matching L4. */
42.     ovs_be16 pad3; /* Pad to 64 bits. */
43.  
44.     /* L4 (64-bit aligned) */
45.     ovs_be16 tp_src; /* TCP/UDP/SCTP source port/ICMP type. */
46.     ovs_be16 tp_dst; /* TCP/UDP/SCTP destination port/ICMP code. */
47.     ovs_be32 igmp_group_ip4; /* IGMP group IPv4 address.
48.                                  * Keep last for BUILD_ASSERT_DECL below. */
49. };

 

(3) 然后调用static int process_upcall(struct udpif *udpif, struct upcall *upcall, struct ofpbuf *odp_actions, struct flow_wildcards *wc)来处理upcall。

 

对于MISS_UPCALL，调用static void upcall_xlate(struct udpif *udpif, struct upcall *upcall, struct ofpbuf *odp_actions, struct flow_wildcards *wc)

1. switch (classify_upcall(upcall->type, userdata)) {
2. case MISS_UPCALL:
3.     upcall_xlate(udpif, upcall, odp_actions, wc);
4.     return 0;

 

会调用enum xlate_error xlate_actions(struct xlate_in *xin, struct xlate_out *xout)

在这个函数里面，会在flow table里面查找rule

ctx.rule = rule_dpif_lookup_from_table( ctx.xbridge->ofproto, ctx.tables_version, flow, xin->wc, ctx.xin->resubmit_stats, &ctx.table_id, flow->in_port.ofp_port, true, true);

找到rule之后，调用static void do_xlate_actions(const struct ofpact *ofpacts, size_t ofpacts_len, struct xlate_ctx *ctx)在这个函数里面，根据action的不同，修改flow的内容。

1. switch (a->type) {
2. case OFPACT_OUTPUT:
3.     xlate_output_action(ctx, ofpact_get_OUTPUT(a)->port,
4.                         ofpact_get_OUTPUT(a)->max_len, true);
5.     break;
6.  
7. case OFPACT_SET_VLAN_VID:
8.     wc->masks.vlan_tci |= htons(VLAN_VID_MASK | VLAN_CFI);
9.     if (flow->vlan_tci & htons(VLAN_CFI) ||
10.         ofpact_get_SET_VLAN_VID(a)->push_vlan_if_needed) {
11.         flow->vlan_tci &= ~htons(VLAN_VID_MASK);
12.         flow->vlan_tci |= (htons(ofpact_get_SET_VLAN_VID(a)->vlan_vid)
13.                            | htons(VLAN_CFI));
14.     }
15.     break;
16.  
17. case OFPACT_SET_ETH_SRC:
18.     WC_MASK_FIELD(wc, dl_src);
19.     flow->dl_src = ofpact_get_SET_ETH_SRC(a)->mac;
20.     break;
21.  
22. case OFPACT_SET_ETH_DST:
23.     WC_MASK_FIELD(wc, dl_dst);
24.     flow->dl_dst = ofpact_get_SET_ETH_DST(a)->mac;
25.     break;
26.  
27. case OFPACT_SET_IPV4_SRC:
28.     CHECK_MPLS_RECIRCULATION();
29.     if (flow->dl_type == htons(ETH_TYPE_IP)) {
30.         memset(&wc->masks.nw_src, 0xff, sizeof wc->masks.nw_src);
31.         flow->nw_src = ofpact_get_SET_IPV4_SRC(a)->ipv4;
32.     }
33.     break;
34.  
35. case OFPACT_SET_IPV4_DST:
36.     CHECK_MPLS_RECIRCULATION();
37.     if (flow->dl_type == htons(ETH_TYPE_IP)) {
38.         memset(&wc->masks.nw_dst, 0xff, sizeof wc->masks.nw_dst);
39.         flow->nw_dst = ofpact_get_SET_IPV4_DST(a)->ipv4;
40.     }
41.     break;
42.  
43. case OFPACT_SET_L4_SRC_PORT:
44.     CHECK_MPLS_RECIRCULATION();
45.     if (is_ip_any(flow) && !(flow->nw_frag & FLOW_NW_FRAG_LATER)) {
46.         memset(&wc->masks.nw_proto, 0xff, sizeof wc->masks.nw_proto);
47.         memset(&wc->masks.tp_src, 0xff, sizeof wc->masks.tp_src);
48.         flow->tp_src = htons(ofpact_get_SET_L4_SRC_PORT(a)->port);
49.     }
50.     break;
51.  
52. case OFPACT_SET_L4_DST_PORT:
53.     CHECK_MPLS_RECIRCULATION();
54.     if (is_ip_any(flow) && !(flow->nw_frag & FLOW_NW_FRAG_LATER)) {
55.         memset(&wc->masks.nw_proto, 0xff, sizeof wc->masks.nw_proto);
56.         memset(&wc->masks.tp_dst, 0xff, sizeof wc->masks.tp_dst);
57.         flow->tp_dst = htons(ofpact_get_SET_L4_DST_PORT(a)->port);
58.     }
59.     break;

 

 

(4) 最后调用static void handle_upcalls(struct udpif *udpif, struct upcall *upcalls, size_t n_upcalls)将flow rule添加到内核中的datapath

他会调用void dpif_operate(struct dpif *dpif, struct dpif_op **ops, size_t n_ops)，他会调用dpif->dpif_class->operate(dpif, ops, chunk);

会调用dpif_netlink_operate()

1. static
   void
2. dpif_netlink_operate(struct dpif *dpif_, struct dpif_op **ops, size_t n_ops)
3. {
4.     struct dpif_netlink *dpif = dpif_netlink_cast(dpif_);
5.  
6.     while (n_ops > 0) {
7.         size_t chunk = dpif_netlink_operate__(dpif, ops, n_ops);
8.         ops += chunk;
9.         n_ops -= chunk;
10.     }
11. }

 

在static size_t dpif_netlink_operate__(struct dpif_netlink *dpif, struct dpif_op **ops, size_t n_ops)中，有以下的代码：

1. switch (op->type) {
2. case DPIF_OP_FLOW_PUT:
3.     put = &op->u.flow_put;
4.     dpif_netlink_init_flow_put(dpif, put, &flow);
5.     if (put->stats) {
6.         flow.nlmsg_flags |= NLM_F_ECHO;
7.         aux->txn.reply = &aux->reply;
8.     }
9.     dpif_netlink_flow_to_ofpbuf(&flow, &aux->request);
10.     break;
11.  
12. case DPIF_OP_FLOW_DEL:
13.     del = &op->u.flow_del;
14.     dpif_netlink_init_flow_del(dpif, del, &flow);
15.     if (del->stats) {
16.         flow.nlmsg_flags |= NLM_F_ECHO;
17.         aux->txn.reply = &aux->reply;
18.     }
19.     dpif_netlink_flow_to_ofpbuf(&flow, &aux->request);
20.     break;

 

会调用netlink修改内核中datapath的规则。