Openvswitch原理与代码分析: 添加一条流表flow

Posted 2020-08-10 刘超的通俗云计算

添加一个flow，调用的命令为

ovs-ofctl add-flow hello "hard_timeout=0 idle_timeout=0 priority=1 table=21 pkt_mark=0x55 tun_id=0x55 actions=mod_nw_dst:192.168.56.101,output:2"

这里调用的是调用ovs/utilities/ovs-ofctl.c的命令行工具

这个命令行工具支持的所有的命令及处理函数定义如下：

static const struct ovs_cmdl_command all_commands[] = { ????{ "show", "switch", ??????1, 1, ofctl_show }, ????{ "monitor", "switch [misslen] [invalid_ttl] [watch:[...]]", ??????1, 3, ofctl_monitor }, ????{ "snoop", "switch", ??????1, 1, ofctl_snoop }, ????{ "dump-desc", "switch", ??????1, 1, ofctl_dump_desc }, ????{ "dump-tables", "switch", ??????1, 1, ofctl_dump_tables }, ????{ "dump-table-features", "switch", ??????1, 1, ofctl_dump_table_features }, ????{ "dump-table-desc", "switch", ??????1, 1, ofctl_dump_table_desc }, ????{ "dump-flows", "switch", ??????1, 2, ofctl_dump_flows }, ????{ "dump-aggregate", "switch", ??????1, 2, ofctl_dump_aggregate }, ????{ "queue-stats", "switch [port [queue]]", ??????1, 3, ofctl_queue_stats }, ????{ "queue-get-config", "switch port", ??????2, 2, ofctl_queue_get_config }, ????{ "add-flow", "switch flow", ??????2, 2, ofctl_add_flow }, ????{ "add-flows", "switch file", ??????2, 2, ofctl_add_flows }, ????{ "mod-flows", "switch flow", ??????2, 2, ofctl_mod_flows }, ????{ "del-flows", "switch [flow]", ??????1, 2, ofctl_del_flows }, ????{ "replace-flows", "switch file", ??????2, 2, ofctl_replace_flows }, ????{ "diff-flows", "source1 source2", ??????2, 2, ofctl_diff_flows }, ????{ "add-meter", "switch meter", ??????2, 2, ofctl_add_meter }, ????{ "mod-meter", "switch meter", ??????2, 2, ofctl_mod_meter }, ????{ "del-meter", "switch meter", ??????2, 2, ofctl_del_meters }, ????{ "del-meters", "switch", ??????1, 1, ofctl_del_meters }, ????{ "dump-meter", "switch meter", ??????2, 2, ofctl_dump_meters }, ????{ "dump-meters", "switch", ??????1, 1, ofctl_dump_meters }, ????{ "meter-stats", "switch [meter]", ??????1, 2, ofctl_meter_stats }, ????{ "meter-features", "switch", ??????1, 1, ofctl_meter_features }, ????{ "packet-out", "switch in_port actions packet...", ??????4, INT_MAX, ofctl_packet_out }, ????{ "dump-ports", "switch [port]", ??????1, 2, ofctl_dump_ports }, ????{ "dump-ports-desc", "switch [port]", ??????1, 2, ofctl_dump_ports_desc }, ????{ "mod-port", "switch iface act", ??????3, 3, ofctl_mod_port }, ????{ "mod-table", "switch mod", ??????3, 3, ofctl_mod_table }, ????{ "get-frags", "switch", ??????1, 1, ofctl_get_frags }, ????{ "set-frags", "switch frag_mode", ??????2, 2, ofctl_set_frags }, ????{ "probe", "target", ??????1, 1, ofctl_probe }, ????{ "ping", "target [n]", ??????1, 2, ofctl_ping }, ????{ "benchmark", "target n count", ??????3, 3, ofctl_benchmark }, ? ????{ "ofp-parse", "file", ??????1, 1, ofctl_ofp_parse }, ????{ "ofp-parse-pcap", "pcap", ??????1, INT_MAX, ofctl_ofp_parse_pcap }, ? ????{ "add-group", "switch group", ??????1, 2, ofctl_add_group }, ????{ "add-groups", "switch file", ??????1, 2, ofctl_add_groups }, ????{ "mod-group", "switch group", ??????1, 2, ofctl_mod_group }, ????{ "del-groups", "switch [group]", ??????1, 2, ofctl_del_groups }, ????{ "insert-buckets", "switch [group]", ??????1, 2, ofctl_insert_bucket }, ????{ "remove-buckets", "switch [group]", ??????1, 2, ofctl_remove_bucket }, ????{ "dump-groups", "switch [group]", ??????1, 2, ofctl_dump_group_desc }, ????{ "dump-group-stats", "switch [group]", ??????1, 2, ofctl_dump_group_stats }, ????{ "dump-group-features", "switch", ??????1, 1, ofctl_dump_group_features }, ????{ "add-tlv-map", "switch map", ??????2, 2, ofctl_add_tlv_map }, ????{ "del-tlv-map", "switch [map]", ??????1, 2, ofctl_del_tlv_map }, ????{ "dump-tlv-map", "switch", ??????1, 1, ofctl_dump_tlv_map }, ????{ "help", NULL, 0, INT_MAX, ofctl_help }, ????{ "list-commands", NULL, 0, INT_MAX, ofctl_list_commands }, ? ????/* Undocumented commands for testing. */ ????{ "parse-flow", NULL, 1, 1, ofctl_parse_flow }, ????{ "parse-flows", NULL, 1, 1, ofctl_parse_flows }, ????{ "parse-nx-match", NULL, 0, 0, ofctl_parse_nxm }, ????{ "parse-nxm", NULL, 0, 0, ofctl_parse_nxm }, ????{ "parse-oxm", NULL, 1, 1, ofctl_parse_oxm }, ????{ "parse-actions", NULL, 1, 1, ofctl_parse_actions }, ????{ "parse-instructions", NULL, 1, 1, ofctl_parse_instructions }, ????{ "parse-ofp10-match", NULL, 0, 0, ofctl_parse_ofp10_match }, ????{ "parse-ofp11-match", NULL, 0, 0, ofctl_parse_ofp11_match }, ????{ "parse-pcap", NULL, 1, 1, ofctl_parse_pcap }, ????{ "check-vlan", NULL, 2, 2, ofctl_check_vlan }, ????{ "print-error", NULL, 1, 1, ofctl_print_error }, ????{ "encode-error-reply", NULL, 2, 2, ofctl_encode_error_reply }, ????{ "ofp-print", NULL, 1, 2, ofctl_ofp_print }, ????{ "encode-hello", NULL, 1, 1, ofctl_encode_hello }, ? ????{ NULL, NULL, 0, 0, NULL }, };

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根据这个数据结构的定义，"add-flow"调用的函数为

static void ofctl_add_flow(struct ovs_cmdl_context *ctx) { ????ofctl_flow_mod(ctx->argc, ctx->argv, OFPFC_ADD); }

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调用ofctl_flow_mod，parse_ofp_flow_mod_str将字符串解析为ofputil_flow_mod fm

ofputil_flow_mod包含两个最重要的成员变量：

struct match match，所谓match就是一个key。

struct ofpact *ofpacts; /* Series of "struct ofpact"s. */

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static void ofctl_flow_mod(int argc, char *argv[], uint16_t command) { ????if (argc > 2 && !strcmp(argv[2], "-")) { ????????ofctl_flow_mod_file(argc, argv, command); ????} else { ????????struct ofputil_flow_mod fm; ????????char *error; ????????enum ofputil_protocol usable_protocols; ? ????????error = parse_ofp_flow_mod_str(&fm, argc > 2 ? argv[2] : "", command, ???????????????????????????????????????&usable_protocols); ????????if (error) { ????????????ovs_fatal(0, "%s", error); ????????} ????????ofctl_flow_mod__(argv[1], &fm, 1, usable_protocols); ????} }

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ofctl_flow_mod__会打开一个指向ovs-vswitchd的socket，将flow match变成openflow的协议，发出去transact_noreply

static void ofctl_flow_mod__(const char *remote, struct ofputil_flow_mod *fms, ?????????????????size_t n_fms, enum ofputil_protocol usable_protocols) { ????enum ofputil_protocol protocol; ????struct vconn *vconn; ????size_t i; ? ????if (bundle) { ????????bundle_flow_mod__(remote, fms, n_fms, usable_protocols); ????????return; ????} ? ????protocol = open_vconn_for_flow_mod(remote, &vconn, usable_protocols); ? ????for (i = 0; i < n_fms; i++) { ????????struct ofputil_flow_mod *fm = &fms[i]; ? ????????transact_noreply(vconn, ofputil_encode_flow_mod(fm, protocol)); ????????free(CONST_CAST(struct ofpact *, fm->ofpacts)); ????} ????vconn_close(vconn); }

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Ovs-vswitchd会监听socket，在ovs-vswitchd.c中bridge_run每个bridge会监听消息，ofproto_run监听openflow的调用，connmgr_run网络连接管理，ofconn_run管理socket连接。

connmgr_run(p->connmgr, handle_openflow);会设置当有openflow调用的时候，handle_openflow会被调用。

static void handle_openflow(struct ofconn *ofconn, const struct ofpbuf *ofp_msg) ????OVS_EXCLUDED(ofproto_mutex) { ????enum ofperr error = handle_openflow__(ofconn, ofp_msg); ? ????if (error) { ????????ofconn_send_error(ofconn, ofp_msg->data, error); ????} ????COVERAGE_INC(ofproto_recv_openflow); }

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handle_openflow__会做如下的调用：

case OFPTYPE_FLOW_MOD: ????return handle_flow_mod(ofconn, oh);

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handle_flow_mod首先将openflow协议解析为fm和ofpacts

error = ofputil_decode_flow_mod(&ofm.fm, oh, ofconn_get_protocol(ofconn), ????????????????????????????????&ofpacts, ????????????????????????????????u16_to_ofp(ofproto->max_ports), ????????????????????????????????ofproto->n_tables);

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然后调用static enum ofperr handle_flow_mod__(struct ofproto *ofproto, struct ofproto_flow_mod *ofm, const struct flow_mod_requester *req)

会调用static enum ofperr ofproto_flow_mod_start(struct ofproto *ofproto, struct ofproto_flow_mod *ofm) OVS_REQUIRES(ofproto_mutex)

static enum ofperr ofproto_flow_mod_start(struct ofproto *ofproto, struct ofproto_flow_mod *ofm) ????OVS_REQUIRES(ofproto_mutex) { ????switch (ofm->fm.command) { ????case OFPFC_ADD: ????????return add_flow_start(ofproto, ofm); ????????/* , &be->old_rules.stub[0], ???????????&be->new_rules.stub[0]); */ ????case OFPFC_MODIFY: ????????return modify_flows_start_loose(ofproto, ofm); ????case OFPFC_MODIFY_STRICT: ????????return modify_flow_start_strict(ofproto, ofm); ????case OFPFC_DELETE: ????????return delete_flows_start_loose(ofproto, ofm); ? ????case OFPFC_DELETE_STRICT: ????????return delete_flow_start_strict(ofproto, ofm); ????} ? ????return OFPERR_OFPFMFC_BAD_COMMAND; }

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在函数add_flow_start中，首先cls_rule_init(&cr, &fm->match, fm->priority); 将match也即key变成一个cls_rule，cls_rule是一个压缩版本的match，match是一个整个数据结构保存整个package，从L1一直到L4全都有，比较大，如果保存在内存太浪费，cls_rule中有一个minimatch，是用压缩的方式保存match，也即如果match中为0的部分不保存，采取稀疏矩阵的方式。

接下来创建一个新的rule，error = replace_rule_create(ofproto, fm, &cr, table - ofproto->tables, rule, new_rule);

最后replace_rule_start(ofproto, ofm->version, rule, *new_rule, conjs, n_conjs); 将rule替换现在的rule，有则替换，没有则插入。

static void replace_rule_start(struct ofproto *ofproto, cls_version_t version, ???????????????????struct rule *old_rule, struct rule *new_rule, ???????????????????struct cls_conjunction *conjs, size_t n_conjs) { ????struct oftable *table = &ofproto->tables[new_rule->table_id]; ? ????/* ‘old_rule‘ may be either an evicted rule or replaced rule. */ ????if (old_rule) { ????????/* Mark the old rule for removal in the next version. */ ????????cls_rule_make_invisible_in_version(&old_rule->cr, version); ????} else { ????????table->n_flows++; ????} ????/* Insert flow to the classifier, so that later flow_mods may relate ?????* to it. This is reversible, in case later errors require this to ?????* be reverted. */ ????ofproto_rule_insert__(ofproto, new_rule); ????/* Make the new rule visible for classifier lookups only from the next ?????* version. */ ????classifier_insert(&table->cls, &new_rule->cr, version, conjs, n_conjs); }