IPv4-route-fib-create-info

0.0.1. summary

根据用户参数，创建并返回fib_create_info节点。

1. 如果用户参数有问题，则返回空。
   参数检查过程中，会创建一个新的struct fib_info 节点，如果参数检查失败，
   该节点会被free_fib_info释放（通过rcu模式）
2. 如果存在一个相同配置参数的节点，则返回已有的struct fib_info 节点。
   其实已经创建了一个新的struct fib_info 节点，该节点会被free_fib_info释放（通过rcu模式）同1。
3. 否则，创建一个struct fib_info 节点，并初始化，
   节点里相关的ref会被increase,同时将该节点链接到 struct fib_info
   相关的3个hash链(fib_info_hash, fib_info_laddrhash, fib_info_devhash)上.
4. 最后返回新建的节点。

0.0.1.1. NOTE:

After this function struct fib_info *fib_create_info(struct fib_config *cfg),
struct fib_info is only inserted into fib_info hash lists, not the fib table(tree).

struct fib_info *fib_create_info(struct fib_config *cfg)只是把一个创建了一个
struct fib_info节点，并没有真正链接到路由表（fib_tree）里。

774 struct fib_info *fib_create_info(struct fib_config *cfg) 
775 { 
776         int err;
777         struct fib_info *fi = NULL;
778         struct fib_info *ofi;
779         int nhs = 1;
780         struct net *net = cfg->fc_nlinfo.nl_net;
781   
782         if (cfg->fc_type > RTN_MAX)
783                 goto err_inval;
784                    
785         /* Fast check to catch the most weird cases */
786         if (fib_props[cfg->fc_type].scope > cfg->fc_scope)
787                 goto err_inval;
788   
789 #ifdef CONFIG_IP_ROUTE_MULTIPATH
790         if (cfg->fc_mp) {
791                 nhs = fib_count_nexthops(cfg->fc_mp, cfg->fc_mp_len);
792                 if (nhs == 0)
793                         goto err_inval;
794         }
795 #endif
796   
797         err = -ENOBUFS;
798         if (fib_info_cnt >= fib_info_hash_size) {
799                 unsigned int new_size = fib_info_hash_size << 1;
800                 struct hlist_head *new_info_hash;        
801                 struct hlist_head *new_laddrhash;
802                 unsigned int bytes;
803   
804                 if (!new_size)
805                         new_size = 16;
806                 bytes = new_size * sizeof(struct hlist_head *);
807                 new_info_hash = fib_info_hash_alloc(bytes);
808                 new_laddrhash = fib_info_hash_alloc(bytes);
809                 if (!new_info_hash || !new_laddrhash) {  
810                         fib_info_hash_free(new_info_hash, bytes);
811                         fib_info_hash_free(new_laddrhash, bytes);
812                 } else
813                         fib_info_hash_move(new_info_hash, new_laddrhash, new_size);
814   
815                 if (!fib_info_hash_size)
816                         goto failure;
817         }    
818 
819         fi = kzalloc(sizeof(*fi)+nhs*sizeof(struct fib_nh), GFP_KERNEL);
820         if (fi == NULL)
821                 goto failure;
822         if (cfg->fc_mx) {
823                 fi->fib_metrics = kzalloc(sizeof(u32) * RTAX_MAX, GFP_KERNEL);
824                 if (!fi->fib_metrics)
825                         goto failure;
826         } else
827                 fi->fib_metrics = (u32 *) dst_default_metrics;
828         fib_info_cnt++;
829 
830         fi->fib_net = hold_net(net);
831         fi->fib_protocol = cfg->fc_protocol;
832         fi->fib_scope = cfg->fc_scope;
833         fi->fib_flags = cfg->fc_flags;
834         fi->fib_priority = cfg->fc_priority;
835         fi->fib_prefsrc = cfg->fc_prefsrc;
836         fi->fib_type = cfg->fc_type;
837 
838         fi->fib_nhs = nhs;
839         change_nexthops(fi) {
840                 nexthop_nh->nh_parent = fi;
841                 nexthop_nh->nh_pcpu_rth_output = alloc_percpu(struct rtable __rcu *);
842                 if (!nexthop_nh->nh_pcpu_rth_output)
843                         goto failure;
844         } endfor_nexthops(fi)
845         /*  初始化 fib_metric 根据struct nlattr */
846         if (cfg->fc_mx) {
847                 struct nlattr *nla;
848                 int remaining;
849 
850                 nla_for_each_attr(nla, cfg->fc_mx, cfg->fc_mx_len, remaining) {
851                         int type = nla_type(nla);
852 
853                         if (type) {
854                                 u32 val;
855 
856                                 if (type > RTAX_MAX)
857                                         goto err_inval;
858                                 val = nla_get_u32(nla);
859                                 if (type == RTAX_ADVMSS && val > 65535 - 40)
860                                         val = 65535 - 40;
861                                 if (type == RTAX_MTU && val > 65535 - 15)
862                                         val = 65535 - 15;
863                                 fi->fib_metrics[type - 1] = val;
864                         }
865                 }
866         }
867 
868         if (cfg->fc_mp) { /* 多个下一跳 */
869 #ifdef CONFIG_IP_ROUTE_MULTIPATH
870                 err = fib_get_nhs(fi, cfg->fc_mp, cfg->fc_mp_len, cfg);
871                 if (err != 0)
872                         goto failure;
873                 if (cfg->fc_oif && fi->fib_nh->nh_oif != cfg->fc_oif)
874                         goto err_inval;
875                 if (cfg->fc_gw && fi->fib_nh->nh_gw != cfg->fc_gw)
876                         goto err_inval;
877 #ifdef CONFIG_IP_ROUTE_CLASSID
878                 if (cfg->fc_flow && fi->fib_nh->nh_tclassid != cfg->fc_flow)
879                         goto err_inval;
880 #endif
881 #else
882                 goto err_inval;
883 #endif
884         } else { /* 单下一跳 */
885                 struct fib_nh *nh = fi->fib_nh;
886 
887                 nh->nh_oif = cfg->fc_oif;
888                 nh->nh_gw = cfg->fc_gw;
889                 nh->nh_flags = cfg->fc_flags;
890 #ifdef CONFIG_IP_ROUTE_CLASSID
891                 nh->nh_tclassid = cfg->fc_flow;
892                 if (nh->nh_tclassid)
893                         fi->fib_net->ipv4.fib_num_tclassid_users++;
894 #endif
895 #ifdef CONFIG_IP_ROUTE_MULTIPATH
896                 nh->nh_weight = 1;
897 #endif
898         }
899 
900         if (fib_props[cfg->fc_type].error) { /* 有些特殊的路由，如blackhole, 不允许配置 gw, oif(指定出口 out interface）等参数。*/
901                 if (cfg->fc_gw || cfg->fc_oif || cfg->fc_mp)
902                         goto err_inval;
903                 goto link_it;
904         } else {
905                 switch (cfg->fc_type) {
906                 case RTN_UNICAST:
907                 case RTN_LOCAL:
908                 case RTN_BROADCAST:
909                 case RTN_ANYCAST:
910                 case RTN_MULTICAST:
911                         break;
912                 default:
913                         goto err_inval;
914                 }
915         }
916 
917         if (cfg->fc_scope > RT_SCOPE_HOST)
918                 goto err_inval;
919 
920         if (cfg->fc_scope == RT_SCOPE_HOST) { /*  Local address 没有下一跳 */
921                 struct fib_nh *nh = fi->fib_nh;
922 
923                 /* Local address is added. */
924                 if (nhs != 1 || nh->nh_gw)
925                         goto err_inval;
926                 nh->nh_scope = RT_SCOPE_NOWHERE;
927                 nh->nh_dev = dev_get_by_index(net, fi->fib_nh->nh_oif);
928                 err = -ENODEV;
929                 if (nh->nh_dev == NULL)
930                         goto failure;
931         } else { /*  非Local address 必须配置下一跳 (gw,oif) */
932                 change_nexthops(fi) {
933                         err = fib_check_nh(cfg, fi, nexthop_nh);
934                         if (err != 0)
935                                 goto failure;
936                 } endfor_nexthops(fi)
937         }
938 
939         if (fi->fib_prefsrc) {
940                 if (cfg->fc_type != RTN_LOCAL || !cfg->fc_dst ||
941                     fi->fib_prefsrc != cfg->fc_dst)
942                         if (inet_addr_type(net, fi->fib_prefsrc) != RTN_LOCAL)
943                                 goto err_inval;
944         }
945 
946         change_nexthops(fi) {
947                 fib_info_update_nh_saddr(net, nexthop_nh);
948         } endfor_nexthops(fi)
949 
950 link_it:
951         ofi = fib_find_info(fi); /* 如果已经有相同的 fib，则是否新建的fib(fi), 并返回已有的fib节点  */
952         if (ofi) {
953                 fi->fib_dead = 1;
954                 free_fib_info(fi);
955                 ofi->fib_treeref++;
956                 return ofi;
957         }
958        /* 至此，这是一个有效的fib， 加锁，增加ref， 并将其链接到 fib 3个hash链里(fib_info_hash, fib_info_laddrhash,fib_info_devhash) */
959         fi->fib_treeref++;
960         atomic_inc(&fi->fib_clntref); 
961         spin_lock_bh(&fib_info_lock);
962         hlist_add_head(&fi->fib_hash,  
963                        &fib_info_hash[fib_info_hashfn(fi)]);
964         if (fi->fib_prefsrc) {
965                 struct hlist_head *head;
966 
967                 head = &fib_info_laddrhash[fib_laddr_hashfn(fi->fib_prefsrc)];
968                 hlist_add_head(&fi->fib_lhash, head);
969         }
970         change_nexthops(fi) {
971                 struct hlist_head *head;
972                 unsigned int hash;
973 
974                 if (!nexthop_nh->nh_dev)
975                         continue;
976                 hash = fib_devindex_hashfn(nexthop_nh->nh_dev->ifindex);
977                 head = &fib_info_devhash[hash];
978                 hlist_add_head(&nexthop_nh->nh_hash, head);
979         } endfor_nexthops(fi)
980         spin_unlock_bh(&fib_info_lock);
981         return fi;
982 
983 err_inval:
984         err = -EINVAL;
985 
986 failure:
987         if (fi) {
988                 fi->fib_dead = 1;
989                 free_fib_info(fi);
990         }
991 
992         return ERR_PTR(err);
993 }