(2) quagga源码分析--路由信息处理zebra-rib

http://www.cnblogs.com/danxi/p/6285545.html

对于各个协议生成的路由信息的处理属于quagga中非常重要的一个功能，如何在内核进行路由增加，更新，删除是一个复杂的过程。

quagga在thread任务调度中加入了一种工作队列，work_queue，与内核的工作队列类似，是一种相对而言，低优先级的任务，这里的任务看成类似的系统进程。

1、队列初始化：

 1 /* initialise zebra rib work queue */ 2 static void 3 rib_queue_init(struct zebra_t *zebra) 4 { 5     assert(zebra); 6  7     if (!(zebra->ribq = work_queue_new(zebra->master, 8                                        "route_node processing"))) 9     {10         zlog_err("%s: could not initialise work queue!", __func__);11         return;12     }13 14     /* fill in the work queue spec */15     zebra->ribq->spec.workfunc = &meta_queue_process;16     zebra->ribq->spec.errorfunc = NULL;17     /* XXX: TODO: These should be runtime configurable via vty */18     zebra->ribq->spec.max_retries = 3;19     zebra->ribq->spec.hold = rib_process_hold_time;20 21     if (!(zebra->mq = meta_queue_new()))22     {23         zlog_err("%s: could not initialise meta queue!", __func__);24         return;25     }26     return;27 }

第19行，zebra->ribq->spec.hold = rib_process_hold_time; 指定了rib工作队列在thread_fetch的时候会等待10毫秒

 

1 /* Hold time for RIB process, should be very minimal.2  * it is useful to able to set it otherwise for testing, hence exported3  * as global here for test-rig code.4  */5 int rib_process_hold_time = 10;

 

在添加thread任务的时候进行了时间单位换算：

 1 /* Add a background thread, with an optional millisec delay */ 2 struct thread* 3 funcname_thread_add_background(struct thread_master *m, 4                                int (*func)(struct thread *), 5                                void *arg, long delay, 6                                debugargdef) { 7     struct timeval trel; 8  9     assert(m != NULL);10 11     if (delay) {12         trel.tv_sec = delay / 1000;13         trel.tv_usec = 1000 * (delay % 1000);14     } else {15         trel.tv_sec = 0;16         trel.tv_usec = 0;17     }18 19     return funcname_thread_add_timer_timeval(m, func, THREAD_BACKGROUND,20                                              arg, &trel, debugargpass);21 }

OK，meta_queue_process，就指定了工作队列在调度执行的处理函数，由此guagga就会一直同步更新路由了。

2、每个子网的下一跳路由表项的描述：

quagga使用了双向链表来管理表项，定义了路由表现的详细信息，但比如 status 这个字段是用来在更新路由时来做比较的关键字段。如下宏定义了3种状态：

#define RIB_ENTRY_REMOVED    (1 << 0)
#define RIB_ENTRY_CHANGED    (1 << 1)
#define RIB_ENTRY_SELECTED_FIB    (1 << 2)

 1 struct rib {  2   struct rib *next;         /* Link list. */ 3   struct rib *prev; 4   struct nexthop *nexthop; /* Nexthop structure */ 5   unsigned long refcnt;    /* Refrence count. */ 6   time_t uptime;           /* Uptime. */ 7   int type;                /* Type fo this route. */ 8   vrf_id_t vrf_id;         /* VRF identifier. */ 9   int table;               /* Which routing table */10   u_int32_t metric;        /* Metric */11   u_int32_t mtu;           /* MTU */12   u_int32_t nexthop_mtu;13   u_char distance;         /* Distance. */14   u_char flags;             /* Flags of this route. in lib/zebra.h ZEBRA_FLAG_* */15   u_char status;            /* RIB internal status */16 #define RIB_ENTRY_REMOVED    (1 << 0)17 #define RIB_ENTRY_CHANGED    (1 << 1)18 #define RIB_ENTRY_SELECTED_FIB    (1 << 2)19   u_char nexthop_num;        /* Nexthop information. */20   u_char nexthop_active_num;21   u_char nexthop_fib_num;22 };

 3、整个路由表的描述：

/* Routing table top structure. */struct route_table {  struct route_node *top;  /*   * Delegate that performs certain functions for this table.   */  route_table_delegate_t *delegate;  unsigned long count;  void *info;     /* User data. */};

route_table包含了一个二叉树结构来保存所有的路由前缀和下一跳路由表项，prefix结构保持了路由前缀的长度和值，用来做最长前缀匹配：

 1 /* Each routing entry. */ 2 struct route_node { 3   struct prefix p;   /* Actual prefix of this radix. */ 4   struct route_table *table;   /* Tree link. */ 5   struct route_node *parent; 6   struct route_node *link[2]; 7   unsigned int lock; /* Lock of this radix */ 8   void *info;        /* Each node of route. */ 9   void *aggregate;   /* Aggregation. */10 11 #define l_left   link[0]12 #define l_right  link[1]13 };

呃，说好的mtire树呢? 好吧，我们不太可能把成千上万的路由表项塞给linux内核，够用就行。