quagga源码分析--路由信息处理zebra-rib

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：

 /* initialise zebra rib work queue */
 static void
 rib_queue_init(struct zebra_t *zebra)
 {
     assert(zebra);
 
     if (!(zebra->ribq = work_queue_new(zebra->master,
                                        "route_node processing")))
     {
         zlog_err("%s: could not initialise work queue!", __func__);
         return;
     }
 
     /* fill in the work queue spec */
     zebra->ribq->spec.workfunc = &meta_queue_process;
     zebra->ribq->spec.errorfunc = NULL;
     /* XXX: TODO: These should be runtime configurable via vty */
     zebra->ribq->spec.max_retries = ;
     zebra->ribq->spec.hold = rib_process_hold_time;
 
     if (!(zebra->mq = meta_queue_new()))
     {
         zlog_err("%s: could not initialise meta queue!", __func__);
         return;
     }
     return;
 }

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

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

在添加thread任务的时候进行了时间单位换算：

 /* Add a background thread, with an optional millisec delay */
 struct thread*
 funcname_thread_add_background(struct thread_master *m,
                                int (*func)(struct thread *),
                                void *arg, long delay,
                                debugargdef) {
     struct timeval trel;
 
     assert(m != NULL);
 
     if (delay) {
         trel.tv_sec = delay / ;
         trel.tv_usec =  * (delay % );
     } else {
         trel.tv_sec = ;
         trel.tv_usec = ;
     }
 
     return funcname_thread_add_timer_timeval(m, func, THREAD_BACKGROUND,
                                              arg, &trel, debugargpass);
 }

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)

 struct rib {
   struct rib *next;         /* Link list. */
   struct rib *prev;
   struct nexthop *nexthop; /* Nexthop structure */
   unsigned long refcnt;    /* Refrence count. */
   time_t uptime;           /* Uptime. */
   int type;                /* Type fo this route. */
   vrf_id_t vrf_id;         /* VRF identifier. */
   int table;               /* Which routing table */
   u_int32_t metric;        /* Metric */
   u_int32_t mtu;           /* MTU */
   u_int32_t nexthop_mtu;
   u_char distance;         /* Distance. */
   u_char flags;             /* Flags of this route. in lib/zebra.h ZEBRA_FLAG_* */
   u_char status;            /* RIB internal status */
 #define RIB_ENTRY_REMOVED    (1 << 0)
 #define RIB_ENTRY_CHANGED    (1 << 1)
 #define RIB_ENTRY_SELECTED_FIB    (1 << 2)
   u_char nexthop_num;        /* Nexthop information. */
   u_char nexthop_active_num;
   u_char nexthop_fib_num;
 };

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：

 /* Each routing entry. */
 struct route_node {
   struct prefix p;   /* Actual prefix of this radix. */
   struct route_table *table;   /* Tree link. */
   struct route_node *parent;
   struct route_node *link[];
   unsigned int lock; /* Lock of this radix */
   void *info;        /* Each node of route. */
   void *aggregate;   /* Aggregation. */
 
 #define l_left   link[0]
 #define l_right  link[1]
 };

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。