lwIP协议栈的pbuf结构体

矫情吗；* 2022-10-01 02:00 145阅读 0赞

pbuf结构体位于src/include/lwip/pbuf.h中

以太网中断收到的数据就先存放到这个结构体组成的数据链中,然后将它交付给上层协议.

这个结构体可以说是无处不在.

struct pbuf {
      /** next pbuf in singly linked pbuf chain 指向下一个pbuf*/
      struct pbuf *next;
    
      /** pointer to the actual data in the buffer 指向有效数据区*/
      void *payload;
      
      /**
       * total length of this buffer and all next buffers in chain
       * belonging to the same packet.
       * 数据链的总长度
       * For non-queue packet chains this is the invariant:
       * p->tot_len == p->len + (p->next? p->next->tot_len: 0)
       */
      u16_t tot_len;
      
      /** length of this buffer 这个缓冲区的长度*/
      u16_t len;  
    
      /** pbuf_type as u8_t instead of enum to save space 
          pbuf的类型，有PBUF_RAM、PBUF_ROM、PBUF_REF和PBUF_POOL，这些类型指明指针payload指向的数据的类型*/
      u8_t /*pbuf_type*/ type;
    
      /** misc flags 混合标志位,每一位代表一个标志*/
      u8_t flags;
    
      /**
       * the reference count always equals the number of pointers
       * that refer to this pbuf. This can be pointers from an application,
       * the stack itself, or pbuf->next pointers from a chain.
         统计有多少个指针指向这个pbuf.这些指针可能是应用程序的指针,
    	 协议栈自己的指针或者数据链中的pbuf->next指针,ref为0时，才可以释放该pbuf
    
       */
      u16_t ref;
    
    #if LWIP_PTPD		   //如果使能了网络测量和控制系统的精密时钟同步协议标准
      /* the time at which the packet was received, seconds component */
      u32_t time_s;
    
      /* the time at which the packet was received, nanoseconds component */
      u32_t time_ns;
    #endif /* #if LWIP_PTPD */
    };