【lwip】11-UDP协议&源码分析( 四 ) _生活百科

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从MEMP_UDP_PCB内存池中获取UDP控制块资源。
初始化部分字段。

/** * @ingroup udp_raw * Creates a new UDP pcb which can be used for UDP communication. The * pcb is not active until it has either been bound to a local address * or connected to a remote address. * @see MEMP_NUM_UDP_PCB * * @return The UDP PCB which was created. NULL if the PCB data structure * could not be allocated. * * @see udp_remove() */struct udp_pcb *udp_new(void){struct udp_pcb *pcb;LWIP_ASSERT_CORE_LOCKED(); /* 内核锁确认 */pcb = (struct udp_pcb *)memp_malloc(MEMP_UDP_PCB); /* 申请UDP控制块资源 */if (pcb != NULL) {memset(pcb, 0, sizeof(struct udp_pcb));pcb->ttl = UDP_TTL; /* UDP数据出口默认的TTL值 */#if LWIP_MULTICAST_TX_OPTIONS /* 多播TX相关 */udp_set_multicast_ttl(pcb, UDP_TTL);#endif /* LWIP_MULTICAST_TX_OPTIONS */}return pcb;}

11.11.2 udp_remove()：删除UDP控制块udp_remove()：

struct udp_pcb *pcb：需要删除的UDP控制块。

/** * @ingroup udp_raw * Removes and deallocates the pcb. * * @param pcb UDP PCB to be removed. The PCB is removed from the list of * UDP PCB's and the data structure is freed from memory. * * @see udp_new() */voidudp_remove(struct udp_pcb *pcb){struct udp_pcb *pcb2;LWIP_ASSERT_CORE_LOCKED(); /* 内核所内 */LWIP_ERROR("udp_remove: invalid pcb", pcb != NULL, return);mib2_udp_unbind(pcb);/* 先从udp_pcbs链表中移除 */if (udp_pcbs == pcb) {/* 如果当前UDP控制块是udp_pcbs的链表头 ， 则直接更新链表头即可移除 */udp_pcbs = udp_pcbs->next;} else { /* 需要遍历udp_pcbs ， 把当前UDP控制块移除 */for (pcb2 = udp_pcbs; pcb2 != NULL; pcb2 = pcb2->next) {if (pcb2->next != NULL && pcb2->next == pcb) {pcb2->next = pcb->next;break;}}}/* 释放内存资源 */memp_free(MEMP_UDP_PCB, pcb);}

11.11.3 udp_bind()：绑定控制块当UDP服务于应用程序时，数据流需要底层和应用层进行对接，就需要把UDP控制块绑定到本地IP和端口号。
绑定控制块时需要注意的是：