lwip's netif state management

The state change of netif can set the callback function,

There are three main changes,

1 netif up or down，address change，address state change（IPv6）

2 link up or down；

3 netif removal

These three state changes can trigger a user-written callback function

 1 #if LWIP_NETIF_STATUS_CALLBACK
 2   /** This function is called when the netif state is set to up or down
 3    */
 4   netif_status_callback_fn status_callback;
 5 #endif /* LWIP_NETIF_STATUS_CALLBACK */
 6 #if LWIP_NETIF_LINK_CALLBACK
 7   /** This function is called when the netif link is set to up or down
 8    */
 9   netif_status_callback_fn link_callback;
10 #endif /* LWIP_NETIF_LINK_CALLBACK */
11 #if LWIP_NETIF_REMOVE_CALLBACK
12   /** This function is called when the netif has been removed */
13   netif_status_callback_fn remove_callback;
14 #endif /* LWIP_NETIF_REMOVE_CALLBACK */

In addition, netif changes can also trigger protocols such as IP, using netif_issue_reports,

The main changes of netif are: 1 netif up; 2 link up; 3 address change; 4 address state change (IPv6)

For IPv4, ARP, IGMP can be sent; for IPv6, MLD can be sent, RS re-sent, etc.

 1 /** Send ARP/IGMP/MLD/RS events, e.g. on link-up/netif-up or addr-change
 2  */
 3 static void
 4 netif_issue_reports(struct netif* netif, u8_t report_type)
 5 {
 6 #if LWIP_IPV4
 7   if ((report_type & NETIF_REPORT_TYPE_IPV4) &&
 8       !ip4_addr_isany_val(*netif_ip4_addr(netif))) {
 9 #if LWIP_ARP
10     /* For Ethernet network interfaces, we would like to send a "gratuitous ARP" */
11     if (netif->flags & (NETIF_FLAG_ETHARP)) {
12       etharp_gratuitous(netif);
13     }
14 #endif /* LWIP_ARP */
15 
16 #if LWIP_IGMP
17     /* resend IGMP memberships */
18     if (netif->flags & NETIF_FLAG_IGMP) {
19       igmp_report_groups(netif);
20     }
21 #endif /* LWIP_IGMP */
22   }
23 #endif /* LWIP_IPV4 */
24 
25 #if LWIP_IPV6
26   if (report_type & NETIF_REPORT_TYPE_IPV6) {
27 #if LWIP_IPV6_MLD
28     /* send mld memberships */
29     mld6_report_groups(netif);
30 #endif /* LWIP_IPV6_MLD */
31 #if LWIP_IPV6_SEND_ROUTER_SOLICIT
32     /* Send Router Solicitation messages. */
33     netif->rs_count = LWIP_ND6_MAX_MULTICAST_SOLICIT;
34 #endif /* LWIP_IPV6_SEND_ROUTER_SOLICIT */
35   }
36 #endif /* LWIP_IPV6 */
37 }

For the ND protocol, rs_count is mainly set to the initial value.

1 netif up;

2 link up;

3 address change；

4 address state change（IPv6）

lwip's netif state management

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