[components/net] add dns server ip address config, may custom in menuconfig

Signed-off-by: NMurphyZhao <d2014zjt@163.com>

components/net/Kconfig

@@ -217,7 +217,17 @@ config LWIP_USING_DHCPD
         config DHCPD_USING_ROUTER
             bool "alloc gateway ip for router"
             default y
+
+        config LWIP_USING_CUSTOMER_DNS_SERVER
+            bool "Enable customer DNS server config"
+            default n
+        if LWIP_USING_CUSTOMER_DNS_SERVER
+            config DHCP_DNS_SERVER_IP
+                string "Custom DNS server IP address"
+                default 1.1.1.1
+        endif
     endif
+    
 
 endif
 

components/net/lwip_dhcpd/dhcp_server.c

@@ -434,10 +434,25 @@ static void dhcpd_thread_entry(void *parameter)
                 // DHCP_OPTION_DNS_SERVER, use the default DNS server address in lwIP
                 *dhcp_opt++ = DHCP_OPTION_DNS_SERVER;
                 *dhcp_opt++ = 4;
-                *dhcp_opt++ = 208;
-                *dhcp_opt++ = 67;
-                *dhcp_opt++ = 222;
-                *dhcp_opt++ = 222;
+
+#ifndef DHCP_DNS_SERVER_IP
+                *dhcp_opt++ = DHCPD_SERVER_IPADDR0;
+                *dhcp_opt++ = DHCPD_SERVER_IPADDR1;
+                *dhcp_opt++ = DHCPD_SERVER_IPADDR2;
+                *dhcp_opt++ = 1;
+#else
+                struct ip_addr dns_addr;
+                ip4addr_aton(DHCP_DNS_SERVER_IP, &dns_addr);
+                DNS_SERVER_IPADDR0 = (ntohl(dns_addr.addr) >> 24) & 0xFF;
+                DNS_SERVER_IPADDR1 = (ntohl(dns_addr.addr) >> 16) & 0xFF;
+                DNS_SERVER_IPADDR2 = (ntohl(dns_addr.addr) >>  8) & 0xFF;
+                DNS_SERVER_IPADDR3 = (ntohl(dns_addr.addr) >>  0) & 0xFF;
+
+                *dhcp_opt++ = DNS_SERVER_IPADDR0;
+                *dhcp_opt++ = DNS_SERVER_IPADDR1;
+                *dhcp_opt++ = DNS_SERVER_IPADDR2;
+                *dhcp_opt++ = DNS_SERVER_IPADDR3;
+#endif
 
                 // DHCP_OPTION_LEASE_TIME
                 *dhcp_opt++ = DHCP_OPTION_LEASE_TIME;