Re: [lwip-users] issue adding static arp entries.

[Joel Cunningham]

On 12/19/2017 1:59 PM, Kent Pluntze wrote:
> Hello,
>
> I am trying to create a network with limited traffic so I am 
> attempting to initialize all ARP tables to static. Currently I am 
> calling a function in the application which does the following.
>
> makeArpTableStatic(void){
>
> /*inits*/
> int i;
> u8_t count = 0;
> u8_t entry_ret = 0;
> s8_t ret =0;
> ip_addr_t **ip_addr_ret = NULL;
> struct netif **netif = NULL;
> struct eth_addr **eth_ret = NULL;
>
> for(i=0; i<ARP_TABLE_SIZE; i++){
>      count = (u8_t) i;
>      entry_ret= etharp_get_entry(count, ip_addr_ret, netif, eth_ret);
>      if( entry_ret == 1){
>           ret = etharp_add_static_entry(*ip_addr_ret, *eth_ret);

These are RAW APIs that may not be safe to be called from application 
code depending on your system and LwIP's configuration. See 
http://www.nongnu.org/lwip/2_0_x/pitfalls.html

> #ifdef DEBUG_ON
>           printf("return of %d = %d\n",i ,ret);
> #endif
>       }
> ip_addr_ret = NULL;
> netif = NULL;
> eth_ret = NULL;
> }
>
> }/*eof*/
>
> This code crashes when it reaches etharp_add_static_entry. It runs if 
> that function is removed. currently there are no other ways to make an 
> entry static from the application layer. Any help you could offer 
> would be appreciated.

We added thread safe ARP cache APIs in git master (though there's not a 
getter, only add/remove).  See 
http://git.savannah.nongnu.org/cgit/lwip.git/commit/?id=c47d161d4a8946028fff6143160e9f58d1a4be49

Joel