5.1 The network interface list

The link layer at each node is intialized by the simulated kernel at boot time. The kernel boot code reads the network configuration file (Section 2.1) and creates a list of networking interfaces on the node. Each element on this list is a struct ifnet defined in $PDIR/include/if.h:

  struct ifnet {
    TAILQ_ENTRY(ifnet)      if_next;

    int                     if_index;       /* interface number */
    struct sockaddr_in      if_addr;        /* address of interface */
    struct sockaddr_in      if_netmask;     /* netmask of if_addr */
    int                     if_mtu;         /* MTU of interface */

    void (*if_start)(struct ifnet *ifp, struct pbuf *p);

    struct hwif             *if_hwif;       /* hardware device */
  };

The head of this list can be accessed by calling the function ifnet_listhead() provided by the simulator. The TAILQ_ENTRY() macro is a macro defined in $PDIR/include/queue.h that is useful for creating linked lists. Iterating over the interface list can be done as follows:

  struct ifnet *ifp = ifnet_listhead();

  for( ; ifp; ifp = TAILQ_NEXT(ifp, if_next)) {
    printf(``interface index: %d\n'', ifp->if_index);
  }