Linux kernel udp lookup

Question

struct sock *udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
                 __be32 daddr, __be16 dport, int dif)

Here is declaration of function, that converts connection attributes to struct sock. As I googled, first argument should be &init_net. But what should be last argument?

Answer 1

The dif argument is the device interface.