c
// (Define this function somewhere appropriate)
static struct sk_buff *alloc_rtm_phonet_skb(u32 extra_data_len) {
    if (extra_data_len > MAX_EXTRA_DATA_SIZE) {
        // Handle error 
        return NULL;
    }
    struct sk_buff *skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct ifaddrmsg)) + extra_data_len, GFP_KERNEL);
    if (!skb) {
        // Handle allocation failure
        return NULL;
    }
    return skb;
}

// ... inside rtm_phonet_notify ...

6 	skb = alloc_rtm_phonet_skb(extra_data_len);
    if (!skb) {
        // Handle allocation failure
        return; 
    }
