+
+/* This routine returns the IP overhead imposed by a socket i.e.
+ * the length of the underlying IP header, depending on whether
+ * this is an IPv4 or IPv6 socket and the length from IP options turned
+ * on at the socket. Assumes that the caller has a lock on the socket.
+ */
+u32 kernel_sock_ip_overhead(struct sock *sk)
+{
+ struct inet_sock *inet;
+ struct ip_options_rcu *opt;
+ u32 overhead = 0;
+ bool owned_by_user;
+#if IS_ENABLED(CONFIG_IPV6)
+ struct ipv6_pinfo *np;
+ struct ipv6_txoptions *optv6 = NULL;
+#endif /* IS_ENABLED(CONFIG_IPV6) */
+
+ if (!sk)
+ return overhead;
+
+ owned_by_user = sock_owned_by_user(sk);
+ switch (sk->sk_family) {
+ case AF_INET:
+ inet = inet_sk(sk);
+ overhead += sizeof(struct iphdr);
+ opt = rcu_dereference_protected(inet->inet_opt,
+ owned_by_user);
+ if (opt)
+ overhead += opt->opt.optlen;
+ return overhead;
+#if IS_ENABLED(CONFIG_IPV6)
+ case AF_INET6:
+ np = inet6_sk(sk);
+ overhead += sizeof(struct ipv6hdr);
+ if (np)
+ optv6 = rcu_dereference_protected(np->opt,
+ owned_by_user);
+ if (optv6)
+ overhead += (optv6->opt_flen + optv6->opt_nflen);
+ return overhead;
+#endif /* IS_ENABLED(CONFIG_IPV6) */
+ default: /* Returns 0 overhead if the socket is not ipv4 or ipv6 */
+ return overhead;
+ }
+}
+EXPORT_SYMBOL(kernel_sock_ip_overhead);