Returns true or false. */
extern int skb_make_writable(struct sk_buff **pskb, unsigned int writable_len);
+extern u_int16_t nf_csum_update(u_int32_t oldval, u_int32_t newval,
+ u_int32_t csum);
+extern u_int16_t nf_proto_csum_update(struct sk_buff *skb,
+ u_int32_t oldval, u_int32_t newval,
+ u_int16_t csum, int pseudohdr);
+
struct nf_afinfo {
unsigned short family;
unsigned int (*checksum)(struct sk_buff *skb, unsigned int hook,