exthdr: Implement existence check

This allows to check for existence of an IPv6 extension or TCP
option header by using the following syntax:

| exthdr frag exists
| tcpopt window exists

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/exthdr.h b/include/exthdr.h
index c7f806eb..a2647ee1 100644
--- a/include/exthdr.h
+++ b/include/exthdr.h
@@ -21,6 +21,8 @@ extern struct expr *exthdr_expr_alloc(const struct location *loc,
 				      const struct exthdr_desc *desc,
 				      uint8_t type);
 
+extern const struct exthdr_desc *exthdr_find_proto(uint8_t proto);
+
 extern void exthdr_init_raw(struct expr *expr, uint8_t type,
 			    unsigned int offset, unsigned int len,
 			    enum nft_exthdr_op op, uint32_t flags);