net: ipv6: add support for rpl sr exthdr

This patch adds rpl source routing receive handling. Everything works
only if sysconf "rpl_seg_enabled" and source routing is enabled. Mostly
the same behaviour as IPv6 segmentation routing. To handle compression
and uncompression a rpl.c file is created which contains the necessary
functionality. The receive handling will also care about IPv6
encapsulated so far it's specified as possible nexthdr in RFC 6554.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/rpl.h

@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ *  RPL implementation
+ *
+ *  Author:
+ *  (C) 2020 Alexander Aring <alex.aring@gmail.com>
+ */
+
+#ifndef _NET_RPL_H
+#define _NET_RPL_H
+
+#include <linux/rpl.h>
+
+/* Worst decompression memory usage ipv6 address (16) + pad 7 */
+#define IPV6_RPL_SRH_WORST_SWAP_SIZE (sizeof(struct in6_addr) + 7)
+
+static inline size_t ipv6_rpl_srh_alloc_size(unsigned char n)
+{
+	return sizeof(struct ipv6_rpl_sr_hdr) +
+		((n + 1) * sizeof(struct in6_addr));
+}
+
+size_t ipv6_rpl_srh_size(unsigned char n, unsigned char cmpri,
+			 unsigned char cmpre);
+
+void ipv6_rpl_srh_decompress(struct ipv6_rpl_sr_hdr *outhdr,
+			     const struct ipv6_rpl_sr_hdr *inhdr,
+			     const struct in6_addr *daddr, unsigned char n);
+
+void ipv6_rpl_srh_compress(struct ipv6_rpl_sr_hdr *outhdr,
+			   const struct ipv6_rpl_sr_hdr *inhdr,
+			   const struct in6_addr *daddr, unsigned char n);
+
+#endif /* _NET_RPL_H */