ipv6: ioam: Support for IOAM injection with lwtunnels

Add support for the IOAM inline insertion (only for the host-to-host use case)
which is per-route configured with lightweight tunnels. The target is iproute2
and the patch is ready. It will be posted as soon as this patchset is merged.
Here is an overview:

$ ip -6 ro ad fc00::1/128 encap ioam6 trace type 0x800000 ns 1 size 12 dev eth0

This example configures an IOAM Pre-allocated Trace option attached to the
fc00::1/128 prefix. The IOAM namespace (ns) is 1, the size of the pre-allocated
trace data block is 12 octets (size) and only the first IOAM data (bit 0:
hop_limit + node id) is included in the trace (type) represented as a bitfield.

The reason why the in-transit (IPv6-in-IPv6 encapsulation) use case is not
implemented is explained on the patchset cover.

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/ioam6.h

@@ -126,6 +126,7 @@ struct ioam6_trace_hdr {
 #error "Please fix <asm/byteorder.h>"
 #endif
 
+#define IOAM6_TRACE_DATA_SIZE_MAX 244
 	__u8	data[0];
 } __attribute__((packed));
 

include/uapi/linux/ioam6_iptunnel.h

@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+/*
+ *  IPv6 IOAM Lightweight Tunnel API
+ *
+ *  Author:
+ *  Justin Iurman <justin.iurman@uliege.be>
+ */
+
+#ifndef _UAPI_LINUX_IOAM6_IPTUNNEL_H
+#define _UAPI_LINUX_IOAM6_IPTUNNEL_H
+
+enum {
+	IOAM6_IPTUNNEL_UNSPEC,
+	IOAM6_IPTUNNEL_TRACE,		/* struct ioam6_trace_hdr */
+	__IOAM6_IPTUNNEL_MAX,
+};
+
+#define IOAM6_IPTUNNEL_MAX (__IOAM6_IPTUNNEL_MAX - 1)
+
+#endif /* _UAPI_LINUX_IOAM6_IPTUNNEL_H */

include/uapi/linux/lwtunnel.h

@@ -14,6 +14,7 @@ enum lwtunnel_encap_types {
 	LWTUNNEL_ENCAP_BPF,
 	LWTUNNEL_ENCAP_SEG6_LOCAL,
 	LWTUNNEL_ENCAP_RPL,
+	LWTUNNEL_ENCAP_IOAM6,
 	__LWTUNNEL_ENCAP_MAX,
 };