Re: [PATCH net-next 1/2] ipv6: ioam: Add support for the ip6ip6 encapsulation

quoted

 static const struct nla_policy ioam6_iptunnel_policy[IOAM6_IPTUNNEL_MAX + 1] = {
-	[IOAM6_IPTUNNEL_TRACE]	= NLA_POLICY_EXACT_LEN(sizeof(struct ioam6_trace_hdr)),
+	[IOAM6_IPTUNNEL_TRACE]	= NLA_POLICY_EXACT_LEN(sizeof(struct
ioam6_iptunnel_trace)),

you can't do that. Once a kernel is released with a given UAPI, it can
not be changed. You could go the other way and handle

struct ioam6_iptunnel_trace {
+	struct ioam6_trace_hdr trace;
+	__u8 mode;
+	struct in6_addr tundst;	/* unused for inline mode */
+};

Makes sense. But I'm not sure what you mean by "go the other way". Should I handle ioam6_iptunnel_trace as well, in addition to ioam6_trace_hdr, so that the uapi is backward compatible?

Also, no gaps in uapi. Make sure all holes are stated; an anonymous
entry is best.

Would something like this do the trick?

struct ioam6_iptunnel_trace {
	struct ioam6_trace_hdr trace;
	__u8 mode;
	union { /* anonymous field only used by both the encap and auto modes */
		struct in6_addr tundst;
	};
};

quoted

 };
 
-static int nla_put_ioam6_trace(struct sk_buff *skb, int attrtype,
-			       struct ioam6_trace_hdr *trace)
-{
-	struct ioam6_trace_hdr *data;
-	struct nlattr *nla;
-	int len;
-
-	len = sizeof(*trace);
-
-	nla = nla_reserve(skb, attrtype, len);
-	if (!nla)
-		return -EMSGSIZE;
-
-	data = nla_data(nla);
-	memcpy(data, trace, len);
-
-	return 0;
-}
-

quite a bit of the change seems like refactoring from existing feature
to allow the new ones. Please submit refactoring changes as a
prerequisite patch. The patch that introduces your new feature should be
focused solely on what is needed to implement that feature.

+1, will do.