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

quoted

quoted

quoted

quoted

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?

by "the other way" I meant let ioam6_trace_hdr be the top element in the
new ioam6_iptunnel_trace struct. If the IOAM6_IPTUNNEL_TRACE size ==
ioam6_trace_hdr then you know it is the legacy argument vs sizeof
ioam6_iptunnel_trace which is the new.

OK, I see. The problem is ioam6_trace_hdr must be the last entry because of its
last field, which is "__u8 data[0]". But, anyway, I could still apply the same
kind of logic with the size.

ok, forgot about the data field.

Why not make the new data separate attributes then? Avoids the alignment
problem.

Great idea, I'll do that.