From: Martin KaFai Lau <kafai@fb.com>
Date: Wed, 2 Mar 2022 11:56:09 -0800
Subject: net: ipv6: Get rcv timestamp if needed when handling hop-by-hop IOAM
 option
Patch-mainline: v5.18-rc1
Git-commit: b6561f8491ca899e5a08311796085c9738d631ae
References: jsc#PED-1377
X-info: ignore changes in net/ipv6/ioam6.c since we did not backport 9ee11f0fff20 "ipv6: ioam: Data plane support for Pre-allocated Trace" from v5.15

IOAM is a hop-by-hop option with a temporary iana allocation (49).
Since it is hop-by-hop, it is done before the input routing decision.
One of the traced data field is the (rcv) timestamp.

When the locally generated skb is looping from egress to ingress over
a virtual interface (e.g. veth, loopback...), skb->tstamp may have the
delivery time before it is known that it will be delivered locally
and received by another sk.

Like handling the network tapping (tcpdump) in the earlier patch,
this patch gets the timestamp if needed without over-writing the
delivery_time in the skb->tstamp.  skb_tstamp_cond() is added to do the
ktime_get_real() with an extra cond arg to check on top of the
netstamp_needed_key static key.  skb_tstamp_cond() will also be used in
a latter patch and it needs the netstamp_needed_key check.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 include/linux/skbuff.h |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3883,6 +3883,17 @@ static inline ktime_t skb_tstamp(const s
 	return skb->tstamp;
 }
 
+static inline ktime_t skb_tstamp_cond(const struct sk_buff *skb, bool cond)
+{
+	if (!skb->mono_delivery_time && skb->tstamp)
+		return skb->tstamp;
+
+	if (static_branch_unlikely(&netstamp_needed_key) || cond)
+		return ktime_get_real();
+
+	return 0;
+}
+
 static inline u8 skb_metadata_len(const struct sk_buff *skb)
 {
 	return skb_shinfo(skb)->meta_len;