net: ipv6: Get rcv timestamp if needed when handling hop-by-hop IOAM option

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>

include/linux/skbuff.h

@@ -4028,6 +4028,17 @@ static inline ktime_t skb_tstamp(const struct sk_buff *skb)
 	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;

net/ipv6/ioam6.c

@@ -635,7 +635,8 @@ static void __ioam6_fill_trace_data(struct sk_buff *skb,
 				    struct ioam6_schema *sc,
 				    u8 sclen, bool is_input)
 {
-	struct __kernel_sock_timeval ts;
+	struct timespec64 ts;
+	ktime_t tstamp;
 	u64 raw64;
 	u32 raw32;
 	u16 raw16;
@@ -680,10 +681,9 @@ static void __ioam6_fill_trace_data(struct sk_buff *skb,
 		if (!skb->dev) {
 			*(__be32 *)data = cpu_to_be32(IOAM6_U32_UNAVAILABLE);
 		} else {
-			if (!skb->tstamp)
-				__net_timestamp(skb);
+			tstamp = skb_tstamp_cond(skb, true);
+			ts = ktime_to_timespec64(tstamp);
 
-			skb_get_new_timestamp(skb, &ts);
 			*(__be32 *)data = cpu_to_be32((u32)ts.tv_sec);
 		}
 		data += sizeof(__be32);
@@ -694,13 +694,12 @@ static void __ioam6_fill_trace_data(struct sk_buff *skb,
 		if (!skb->dev) {
 			*(__be32 *)data = cpu_to_be32(IOAM6_U32_UNAVAILABLE);
 		} else {
-			if (!skb->tstamp)
-				__net_timestamp(skb);
+			if (!trace->type.bit2) {
+				tstamp = skb_tstamp_cond(skb, true);
+				ts = ktime_to_timespec64(tstamp);
+			}
 
-			if (!trace->type.bit2)
-				skb_get_new_timestamp(skb, &ts);
-
-			*(__be32 *)data = cpu_to_be32((u32)ts.tv_usec);
+			*(__be32 *)data = cpu_to_be32((u32)(ts.tv_nsec / NSEC_PER_USEC));
 		}
 		data += sizeof(__be32);
 	}