mono_delivery_time was added to check if skb->tstamp has delivery
time in mono clock base (i.e. EDT) otherwise skb->tstamp has
timestamp in ingress and delivery_time at egress.

Renaming the bitfield from mono_delivery_time to tstamp_type is for
extensibilty for other timestamps such as userspace timestamp
(i.e. SO_TXTIME) set via sock opts.

As we are renaming the mono_delivery_time to tstamp_type, it makes
sense to start assigning tstamp_type based on enum defined
in this commit.

Earlier we used bool arg flag to check if the tstamp is mono in
function skb_set_delivery_time, Now the signature of the functions
accepts tstamp_type to distinguish between mono and real time.

Also skb_set_delivery_type_by_clockid is a new function which accepts
clockid to determine the tstamp_type.

In future tstamp_type:1 can be extended to support userspace timestamp
by increasing the bitfield.

Link: https://lore.kernel.org/netdev/bc037db4-58bb-4861-ac31-a361a93841d3@linux.dev/
Signed-off-by: Abhishek Chauhan <quic_abchauha@quicinc.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Martin KaFai Lau <martin.lau@kernel.org>
---
Changes since v7
- Added reviewed by tags and removed RFC 

Changes since v6
- Moved documentation comment from patch 2 to patch 1 (Minor)
- Instead of calling the wrapper api to set tstamp_type
  for tcp, directly call main api to set the tstamp_type
  as suggested by Willem

Changes since v5
- Avoided using garble function names as mentioned by
  Willem.
- Implemented a conversion function stead of duplicating 
  the same logic as mentioned by Willem.
- Fixed indentation problems and minor documentation issues
  which mentions tstamp_type as a whole instead of bitfield
  notations. (Mentioned both by Willem and Martin)
  
Changes since v4
- Introduce new function to directly delivery_time and
  another to set tstamp_type based on clockid. 
- Removed un-necessary comments in skbuff.h as 
  enums were obvious and understood.

Changes since v3
- Fixed inconsistent capitalization in skbuff.h
- remove reference to MONO_DELIVERY_TIME_MASK in skbuff.h
  and point it to skb_tstamp_type now.
- Explicitely setting SKB_CLOCK_MONO if valid transmit_time
  ip_send_unicast_reply 
- Keeping skb_tstamp inline with skb_clear_tstamp. 
- skb_set_delivery_time checks if timstamp is 0 and 
  sets the tstamp_type to SKB_CLOCK_REAL.
- Above comments are given by Willem 
- Found out that skbuff.h has access to uapi/linux/time.h
  So now instead of using  CLOCK_REAL/CLOCK_MONO 
  i am checking actual clockid_t directly to set tstamp_type 
  example:- CLOCK_REALTIME/CLOCK_MONOTONIC 
- Compilation error fixed in 
  net/ieee802154/6lowpan/reassembly.c

Changes since v2
- Minor changes to commit subject

Changes since v1
- Squashed the two commits into one as mentioned by Willem.
- Introduced switch in skb_set_delivery_time.
- Renamed and removed directionality aspects w.r.t tstamp_type 
  as mentioned by Willem.


 include/linux/skbuff.h                     | 52 ++++++++++++++++------
 include/net/inet_frag.h                    |  4 +-
 net/bridge/netfilter/nf_conntrack_bridge.c |  6 +--
 net/core/dev.c                             |  2 +-
 net/core/filter.c                          | 10 ++---
 net/ieee802154/6lowpan/reassembly.c        |  2 +-
 net/ipv4/inet_fragment.c                   |  2 +-
 net/ipv4/ip_fragment.c                     |  2 +-
 net/ipv4/ip_output.c                       |  9 ++--
 net/ipv4/tcp_output.c                      | 14 +++---
 net/ipv6/ip6_output.c                      |  6 +--
 net/ipv6/netfilter.c                       |  6 +--
 net/ipv6/netfilter/nf_conntrack_reasm.c    |  2 +-
 net/ipv6/reassembly.c                      |  2 +-
 net/ipv6/tcp_ipv6.c                        |  2 +-
 net/sched/act_bpf.c                        |  4 +-
 net/sched/cls_bpf.c                        |  4 +-
 17 files changed, 78 insertions(+), 51 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 1c2902eaebd3..05aec712d16d 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -706,6 +706,11 @@ typedef unsigned int sk_buff_data_t;
 typedef unsigned char *sk_buff_data_t;
 #endif
 
+enum skb_tstamp_type {
+	SKB_CLOCK_REALTIME,
+	SKB_CLOCK_MONOTONIC,
+};
+
 /**
  * DOC: Basic sk_buff geometry
  *
@@ -823,10 +828,8 @@ typedef unsigned char *sk_buff_data_t;
  *	@dst_pending_confirm: need to confirm neighbour
  *	@decrypted: Decrypted SKB
  *	@slow_gro: state present at GRO time, slower prepare step required
- *	@mono_delivery_time: When set, skb->tstamp has the
- *		delivery_time in mono clock base (i.e. EDT).  Otherwise, the
- *		skb->tstamp has the (rcv) timestamp at ingress and
- *		delivery_time at egress.
+ *	@tstamp_type: When set, skb->tstamp has the
+ *		delivery_time clock base of skb->tstamp.
  *	@napi_id: id of the NAPI struct this skb came from
  *	@sender_cpu: (aka @napi_id) source CPU in XPS
  *	@alloc_cpu: CPU which did the skb allocation.
@@ -954,7 +957,7 @@ struct sk_buff {
 	/* private: */
 	__u8			__mono_tc_offset[0];
 	/* public: */
-	__u8			mono_delivery_time:1;	/* See SKB_MONO_DELIVERY_TIME_MASK */
+	__u8			tstamp_type:1;	/* See skb_tstamp_type */
 #ifdef CONFIG_NET_XGRESS
 	__u8			tc_at_ingress:1;	/* See TC_AT_INGRESS_MASK */
 	__u8			tc_skip_classify:1;
@@ -4179,7 +4182,7 @@ static inline void skb_get_new_timestampns(const struct sk_buff *skb,
 static inline void __net_timestamp(struct sk_buff *skb)
 {
 	skb->tstamp = ktime_get_real();
-	skb->mono_delivery_time = 0;
+	skb->tstamp_type = SKB_CLOCK_REALTIME;
 }
 
 static inline ktime_t net_timedelta(ktime_t t)
@@ -4188,10 +4191,33 @@ static inline ktime_t net_timedelta(ktime_t t)
 }
 
 static inline void skb_set_delivery_time(struct sk_buff *skb, ktime_t kt,
-					 bool mono)
+					 u8 tstamp_type)
 {
 	skb->tstamp = kt;
-	skb->mono_delivery_time = kt && mono;
+
+	if (kt)
+		skb->tstamp_type = tstamp_type;
+	else
+		skb->tstamp_type = SKB_CLOCK_REALTIME;
+}
+
+static inline void skb_set_delivery_type_by_clockid(struct sk_buff *skb,
+						    ktime_t kt, clockid_t clockid)
+{
+	u8 tstamp_type = SKB_CLOCK_REALTIME;
+
+	switch (clockid) {
+	case CLOCK_REALTIME:
+		break;
+	case CLOCK_MONOTONIC:
+		tstamp_type = SKB_CLOCK_MONOTONIC;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		kt = 0;
+	}
+
+	skb_set_delivery_time(skb, kt, tstamp_type);
 }
 
 DECLARE_STATIC_KEY_FALSE(netstamp_needed_key);
@@ -4201,8 +4227,8 @@ DECLARE_STATIC_KEY_FALSE(netstamp_needed_key);
  */
 static inline void skb_clear_delivery_time(struct sk_buff *skb)
 {
-	if (skb->mono_delivery_time) {
-		skb->mono_delivery_time = 0;
+	if (skb->tstamp_type) {
+		skb->tstamp_type = SKB_CLOCK_REALTIME;
 		if (static_branch_unlikely(&netstamp_needed_key))
 			skb->tstamp = ktime_get_real();
 		else
@@ -4212,7 +4238,7 @@ static inline void skb_clear_delivery_time(struct sk_buff *skb)
 
 static inline void skb_clear_tstamp(struct sk_buff *skb)
 {
-	if (skb->mono_delivery_time)
+	if (skb->tstamp_type)
 		return;
 
 	skb->tstamp = 0;
@@ -4220,7 +4246,7 @@ static inline void skb_clear_tstamp(struct sk_buff *skb)
 
 static inline ktime_t skb_tstamp(const struct sk_buff *skb)
 {
-	if (skb->mono_delivery_time)
+	if (skb->tstamp_type)
 		return 0;
 
 	return skb->tstamp;
@@ -4228,7 +4254,7 @@ static inline ktime_t skb_tstamp(const struct sk_buff *skb)
 
 static inline ktime_t skb_tstamp_cond(const struct sk_buff *skb, bool cond)
 {
-	if (!skb->mono_delivery_time && skb->tstamp)
+	if (skb->tstamp_type != SKB_CLOCK_MONOTONIC && skb->tstamp)
 		return skb->tstamp;
 
 	if (static_branch_unlikely(&netstamp_needed_key) || cond)
diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index 153960663ce4..5af6eb14c5db 100644
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -76,7 +76,7 @@ struct frag_v6_compare_key {
  * @stamp: timestamp of the last received fragment
  * @len: total length of the original datagram
  * @meat: length of received fragments so far
- * @mono_delivery_time: stamp has a mono delivery time (EDT)
+ * @tstamp_type: stamp has a mono delivery time (EDT)
  * @flags: fragment queue flags
  * @max_size: maximum received fragment size
  * @fqdir: pointer to struct fqdir
@@ -97,7 +97,7 @@ struct inet_frag_queue {
 	ktime_t			stamp;
 	int			len;
 	int			meat;
-	u8			mono_delivery_time;
+	u8			tstamp_type;
 	__u8			flags;
 	u16			max_size;
 	struct fqdir		*fqdir;
diff --git a/net/bridge/netfilter/nf_conntrack_bridge.c b/net/bridge/netfilter/nf_conntrack_bridge.c
index c3c51b9a6826..816bb0fde718 100644
--- a/net/bridge/netfilter/nf_conntrack_bridge.c
+++ b/net/bridge/netfilter/nf_conntrack_bridge.c
@@ -32,7 +32,7 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk,
 					   struct sk_buff *))
 {
 	int frag_max_size = BR_INPUT_SKB_CB(skb)->frag_max_size;
-	bool mono_delivery_time = skb->mono_delivery_time;
+	u8 tstamp_type = skb->tstamp_type;
 	unsigned int hlen, ll_rs, mtu;
 	ktime_t tstamp = skb->tstamp;
 	struct ip_frag_state state;
@@ -82,7 +82,7 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk,
 			if (iter.frag)
 				ip_fraglist_prepare(skb, &iter);
 
-			skb_set_delivery_time(skb, tstamp, mono_delivery_time);
+			skb_set_delivery_time(skb, tstamp, tstamp_type);
 			err = output(net, sk, data, skb);
 			if (err || !iter.frag)
 				break;
@@ -113,7 +113,7 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk,
 			goto blackhole;
 		}
 
-		skb_set_delivery_time(skb2, tstamp, mono_delivery_time);
+		skb_set_delivery_time(skb2, tstamp, tstamp_type);
 		err = output(net, sk, data, skb2);
 		if (err)
 			goto blackhole;
diff --git a/net/core/dev.c b/net/core/dev.c
index d2ce91a334c1..652b1979796b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2161,7 +2161,7 @@ EXPORT_SYMBOL(net_disable_timestamp);
 static inline void net_timestamp_set(struct sk_buff *skb)
 {
 	skb->tstamp = 0;
-	skb->mono_delivery_time = 0;
+	skb->tstamp_type = SKB_CLOCK_REALTIME;
 	if (static_branch_unlikely(&netstamp_needed_key))
 		skb->tstamp = ktime_get_real();
 }
diff --git a/net/core/filter.c b/net/core/filter.c
index 2510464692af..a3781a796da4 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7730,13 +7730,13 @@ BPF_CALL_3(bpf_skb_set_tstamp, struct sk_buff *, skb,
 		if (!tstamp)
 			return -EINVAL;
 		skb->tstamp = tstamp;
-		skb->mono_delivery_time = 1;
+		skb->tstamp_type = SKB_CLOCK_MONOTONIC;
 		break;
 	case BPF_SKB_TSTAMP_UNSPEC:
 		if (tstamp)
 			return -EINVAL;
 		skb->tstamp = 0;
-		skb->mono_delivery_time = 0;
+		skb->tstamp_type = SKB_CLOCK_REALTIME;
 		break;
 	default:
 		return -EINVAL;
@@ -9443,7 +9443,7 @@ static struct bpf_insn *bpf_convert_tstamp_read(const struct bpf_prog *prog,
 					TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK);
 		*insn++ = BPF_JMP32_IMM(BPF_JNE, tmp_reg,
 					TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK, 2);
-		/* skb->tc_at_ingress && skb->mono_delivery_time,
+		/* skb->tc_at_ingress && skb->tstamp_type,
 		 * read 0 as the (rcv) timestamp.
 		 */
 		*insn++ = BPF_MOV64_IMM(value_reg, 0);
@@ -9468,7 +9468,7 @@ static struct bpf_insn *bpf_convert_tstamp_write(const struct bpf_prog *prog,
 	 * the bpf prog is aware the tstamp could have delivery time.
 	 * Thus, write skb->tstamp as is if tstamp_type_access is true.
 	 * Otherwise, writing at ingress will have to clear the
-	 * mono_delivery_time bit also.
+	 * skb->tstamp_type bit also.
 	 */
 	if (!prog->tstamp_type_access) {
 		__u8 tmp_reg = BPF_REG_AX;
@@ -9478,7 +9478,7 @@ static struct bpf_insn *bpf_convert_tstamp_write(const struct bpf_prog *prog,
 		*insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg, TC_AT_INGRESS_MASK, 1);
 		/* goto <store> */
 		*insn++ = BPF_JMP_A(2);
-		/* <clear>: mono_delivery_time */
+		/* <clear>: skb->tstamp_type */
 		*insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg, ~SKB_MONO_DELIVERY_TIME_MASK);
 		*insn++ = BPF_STX_MEM(BPF_B, skb_reg, tmp_reg, SKB_BF_MONO_TC_OFFSET);
 	}
diff --git a/net/ieee802154/6lowpan/reassembly.c b/net/ieee802154/6lowpan/reassembly.c
index 56ef873828f4..867d637d86f0 100644
--- a/net/ieee802154/6lowpan/reassembly.c
+++ b/net/ieee802154/6lowpan/reassembly.c
@@ -130,7 +130,7 @@ static int lowpan_frag_queue(struct lowpan_frag_queue *fq,
 		goto err;
 
 	fq->q.stamp = skb->tstamp;
-	fq->q.mono_delivery_time = skb->mono_delivery_time;
+	fq->q.tstamp_type = skb->tstamp_type;
 	if (frag_type == LOWPAN_DISPATCH_FRAG1)
 		fq->q.flags |= INET_FRAG_FIRST_IN;
 
diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index faaec92a46ac..d179a2c84222 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -619,7 +619,7 @@ void inet_frag_reasm_finish(struct inet_frag_queue *q, struct sk_buff *head,
 	skb_mark_not_on_list(head);
 	head->prev = NULL;
 	head->tstamp = q->stamp;
-	head->mono_delivery_time = q->mono_delivery_time;
+	head->tstamp_type = q->tstamp_type;
 
 	if (sk)
 		refcount_add(sum_truesize - head_truesize, &sk->sk_wmem_alloc);
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 08e2c92e25ab..a92664a5ef2e 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -355,7 +355,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 		qp->iif = dev->ifindex;
 
 	qp->q.stamp = skb->tstamp;
-	qp->q.mono_delivery_time = skb->mono_delivery_time;
+	qp->q.tstamp_type = skb->tstamp_type;
 	qp->q.meat += skb->len;
 	qp->ecn |= ecn;
 	add_frag_mem_limit(qp->q.fqdir, skb->truesize);
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 9500031a1f55..fe86cadfa85b 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -764,7 +764,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 {
 	struct iphdr *iph;
 	struct sk_buff *skb2;
-	bool mono_delivery_time = skb->mono_delivery_time;
+	u8 tstamp_type = skb->tstamp_type;
 	struct rtable *rt = skb_rtable(skb);
 	unsigned int mtu, hlen, ll_rs;
 	struct ip_fraglist_iter iter;
@@ -856,7 +856,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 				}
 			}
 
-			skb_set_delivery_time(skb, tstamp, mono_delivery_time);
+			skb_set_delivery_time(skb, tstamp, tstamp_type);
 			err = output(net, sk, skb);
 
 			if (!err)
@@ -912,7 +912,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 		/*
 		 *	Put this fragment into the sending queue.
 		 */
-		skb_set_delivery_time(skb2, tstamp, mono_delivery_time);
+		skb_set_delivery_time(skb2, tstamp, tstamp_type);
 		err = output(net, sk, skb2);
 		if (err)
 			goto fail;
@@ -1649,7 +1649,8 @@ void ip_send_unicast_reply(struct sock *sk, struct sk_buff *skb,
 			  arg->csumoffset) = csum_fold(csum_add(nskb->csum,
 								arg->csum));
 		nskb->ip_summed = CHECKSUM_NONE;
-		nskb->mono_delivery_time = !!transmit_time;
+		if (transmit_time)
+			nskb->tstamp_type = SKB_CLOCK_MONOTONIC;
 		if (txhash)
 			skb_set_hash(nskb, txhash, PKT_HASH_TYPE_L4);
 		ip_push_pending_frames(sk, &fl4);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 95caf8aaa8be..d44371cfa6ec 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1301,7 +1301,7 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
 	tp = tcp_sk(sk);
 	prior_wstamp = tp->tcp_wstamp_ns;
 	tp->tcp_wstamp_ns = max(tp->tcp_wstamp_ns, tp->tcp_clock_cache);
-	skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true);
+	skb_set_delivery_time(skb, tp->tcp_wstamp_ns, SKB_CLOCK_MONOTONIC);
 	if (clone_it) {
 		oskb = skb;
 
@@ -1655,7 +1655,7 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
 
 	skb_split(skb, buff, len);
 
-	skb_set_delivery_time(buff, skb->tstamp, true);
+	skb_set_delivery_time(buff, skb->tstamp, SKB_CLOCK_MONOTONIC);
 	tcp_fragment_tstamp(skb, buff);
 
 	old_factor = tcp_skb_pcount(skb);
@@ -2764,7 +2764,7 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
 		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
 			/* "skb_mstamp_ns" is used as a start point for the retransmit timer */
 			tp->tcp_wstamp_ns = tp->tcp_clock_cache;
-			skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true);
+			skb_set_delivery_time(skb, tp->tcp_wstamp_ns, SKB_CLOCK_MONOTONIC);
 			list_move_tail(&skb->tcp_tsorted_anchor, &tp->tsorted_sent_queue);
 			tcp_init_tso_segs(skb, mss_now);
 			goto repair; /* Skip network transmission */
@@ -3752,11 +3752,11 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 #ifdef CONFIG_SYN_COOKIES
 	if (unlikely(synack_type == TCP_SYNACK_COOKIE && ireq->tstamp_ok))
 		skb_set_delivery_time(skb, cookie_init_timestamp(req, now),
-				      true);
+				      SKB_CLOCK_MONOTONIC);
 	else
 #endif
 	{
-		skb_set_delivery_time(skb, now, true);
+		skb_set_delivery_time(skb, now, SKB_CLOCK_MONOTONIC);
 		if (!tcp_rsk(req)->snt_synack) /* Timestamp first SYNACK */
 			tcp_rsk(req)->snt_synack = tcp_skb_timestamp_us(skb);
 	}
@@ -3843,7 +3843,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 	bpf_skops_write_hdr_opt((struct sock *)sk, skb, req, syn_skb,
 				synack_type, &opts);
 
-	skb_set_delivery_time(skb, now, true);
+	skb_set_delivery_time(skb, now, SKB_CLOCK_MONOTONIC);
 	tcp_add_tx_delay(skb, tp);
 
 	return skb;
@@ -4027,7 +4027,7 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
 
 	err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
 
-	skb_set_delivery_time(syn, syn_data->skb_mstamp_ns, true);
+	skb_set_delivery_time(syn, syn_data->skb_mstamp_ns, SKB_CLOCK_MONOTONIC);
 
 	/* Now full SYN+DATA was cloned and sent (or not),
 	 * remove the SYN from the original skb (syn_data)
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index f4c018b6aa7d..8fd5bf85c657 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -859,7 +859,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 	struct rt6_info *rt = dst_rt6_info(skb_dst(skb));
 	struct ipv6_pinfo *np = skb->sk && !dev_recursion_level() ?
 				inet6_sk(skb->sk) : NULL;
-	bool mono_delivery_time = skb->mono_delivery_time;
+	u8 tstamp_type = skb->tstamp_type;
 	struct ip6_frag_state state;
 	unsigned int mtu, hlen, nexthdr_offset;
 	ktime_t tstamp = skb->tstamp;
@@ -955,7 +955,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 			if (iter.frag)
 				ip6_fraglist_prepare(skb, &iter);
 
-			skb_set_delivery_time(skb, tstamp, mono_delivery_time);
+			skb_set_delivery_time(skb, tstamp, tstamp_type);
 			err = output(net, sk, skb);
 			if (!err)
 				IP6_INC_STATS(net, ip6_dst_idev(&rt->dst),
@@ -1016,7 +1016,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 		/*
 		 *	Put this fragment into the sending queue.
 		 */
-		skb_set_delivery_time(frag, tstamp, mono_delivery_time);
+		skb_set_delivery_time(frag, tstamp, tstamp_type);
 		err = output(net, sk, frag);
 		if (err)
 			goto fail;
diff --git a/net/ipv6/netfilter.c b/net/ipv6/netfilter.c
index 53d255838e6a..e0c2347b4dc6 100644
--- a/net/ipv6/netfilter.c
+++ b/net/ipv6/netfilter.c
@@ -126,7 +126,7 @@ int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 				  struct sk_buff *))
 {
 	int frag_max_size = BR_INPUT_SKB_CB(skb)->frag_max_size;
-	bool mono_delivery_time = skb->mono_delivery_time;
+	u8 tstamp_type = skb->tstamp_type;
 	ktime_t tstamp = skb->tstamp;
 	struct ip6_frag_state state;
 	u8 *prevhdr, nexthdr = 0;
@@ -192,7 +192,7 @@ int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 			if (iter.frag)
 				ip6_fraglist_prepare(skb, &iter);
 
-			skb_set_delivery_time(skb, tstamp, mono_delivery_time);
+			skb_set_delivery_time(skb, tstamp, tstamp_type);
 			err = output(net, sk, data, skb);
 			if (err || !iter.frag)
 				break;
@@ -225,7 +225,7 @@ int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 			goto blackhole;
 		}
 
-		skb_set_delivery_time(skb2, tstamp, mono_delivery_time);
+		skb_set_delivery_time(skb2, tstamp, tstamp_type);
 		err = output(net, sk, data, skb2);
 		if (err)
 			goto blackhole;
diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 5e1b50c6a44d..6f0844c9315d 100644
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -263,7 +263,7 @@ static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
 		fq->iif = dev->ifindex;
 
 	fq->q.stamp = skb->tstamp;
-	fq->q.mono_delivery_time = skb->mono_delivery_time;
+	fq->q.tstamp_type = skb->tstamp_type;
 	fq->q.meat += skb->len;
 	fq->ecn |= ecn;
 	if (payload_len > fq->q.max_size)
diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 439f93512b0a..4a84b9348913 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -198,7 +198,7 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
 		fq->iif = dev->ifindex;
 
 	fq->q.stamp = skb->tstamp;
-	fq->q.mono_delivery_time = skb->mono_delivery_time;
+	fq->q.tstamp_type = skb->tstamp_type;
 	fq->q.meat += skb->len;
 	fq->ecn |= ecn;
 	add_frag_mem_limit(fq->q.fqdir, skb->truesize);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 37201c4fb393..16c545f0d064 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -975,7 +975,7 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
 			mark = inet_twsk(sk)->tw_mark;
 		else
 			mark = READ_ONCE(sk->sk_mark);
-		skb_set_delivery_time(buff, tcp_transmit_time(sk), true);
+		skb_set_delivery_time(buff, tcp_transmit_time(sk), SKB_CLOCK_MONOTONIC);
 	}
 	if (txhash) {
 		/* autoflowlabel/skb_get_hash_flowi6 rely on buff->hash */
diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c
index 0e3cf11ae5fc..396b576390d0 100644
--- a/net/sched/act_bpf.c
+++ b/net/sched/act_bpf.c
@@ -54,8 +54,8 @@ TC_INDIRECT_SCOPE int tcf_bpf_act(struct sk_buff *skb,
 		bpf_compute_data_pointers(skb);
 		filter_res = bpf_prog_run(filter, skb);
 	}
-	if (unlikely(!skb->tstamp && skb->mono_delivery_time))
-		skb->mono_delivery_time = 0;
+	if (unlikely(!skb->tstamp && skb->tstamp_type))
+		skb->tstamp_type = SKB_CLOCK_REALTIME;
 	if (skb_sk_is_prefetched(skb) && filter_res != TC_ACT_OK)
 		skb_orphan(skb);
 
diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
index 5e83e890f6a4..1941ebec23ff 100644
--- a/net/sched/cls_bpf.c
+++ b/net/sched/cls_bpf.c
@@ -104,8 +104,8 @@ TC_INDIRECT_SCOPE int cls_bpf_classify(struct sk_buff *skb,
 			bpf_compute_data_pointers(skb);
 			filter_res = bpf_prog_run(prog->filter, skb);
 		}
-		if (unlikely(!skb->tstamp && skb->mono_delivery_time))
-			skb->mono_delivery_time = 0;
+		if (unlikely(!skb->tstamp && skb->tstamp_type))
+			skb->tstamp_type = SKB_CLOCK_REALTIME;
 
 		if (prog->exts_integrated) {
 			res->class   = 0;
-- 
2.25.1

On 5/9/2024 2:18 PM, Abhishek Chauhan wrote:
> mono_delivery_time was added to check if skb->tstamp has delivery
> time in mono clock base (i.e. EDT) otherwise skb->tstamp has
> timestamp in ingress and delivery_time at egress.
> 
> Renaming the bitfield from mono_delivery_time to tstamp_type is for
> extensibilty for other timestamps such as userspace timestamp
> (i.e. SO_TXTIME) set via sock opts.
> 
> As we are renaming the mono_delivery_time to tstamp_type, it makes
> sense to start assigning tstamp_type based on enum defined
> in this commit.
> 
> Earlier we used bool arg flag to check if the tstamp is mono in
> function skb_set_delivery_time, Now the signature of the functions
> accepts tstamp_type to distinguish between mono and real time.
> 
> Also skb_set_delivery_type_by_clockid is a new function which accepts
> clockid to determine the tstamp_type.
> 
> In future tstamp_type:1 can be extended to support userspace timestamp
> by increasing the bitfield.
> 
> Link: https://lore.kernel.org/netdev/bc037db4-58bb-4861-ac31-a361a93841d3@linux.dev/
> Signed-off-by: Abhishek Chauhan <quic_abchauha@quicinc.com>
> Reviewed-by: Willem de Bruijn <willemb@google.com>
> Reviewed-by: Martin KaFai Lau <martin.lau@kernel.org>
> ---
> Changes since v7
> - Added reviewed by tags and removed RFC 
> 
> Changes since v6
> - Moved documentation comment from patch 2 to patch 1 (Minor)
> - Instead of calling the wrapper api to set tstamp_type
>   for tcp, directly call main api to set the tstamp_type
>   as suggested by Willem
> 
> Changes since v5
> - Avoided using garble function names as mentioned by
>   Willem.
> - Implemented a conversion function stead of duplicating 
>   the same logic as mentioned by Willem.
> - Fixed indentation problems and minor documentation issues
>   which mentions tstamp_type as a whole instead of bitfield
>   notations. (Mentioned both by Willem and Martin)
>   
> Changes since v4
> - Introduce new function to directly delivery_time and
>   another to set tstamp_type based on clockid. 
> - Removed un-necessary comments in skbuff.h as 
>   enums were obvious and understood.
> 
> Changes since v3
> - Fixed inconsistent capitalization in skbuff.h
> - remove reference to MONO_DELIVERY_TIME_MASK in skbuff.h
>   and point it to skb_tstamp_type now.
> - Explicitely setting SKB_CLOCK_MONO if valid transmit_time
>   ip_send_unicast_reply 
> - Keeping skb_tstamp inline with skb_clear_tstamp. 
> - skb_set_delivery_time checks if timstamp is 0 and 
>   sets the tstamp_type to SKB_CLOCK_REAL.
> - Above comments are given by Willem 
> - Found out that skbuff.h has access to uapi/linux/time.h
>   So now instead of using  CLOCK_REAL/CLOCK_MONO 
>   i am checking actual clockid_t directly to set tstamp_type 
>   example:- CLOCK_REALTIME/CLOCK_MONOTONIC 
> - Compilation error fixed in 
>   net/ieee802154/6lowpan/reassembly.c
> 
> Changes since v2
> - Minor changes to commit subject
> 
> Changes since v1
> - Squashed the two commits into one as mentioned by Willem.
> - Introduced switch in skb_set_delivery_time.
> - Renamed and removed directionality aspects w.r.t tstamp_type 
>   as mentioned by Willem.
> 
> 
>  include/linux/skbuff.h                     | 52 ++++++++++++++++------
>  include/net/inet_frag.h                    |  4 +-
>  net/bridge/netfilter/nf_conntrack_bridge.c |  6 +--
>  net/core/dev.c                             |  2 +-
>  net/core/filter.c                          | 10 ++---
>  net/ieee802154/6lowpan/reassembly.c        |  2 +-
>  net/ipv4/inet_fragment.c                   |  2 +-
>  net/ipv4/ip_fragment.c                     |  2 +-
>  net/ipv4/ip_output.c                       |  9 ++--
>  net/ipv4/tcp_output.c                      | 14 +++---
>  net/ipv6/ip6_output.c                      |  6 +--
>  net/ipv6/netfilter.c                       |  6 +--
>  net/ipv6/netfilter/nf_conntrack_reasm.c    |  2 +-
>  net/ipv6/reassembly.c                      |  2 +-
>  net/ipv6/tcp_ipv6.c                        |  2 +-
>  net/sched/act_bpf.c                        |  4 +-
>  net/sched/cls_bpf.c                        |  4 +-
>  17 files changed, 78 insertions(+), 51 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 1c2902eaebd3..05aec712d16d 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -706,6 +706,11 @@ typedef unsigned int sk_buff_data_t;
>  typedef unsigned char *sk_buff_data_t;
>  #endif
>  
> +enum skb_tstamp_type {
> +	SKB_CLOCK_REALTIME,
> +	SKB_CLOCK_MONOTONIC,
> +};
> +
>  /**
>   * DOC: Basic sk_buff geometry
>   *
> @@ -823,10 +828,8 @@ typedef unsigned char *sk_buff_data_t;
>   *	@dst_pending_confirm: need to confirm neighbour
>   *	@decrypted: Decrypted SKB
>   *	@slow_gro: state present at GRO time, slower prepare step required
> - *	@mono_delivery_time: When set, skb->tstamp has the
> - *		delivery_time in mono clock base (i.e. EDT).  Otherwise, the
> - *		skb->tstamp has the (rcv) timestamp at ingress and
> - *		delivery_time at egress.
> + *	@tstamp_type: When set, skb->tstamp has the
> + *		delivery_time clock base of skb->tstamp.
>   *	@napi_id: id of the NAPI struct this skb came from
>   *	@sender_cpu: (aka @napi_id) source CPU in XPS
>   *	@alloc_cpu: CPU which did the skb allocation.
> @@ -954,7 +957,7 @@ struct sk_buff {
>  	/* private: */
>  	__u8			__mono_tc_offset[0];
>  	/* public: */
> -	__u8			mono_delivery_time:1;	/* See SKB_MONO_DELIVERY_TIME_MASK */
> +	__u8			tstamp_type:1;	/* See skb_tstamp_type */
>  #ifdef CONFIG_NET_XGRESS
>  	__u8			tc_at_ingress:1;	/* See TC_AT_INGRESS_MASK */
>  	__u8			tc_skip_classify:1;
> @@ -4179,7 +4182,7 @@ static inline void skb_get_new_timestampns(const struct sk_buff *skb,
>  static inline void __net_timestamp(struct sk_buff *skb)
>  {
>  	skb->tstamp = ktime_get_real();
> -	skb->mono_delivery_time = 0;
> +	skb->tstamp_type = SKB_CLOCK_REALTIME;
>  }
>  
>  static inline ktime_t net_timedelta(ktime_t t)
> @@ -4188,10 +4191,33 @@ static inline ktime_t net_timedelta(ktime_t t)
>  }
>  
>  static inline void skb_set_delivery_time(struct sk_buff *skb, ktime_t kt,
> -					 bool mono)
> +					 u8 tstamp_type)
>  {
>  	skb->tstamp = kt;
> -	skb->mono_delivery_time = kt && mono;
> +
> +	if (kt)
> +		skb->tstamp_type = tstamp_type;
> +	else
> +		skb->tstamp_type = SKB_CLOCK_REALTIME;
> +}
> +
> +static inline void skb_set_delivery_type_by_clockid(struct sk_buff *skb,
> +						    ktime_t kt, clockid_t clockid)
> +{
> +	u8 tstamp_type = SKB_CLOCK_REALTIME;
> +
> +	switch (clockid) {
> +	case CLOCK_REALTIME:
> +		break;
> +	case CLOCK_MONOTONIC:
> +		tstamp_type = SKB_CLOCK_MONOTONIC;
> +		break;
> +	default:

Willem and Martin, I was thinking we should remove this warn_on_once from below line. Some systems also use panic on warn. 
So i think this might result in unnecessary crashes. 

Let me know what you think. 

Logs which are complaining. 
https://syzkaller.appspot.com/x/log.txt?x=118c3ae8980000

> +		WARN_ON_ONCE(1);
> +		kt = 0;
> +	}
> +
> +	skb_set_delivery_time(skb, kt, tstamp_type);
>  }
>

Abhishek Chauhan (ABC) wrote:

> > +static inline void skb_set_delivery_type_by_clockid(struct sk_buff *skb,
> > +						    ktime_t kt, clockid_t clockid)
> > +{
> > +	u8 tstamp_type = SKB_CLOCK_REALTIME;
> > +
> > +	switch (clockid) {
> > +	case CLOCK_REALTIME:
> > +		break;
> > +	case CLOCK_MONOTONIC:
> > +		tstamp_type = SKB_CLOCK_MONOTONIC;
> > +		break;
> > +	default:
> 
> Willem and Martin, I was thinking we should remove this warn_on_once from below line. Some systems also use panic on warn. 
> So i think this might result in unnecessary crashes. 
> 
> Let me know what you think. 
> 
> Logs which are complaining. 
> https://syzkaller.appspot.com/x/log.txt?x=118c3ae8980000

I received reports too. Agreed that we need to fix these reports.

The alternative is to limit sk_clockid to supported ones, by failing
setsockopt SO_TXTIME on an unsupported clock.

That changes established ABI behavior. But I don't see how another
clock can be used in any realistic way anyway.

Putting it out there as an option. It's riskier, but in the end I
believe a better fix than just allowing this state to continue.

A third option would be to not fail the system call, but silently
fall back to CLOCK_REALTIME. Essentially what happens in the datapath
in skb_set_delivery_type_by_clockid now. That is surprising behavior,
we should not do that.

On 5/28/24 10:24 AM, Willem de Bruijn wrote:
> Abhishek Chauhan (ABC) wrote:
> 
>>> +static inline void skb_set_delivery_type_by_clockid(struct sk_buff *skb,
>>> +						    ktime_t kt, clockid_t clockid)
>>> +{
>>> +	u8 tstamp_type = SKB_CLOCK_REALTIME;
>>> +
>>> +	switch (clockid) {
>>> +	case CLOCK_REALTIME:
>>> +		break;
>>> +	case CLOCK_MONOTONIC:
>>> +		tstamp_type = SKB_CLOCK_MONOTONIC;
>>> +		break;
>>> +	default:
>>
>> Willem and Martin, I was thinking we should remove this warn_on_once from below line. Some systems also use panic on warn.
>> So i think this might result in unnecessary crashes.
>>
>> Let me know what you think.
>>
>> Logs which are complaining.
>> https://syzkaller.appspot.com/x/log.txt?x=118c3ae8980000
> 
> I received reports too. Agreed that we need to fix these reports.
> 
> The alternative is to limit sk_clockid to supported ones, by failing
> setsockopt SO_TXTIME on an unsupported clock.
> 
> That changes established ABI behavior. But I don't see how another
> clock can be used in any realistic way anyway.
> 
> Putting it out there as an option. It's riskier, but in the end I
> believe a better fix than just allowing this state to continue.

Failing early would be my preference also. The current ABI is arguably at least 
confusing (if not broken) considering other clockid is silently ignored by the 
kernel.

> 
> A third option would be to not fail the system call, but silently
> fall back to CLOCK_REALTIME. Essentially what happens in the datapath
> in skb_set_delivery_type_by_clockid now. That is surprising behavior,
> we should not do that.

Not sure if it makes sense to go back to this option only after there is 
breakage report with a legit usage?

Martin KaFai Lau wrote:
> On 5/28/24 10:24 AM, Willem de Bruijn wrote:
> > Abhishek Chauhan (ABC) wrote:
> > 
> >>> +static inline void skb_set_delivery_type_by_clockid(struct sk_buff *skb,
> >>> +						    ktime_t kt, clockid_t clockid)
> >>> +{
> >>> +	u8 tstamp_type = SKB_CLOCK_REALTIME;
> >>> +
> >>> +	switch (clockid) {
> >>> +	case CLOCK_REALTIME:
> >>> +		break;
> >>> +	case CLOCK_MONOTONIC:
> >>> +		tstamp_type = SKB_CLOCK_MONOTONIC;
> >>> +		break;
> >>> +	default:
> >>
> >> Willem and Martin, I was thinking we should remove this warn_on_once from below line. Some systems also use panic on warn.
> >> So i think this might result in unnecessary crashes.
> >>
> >> Let me know what you think.
> >>
> >> Logs which are complaining.
> >> https://syzkaller.appspot.com/x/log.txt?x=118c3ae8980000
> > 
> > I received reports too. Agreed that we need to fix these reports.
> > 
> > The alternative is to limit sk_clockid to supported ones, by failing
> > setsockopt SO_TXTIME on an unsupported clock.
> > 
> > That changes established ABI behavior. But I don't see how another
> > clock can be used in any realistic way anyway.
> > 
> > Putting it out there as an option. It's riskier, but in the end I
> > believe a better fix than just allowing this state to continue.
> 
> Failing early would be my preference also. The current ABI is arguably at least 
> confusing (if not broken) considering other clockid is silently ignored by the 
> kernel.
>
> > 
> > A third option would be to not fail the system call, but silently
> > fall back to CLOCK_REALTIME. Essentially what happens in the datapath
> > in skb_set_delivery_type_by_clockid now. That is surprising behavior,
> > we should not do that.
> 
> Not sure if it makes sense to go back to this option only after there is 
> breakage report with a legit usage?

Agreed. We cannot break users. But I don't see how there are real
users for the current permissive API.

On 5/28/2024 12:30 PM, Martin KaFai Lau wrote:
> On 5/28/24 10:24 AM, Willem de Bruijn wrote:
>> Abhishek Chauhan (ABC) wrote:
>>
>>>> +static inline void skb_set_delivery_type_by_clockid(struct sk_buff *skb,
>>>> +                            ktime_t kt, clockid_t clockid)
>>>> +{
>>>> +    u8 tstamp_type = SKB_CLOCK_REALTIME;
>>>> +
>>>> +    switch (clockid) {
>>>> +    case CLOCK_REALTIME:
>>>> +        break;
>>>> +    case CLOCK_MONOTONIC:
>>>> +        tstamp_type = SKB_CLOCK_MONOTONIC;
>>>> +        break;
>>>> +    default:
>>>
>>> Willem and Martin, I was thinking we should remove this warn_on_once from below line. Some systems also use panic on warn.
>>> So i think this might result in unnecessary crashes.
>>>
>>> Let me know what you think.
>>>
>>> Logs which are complaining.
>>> https://syzkaller.appspot.com/x/log.txt?x=118c3ae8980000
>>
>> I received reports too. Agreed that we need to fix these reports.
>>
>> The alternative is to limit sk_clockid to supported ones, by failing
>> setsockopt SO_TXTIME on an unsupported clock.
>>
>> That changes established ABI behavior. But I don't see how another
>> clock can be used in any realistic way anyway.
>>
>> Putting it out there as an option. It's riskier, but in the end I
>> believe a better fix than just allowing this state to continue.
> 
> Failing early would be my preference also. The current ABI is arguably at least confusing (if not broken) considering other clockid is silently ignored by the kernel.
> 

Okay since we all agree to fix the setsockopt SO_TXTIME  to only limit sk_clockid be set to supported ones (MONO/TAI/REAL).
All other clocks needs to return -EINVAL for setsockopt. 

I will raise the patch and also add the fixes and reported-by tag accordingly. 

>>
>> A third option would be to not fail the system call, but silently
>> fall back to CLOCK_REALTIME. Essentially what happens in the datapath
>> in skb_set_delivery_type_by_clockid now. That is surprising behavior,
>> we should not do that.
> 
> Not sure if it makes sense to go back to this option only after there is breakage report with a legit usage?
> 

On 5/28/2024 10:24 AM, Willem de Bruijn wrote:
> Abhishek Chauhan (ABC) wrote:
> 
>>> +static inline void skb_set_delivery_type_by_clockid(struct sk_buff *skb,
>>> +						    ktime_t kt, clockid_t clockid)
>>> +{
>>> +	u8 tstamp_type = SKB_CLOCK_REALTIME;
>>> +
>>> +	switch (clockid) {
>>> +	case CLOCK_REALTIME:
>>> +		break;
>>> +	case CLOCK_MONOTONIC:
>>> +		tstamp_type = SKB_CLOCK_MONOTONIC;
>>> +		break;
>>> +	default:
>>
>> Willem and Martin, I was thinking we should remove this warn_on_once from below line. Some systems also use panic on warn. 
>> So i think this might result in unnecessary crashes. 
>>
>> Let me know what you think. 
>>
>> Logs which are complaining. 
>> https://syzkaller.appspot.com/x/log.txt?x=118c3ae8980000
> 
> I received reports too. Agreed that we need to fix these reports.
> 
> The alternative is to limit sk_clockid to supported ones, by failing
> setsockopt SO_TXTIME on an unsupported clock.
> 
> That changes established ABI behavior. But I don't see how another
> clock can be used in any realistic way anyway.
> 
> Putting it out there as an option. It's riskier, but in the end I
> believe a better fix than just allowing this state to continue.
> 
I understand your thought process here, but i think doing this option means 
no application from userspace can use any other clocks except REALTIME, MONO and TAI.

That being said application which are using different sock options to set other clocks needs
to change and work with just REALTIME , MONO or TAI. (Meaning the above warning from google compute engine
would be gone because setsock option itself failed in the first place, I suspect here the clockid being used is 
CLOCK_BOOTTIME which is similar to CLOCK_MONOTONIC with system suspend time as well)

I feel that the options which are exposed by SO_TXTIME are limitless as of today the code 
lacks basic checks such as not checking if the userspace gave a correct input. Meaning if i set
value 100 as the clockid and write a small application in userspace to set SO_TXTIME. The funny part is the 
clockid is successfully set even though there is no clock id 100 in kernel 

example :- 

[root@auto-lvarm-004 ~]# ./a.out -4 -S 192.168.1.1 -D 192.168.1.10 a,10

value from getsockopt is 100 <== Which means the setsockopt was successful with clockid 100 (which is junk)


I also agree that even without my patch, the code in fragmentation case was defaulting it to CLOCK_REALTIME 
if the mono_delivery_time bool was not set. (So we tried to keep the logic as close to the one which was available in upstream today)


I can propose 2 solutions to this 
1. Have stricter checks in setsockopt functions to set only REALTIME, MONO and TAI 
OR
2. Allow all clock id but only set tstamp_type for TAI, MONO and REALTIME to be forwarded to userspace(logic) 

static inline void skb_set_delivery_type_by_clockid(struct sk_buff *skb,
						    ktime_t kt, clockid_t clockid)
{
	u8 tstamp_type = SKB_CLOCK_REALTIME;

	switch (clockid) {
	case CLOCK_REALTIME:
		break;
	case CLOCK_MONOTONIC:
		tstamp_type = SKB_CLOCK_MONOTONIC;
		break;
	case CLOCK_TAI:
		tstamp_type = SKB_CLOCK_TAI;
		break;
	default:
		WARN_ON_ONCE(1); <== remove this 
		kt = 0; <== remove this
	}

	skb_set_delivery_time(skb, kt, tstamp_type); <== pass kt as ease (as it is done previously too) and tstamp_type internally remains REAL
}

Let me know what you think. !

> A third option would be to not fail the system call, but silently
> fall back to CLOCK_REALTIME. Essentially what happens in the datapath
> in skb_set_delivery_type_by_clockid now. That is surprising behavior,
> we should not do that.