netdev - [PATCH v6 net-next 05/13] net: Set skb->mono_delivery_time and clear it after sch_handle

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Date:   Wed, 2 Mar 2022 11:55:50 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, <kernel-team@...com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH v6 net-next 05/13] net: Set skb->mono_delivery_time and clear it after sch_handle_ingress()

The previous patches handled the delivery_time before sch_handle_ingress().

This patch can now set the skb->mono_delivery_time to flag the skb->tstamp
is used as the mono delivery_time (EDT) instead of the (rcv) timestamp
and also clear it with skb_clear_delivery_time() after
sch_handle_ingress().  This will make the bpf_redirect_*()
to keep the mono delivery_time and used by a qdisc (fq) of
the egress-ing interface.

A latter patch will postpone the skb_clear_delivery_time() until the
stack learns that the skb is being delivered locally and that will
make other kernel forwarding paths (ip[6]_forward) able to keep
the delivery_time also.  Thus, like the previous patches on using
the skb->mono_delivery_time bit, calling skb_clear_delivery_time()
is not limited within the CONFIG_NET_INGRESS to avoid too many code
churns among this set.

Signed-off-by: Martin KaFai Lau <kafai@...com>
---
 include/linux/skbuff.h | 3 +--
 net/core/dev.c         | 8 ++++++--
 net/ipv4/ip_output.c   | 3 +--
 3 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 8e8a4af4f9e2..0f5fd53059cd 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3993,8 +3993,7 @@ static inline void skb_set_delivery_time(struct sk_buff *skb, ktime_t kt,
 					 bool mono)
 {
 	skb->tstamp = kt;
-	/* Setting mono_delivery_time will be enabled later */
-	skb->mono_delivery_time = 0;
+	skb->mono_delivery_time = kt && mono;
 }
 
 DECLARE_STATIC_KEY_FALSE(netstamp_needed_key);
diff --git a/net/core/dev.c b/net/core/dev.c
index 3ff686cc8c84..0fc02cf32476 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5193,8 +5193,10 @@ static int __netif_receive_skb_core(struct sk_buff **pskb, bool pfmemalloc,
 			goto out;
 	}
 
-	if (skb_skip_tc_classify(skb))
+	if (skb_skip_tc_classify(skb)) {
+		skb_clear_delivery_time(skb);
 		goto skip_classify;
+	}
 
 	if (pfmemalloc)
 		goto skip_taps;
@@ -5223,12 +5225,14 @@ static int __netif_receive_skb_core(struct sk_buff **pskb, bool pfmemalloc,
 			goto another_round;
 		if (!skb)
 			goto out;
+		skb_clear_delivery_time(skb);
 
 		nf_skip_egress(skb, false);
 		if (nf_ingress(skb, &pt_prev, &ret, orig_dev) < 0)
 			goto out;
-	}
+	} else
 #endif
+		skb_clear_delivery_time(skb);
 	skb_reset_redirect(skb);
 skip_classify:
 	if (pfmemalloc && !skb_pfmemalloc_protocol(skb))
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index a9588e0c82c5..00b4bf26fd93 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1728,8 +1728,7 @@ 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;
-		/* Setting mono_delivery_time will be enabled later */
-		nskb->mono_delivery_time = 0;
+		nskb->mono_delivery_time = !!transmit_time;
 		ip_push_pending_frames(sk, &fl4);
 	}
 out:
-- 
2.30.2