Subject: [PATCH bpf-next v13 07/12] bpf: add BPF_SOCK_OPS_TSTAMP_SND_SW_CB callback

From: Jason Xing <[email-masked]>
Date: Thu, 20 Feb 2025 15:29:35 +0800

Support sw SCM_TSTAMP_SND case for bpf timestamping.

Add a new sock_ops callback, BPF_SOCK_OPS_TSTAMP_SND_SW_CB. This
callback will occur at the same timestamping point as the user
space's software SCM_TSTAMP_SND. The BPF program can use it to
get the same SCM_TSTAMP_SND timestamp without modifying the
user-space application.

Based on this patch, BPF program will get the software
timestamp when the driver is ready to send the skb. In the
sebsequent patch, the hardware timestamp will be supported.

Reviewed-by: Willem de Bruijn <[email-masked]>
Signed-off-by: Jason Xing <[email-masked]>
---
 include/linux/skbuff.h         | 2 +-
 include/uapi/linux/bpf.h       | 4 ++++
 net/core/skbuff.c              | 9 ++++++++-
 tools/include/uapi/linux/bpf.h | 4 ++++
 4 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 52f6e033e704..76582500c5ea 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4568,7 +4568,7 @@ void skb_tstamp_tx(struct sk_buff *orig_skb,
 static inline void skb_tx_timestamp(struct sk_buff *skb)
 {
 	skb_clone_tx_timestamp(skb);
-	if (skb_shinfo(skb)->tx_flags & SKBTX_SW_TSTAMP)
+	if (skb_shinfo(skb)->tx_flags & (SKBTX_SW_TSTAMP | SKBTX_BPF))
 		skb_tstamp_tx(skb, NULL);
 }
 
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 7bcd8b955598..59adcef3326a 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7040,6 +7040,10 @@ enum {
 					 * SK_BPF_CB_TX_TIMESTAMPING
 					 * feature is on.
 					 */
+	BPF_SOCK_OPS_TSTAMP_SND_SW_CB,	/* Called when skb is about to send
+					 * to the nic when SK_BPF_CB_TX_TIMESTAMPING
+					 * feature is on.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 3206f7708974..308db7dae1ab 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5557,6 +5557,7 @@ static bool skb_tstamp_tx_report_so_timestamping(struct sk_buff *skb,
 }
 
 static void skb_tstamp_tx_report_bpf_timestamping(struct sk_buff *skb,
+						  struct skb_shared_hwtstamps *hwtstamps,
 						  struct sock *sk,
 						  int tstype)
 {
@@ -5566,6 +5567,11 @@ static void skb_tstamp_tx_report_bpf_timestamping(struct sk_buff *skb,
 	case SCM_TSTAMP_SCHED:
 		op = BPF_SOCK_OPS_TSTAMP_SCHED_CB;
 		break;
+	case SCM_TSTAMP_SND:
+		if (hwtstamps)
+			return;
+		op = BPF_SOCK_OPS_TSTAMP_SND_SW_CB;
+		break;
 	default:
 		return;
 	}
@@ -5586,7 +5592,8 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb,
 		return;
 
 	if (skb_shinfo(orig_skb)->tx_flags & SKBTX_BPF)
-		skb_tstamp_tx_report_bpf_timestamping(orig_skb, sk, tstype);
+		skb_tstamp_tx_report_bpf_timestamping(orig_skb, hwtstamps,
+						      sk, tstype);
 
 	if (!skb_tstamp_tx_report_so_timestamping(orig_skb, hwtstamps, tstype))
 		return;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index c3b950325846..1ead1e9d31be 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7037,6 +7037,10 @@ enum {
 					 * SK_BPF_CB_TX_TIMESTAMPING
 					 * feature is on.
 					 */
+	BPF_SOCK_OPS_TSTAMP_SND_SW_CB,	/* Called when skb is about to send
+					 * to the nic when SK_BPF_CB_TX_TIMESTAMPING
+					 * feature is on.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
-- 
2.43.5