bpf: Add BPF_SOCK_OPS_TSTAMP_ACK_CB callback

Support the ACK case for bpf timestamping. Add a new sock_ops callback, BPF_SOCK_OPS_TSTAMP_ACK_CB. This callback will occur at the same timestamping point as the user space's SCM_TSTAMP_ACK. The BPF program can use it to get the same SCM_TSTAMP_ACK timestamp without modifying the user-space application. This patch extends txstamp_ack to two bits: 1 stands for SO_TIMESTAMPING mode, 2 bpf extension. Signed-off-by: Jason Xing <kerneljasonxing@gmail.com> Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org> Reviewed-by: Willem de Bruijn <willemb@google.com> Link: https://patch.msgid.link/20250220072940.99994-10-kerneljasonxing@gmail.com
mariux64 · Feb 20, 2025 · b3b81e6 · b3b81e6
1 parent 2deaf7f
commit b3b81e6
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Showing 5 changed files with 19 additions and 4 deletions.
diff --git a/include/net/tcp.h b/include/net/tcp.h
@@ -964,10 +964,12 @@ struct tcp_skb_cb {
 
 	__u8		sacked;		/* State flags for SACK.	*/
 	__u8		ip_dsfield;	/* IPv4 tos or IPv6 dsfield	*/
-	__u8		txstamp_ack:1,	/* Record TX timestamp for ack? */
+#define TSTAMP_ACK_SK	0x1
+#define TSTAMP_ACK_BPF	0x2
+	__u8		txstamp_ack:2,	/* Record TX timestamp for ack? */
 			eor:1,		/* Is skb MSG_EOR marked? */
 			has_rxtstamp:1,	/* SKB has a RX timestamp	*/
-			unused:5;
+			unused:4;
 	__u32		ack_seq;	/* Sequence number ACK'd	*/
 	union {
 		struct {

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
@@ -7044,6 +7044,11 @@ enum {
 					 * SK_BPF_CB_TX_TIMESTAMPING feature
 					 * is on.
 					 */
+	BPF_SOCK_OPS_TSTAMP_ACK_CB,	/* Called when all the skbs in the
+					 * same sendmsg call are acked
+					 * 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
@@ -5550,7 +5550,7 @@ static bool skb_tstamp_tx_report_so_timestamping(struct sk_buff *skb,
 		return skb_shinfo(skb)->tx_flags & (hwtstamps ? SKBTX_HW_TSTAMP_NOBPF :
 						    SKBTX_SW_TSTAMP);
 	case SCM_TSTAMP_ACK:
-		return TCP_SKB_CB(skb)->txstamp_ack;
+		return TCP_SKB_CB(skb)->txstamp_ack & TSTAMP_ACK_SK;
 	}
 
 	return false;
@@ -5575,6 +5575,9 @@ static void skb_tstamp_tx_report_bpf_timestamping(struct sk_buff *skb,
 			op = BPF_SOCK_OPS_TSTAMP_SND_SW_CB;
 		}
 		break;
+	case SCM_TSTAMP_ACK:
+		op = BPF_SOCK_OPS_TSTAMP_ACK_CB;
+		break;
 	default:
 		return;
 	}

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
@@ -492,7 +492,7 @@ static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc)
 
 		sock_tx_timestamp(sk, sockc, &shinfo->tx_flags);
 		if (tsflags & SOF_TIMESTAMPING_TX_ACK)
-			tcb->txstamp_ack = 1;
+			tcb->txstamp_ack |= TSTAMP_ACK_SK;
 		if (tsflags & SOF_TIMESTAMPING_TX_RECORD_MASK)
 			shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
 	}

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
@@ -7044,6 +7044,11 @@ enum {
 					 * SK_BPF_CB_TX_TIMESTAMPING feature
 					 * is on.
 					 */
+	BPF_SOCK_OPS_TSTAMP_ACK_CB,	/* Called when all the skbs in the
+					 * same sendmsg call are acked
+					 * 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