Subject: [PATCH bpf-next v12 11/12] bpf: support selective sampling for bpf timestamping

From: Jason Xing <[email-masked]>
Date: Tue, 18 Feb 2025 13:01:24 +0800

Add the bpf_sock_ops_enable_tx_tstamp kfunc to allow BPF programs to
selectively enable TX timestamping on a skb during tcp_sendmsg().

For example, BPF program will limit tracking X numbers of packets
and then will stop there instead of tracing all the sendmsgs of
matched flow all along. It would be helpful for users who cannot
afford to calculate latencies from every sendmsg call probably
due to the performance or storage space consideration.

Signed-off-by: Jason Xing <[email-masked]>
---
 kernel/bpf/btf.c  |  1 +
 net/core/filter.c | 31 ++++++++++++++++++++++++++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 9433b6467bbe..740210f883dc 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -8522,6 +8522,7 @@ static int bpf_prog_type_to_kfunc_hook(enum bpf_prog_type prog_type)
 	case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
 	case BPF_PROG_TYPE_CGROUP_SOCKOPT:
 	case BPF_PROG_TYPE_CGROUP_SYSCTL:
+	case BPF_PROG_TYPE_SOCK_OPS:
 		return BTF_KFUNC_HOOK_CGROUP;
 	case BPF_PROG_TYPE_SCHED_ACT:
 		return BTF_KFUNC_HOOK_SCHED_ACT;
diff --git a/net/core/filter.c b/net/core/filter.c
index 7f56d0bbeb00..5611d4a7cf89 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -12102,6 +12102,25 @@ __bpf_kfunc int bpf_sk_assign_tcp_reqsk(struct __sk_buff *s, struct sock *sk,
 #endif
 }
 
+__bpf_kfunc int bpf_sock_ops_enable_tx_tstamp(struct bpf_sock_ops_kern *skops,
+					      u64 flags)
+{
+	struct sk_buff *skb;
+
+	if (skops->op != BPF_SOCK_OPS_TS_SND_CB)
+		return -EOPNOTSUPP;
+
+	if (flags)
+		return -EINVAL;
+
+	skb = skops->skb;
+	skb_shinfo(skb)->tx_flags |= SKBTX_BPF;
+	TCP_SKB_CB(skb)->txstamp_ack |= TSTAMP_ACK_BPF;
+	skb_shinfo(skb)->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
+
+	return 0;
+}
+
 __bpf_kfunc_end_defs();
 
 int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
@@ -12135,6 +12154,10 @@ BTF_KFUNCS_START(bpf_kfunc_check_set_tcp_reqsk)
 BTF_ID_FLAGS(func, bpf_sk_assign_tcp_reqsk, KF_TRUSTED_ARGS)
 BTF_KFUNCS_END(bpf_kfunc_check_set_tcp_reqsk)
 
+BTF_KFUNCS_START(bpf_kfunc_check_set_sock_ops)
+BTF_ID_FLAGS(func, bpf_sock_ops_enable_tx_tstamp, KF_TRUSTED_ARGS)
+BTF_KFUNCS_END(bpf_kfunc_check_set_sock_ops)
+
 static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
 	.owner = THIS_MODULE,
 	.set = &bpf_kfunc_check_set_skb,
@@ -12155,6 +12178,11 @@ static const struct btf_kfunc_id_set bpf_kfunc_set_tcp_reqsk = {
 	.set = &bpf_kfunc_check_set_tcp_reqsk,
 };
 
+static const struct btf_kfunc_id_set bpf_kfunc_set_sock_ops = {
+	.owner = THIS_MODULE,
+	.set = &bpf_kfunc_check_set_sock_ops,
+};
+
 static int __init bpf_kfunc_init(void)
 {
 	int ret;
@@ -12173,7 +12201,8 @@ static int __init bpf_kfunc_init(void)
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &bpf_kfunc_set_xdp);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
 					       &bpf_kfunc_set_sock_addr);
-	return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_kfunc_set_tcp_reqsk);
+	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_kfunc_set_tcp_reqsk);
+	return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SOCK_OPS, &bpf_kfunc_set_sock_ops);
 }
 late_initcall(bpf_kfunc_init);
 
-- 
2.43.5