[PATCH bpf-next v9 11/12] bpf: support selective sampling for bpf timestamping

[Jason Xing <kerneljasonxing@gmail.com>]

Use __bpf_kfunc feature to allow bpf prog dynamically and selectively
to sample/track the skb. For example, the bpf prog will limit tracking
X numbers of packets and then will stop there instead of tracing
all the sendmsgs of matched flow all along.

Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
---
 kernel/bpf/btf.c  |  1 +
 net/core/filter.c | 27 ++++++++++++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 8396ce1d0fba..a65e2eeffb88 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -8535,6 +8535,7 @@ 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..db20a947e757 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -12102,6 +12102,21 @@ __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)
+{
+	struct sk_buff *skb;
+
+	if (skops->op != BPF_SOCK_OPS_TS_SND_CB)
+		return -EOPNOTSUPP;
+
+	skb = skops->skb;
+	TCP_SKB_CB(skb)->txstamp_ack = 2;
+	skb_shinfo(skb)->tx_flags |= SKBTX_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 +12150,10 @@ 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 +12174,11 @@ 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 +12197,8 @@ 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