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[bpf-next,v8,10/12] bpf: make TCP tx timestamp bpf extension work

Message ID 20250204183024.87508-11-kerneljasonxing@gmail.com (mailing list archive)
State New
Delegated to: BPF
Headers show
Series net-timestamp: bpf extension to equip applications transparently | expand

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Commit Message

Jason Xing Feb. 4, 2025, 6:30 p.m. UTC 
After this patch, people can fully use the bpf prog to trace the
tx path for TCP type.

Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
---
 net/ipv4/tcp.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

Comments

Jakub Kicinski Feb. 5, 2025, 1:57 a.m. UTC | #1 
On Wed,  5 Feb 2025 02:30:22 +0800 Jason Xing wrote:
> +	if (cgroup_bpf_enabled(CGROUP_SOCK_OPS) &&
> +	    SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_TX_TIMESTAMPING) && skb) {
> +		struct skb_shared_info *shinfo = skb_shinfo(skb);
> +		struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
> +
> +		tcb->txstamp_ack_bpf = 1;
> +		shinfo->tx_flags |= SKBTX_BPF;
> +		shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
> +	}

If BPF program is attached we'll timestamp all skbs? Am I reading this
right?

Wouldn't it be better to let BPF_SOCK_OPS_TS_SND_CB return whether it's
interested in tracing current packet all the way thru the stack?
Jason Xing Feb. 5, 2025, 2:15 a.m. UTC | #2 
On Wed, Feb 5, 2025 at 9:57 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Wed,  5 Feb 2025 02:30:22 +0800 Jason Xing wrote:
> > +     if (cgroup_bpf_enabled(CGROUP_SOCK_OPS) &&
> > +         SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_TX_TIMESTAMPING) && skb) {
> > +             struct skb_shared_info *shinfo = skb_shinfo(skb);
> > +             struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
> > +
> > +             tcb->txstamp_ack_bpf = 1;
> > +             shinfo->tx_flags |= SKBTX_BPF;
> > +             shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
> > +     }
>
> If BPF program is attached we'll timestamp all skbs? Am I reading this
> right?

For now, not really because tcp_tx_timestamp() gets called only when
dealing with the last part of this sendmsg(). So not all the skbs will
be traced.

>
> Wouldn't it be better to let BPF_SOCK_OPS_TS_SND_CB return whether it's
> interested in tracing current packet all the way thru the stack?

This flag is mainly used to correlate the sendmsg timestamp with
corresponding tskey, or else the skb travers the qdisc layer without
knowing how to match its sendmsg.

Thanks,
Jason
diff mbox series

Patch

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 0d704bda6c41..3df802410ebf 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -492,6 +492,16 @@  static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc)
 		if (tsflags & SOF_TIMESTAMPING_TX_RECORD_MASK)
 			shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
 	}
+
+	if (cgroup_bpf_enabled(CGROUP_SOCK_OPS) &&
+	    SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_TX_TIMESTAMPING) && skb) {
+		struct skb_shared_info *shinfo = skb_shinfo(skb);
+		struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
+
+		tcb->txstamp_ack_bpf = 1;
+		shinfo->tx_flags |= SKBTX_BPF;
+		shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
+	}
 }
 
 static bool tcp_stream_is_readable(struct sock *sk, int target)