Re: [PATCH net-next 5/9] net-timestamp: ready to turn on the button to generate tx timestamps

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Jason Xing wrote:
> From: Jason Xing <kernelxing@tencent.com>
> 
> Once we set BPF_SOCK_OPS_TX_TIMESTAMP_OPT_CB_FLAG flag here, there
> are three points in the previous patches where generating timestamps
> works. Let us make the basic bpf mechanism for timestamping feature
>  work finally.
> 
> We can use like this as a simple example in bpf program:
> __section("sockops")
> 
> case BPF_SOCK_OPS_TX_TIMESTAMP_OPT_CB:
> 	dport = bpf_ntohl(skops->remote_port);
> 	sport = skops->local_port;
> 	skops->reply = SOF_TIMESTAMPING_TX_SCHED;
> 	bpf_sock_ops_cb_flags_set(skops, BPF_SOCK_OPS_TX_TIMESTAMP_OPT_CB_FLAG);
> case BPF_SOCK_OPS_TS_SCHED_OPT_CB:
> 	bpf_printk(...);
> 
> Signed-off-by: Jason Xing <kernelxing@tencent.com>

>  /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 82cc4a5633ce..ddf4089779b5 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -477,12 +477,37 @@ void tcp_init_sock(struct sock *sk)
>  }
>  EXPORT_SYMBOL(tcp_init_sock);
>  
> +static u32 bpf_tcp_tx_timestamp(struct sock *sk)
> +{
> +	u32 flags;
> +
> +	flags = tcp_call_bpf(sk, BPF_SOCK_OPS_TX_TS_OPT_CB, 0, NULL);
> +	if (flags <= 0)
> +		return 0;
> +
> +	if (flags & ~SOF_TIMESTAMPING_MASK)
> +		return 0;
> +
> +	if (!(flags & SOF_TIMESTAMPING_TX_RECORD_MASK))
> +		return 0;
> +
> +	return flags;
> +}
> +
>  static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc)
>  {
>  	struct sk_buff *skb = tcp_write_queue_tail(sk);
>  	u32 tsflags = sockc->tsflags;
> +	u32 flags;
> +
> +	if (!skb)
> +		return;
> +
> +	flags = bpf_tcp_tx_timestamp(sk);
> +	if (flags)
> +		tsflags = flags;

So this feature overwrites the flags set by the user?

Ideally we would use an entirely separate field for BPF admin
timestamping requests.

>  
> -	if (tsflags && skb) {
> +	if (tsflags) {
>  		struct skb_shared_info *shinfo = skb_shinfo(skb);
>  		struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);