netdev - Re: [PATCH net-next v3 07/14] net-timestamp: add a new triggered point to set sk_tsflags

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Message-ID: <6720356328c26_24dce6294ce@willemb.c.googlers.com.notmuch>
Date: Mon, 28 Oct 2024 21:07:47 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jason Xing <kerneljasonxing@...il.com>, 
 davem@...emloft.net, 
 edumazet@...gle.com, 
 kuba@...nel.org, 
 pabeni@...hat.com, 
 dsahern@...nel.org, 
 willemdebruijn.kernel@...il.com, 
 willemb@...gle.com, 
 ast@...nel.org, 
 daniel@...earbox.net, 
 andrii@...nel.org, 
 martin.lau@...ux.dev, 
 eddyz87@...il.com, 
 song@...nel.org, 
 yonghong.song@...ux.dev, 
 john.fastabend@...il.com, 
 kpsingh@...nel.org, 
 sdf@...ichev.me, 
 haoluo@...gle.com, 
 jolsa@...nel.org, 
 shuah@...nel.org, 
 ykolal@...com
Cc: bpf@...r.kernel.org, 
 netdev@...r.kernel.org, 
 Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v3 07/14] net-timestamp: add a new triggered
 point to set sk_tsflags_bpf in UDP layer

Jason Xing wrote:
> From: Jason Xing <kernelxing@...cent.com>
> 
> This patch behaves like how cmsg feature works, that is to say,
> check and set on each call of udp_sendmsg before passing sk_tsflags_bpf
> to cork tsflags.
> 
> Signed-off-by: Jason Xing <kernelxing@...cent.com>
> ---
>  include/net/sock.h             | 1 +
>  include/uapi/linux/bpf.h       | 3 +++
>  net/core/skbuff.c              | 2 +-
>  net/ipv4/udp.c                 | 1 +
>  tools/include/uapi/linux/bpf.h | 3 +++
>  5 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 062f405c744e..cf7fea456455 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -2828,6 +2828,7 @@ static inline bool sk_listener_or_tw(const struct sock *sk)
>  }
>  
>  void sock_enable_timestamp(struct sock *sk, enum sock_flags flag);
> +void timestamp_call_bpf(struct sock *sk, int op, u32 nargs, u32 *args);
>  int sock_recv_errqueue(struct sock *sk, struct msghdr *msg, int len, int level,
>  		       int type);
>  
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 6fc3bd12b650..055ffa7c965c 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -7028,6 +7028,9 @@ enum {
>  					 * feature is on. It indicates the
>  					 * recorded timestamp.
>  					 */
> +	BPF_SOCK_OPS_TS_UDP_SND_CB,	/* Called when every udp_sendmsg
> +					 * syscall is triggered
> +					 */
>  };
>  
>  /* 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
> index 8b2a79c0fe1c..0b571306f7ea 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -5622,7 +5622,7 @@ static void skb_tstamp_tx_output(struct sk_buff *orig_skb,
>  	__skb_complete_tx_timestamp(skb, sk, tstype, opt_stats);
>  }
>  
> -static void timestamp_call_bpf(struct sock *sk, int op, u32 nargs, u32 *args)
> +void timestamp_call_bpf(struct sock *sk, int op, u32 nargs, u32 *args)
>  {
>  	struct bpf_sock_ops_kern sock_ops;
>  
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 9a20af41e272..e768421abc37 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1264,6 +1264,7 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
>  	if (!corkreq) {
>  		struct inet_cork cork;
>  
> +		timestamp_call_bpf(sk, BPF_SOCK_OPS_TS_UDP_SND_CB, 0, NULL);
>  		skb = ip_make_skb(sk, fl4, getfrag, msg, ulen,
>  				  sizeof(struct udphdr), &ipc, &rt,
>  				  &cork, msg->msg_flags);
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 6fc3bd12b650..055ffa7c965c 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -7028,6 +7028,9 @@ enum {
>  					 * feature is on. It indicates the
>  					 * recorded timestamp.
>  					 */
> +	BPF_SOCK_OPS_TS_UDP_SND_CB,	/* Called when every udp_sendmsg
> +					 * syscall is triggered
> +					 */

If adding a timestamp as close to syscall entry as possible, give it a
generic name, not specific to UDP.

And please explain in the commit message the reason for a new
timestamp recording point: with existing timestamping the application
can call clock_gettime before (and optionally after) the send call.
An admin using BPF does not have this option, so needs this as part of
the BPF timestamping API.


>  };
>  
>  /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
> -- 
> 2.37.3
>