netdev - Re: [PATCH bpf-next v9 09/12] bpf: support SCM_TSTAMP_ACK of SO

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Message-ID: <67a79a3f9c7ed_3488ef294cf@willemb.c.googlers.com.notmuch>
Date: Sat, 08 Feb 2025 12:54:07 -0500
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, 
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 jolsa@...nel.org, 
 horms@...nel.org
Cc: bpf@...r.kernel.org, 
 netdev@...r.kernel.org, 
 Jason Xing <kerneljasonxing@...il.com>
Subject: Re: [PATCH bpf-next v9 09/12] bpf: support SCM_TSTAMP_ACK of
 SO_TIMESTAMPING

Jason Xing wrote:
> Support the ACK timestamp case. Extend txstamp_ack to two bits:
> 1 stands for SO_TIMESTAMPING mode, 2 bpf extension. The latter
> will be used later.
> 
> Signed-off-by: Jason Xing <kerneljasonxing@...il.com>
> ---
>  include/net/tcp.h              | 4 ++--
>  include/uapi/linux/bpf.h       | 5 +++++
>  net/core/skbuff.c              | 5 ++++-
>  tools/include/uapi/linux/bpf.h | 5 +++++
>  4 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 4c4dca59352b..ef30f3605e04 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -958,10 +958,10 @@ struct tcp_skb_cb {
>  
>  	__u8		sacked;		/* State flags for SACK.	*/
>  	__u8		ip_dsfield;	/* IPv4 tos or IPv6 dsfield	*/
> -	__u8		txstamp_ack:1,	/* Record TX timestamp for ack? */
> +	__u8		txstamp_ack:2,	/* Record TX timestamp for ack? */
>  			eor:1,		/* Is skb MSG_EOR marked? */
>  			has_rxtstamp:1,	/* SKB has a RX timestamp	*/
> -			unused:5;
> +			unused:4;
>  	__u32		ack_seq;	/* Sequence number ACK'd	*/
>  	union {
>  		struct {
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index e71a9b53e7bc..c04e788125a7 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -7044,6 +7044,11 @@ enum {
>  					 * SK_BPF_CB_TX_TIMESTAMPING feature
>  					 * is on.
>  					 */
> +	BPF_SOCK_OPS_TS_ACK_OPT_CB,	/* Called when all the skbs in the
> +					 * same sendmsg call are acked
> +					 * when SK_BPF_CB_TX_TIMESTAMPING
> +					 * feature is on.
> +					 */
>  };
>  
>  /* 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 ca1ba4252ca5..c0f4d6f6583d 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -5549,7 +5549,7 @@ static bool skb_tstamp_tx_report_so_timestamping(struct sk_buff *skb,
>  		return skb_shinfo(skb)->tx_flags & (sw ? SKBTX_SW_TSTAMP :
>  						    SKBTX_HW_TSTAMP_NOBPF);
>  	case SCM_TSTAMP_ACK:
> -		return TCP_SKB_CB(skb)->txstamp_ack;
> +		return TCP_SKB_CB(skb)->txstamp_ack == 1;

For the two to coexist, this should be txstamp_ack & 1

And in the patch that introduces the BPF bit, txstamp_ack |= 2, rather than txstamp_ack = 2.

And let's define labels rather than use constants directly: 

  #define TSTAMP_ACK_SK  0x1
  #define TSTAMP_ACK_BPF 0x2