Subject: Re: [RFC PATCH net-next v6 08/13] net-timestamp: support hw SCM_TSTAMP_SND for bpf extension

From: Martin KaFai Lau <[email-masked]>
Date: Fri, 24 Jan 2025 16:46:47 -0800

On 1/20/25 5:28 PM, Jason Xing wrote:
> In this patch, we finish the hardware part. Then bpf program can
> fetch the hwstamp from skb directly.
> 
> To avoid changing so many callers using SKBTX_HW_TSTAMP from drivers,
> use this simple modification like this patch does to support printing
> hardware timestamp.
> 
> Signed-off-by: Jason Xing <[email-masked]>
> ---
>   include/linux/skbuff.h         |  4 +++-
>   include/uapi/linux/bpf.h       |  5 +++++
>   net/core/skbuff.c              | 11 ++++++-----
>   net/dsa/user.c                 |  2 +-
>   net/socket.c                   |  2 +-
>   tools/include/uapi/linux/bpf.h |  5 +++++
>   6 files changed, 21 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index de8d3bd311f5..df2d790ae36b 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -471,7 +471,7 @@ struct skb_shared_hwtstamps {
>   /* Definitions for tx_flags in struct skb_shared_info */
>   enum {
>   	/* generate hardware time stamp */
> -	SKBTX_HW_TSTAMP = 1 << 0,
> +	__SKBTX_HW_TSTAMP = 1 << 0,
>   
>   	/* generate software time stamp when queueing packet to NIC */
>   	SKBTX_SW_TSTAMP = 1 << 1,
> @@ -495,6 +495,8 @@ enum {
>   	SKBTX_BPF = 1 << 7,
>   };
>   
> +#define SKBTX_HW_TSTAMP		(__SKBTX_HW_TSTAMP | SKBTX_BPF)
> +
>   #define SKBTX_ANY_SW_TSTAMP	(SKBTX_SW_TSTAMP    | \
>   				 SKBTX_SCHED_TSTAMP | \
>   				 SKBTX_BPF)
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index a6d761f07f67..8936e1061e71 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -7032,6 +7032,11 @@ enum {
>   					 * feature is on. It indicates the
>   					 * recorded timestamp.
>   					 */
> +	BPF_SOCK_OPS_TS_HW_OPT_CB,	/* Called in hardware phase when
> +					 * SO_TIMESTAMPING feature is on.

Same comment on the "SO_TIMESTAMPING".

It will be useful to elaborate more on "hardware phase", like exactly when it 
will be called,

> +					 * It indicates the recorded
> +					 * timestamp.

and the hwtstamps will be in the skb.

> +					 */
>   };
>   
>   /* 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 288eb9869827..c769feae5162 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -5548,7 +5548,7 @@ static bool skb_enable_app_tstamp(struct sk_buff *skb, int tstype, bool sw)
>   		flag = SKBTX_SCHED_TSTAMP;
>   		break;
>   	case SCM_TSTAMP_SND:
> -		flag = sw ? SKBTX_SW_TSTAMP : SKBTX_HW_TSTAMP;
> +		flag = sw ? SKBTX_SW_TSTAMP : __SKBTX_HW_TSTAMP;
>   		break;
>   	case SCM_TSTAMP_ACK:
>   		if (TCP_SKB_CB(skb)->txstamp_ack)
> @@ -5565,7 +5565,8 @@ static bool skb_enable_app_tstamp(struct sk_buff *skb, int tstype, bool sw)
>   }
>   
>   static void skb_tstamp_tx_bpf(struct sk_buff *skb, struct sock *sk,
> -			      int tstype, bool sw)
> +			      int tstype, bool sw,
> +			      struct skb_shared_hwtstamps *hwtstamps)
>   {
>   	int op;
>   
> @@ -5577,9 +5578,9 @@ static void skb_tstamp_tx_bpf(struct sk_buff *skb, struct sock *sk,
>   		op = BPF_SOCK_OPS_TS_SCHED_OPT_CB;
>   		break;
>   	case SCM_TSTAMP_SND:
> +		op = sw ? BPF_SOCK_OPS_TS_SW_OPT_CB : BPF_SOCK_OPS_TS_HW_OPT_CB;
>   		if (!sw)
> -			return;
> -		op = BPF_SOCK_OPS_TS_SW_OPT_CB;
> +			*skb_hwtstamps(skb) = *hwtstamps;

hwtstamps may still be NULL, no?