Re: [PATCH net-next v4 07/11] net-timestamp: support hwtstamp print for bpf extension

[Martin KaFai Lau <martin.lau@linux.dev>]

On 12/7/24 9:37 AM, Jason Xing wrote:
> From: Jason Xing <kernelxing@tencent.com>
> 
> Passing the hwtstamp to bpf prog which can print.
> 
> Signed-off-by: Jason Xing <kernelxing@tencent.com>
> ---
>   include/net/sock.h |  6 ++++--
>   net/core/skbuff.c  | 17 +++++++++++++----
>   net/core/sock.c    |  4 +++-
>   3 files changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index f88a00108a2f..9bc883573208 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -2921,9 +2921,11 @@ int sock_set_timestamping(struct sock *sk, int optname,
>   
>   void sock_enable_timestamps(struct sock *sk);
>   #if defined(CONFIG_CGROUP_BPF) && defined(CONFIG_BPF_SYSCALL)
> -void bpf_skops_tx_timestamping(struct sock *sk, struct sk_buff *skb, int op);
> +void bpf_skops_tx_timestamping(struct sock *sk, struct sk_buff *skb, int op,
> +			       u32 nargs, u32 *args);
>   #else
> -static inline void bpf_skops_tx_timestamping(struct sock *sk, struct sk_buff *skb, int op)
> +static inline void bpf_skops_tx_timestamping(struct sock *sk, struct sk_buff *skb, int op,
> +					     u32 nargs, u32 *args)
>   {
>   }
>   #endif
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 48b0c71e9522..182a44815630 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -5539,8 +5539,12 @@ void skb_complete_tx_timestamp(struct sk_buff *skb,
>   }
>   EXPORT_SYMBOL_GPL(skb_complete_tx_timestamp);
>   
> -static void __skb_tstamp_tx_bpf(struct sock *sk, struct sk_buff *skb, int tstype)
> +static void __skb_tstamp_tx_bpf(struct sock *sk, struct sk_buff *skb,
> +				struct skb_shared_hwtstamps *hwtstamps,
> +				int tstype)
>   {
> +	struct timespec64 tstamp;
> +	u32 args[2] = {0, 0};
>   	int op;
>   
>   	if (!sk)
> @@ -5552,6 +5556,11 @@ static void __skb_tstamp_tx_bpf(struct sock *sk, struct sk_buff *skb, int tstype
>   		break;
>   	case SCM_TSTAMP_SND:
>   		op = BPF_SOCK_OPS_TS_SW_OPT_CB;

> +		if (hwtstamps) {
> +			tstamp = ktime_to_timespec64(hwtstamps->hwtstamp);

Avoid this conversion which is likely not useful to the bpf prog. Directly pass 
hwtstamps->hwtstamp (in ns?) to the bpf prog. Put lower 32bits in args[0] and 
higher 32bits in args[1].

Also, how about adding a BPF_SOCK_OPS_TS_"HW"_OPT_CB for the "hwtstamps != NULL" 
case instead of reusing the BPF_SOCK_OPS_TS_"SW"_OPT_CB?

A more subtle thing for the hwtstamps case is, afaik the bpf prog will not be 
called. All drivers are still only testing SKBTX_HW_TSTAMP instead of testing
(SKBTX_HW_TSTAMP | SKBTX_BPF).

There are a lot of drivers to change though. A quick thought is to rename the 
existing SKBTX_HW_TSTAMP (e.g. __SKBTX_HW_TSTAMP = 1 << 0) and define 
SKBTX_HW_TSTAMP like:

#define SKBTX_HW_TSTAMP (__SKBTX_HW_TSTAMP | SKBTX_BPF)

Then change some of the existing skb_shinfo(skb)->tx_flags "setting" site to use 
__SKBTX_HW_TSTAMP instead. e.g. in __sock_tx_timestamp(). Not very pretty but 
may be still better than changing many drivers. May be there is a better way...

While talking about where to test the SKBTX_BPF bit, I wonder if the new 
skb_tstamp_is_set() is needed. For the non SKBTX_HW_TSTAMP case, the number of 
tx_flags testing sites should be limited, so should be easy to add the SKBTX_BPF 
bit test. e.g. at the __dev_queue_xmit, test "if 
(unlikely(skb_shinfo(skb)->tx_flags & (SKBTX_SCHED_TSTAMP | SKBTX_BPF)))". Patch 
6 has also tested the bpf specific bit at tcp_ack_tstamp() before calling the 
__skb_tstamp_tx().

At the beginning of __skb_tstamp_tx(), do something like this:

void __skb_tstamp_tx(struct sk_buff *orig_skb,
		     const struct sk_buff *ack_skb,
		     struct skb_shared_hwtstamps *hwtstamps,
		     struct sock *sk, int tstype)
{
	if (cgroup_bpf_enabled(CGROUP_SOCK_OPS) &&
	    unlikely(skb_shinfo(skb)->tx_flags & SKBTX_BPF))
		__skb_tstamp_tx_bpf(sk, orig_skb, hwtstamps, tstype);

	if (unlikely(!(skb_shinfo(skb)->tx_flags & ~SKBTX_BPF)))
		return;

Then the new skb_tstamp_tx_output() shuffle is probably not be needed also.

> +			args[0] = tstamp.tv_sec;
> +			args[1] = tstamp.tv_nsec;
> +		}
>   		break;
>   	case SCM_TSTAMP_ACK:
>   		op = BPF_SOCK_OPS_TS_ACK_OPT_CB;
> @@ -5560,7 +5569,7 @@ static void __skb_tstamp_tx_bpf(struct sock *sk, struct sk_buff *skb, int tstype
>   		return;
>   	}
>   
> -	bpf_skops_tx_timestamping(sk, skb, op);
> +	bpf_skops_tx_timestamping(sk, skb, op, 2, args);
>   }
>   
>   static void skb_tstamp_tx_output(struct sk_buff *orig_skb,
> @@ -5651,7 +5660,7 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb,
>   	if (unlikely(skb_tstamp_is_set(orig_skb, tstype, false)))
>   		skb_tstamp_tx_output(orig_skb, ack_skb, hwtstamps, sk, tstype);
>   	if (unlikely(skb_tstamp_is_set(orig_skb, tstype, true)))
> -		__skb_tstamp_tx_bpf(sk, orig_skb, tstype);
> +		__skb_tstamp_tx_bpf(sk, orig_skb, hwtstamps, tstype);
>   }
>   EXPORT_SYMBOL_GPL(__skb_tstamp_tx);
>   
> @@ -5662,7 +5671,7 @@ void skb_tstamp_tx(struct sk_buff *orig_skb,
>   
>   	skb_tstamp_tx_output(orig_skb, NULL, hwtstamps, orig_skb->sk, tstype);
>   	if (unlikely(skb_tstamp_is_set(orig_skb, tstype, true)))
> -		__skb_tstamp_tx_bpf(orig_skb->sk, orig_skb, tstype);
> +		__skb_tstamp_tx_bpf(orig_skb->sk, orig_skb, hwtstamps, tstype);
>   }
>   EXPORT_SYMBOL_GPL(skb_tstamp_tx);
>   
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 79cb5c74c76c..504939bafe0c 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -942,7 +942,8 @@ int sock_set_timestamping(struct sock *sk, int optname,
>   }
>   
>   #if defined(CONFIG_CGROUP_BPF) && defined(CONFIG_BPF_SYSCALL)
> -void bpf_skops_tx_timestamping(struct sock *sk, struct sk_buff *skb, int op)
> +void bpf_skops_tx_timestamping(struct sock *sk, struct sk_buff *skb, int op,
> +			       u32 nargs, u32 *args)

Directly pass hwtstamps->hwtstamp instead of args and nargs. Save a memcpy below.

>   {
>   	struct bpf_sock_ops_kern sock_ops;
>   
> @@ -952,6 +953,7 @@ void bpf_skops_tx_timestamping(struct sock *sk, struct sk_buff *skb, int op)
>   	sock_ops.op = op;
>   	sock_ops.is_fullsock = 1;
>   	sock_ops.sk = sk;
> +	memcpy(sock_ops.args, args, nargs * sizeof(*args));
>   	__cgroup_bpf_run_filter_sock_ops(sk, &sock_ops, CGROUP_SOCK_OPS);
>   }
>   #endif