Re: [PATCH bpf-next v8 05/12] net-timestamp: prepare for isolating two modes of SO_TIMESTAMPING

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

Jason Xing wrote:
> No functional changes here, only add skb_enable_app_tstamp() to test
> if the orig_skb matches the usage of application SO_TIMESTAMPING
> or its bpf extension. And it's good to support two modes in
> parallel later in this series.
> 
> Also, this patch deliberately distinguish the software and
> hardware SCM_TSTAMP_SND timestamp by passing 'sw' parameter in order
> to avoid such a case where hardware may go wrong and pass a NULL
> hwstamps, which is even though unlikely to happen. If it really
> happens, bpf prog will finally consider it as a software timestamp.
> It will be hardly recognized. Let's make the timestamping part
> more robust.

Disagree. Don't add a crutch that has not shown to be necessary for
all this time.

Just infer hw from hwtstamps != NULL.
 
> Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
> ---
>  include/linux/skbuff.h | 13 +++++++------
>  net/core/dev.c         |  2 +-
>  net/core/skbuff.c      | 32 ++++++++++++++++++++++++++++++--
>  net/ipv4/tcp_input.c   |  3 ++-
>  4 files changed, 40 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index bb2b751d274a..dfc419281cc9 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -39,6 +39,7 @@
>  #include <net/net_debug.h>
>  #include <net/dropreason-core.h>
>  #include <net/netmem.h>
> +#include <uapi/linux/errqueue.h>
>  
>  /**
>   * DOC: skb checksums
> @@ -4533,18 +4534,18 @@ void skb_complete_tx_timestamp(struct sk_buff *skb,
>  
>  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);
> +		     struct sock *sk, bool sw, int tstype);
>  
>  /**
> - * skb_tstamp_tx - queue clone of skb with send time stamps
> + * skb_tstamp_tx - queue clone of skb with send HARDWARE timestamps

Unfortunately this cannot be modified to skb_tstamp_tx_hw, as that
would require updating way too many callers.

>   * @orig_skb:	the original outgoing packet
>   * @hwtstamps:	hardware time stamps, may be NULL if not available
>   *
>   * If the skb has a socket associated, then this function clones the
>   * skb (thus sharing the actual data and optional structures), stores
> - * the optional hardware time stamping information (if non NULL) or
> - * generates a software time stamp (otherwise), then queues the clone
> - * to the error queue of the socket.  Errors are silently ignored.
> + * the optional hardware time stamping information (if non NULL) then
> + * queues the clone to the error queue of the socket.  Errors are
> + * silently ignored.
>   */
>  void skb_tstamp_tx(struct sk_buff *orig_skb,
>  		   struct skb_shared_hwtstamps *hwtstamps);
> @@ -4565,7 +4566,7 @@ static inline void skb_tx_timestamp(struct sk_buff *skb)
>  {
>  	skb_clone_tx_timestamp(skb);
>  	if (skb_shinfo(skb)->tx_flags & SKBTX_SW_TSTAMP)
> -		skb_tstamp_tx(skb, NULL);
> +		__skb_tstamp_tx(skb, NULL, NULL, skb->sk, true, SCM_TSTAMP_SND);

If a separate version for software timestamps were needed, I'd suggest
adding a skb_tstamp_tx_sw() wrapper. But see first comment.

>  }
>  
>  /**
> diff --git a/net/core/dev.c b/net/core/dev.c
> index afa2282f2604..d77b8389753e 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4501,7 +4501,7 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
>  	skb_assert_len(skb);
>  
>  	if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_SCHED_TSTAMP))
> -		__skb_tstamp_tx(skb, NULL, NULL, skb->sk, SCM_TSTAMP_SCHED);
> +		__skb_tstamp_tx(skb, NULL, NULL, skb->sk, true, SCM_TSTAMP_SCHED);
>  
>  	/* Disable soft irqs for various locks below. Also
>  	 * stops preemption for RCU.
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index a441613a1e6c..6042961dfc02 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -5539,10 +5539,35 @@ void skb_complete_tx_timestamp(struct sk_buff *skb,
>  }
>  EXPORT_SYMBOL_GPL(skb_complete_tx_timestamp);
>  
> +static bool skb_enable_app_tstamp(struct sk_buff *skb, int tstype, bool sw)

app is a bit vague. I suggest

skb_tstamp_tx_report_so_timestamping

and

skb_tstamp_tx_report_bpf_timestamping

> +{
> +	int flag;
> +
> +	switch (tstype) {
> +	case SCM_TSTAMP_SCHED:
> +		flag = SKBTX_SCHED_TSTAMP;
> +		break;

Please just have a one line statements in the case directly:

    case SCM_TSTAMP_SCHED:
        return skb_shinfo(skb)->tx_flags & SKBTX_SCHED_TSTAMP;
    case SCM_TSTAMP_SND:
        return skb_shinfo(skb)->tx_flags & (sw ? SKBTX_SW_TSTAMP :
                                                 SKBTX_HW_TSTAMP);
    case SCM_TSTAMP_ACK:
        return TCP_SKB_CB(skb)->txstamp_ack;

> +	case SCM_TSTAMP_SND:
> +		flag = sw ? SKBTX_SW_TSTAMP : SKBTX_HW_TSTAMP;
> +		break;
> +	case SCM_TSTAMP_ACK:
> +		if (TCP_SKB_CB(skb)->txstamp_ack)
> +			return true;
> +		fallthrough;
> +	default:
> +		return false;
> +	}
> +
> +	if (skb_shinfo(skb)->tx_flags & flag)
> +		return true;
> +
> +	return false;
> +}
> +
>  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)
> +		     struct sock *sk, bool sw, int tstype)
>  {
>  	struct sk_buff *skb;
>  	bool tsonly, opt_stats = false;
> @@ -5551,6 +5576,9 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb,
>  	if (!sk)
>  		return;
>  
> +	if (!skb_enable_app_tstamp(orig_skb, tstype, sw))
> +		return;
> +
>  	tsflags = READ_ONCE(sk->sk_tsflags);
>  	if (!hwtstamps && !(tsflags & SOF_TIMESTAMPING_OPT_TX_SWHW) &&
>  	    skb_shinfo(orig_skb)->tx_flags & SKBTX_IN_PROGRESS)
> @@ -5599,7 +5627,7 @@ EXPORT_SYMBOL_GPL(__skb_tstamp_tx);
>  void skb_tstamp_tx(struct sk_buff *orig_skb,
>  		   struct skb_shared_hwtstamps *hwtstamps)
>  {
> -	return __skb_tstamp_tx(orig_skb, NULL, hwtstamps, orig_skb->sk,
> +	return __skb_tstamp_tx(orig_skb, NULL, hwtstamps, orig_skb->sk, false,
>  			       SCM_TSTAMP_SND);
>  }
>  EXPORT_SYMBOL_GPL(skb_tstamp_tx);
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 77185479ed5e..62252702929d 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3330,7 +3330,8 @@ static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
>  	if (!before(shinfo->tskey, prior_snd_una) &&
>  	    before(shinfo->tskey, tcp_sk(sk)->snd_una)) {
>  		tcp_skb_tsorted_save(skb) {
> -			__skb_tstamp_tx(skb, ack_skb, NULL, sk, SCM_TSTAMP_ACK);
> +			__skb_tstamp_tx(skb, ack_skb, NULL, sk, true,
> +					SCM_TSTAMP_ACK);
>  		} tcp_skb_tsorted_restore(skb);
>  	}
>  }
> -- 
> 2.43.5
>