Re: [RFC PATCH bpf-next v5 2/2] net: Add additional bit to support clockid_t timestamp type

Willem de Bruijn
2024-04-25T14:42:49Z

Abhishek Chauhan wrote:
> tstamp_type is now set based on actual clockid_t compressed
> into 2 bits.
>
> To make the design scalable for future needs this commit bring in
> the change to extend the tstamp_type:1 to tstamp_type:2 to support
> other clockid_t timestamp.
>
> We now support CLOCK_TAI as part of tstamp_type as part of this
> commit with exisiting support CLOCK_MONOTONIC and CLOCK_REALTIME.
>
> Link: https://lore.kernel.org/netdev/bc037db4-58bb-4861-ac31-a361a93841d3@linux.dev/
> Signed-off-by: Abhishek Chauhan <quic_abchauha@quicinc.com>
> ---

> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index e464d0ebc9c1..3ad0de07d261 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -711,6 +711,8 @@ typedef unsigned char *sk_buff_data_t;
> enum skb_tstamp_type {
> SKB_CLOCK_REALTIME,
> SKB_CLOCK_MONOTONIC,
> + SKB_CLOCK_TAI,
> + __SKB_CLOCK_MAX = SKB_CLOCK_TAI,
> };
>
> /**
> @@ -831,8 +833,8 @@ enum skb_tstamp_type {
> * @decrypted: Decrypted SKB
> * @slow_gro: state present at GRO time, slower prepare step required
> * @tstamp_type: When set, skb->tstamp has the
> - * delivery_time in mono clock base Otherwise, the
> - * timestamp is considered real clock base.
> + * delivery_time in mono clock base or clock base of skb->tstamp.

drop "in mono clock base or "

> + * Otherwise, the timestamp is considered real clock base

drop this: whenever in realtime clock base, tstamp_type is zero, so
the above shorter statement always holds.

> * @napi_id: id of the NAPI struct this skb came from
> * @sender_cpu: (aka @napi_id) source CPU in XPS
> * @alloc_cpu: CPU which did the skb allocation.
> @@ -960,7 +962,7 @@ struct sk_buff {
> /* private: */
> __u8 __mono_tc_offset[0];
> /* public: */
> - __u8 tstamp_type:1; /* See skb_tstamp_type */
> + __u8 tstamp_type:2; /* See skb_tstamp_type */
> #ifdef CONFIG_NET_XGRESS
> __u8 tc_at_ingress:1; /* See TC_AT_INGRESS_MASK */
> __u8 tc_skip_classify:1;
> @@ -1090,15 +1092,17 @@ struct sk_buff {
> #endif
> #define PKT_TYPE_OFFSET offsetof(struct sk_buff, __pkt_type_offset)
>
> -/* if you move tc_at_ingress or mono_delivery_time
> +/* if you move tc_at_ingress or tstamp_type:2
> * around, you also must adapt these constants.
> */
> #ifdef __BIG_ENDIAN_BITFIELD
> -#define SKB_MONO_DELIVERY_TIME_MASK (1 << 7)
> -#define TC_AT_INGRESS_MASK (1 << 6)
> +#define SKB_TSTAMP_TYPE_MASK (3 << 6)
> +#define SKB_TSTAMP_TYPE_RSH (6)
> +#define TC_AT_INGRESS_RSH (5)

I had to find BPF_RSH to understand this abbreviation.

use SHIFT instead of RSH, as that is so domain specific?

> +#define TC_AT_INGRESS_MASK (1 << 5)
> #else
> -#define SKB_MONO_DELIVERY_TIME_MASK (1 << 0)
> -#define TC_AT_INGRESS_MASK (1 << 1)
> +#define SKB_TSTAMP_TYPE_MASK (3)
> +#define TC_AT_INGRESS_MASK (1 << 2)
> #endif
> #define SKB_BF_MONO_TC_OFFSET offsetof(struct sk_buff, __mono_tc_offset)
>

> - if (skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_MONO) {
> + if (skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_MONO ||
> + skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_TAI) {

Peculiar indentation?

Just FYI that I'm not the best person to review the BPF part.
Thankfully Martin is helping you with that.