Martin KaFai Lau wrote: > On 3/1/24 12:13 PM, Abhishek Chauhan wrote: > > Bridge driver today has no support to forward the userspace timestamp > > packets and ends up resetting the timestamp. ETF qdisc checks the > > packet coming from userspace and encounters to be 0 thereby dropping > > time sensitive packets. These changes will allow userspace timestamps > > packets to be forwarded from the bridge to NIC drivers. > > > > Setting the same bit (mono_delivery_time) to avoid dropping of > > userspace tstamp packets in the forwarding path. > > > > Existing functionality of mono_delivery_time remains unaltered here, > > instead just extended with userspace tstamp support for bridge > > forwarding path. > > The patch currently broke the bpf selftest test_tc_dtime: > https://github.com/kernel-patches/bpf/actions/runs/8242487344/job/22541746675 > > In particular, there is a uapi field __sk_buff->tstamp_type which currently has > BPF_SKB_TSTAMP_DELIVERY_MONO to mean skb->tstamp has the MONO "delivery" time. > BPF_SKB_TSTAMP_UNSPEC means everything else (this could be a rx timestamp at > ingress or a delivery time set by user space). > > __sk_buff->tstamp_type depends on skb->mono_delivery_time which does not > necessarily mean mono after this patch. I thought about fixing it on the bpf > side such that reading __sk_buff->tstamp_type only returns > BPF_SKB_TSTAMP_DELIVERY_MONO when the skb->mono_delivery_time is set and skb->sk > is IPPROTO_TCP. However, it won't work because of bpf_skb_set_tstamp(). > > There is a bpf helper, bpf_skb_set_tstamp(skb, tstamp, > BPF_SKB_TSTAMP_DELIVERY_MONO). This helper changes both the skb->tstamp and the > skb->mono_delivery_time. The expectation is this could change skb->tstamp in the > ingress skb and redirect to egress sch_fq. It could also set a mono time to > skb->tstamp where the udp sk->sk_clockid may not be necessary in mono and then > bpf_redirect to egress sch_fq. When bpf_skb_set_tstamp(skb, tstamp, > BPF_SKB_TSTAMP_DELIVERY_MONO) succeeds, reading __sk_buff->tstamp_type expects > BPF_SKB_TSTAMP_DELIVERY_MONO also. > > I ran out of idea to solve this uapi breakage. > > I am afraid it may need to go back to v1 idea and use another bit > (user_delivery_time) in the skb. Is the only conflict when bpf_skb_set_tstamp is called for an skb from a socket with sk_clockid set (and thus SO_TXTIME called)? Interpreting skb->tstamp as mono if skb->mono_delivery_time is set and skb->sk is NULL is fine. This is the ingress to egress redirect case. I don't see an immediate use for this BPF function on egress where it would overwrite an SO_TXTIME timestamp and now skb->tstamp is mono, but skb->sk != NULL and skb->sk->sk_clockid != CLOCK_MONOTONIC. Perhaps bpf_skb_set_tstamp() can just fail if another delivery time is already explicitly programmed? skb->sk && sock_flag(sk, SOCK_TXTIME) && skb->sk->sk_clockid != CLOCK_MONOTONIC Either that, or unset SOCK_TXTIME to make sk_clockid undefined and fall back on interpreting as monotonic.
