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.
