skb->tstamp was first used as the (rcv) timestamp. The major usage is to report it to the user (e.g. SO_TIMESTAMP). Later, skb->tstamp is also set as the (future) delivery_time (e.g. EDT in TCP) during egress and used by the qdisc (e.g. sch_fq) to make decision on when the skb can be passed to the dev. Currently, there is no way to tell skb->tstamp having the (rcv) timestamp or the delivery_time, so it is always reset to 0 whenever forwarded between egress and ingress. While it makes sense to always clear the (rcv) timestamp in skb->tstamp to avoid confusing sch_fq that expects the delivery_time, it is a performance issue [0] to clear the delivery_time if the skb finally egress to a fq@phy-dev. This set is to keep the mono delivery time and make it available to the final egress interface. Please see individual patch for the details. [0] (slide 22): https://linuxplumbersconf.org/event/11/contributions/953/attachments/867/1658/LPC_2021_BPF_Datapath_Extensions.pdf v4: netdev: - Push the skb_clear_delivery_time() from ip_local_deliver() and ip6_input() to ip_local_deliver_finish() and ip6_input_finish() to accommodate the ipvs forward path. This is the notable change in v4 at the netdev side. - Patch 3/8 first does the skb_clear_delivery_time() after sch_handle_ingress() in dev.c and this will make the tc-bpf forward path work via the bpf_redirect_*() helper. - The next patch 4/8 (new in v4) will then postpone the skb_clear_delivery_time() from dev.c to the ip_local_deliver_finish() and ip6_input_finish() after taking care of the tstamp usage in the ip defrag case. This will make the kernel forward path also work, e.g. the ip[6]_forward(). - Fixed a case v3 which missed setting the skb->mono_delivery_time bit when sending TCP rst/ack in some cases (e.g. from a ctl_sk). That case happens at ip_send_unicast_reply() and tcp_v6_send_response(). It is fixed in patch 1/8 (and then patch 3/8) in v4. bpf: - Adding __sk_buff->delivery_time_type instead of adding __sk_buff->mono_delivery_time as in v3. The tc-bpf can stay with one __sk_buff->tstamp instead of having two 'time' fields while one is 0 and another is not. tc-bpf can use the new __sk_buff->delivery_time_type to tell what is stored in __sk_buff->tstamp. - bpf_skb_set_delivery_time() helper is added to set __sk_buff->tstamp from non mono delivery_time to mono delivery_time - Most of the convert_ctx_access() bpf insn rewrite in v3 is gone, so no new rewrite added for __sk_buff->tstamp. The only rewrite added is for reading the new __sk_buff->delivery_time_type. - Added selftests, test_tc_dtime.c v3: - Feedback from v2 is using shinfo(skb)->tx_flags could be racy. - Considered to reuse a few bits in skb->tstamp to represent different semantics, other than more code churns, it will break the bpf usecase which currently can write and then read back the skb->tstamp. - Went back to v1 idea on adding a bit to skb and address the feedbacks on v1: - Added one bit skb->mono_delivery_time to flag that the skb->tstamp has the mono delivery_time (EDT), instead of adding a bit to flag if the skb->tstamp has been forwarded or not. - Instead of resetting the delivery_time back to the (rcv) timestamp during recvmsg syscall which may be too late and not useful, the delivery_time reset in v3 happens earlier once the stack knows that the skb will be delivered locally. - Handled the tapping@ingress case by af_packet - No need to change the (rcv) timestamp to mono clock base as in v1. The added one bit to flag skb->mono_delivery_time is enough to keep the EDT delivery_time during forward. - Added logic to the bpf side to make the existing bpf running at ingress can still get the (rcv) timestamp when reading the __sk_buff->tstamp. New __sk_buff->mono_delivery_time is also added. Test is still needed to test this piece. Martin KaFai Lau (8): net: Add skb->mono_delivery_time to distinguish mono delivery_time from (rcv) timestamp net: Add skb_clear_tstamp() to keep the mono delivery_time net: Set skb->mono_delivery_time and clear it after sch_handle_ingress() net: Postpone skb_clear_delivery_time() until knowing the skb is delivered locally bpf: Keep the (rcv) timestamp behavior for the existing tc-bpf@ingress bpf: Clear skb->mono_delivery_time bit if needed after running tc-bpf@egress bpf: Add __sk_buff->delivery_time_type and bpf_skb_set_delivery_time() bpf: selftests: test skb->tstamp in redirect_neigh drivers/net/loopback.c | 2 +- include/linux/filter.h | 33 +- include/linux/skbuff.h | 64 ++- include/net/inet_frag.h | 1 + include/uapi/linux/bpf.h | 35 +- net/bridge/br_forward.c | 2 +- net/bridge/netfilter/nf_conntrack_bridge.c | 5 +- net/core/dev.c | 4 +- net/core/filter.c | 85 +++- net/core/skbuff.c | 8 +- net/ipv4/inet_fragment.c | 1 + net/ipv4/ip_forward.c | 2 +- net/ipv4/ip_fragment.c | 1 + net/ipv4/ip_input.c | 1 + net/ipv4/ip_output.c | 6 +- net/ipv4/tcp_output.c | 16 +- net/ipv6/ip6_input.c | 1 + net/ipv6/ip6_output.c | 7 +- net/ipv6/netfilter.c | 5 +- net/ipv6/tcp_ipv6.c | 2 +- net/netfilter/ipvs/ip_vs_xmit.c | 6 +- net/netfilter/nf_dup_netdev.c | 2 +- net/netfilter/nf_flow_table_ip.c | 4 +- net/netfilter/nft_fwd_netdev.c | 2 +- net/openvswitch/vport.c | 2 +- net/packet/af_packet.c | 4 +- net/sched/act_bpf.c | 7 +- net/sched/cls_bpf.c | 8 +- net/xfrm/xfrm_interface.c | 2 +- tools/include/uapi/linux/bpf.h | 35 +- .../selftests/bpf/prog_tests/tc_redirect.c | 434 ++++++++++++++++++ .../selftests/bpf/progs/test_tc_dtime.c | 348 ++++++++++++++ 32 files changed, 1078 insertions(+), 57 deletions(-) create mode 100644 tools/testing/selftests/bpf/progs/test_tc_dtime.c -- 2.30.2
