Merge branch 'skb-mono-delivery-time'

Martin KaFai Lau says:

====================
Preserve mono delivery time (EDT) in skb->tstamp

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

v6:
- Add kdoc and use non-UAPI type in patch 6 (Jakub)

v5:
netdev:
- Patch 3 in v4 is broken down into smaller patches 3, 4, and 5 in v5
- The mono_delivery_time bit clearing in __skb_tstamp_tx() is
  done in __net_timestamp() instead.  This is patch 4 in v5.
- Missed a skb_clear_delivery_time() for the 'skip_classify' case
  in dev.c in v4.  That is fixed in patch 5 in v5 for correctness.
  The skb_clear_delivery_time() will be moved to a later
  stage in Patch 10, so it was an intermediate error in v4.
- Added delivery time handling for nfnetlink_{log, queue}.c in patch 9 (Daniel)
- Added delivery time handling in the IPv6 IOAM hop-by-hop option which has
  an experimental IANA assigned value 49 in patch 8
- Added delivery time handling in nf_conntrack for the ipv6 defrag case
  in patch 7
- Removed unlikely() from testing skb->mono_delivery_time (Daniel)

bpf:
- Remove the skb->tstamp dance in ingress.  Depends on bpf insn
  rewrite to return 0 if skb->tstamp has delivery time in patch 11.
  It is to backward compatible with the existing tc-bpf@ingress in
  patch 11.
- bpf_set_delivery_time() will also allow dtime == 0 and
  dtime_type == BPF_SKB_DELIVERY_TIME_NONE as argument
  in patch 12.

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.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

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