[PATCH net-next 0/2] tcp: update TCPCB_EVER_RETRANS after trace_tcp_retransmit_skb()

[Philo Lu <lulie@linux.alibaba.com>]

Move TCPCB_EVER_RETRANS updating after the trace_tcp_retransmit_skb()
in __tcp_retransmit_skb(), and then we are aware of whether the skb has
ever been retransmitted in this tracepoint. This can be used, e.g., to get
retransmission efficiency by counting skbs w/ and w/o TCPCB_EVER_RETRANS
(through bpf tracing programs).

For this purpose, TCPCB_EVER_RETRANS is also needed to be exposed to bpf.
Previously, the flags are defined as macros in struct tcp_skb_cb. I moved them
out into a new enum, and then they can be accessed with vmlinux.h.

We have discussed to achieve this with BPF_SOCK_OPS in [0], and using
tracepoint is thought to be a better solution.

[0]
https://lore.kernel.org/all/20240417124622.35333-1-lulie@linux.alibaba.com/

Philo Lu (2):
  tcp: move tcp_skb_cb->sacked flags to enum
  tcp: update sacked after tracepoint in __tcp_retransmit_skb

 include/net/tcp.h     | 22 +++++++++++++---------
 net/ipv4/tcp_output.c | 11 ++++++-----
 2 files changed, 19 insertions(+), 14 deletions(-)

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2.32.0.3.g01195cf9f