[PATCH v2 0/5] flow: Introduce flow_epoll_set() to centralize epoll operations

[Laurent Vivier <lvivier@redhat.com>]

Currently, each protocol handler (TCP, TCP splice, ICMP/ping, UDP) has its
own code to add or modify file descriptors in epoll.  This leads to
duplicated boilerplate across icmp.c, tcp.c, tcp_splice.c, and udp_flow.c,
with each setting up epoll_ref unions and calling epoll_ctl() with
flow-type-specific details.

This series introduces flow_epoll_set() in flow.c to handle epoll
operations for all flow types in a unified way.  The function provides
a simpler interface where the caller passes the command, type, events,
and file descriptor, and flow_epoll_set() handles the epoll_ref setup
and epoll_ctl() call.

The API is:

    int flow_epoll_set(int command, enum epoll_type type,
                       const struct flow_common *f, uint32_t events,
                       int fd, unsigned int sidei);

This centralized approach will be essential for queue pair migration in
the upcoming multithreading work, where flows need to be moved between
different epoll instances owned by different threads.

Preparatory patches:
- Patch 1 removes dead timer update code in tcp_epoll_ctl()
- Patch 2 removes unneeded epoll_ref indirection in udp_flow
- Patch 3 refactors udp_flow_sock() to assign the socket internally
- Patch 4 refactors tcp_splice_conn_epoll_events() to per-side computation

Core patch:
- Patch 5 introduces flow_epoll_set() used by all protocol handlers

Changes in v2:
- Added patch 1: Remove dead timer update in tcp_epoll_ctl() since flow
  table compaction was eliminated
- Added patch 2: Remove unnecessary epoll_ref indirection in udp_flow.c
- Dropped v1 patch 6 (compute events inside flow_epoll_set())
- Dropped v1 patch 7 (retrieve fd from flow structure)
- Added epoll_ctl() command parameter (EPOLL_CTL_ADD/EPOLL_CTL_MOD)
- Callers must set epollfd via flow_epollid_set() before calling
  flow_epoll_set()
- Removed FLOW_EPOLL_TIMER_ADD/FLOW_EPOLL_TIMER_MOD constants
- Reduced series from 7 to 5 patches

Laurent Vivier (5):
  tcp: remove timer update in tcp_epoll_ctl()
  udp_flow: remove unneeded epoll_ref indirection
  udp_flow: Assign socket to flow inside udp_flow_sock()
  tcp_splice: Refactor tcp_splice_conn_epoll_events() to per-side
    computation
  flow: Introduce flow_epoll_set() to centralize epoll operations

 flow.c       |  33 +++++++++++++++
 flow.h       |   3 ++
 icmp.c       |  11 ++---
 tcp.c        |  72 ++++++++++++++------------------
 tcp_splice.c | 115 ++++++++++++++++++++++++---------------------------
 udp_flow.c   |  19 +++------
 6 files changed, 131 insertions(+), 122 deletions(-)

-- 
2.52.0