[PATCH 0/5] Refactor epoll handling in preparation for multithreading

[Laurent Vivier <lvivier@redhat.com>]

This series refactors how epoll file descriptors are managed throughout
the codebase in preparation for introducing multithreading support.
Currently, passt uses a single global epollfd accessed through the
context structure. With multithreading, each thread will have its own
epollfd managing its subset of flows.

The key changes are:

1. Simplify epoll_del() to take the epollfd directly rather than
   extracting it from the context structure, reducing tight coupling.

2. Move epoll registration out of the socket creation function
   (sock_l4_sa()) into protocol-specific code, giving callers explicit
   control over which epoll instance manages each socket.

3. Replace the boolean in_epoll flag in TCP connection structures with
   an epollfd field in flow_common. This serves dual purposes: tracking
   whether a flow is registered (zero = not registered) and which epoll
   instance owns it (non-zero = specific epollfd).

4. Apply this pattern consistently across all protocol handlers (TCP,
   ICMP, UDP), storing the managing epollfd in each flow's common
   structure.

These changes make the epoll ownership model explicit in the flow
tracking system, allowing flows to be managed by different epoll
instances - a prerequisite for the per-thread epollfd design in the
upcoming multithreading work.

Laurent Vivier (5):
  util: Simplify epoll_del() interface to take epollfd directly
  util: Move epoll registration out of sock_l4_sa()
  tcp, flow: Replace per-connection in_epoll flag with epollfd in
    flow_common
  icmp: Use epollfd from flow_common structure
  udp: Use epollfd from flow_common structure

 flow.c       | 12 +++++-------
 flow.h       |  4 +++-
 icmp.c       | 23 ++++++++++++++++++-----
 pif.c        | 34 ++++++++++++++++++++++++++++------
 tap.c        |  2 +-
 tcp.c        | 36 ++++++++++++++++++------------------
 tcp_conn.h   |  8 +-------
 tcp_splice.c | 23 +++++++++++------------
 udp_flow.c   | 23 ++++++++++++++++++++---
 util.c       | 21 ++++-----------------
 util.h       |  4 ++--
 vhost_user.c |  6 +++---
 12 files changed, 114 insertions(+), 82 deletions(-)

-- 
2.50.1