[PATCH v2 0/3] Register TCP flows with epoll at creation time

[Laurent Vivier <lvivier@redhat.com>]

This series simplifies epoll registration by moving it to flow creation
time rather than deferring it to the first event update. By registering
sockets with epoll immediately (using events=0), the epoll control
functions can always use EPOLL_CTL_MOD, eliminating the need to track
whether a flow is already registered.

Patch 1 registers both splice sockets with epoll in tcp_splice_connect()
before initiating the connection, allowing tcp_splice_epoll_ctl() to
always use EPOLL_CTL_MOD.

Patch 2 does the same for regular TCP connections in tcp_conn_from_tap(),
tcp_tap_conn_from_sock(), and tcp_flow_migrate_target(), simplifying
tcp_epoll_ctl() by removing the ADD/MOD conditional logic.

Patch 3 removes EPOLLFD_ID_INVALID and related infrastructure now that
all flows are registered at creation: flow_in_epoll(), flow_epollid_clear(),
and the defensive checks in flow_epollfd().

Thanks,
Laurent

Changes in v2:
- Explained error handling and rollback behavior in commit message
  (patch 1)
- Added error handling for flow_epoll_set() in tcp_conn_from_tap() and
  tcp_tap_conn_from_sock() (patch 2)
- Added ASSERT for epollid bounds check in flow_epollid_register()
  (patch 3)

Laurent Vivier (3):
  tcp_splice: Register fds with epoll at flow creation
  tcp: Register fds with epoll at flow creation
  flow: Remove EPOLLFD_ID_INVALID

 flow.c       | 34 +++-------------------------------
 flow.h       |  6 +-----
 icmp.c       |  1 -
 tcp.c        | 47 ++++++++++++++++++++++++-----------------------
 tcp_splice.c | 20 ++++++++++----------
 udp_flow.c   |  1 -
 6 files changed, 38 insertions(+), 71 deletions(-)

-- 
2.52.0