Handling for inet_lookup compilation error

[mpenny-github]

Root cause

The helpers inet_lookup_established(), __inet6_lookup_established(),
inet_lookup_listener(), and inet6_lookup_listener() dropped their
struct inet_hashinfo *hashinfo parameter — the global tcp_hashinfo is now
reached internally via the network namespace, so callers no longer pass
&tcp_hashinfo. Because distributions may backport this change independently of
the mainline version, a LINUX_VERSION_CODE check alone is not reliable.
torvalds/linux@cb16f4b6c73d

Changes

• ipt_GLBREDIRECT.c: introduce a GLB_TCP_HASHINFO_ARG macro that expands
  to &tcp_hashinfo, on kernels that still expect the argument, or to nothing on
  kernels that dropped it. The four call sites now use the macro instead of a
  hard-coded &tcp_hashinfo,. The macro is selected by a build-time probe (see
  below), with a LINUX_VERSION_CODE fallback only when the headers can't be
  read. This mirrors the existing autodetection already used for the
  __cookie_v[46]_check() arity change.
• Makefile: probe include/net/inet_hashtables.h for the
  inet_lookup_established declaration and emit
  -DGLB_INET_LOOKUP_HAS_HASHINFO_ARG or -DGLB_INET_LOOKUP_NO_HASHINFO_ARG
  depending on whether the inet_hashinfo parameter is present. Also adds a
  print-lookup-arg helper target that echoes the resolved flag.
• script/test: add a lookup_arg_detection_check() step that drives the
  Makefile probe against fixture headers for both the old and new API forms,
  asserting the correct macro is selected. This covers both detection branches
  regardless of the host kernel and needs only make + awk (no full kernel
  build).

Why autodetection instead of a version check

The mainline-vs-backport ambiguity means a fixed version boundary can be wrong
on distro kernels. The header probe is deterministic and authoritative; the
LINUX_VERSION_CODE fallback is only a last resort for when the kernel headers
can't be read at build time.

Testing

• compile_check builds the module + userspace target against the running
  kernel.
• lookup_arg_detection_check validates the probe classifies both header forms
  correctly (old form with the inet_hashinfo parameter → "has arg"; new form
  without it → "no arg").
• Verified the module compiles cleanly against a kernel that has removed the
  argument.

[Copilot]

Pull request overview

Adds compatibility handling for Linux socket-lookup helper signature changes.

Changes:

• Detects lookup-helper arity from kernel headers.
• Adapts four socket lookup call sites.
• Tests both detected API variants.

Show a summary per file

File	Description
src/glb-redirect/Makefile	Adds header probing and diagnostic target.
src/glb-redirect/ipt_GLBREDIRECT.c	Adds compatibility macro and updates calls.
src/glb-redirect/script/test	Tests both probe outcomes.

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Review details

• Files reviewed: 3/3 changed files
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• Review effort level: Balanced