selftest: net: Add GC test for temporary routes with exceptions.

Without the prior commit, IPv6 GC cannot track exceptions tied
to permanent routes if they were originally added as temporary
routes.

Let's add a test case for the issue.

  1. Add temporary routes
  2. Create exceptions for the temporary routes
  3. Promote the routes to permanent routes
  4. Check if GC can find and purge the exceptions

A few notes:

  + At step 4, unlike other test cases, we cannot wait for
    $GC_WAIT_TIME.  While the exceptions are always iterable via
    netlink (since it traverses the entire fib tree instead of
    tb6_gc_hlist), rt6_nh_dump_exceptions() skips expired entries.

    If we waited for the expiration time, we would be unable to
    distinguish whether the exceptions were truly purged by GC or
    just hidden due to being expired.

  + For the same reason, at step 2, we use ICMPv6 redirect message
    instead of Packet Too Big message.  This is because MTU exceptions
    always have RTF_EXPIRES, and rt6_age_examine_exception() does not
    respect the period specified by net.ipv6.route.flush=1.

  + We add a neighbour entry for the redirect target with NTF_ROUTER.
    Without this, the exceptions would be removed at step 3 when the
    fib6_may_remove_gc_list() is called.

Without the fix, the exceptions remain even after GC is triggered
by sysctl -wq net.ipv6.route.flush=1.

  FAIL: Expected 0 routes, got 5
      TEST: ipv6 route garbage collection (promote to permanent routes)   [FAIL]

With the fix, GC purges the exceptions properly.

      TEST: ipv6 route garbage collection (promote to permanent routes)   [ OK ]

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20260320072317.2561779-4-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions