When the kernel deletes an IPv6 route on its own, the RTM_DELROUTE notification does not say why. User space cannot tell a route that expired from one the router explicitly withdrew, yet the two call for different reactions: an expired RA route means the router failed to refresh it in time, which points at a misconfigured or unreliable router and may warrant action such as disabling IPv6 on that network, while a zero-lifetime withdrawal is normal, RFC-compliant operation.
Patch 1 adds RTA_DEL_REASON (u8) to RTM_DELROUTE notifications and records the cause in the kernel-initiated IPv6 deletion paths: RTA_DEL_REASON_EXPIRED for routes garbage collected after their RTF_EXPIRES lifetime ran out, and RTA_DEL_REASON_RA_WITHDRAWN for default routes, prefix routes and RFC 4191 route information routes withdrawn by Router Advertisements. The rt-route Netlink spec is extended with the attribute, the route notifications and their multicast groups. Only kernel-initiated deletions that user space cannot otherwise explain are attributed. User-requested deletions are self-explanatory to the requester, so they carry no reason; the UAPI documents that absence and RTA_DEL_REASON_UNSPEC must be treated identically, which keeps the door open for attributing more paths (nexthop removal cascades, device removal) later. Patch 2 adds selftests covering all three producer paths: a GC-expired route, and a default route + PIO prefix route + RIO route advertised and then withdrawn by hand-crafted RAs over a raw ICMPv6 socket (no external RA tool needed), plus a check that user-requested deletions carry no attribute. The notifications are decoded with YNL, which also exercises the rt-route spec additions. Yuyang Huang (2): ipv6: report why a route was deleted in RTM_DELROUTE selftests: net: verify RTA_DEL_REASON on route deletion Documentation/netlink/specs/rt-route.yaml | 33 ++++ include/net/ip6_fib.h | 4 +- include/net/ip6_route.h | 2 + include/uapi/linux/rtnetlink.h | 17 ++ net/ipv6/addrconf.c | 3 +- net/ipv6/ip6_fib.c | 19 +- net/ipv6/ndisc.c | 7 +- net/ipv6/route.c | 66 ++++--- .../testing/selftests/net/lib/py/__init__.py | 4 +- tools/testing/selftests/net/lib/py/ynl.py | 7 +- tools/testing/selftests/net/rtnetlink.py | 181 +++++++++++++++++- 11 files changed, 303 insertions(+), 40 deletions(-) -- 2.43.0
