ipv6: add ip6_del_rt_reason()

Add RTA_DEL_REASON and enum rt_del_reason to the rtnetlink uAPI, and
add ip6_del_rt_reason(), which takes the reason a route is being
deleted. It has no skip_notify argument: a caller that records a
deletion reason wants the notification that carries it.

The reason is unused for now. Subsequent patches propagate it to the
deletion path and report it on RTM_DELROUTE.

Signed-off-by: Yuyang Huang <sigefriedhyy@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260808005642.26901-2-sigefriedhyy@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
index 27265fd31e5f..3988b51db539 100644
--- a/include/uapi/linux/rtnetlink.h
+++ b/include/uapi/linux/rtnetlink.h
@@ -399,6 +399,7 @@ enum rtattr_type_t {
 	RTA_DPORT,
 	RTA_NH_ID,
 	RTA_FLOWLABEL,
+	RTA_DEL_REASON,
 	__RTA_MAX
 };
 
@@ -407,6 +408,30 @@ enum rtattr_type_t {
 #define RTM_RTA(r)  ((struct rtattr*)(((char*)(r)) + NLMSG_ALIGN(sizeof(struct rtmsg))))
 #define RTM_PAYLOAD(n) NLMSG_PAYLOAD(n,sizeof(struct rtmsg))
 
+/* RTA_DEL_REASON: why the kernel deleted the route. u32.
+ * Emitted only on RTM_DELROUTE notifications, and only when the deletion
+ * path records a cause. Absence means either an older kernel or a
+ * deletion path that does not (yet) record its cause - consumers must
+ * treat "absent" and "unspec" identically. New causes may be appended.
+ * Currently only IPv6 deletion paths record a cause.
+ *
+ * The attribute is notification-only: the kernel rejects it in
+ * requests, so a notification must not be echoed back verbatim.
+ *
+ * The value space is family-agnostic: a value must never be
+ * reinterpreted per address family. A cause that only one family can
+ * produce still gets its own value rather than reusing another
+ * family's.
+ */
+enum rt_del_reason {
+	RT_DEL_REASON_UNSPEC,		/* cause not recorded */
+	RT_DEL_REASON_EXPIRED,		/* RTF_EXPIRES lifetime ran out (GC) */
+	RT_DEL_REASON_RA_WITHDRAWN,	/* zero-lifetime RA / PIO / RIO */
+	__RT_DEL_REASON_MAX
+};
+
+#define RT_DEL_REASON_MAX (__RT_DEL_REASON_MAX - 1)
+
 /* RTM_MULTIPATH --- array of struct rtnexthop.
  *
  * "struct rtnexthop" describes all necessary nexthop information,