[PATCH net-next v6 01/10] ipv6: add ip6_del_rt_reason()

[Yuyang Huang]

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@xxxxxxxxx>
---
 include/net/ip6_route.h        |  2 ++
 include/uapi/linux/rtnetlink.h | 25 +++++++++++++++++++++++++
 net/ipv6/route.c               |  8 ++++++++
 3 files changed, 35 insertions(+)

diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 09ffe0f13ce7..cc045705862d 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -126,6 +126,8 @@ int ipv6_route_ioctl(struct net *net, unsigned int cmd,
 int ip6_route_add(struct fib6_config *cfg, gfp_t gfp_flags,
 		  struct netlink_ext_ack *extack);
 int ip6_ins_rt(struct net *net, struct fib6_info *f6i);
+int ip6_del_rt_reason(struct net *net, struct fib6_info *f6i,
+		      enum rt_del_reason del_reason);
 #if IS_ENABLED(CONFIG_IPV6)
 int ip6_del_rt(struct net *net, struct fib6_info *f6i, bool skip_notify);
 #else
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,
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index fc42d67e5822..ca374b056f5a 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -4004,6 +4004,14 @@ int ip6_del_rt(struct net *net, struct fib6_info *rt, bool skip_notify)
 	return __ip6_del_rt(rt, &info);
 }
 
+int ip6_del_rt_reason(struct net *net, struct fib6_info *rt,
+		      enum rt_del_reason del_reason)
+{
+	struct nl_info info = { .nl_net = net };
+
+	return __ip6_del_rt(rt, &info);
+}
+
 static int __ip6_del_rt_siblings(struct fib6_info *rt, struct fib6_config *cfg)
 {
 	struct nl_info *info = &cfg->fc_nlinfo;
-- 
2.43.0