Merge branch 'net-mctp-add-support-for-gateway-routing'

Jeremy Kerr says:

====================
net: mctp: Add support for gateway routing

This series adds a gateway route type for the MCTP core, allowing
non-local EIDs as the match for a route.

Example setup using the mctp tools:

    mctp route add 9 via mctpi2c0
    mctp neigh add 9 dev mctpi2c0 lladdr 0x1d
    mctp route add 10 gw 9

- will route packets to eid 10 through mctpi2c0, using a dest lladdr
of 0x1d (ie, that of the directly-attached eid 9).

The core change to support this is the introduction of a struct
mctp_dst, which represents the result of a route lookup. Since this
involves a bit of surgery through the routing code, we add a few tests
along the way.

We're introducing an ABI change in the new RTM_{NEW,GET,DEL}ROUTE
netlink formats, with the support for a RTA_GATEWAY attribute. Because
we need a network ID specified to fully-qualify a gateway EID, the
RTA_GATEWAY attribute carries the (net, eid) tuple in full:

    struct mctp_fq_addr {
        unsigned int net;
        mctp_eid_t eid;
    }

Of course, any questions, comments etc are most welcome.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
====================

Link: https://patch.msgid.link/20250702-dev-forwarding-v5-0-1468191da8a4@codeconstruct.com.au
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

2 files changed, 51 insertions, 9 deletions

diff --git a/include/net/mctp.h b/include/net/mctp.h
index 07d458990113..ac4f4ecdfc24 100644
--- a/include/net/mctp.h
+++ b/include/net/mctp.h
@@ -183,8 +183,8 @@ struct mctp_sk_key {
 struct mctp_skb_cb {
 	unsigned int	magic;
 	unsigned int	net;
-	int		ifindex; /* extended/direct addressing if set */
-	mctp_eid_t	src;
+	/* fields below provide extended addressing for ingress to recvmsg() */
+	int		ifindex;
 	unsigned char	halen;
 	unsigned char	haddr[MAX_ADDR_LEN];
 };
@@ -222,6 +222,8 @@ struct mctp_flow {
 	struct mctp_sk_key *key;
 };
 
+struct mctp_dst;
+
 /* Route definition.
  *
  * These are held in the pernet->mctp.routes list, with RCU protection for
@@ -229,16 +231,25 @@ struct mctp_flow {
  * dropped on NETDEV_UNREGISTER events.
  *
  * Updates to the route table are performed under rtnl; all reads under RCU,
- * so routes cannot be referenced over a RCU grace period. Specifically: A
- * caller cannot block between mctp_route_lookup and mctp_route_release()
+ * so routes cannot be referenced over a RCU grace period.
  */
 struct mctp_route {
 	mctp_eid_t		min, max;
 
 	unsigned char		type;
+
 	unsigned int		mtu;
-	struct mctp_dev		*dev;
-	int			(*output)(struct mctp_route *route,
+
+	enum {
+		MCTP_ROUTE_DIRECT,
+		MCTP_ROUTE_GATEWAY,
+	} dst_type;
+	union {
+		struct mctp_dev	*dev;
+		struct mctp_fq_addr gateway;
+	};
+
+	int			(*output)(struct mctp_dst *dst,
 					  struct sk_buff *skb);
 
 	struct list_head	list;
@@ -246,12 +257,35 @@ struct mctp_route {
 	struct rcu_head		rcu;
 };
 
+/* Route lookup result: dst. Represents the results of a routing decision,
+ * but is only held over the individual routing operation.
+ *
+ * Will typically be stored on the caller stack, and must be released after
+ * usage.
+ */
+struct mctp_dst {
+	struct mctp_dev *dev;
+	unsigned int mtu;
+	mctp_eid_t nexthop;
+
+	/* set for direct addressing */
+	unsigned char halen;
+	unsigned char haddr[MAX_ADDR_LEN];
+
+	int (*output)(struct mctp_dst *dst, struct sk_buff *skb);
+};
+
+int mctp_dst_from_extaddr(struct mctp_dst *dst, struct net *net, int ifindex,
+			  unsigned char halen, const unsigned char *haddr);
+
 /* route interfaces */
-struct mctp_route *mctp_route_lookup(struct net *net, unsigned int dnet,
-				     mctp_eid_t daddr);
+int mctp_route_lookup(struct net *net, unsigned int dnet,
+		      mctp_eid_t daddr, struct mctp_dst *dst);
+
+void mctp_dst_release(struct mctp_dst *dst);
 
 /* always takes ownership of skb */
-int mctp_local_output(struct sock *sk, struct mctp_route *rt,
+int mctp_local_output(struct sock *sk, struct mctp_dst *dst,
 		      struct sk_buff *skb, mctp_eid_t daddr, u8 req_tag);
 
 void mctp_key_unref(struct mctp_sk_key *key);
diff --git a/include/uapi/linux/mctp.h b/include/uapi/linux/mctp.h
index e1db65df9359..19ad12a0cd4b 100644
--- a/include/uapi/linux/mctp.h
+++ b/include/uapi/linux/mctp.h
@@ -37,6 +37,14 @@ struct sockaddr_mctp_ext {
 	__u8			smctp_haddr[MAX_ADDR_LEN];
 };
 
+/* A "fully qualified" MCTP address, which includes the system-local network ID,
+ * required to uniquely resolve a routable EID.
+ */
+struct mctp_fq_addr {
+	unsigned int	net;
+	mctp_eid_t	eid;
+};
+
 #define MCTP_NET_ANY		0x0
 
 #define MCTP_ADDR_NULL		0x00