l3mdev: add infrastructure for table to VRF mapping

Add infrastructure to l3mdev (the core code for Layer 3 master devices) in
order to find out the corresponding VRF device for a given table id.
Therefore, the l3mdev implementations:
- can register a callback that returns the device index of the l3mdev
associated with a given table id;
- can offer the lookup function (table to VRF device).

Signed-off-by: Andrea Mayer <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/l3mdev.h

···
 #include <net/dst.h>
 #include <net/fib_rules.h>
 
+enum l3mdev_type {
+	L3MDEV_TYPE_UNSPEC,
+	L3MDEV_TYPE_VRF,
+	__L3MDEV_TYPE_MAX
+};
+
+#define L3MDEV_TYPE_MAX (__L3MDEV_TYPE_MAX - 1)
+
+typedef int (*lookup_by_table_id_t)(struct net *net, u32 table_d);
+
 /**
  * struct l3mdev_ops - l3mdev operations
  *
···
 };
 
 #ifdef CONFIG_NET_L3_MASTER_DEV
+
+int l3mdev_table_lookup_register(enum l3mdev_type l3type,
+				 lookup_by_table_id_t fn);
+
+void l3mdev_table_lookup_unregister(enum l3mdev_type l3type,
+				    lookup_by_table_id_t fn);
+
+int l3mdev_ifindex_lookup_by_table_id(enum l3mdev_type l3type, struct net *net,
+				      u32 table_id);
 
 int l3mdev_fib_rule_match(struct net *net, struct flowi *fl,
 			  struct fib_lookup_arg *arg);
···
 struct sk_buff *l3mdev_ip6_out(struct sock *sk, struct sk_buff *skb)
 {
 	return skb;
+}
+
+static inline
+int l3mdev_table_lookup_register(enum l3mdev_type l3type,
+				 lookup_by_table_id_t fn)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline
+void l3mdev_table_lookup_unregister(enum l3mdev_type l3type,
+				    lookup_by_table_id_t fn)
+{
+}
+
+static inline
+int l3mdev_ifindex_lookup_by_table_id(enum l3mdev_type l3type, struct net *net,
+				      u32 table_id)
+{
+	return -ENODEV;
 }
 
 static inline

net/l3mdev/l3mdev.c

···
 #include <net/fib_rules.h>
 #include <net/l3mdev.h>
 
+static DEFINE_SPINLOCK(l3mdev_lock);
+
+struct l3mdev_handler {
+	lookup_by_table_id_t dev_lookup;
+};
+
+static struct l3mdev_handler l3mdev_handlers[L3MDEV_TYPE_MAX + 1];
+
+static int l3mdev_check_type(enum l3mdev_type l3type)
+{
+	if (l3type <= L3MDEV_TYPE_UNSPEC || l3type > L3MDEV_TYPE_MAX)
+		return -EINVAL;
+
+	return 0;
+}
+
+int l3mdev_table_lookup_register(enum l3mdev_type l3type,
+				 lookup_by_table_id_t fn)
+{
+	struct l3mdev_handler *hdlr;
+	int res;
+
+	res = l3mdev_check_type(l3type);
+	if (res)
+		return res;
+
+	hdlr = &l3mdev_handlers[l3type];
+
+	spin_lock(&l3mdev_lock);
+
+	if (hdlr->dev_lookup) {
+		res = -EBUSY;
+		goto unlock;
+	}
+
+	hdlr->dev_lookup = fn;
+	res = 0;
+
+unlock:
+	spin_unlock(&l3mdev_lock);
+
+	return res;
+}
+EXPORT_SYMBOL_GPL(l3mdev_table_lookup_register);
+
+void l3mdev_table_lookup_unregister(enum l3mdev_type l3type,
+				    lookup_by_table_id_t fn)
+{
+	struct l3mdev_handler *hdlr;
+
+	if (l3mdev_check_type(l3type))
+		return;
+
+	hdlr = &l3mdev_handlers[l3type];
+
+	spin_lock(&l3mdev_lock);
+
+	if (hdlr->dev_lookup == fn)
+		hdlr->dev_lookup = NULL;
+
+	spin_unlock(&l3mdev_lock);
+}
+EXPORT_SYMBOL_GPL(l3mdev_table_lookup_unregister);
+
+int l3mdev_ifindex_lookup_by_table_id(enum l3mdev_type l3type,
+				      struct net *net, u32 table_id)
+{
+	lookup_by_table_id_t lookup;
+	struct l3mdev_handler *hdlr;
+	int ifindex = -EINVAL;
+	int res;
+
+	res = l3mdev_check_type(l3type);
+	if (res)
+		return res;
+
+	hdlr = &l3mdev_handlers[l3type];
+
+	spin_lock(&l3mdev_lock);
+
+	lookup = hdlr->dev_lookup;
+	if (!lookup)
+		goto unlock;
+
+	ifindex = lookup(net, table_id);
+
+unlock:
+	spin_unlock(&l3mdev_lock);
+
+	return ifindex;
+}
+EXPORT_SYMBOL_GPL(l3mdev_ifindex_lookup_by_table_id);
+
 /**
  *	l3mdev_master_ifindex - get index of L3 master device
  *	@dev: targeted interface