devlink: introduce object and nested devlink relationship infra

It is a bit tricky to maintain relationship between devlink objects and
nested devlink instances due to following aspects:

1) Locking. It is necessary to lock the devlink instance that contains
   the object first, only after that to lock the nested instance.
2) Lifetimes. Objects (e.g devlink port) may be removed before
   the nested devlink instance.
3) Notifications. If nested instance changes (e.g. gets
   registered/unregistered) the nested-in object needs to send
   appropriate notifications.

Resolve this by introducing an xarray that holds 1:1 relationships
between devlink object and related nested devlink instance.
Use that xarray index to get the object/nested devlink instance on
the other side.

Provide necessary helpers:
devlink_rel_nested_in_add/clear() to add and clear the relationship.
devlink_rel_nested_in_notify() to call the nested-in object to send
	notifications during nested instance register/unregister/netns
	change.
devlink_rel_devlink_handle_put() to be used by nested-in object fill
	function to fill the nested handle.
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/devlink/core.c

@@ -16,6 +16,219 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(devlink_trap_report);
 
 DEFINE_XARRAY_FLAGS(devlinks, XA_FLAGS_ALLOC);
 
+static struct devlink *devlinks_xa_get(unsigned long index)
+{
+	struct devlink *devlink;
+
+	rcu_read_lock();
+	devlink = xa_find(&devlinks, &index, index, DEVLINK_REGISTERED);
+	if (!devlink || !devlink_try_get(devlink))
+		devlink = NULL;
+	rcu_read_unlock();
+	return devlink;
+}
+
+/* devlink_rels xarray contains 1:1 relationships between
+ * devlink object and related nested devlink instance.
+ * The xarray index is used to get the nested object from
+ * the nested-in object code.
+ */
+static DEFINE_XARRAY_FLAGS(devlink_rels, XA_FLAGS_ALLOC1);
+
+#define DEVLINK_REL_IN_USE XA_MARK_0
+
+struct devlink_rel {
+	u32 index;
+	refcount_t refcount;
+	u32 devlink_index;
+	struct {
+		u32 devlink_index;
+		u32 obj_index;
+		devlink_rel_notify_cb_t *notify_cb;
+		devlink_rel_cleanup_cb_t *cleanup_cb;
+		struct work_struct notify_work;
+	} nested_in;
+};
+
+static void devlink_rel_free(struct devlink_rel *rel)
+{
+	xa_erase(&devlink_rels, rel->index);
+	kfree(rel);
+}
+
+static void __devlink_rel_get(struct devlink_rel *rel)
+{
+	refcount_inc(&rel->refcount);
+}
+
+static void __devlink_rel_put(struct devlink_rel *rel)
+{
+	if (refcount_dec_and_test(&rel->refcount))
+		devlink_rel_free(rel);
+}
+
+static void devlink_rel_nested_in_notify_work(struct work_struct *work)
+{
+	struct devlink_rel *rel = container_of(work, struct devlink_rel,
+					       nested_in.notify_work);
+	struct devlink *devlink;
+
+	devlink = devlinks_xa_get(rel->nested_in.devlink_index);
+	if (!devlink)
+		goto rel_put;
+	if (!devl_trylock(devlink)) {
+		devlink_put(devlink);
+		goto reschedule_work;
+	}
+	if (!devl_is_registered(devlink)) {
+		devl_unlock(devlink);
+		devlink_put(devlink);
+		goto rel_put;
+	}
+	if (!xa_get_mark(&devlink_rels, rel->index, DEVLINK_REL_IN_USE))
+		rel->nested_in.cleanup_cb(devlink, rel->nested_in.obj_index, rel->index);
+	rel->nested_in.notify_cb(devlink, rel->nested_in.obj_index);
+	devl_unlock(devlink);
+	devlink_put(devlink);
+
+rel_put:
+	__devlink_rel_put(rel);
+	return;
+
+reschedule_work:
+	schedule_work(&rel->nested_in.notify_work);
+}
+
+static void devlink_rel_nested_in_notify_work_schedule(struct devlink_rel *rel)
+{
+	__devlink_rel_get(rel);
+	schedule_work(&rel->nested_in.notify_work);
+}
+
+static struct devlink_rel *devlink_rel_alloc(void)
+{
+	struct devlink_rel *rel;
+	static u32 next;
+	int err;
+
+	rel = kzalloc(sizeof(*rel), GFP_KERNEL);
+	if (!rel)
+		return ERR_PTR(-ENOMEM);
+
+	err = xa_alloc_cyclic(&devlink_rels, &rel->index, rel,
+			      xa_limit_32b, &next, GFP_KERNEL);
+	if (err) {
+		kfree(rel);
+		return ERR_PTR(err);
+	}
+
+	refcount_set(&rel->refcount, 1);
+	INIT_WORK(&rel->nested_in.notify_work,
+		  &devlink_rel_nested_in_notify_work);
+	return rel;
+}
+
+static void devlink_rel_put(struct devlink *devlink)
+{
+	struct devlink_rel *rel = devlink->rel;
+
+	if (!rel)
+		return;
+	xa_clear_mark(&devlink_rels, rel->index, DEVLINK_REL_IN_USE);
+	devlink_rel_nested_in_notify_work_schedule(rel);
+	__devlink_rel_put(rel);
+	devlink->rel = NULL;
+}
+
+void devlink_rel_nested_in_clear(u32 rel_index)
+{
+	xa_clear_mark(&devlink_rels, rel_index, DEVLINK_REL_IN_USE);
+}
+
+int devlink_rel_nested_in_add(u32 *rel_index, u32 devlink_index,
+			      u32 obj_index, devlink_rel_notify_cb_t *notify_cb,
+			      devlink_rel_cleanup_cb_t *cleanup_cb,
+			      struct devlink *devlink)
+{
+	struct devlink_rel *rel = devlink_rel_alloc();
+
+	ASSERT_DEVLINK_NOT_REGISTERED(devlink);
+
+	if (IS_ERR(rel))
+		return PTR_ERR(rel);
+
+	rel->devlink_index = devlink->index;
+	rel->nested_in.devlink_index = devlink_index;
+	rel->nested_in.obj_index = obj_index;
+	rel->nested_in.notify_cb = notify_cb;
+	rel->nested_in.cleanup_cb = cleanup_cb;
+	*rel_index = rel->index;
+	xa_set_mark(&devlink_rels, rel->index, DEVLINK_REL_IN_USE);
+	devlink->rel = rel;
+	return 0;
+}
+
+void devlink_rel_nested_in_notify(struct devlink *devlink)
+{
+	struct devlink_rel *rel = devlink->rel;
+
+	if (!rel)
+		return;
+	devlink_rel_nested_in_notify_work_schedule(rel);
+}
+
+static struct devlink_rel *devlink_rel_find(unsigned long rel_index)
+{
+	return xa_find(&devlink_rels, &rel_index, rel_index,
+		       DEVLINK_REL_IN_USE);
+}
+
+static struct devlink *devlink_rel_devlink_get_lock(u32 rel_index)
+{
+	struct devlink *devlink;
+	struct devlink_rel *rel;
+	u32 devlink_index;
+
+	if (!rel_index)
+		return NULL;
+	xa_lock(&devlink_rels);
+	rel = devlink_rel_find(rel_index);
+	if (rel)
+		devlink_index = rel->devlink_index;
+	xa_unlock(&devlink_rels);
+	if (!rel)
+		return NULL;
+	devlink = devlinks_xa_get(devlink_index);
+	if (!devlink)
+		return NULL;
+	devl_lock(devlink);
+	if (!devl_is_registered(devlink)) {
+		devl_unlock(devlink);
+		devlink_put(devlink);
+		return NULL;
+	}
+	return devlink;
+}
+
+int devlink_rel_devlink_handle_put(struct sk_buff *msg, struct devlink *devlink,
+				   u32 rel_index, int attrtype,
+				   bool *msg_updated)
+{
+	struct net *net = devlink_net(devlink);
+	struct devlink *rel_devlink;
+	int err;
+
+	rel_devlink = devlink_rel_devlink_get_lock(rel_index);
+	if (!rel_devlink)
+		return 0;
+	err = devlink_nl_put_nested_handle(msg, net, rel_devlink, attrtype);
+	devl_unlock(rel_devlink);
+	devlink_put(rel_devlink);
+	if (!err && msg_updated)
+		*msg_updated = true;
+	return err;
+}
+
 void *devlink_priv(struct devlink *devlink)
 {
 	return &devlink->priv;
@@ -142,6 +355,7 @@ int devl_register(struct devlink *devlink)
 
 	xa_set_mark(&devlinks, devlink->index, DEVLINK_REGISTERED);
 	devlink_notify_register(devlink);
+	devlink_rel_nested_in_notify(devlink);
 
 	return 0;
 }
@@ -166,6 +380,7 @@ void devl_unregister(struct devlink *devlink)
 
 	devlink_notify_unregister(devlink);
 	xa_clear_mark(&devlinks, devlink->index, DEVLINK_REGISTERED);
+	devlink_rel_put(devlink);
 }
 EXPORT_SYMBOL_GPL(devl_unregister);
 

net/devlink/dev.c

@@ -372,6 +372,7 @@ static void devlink_reload_netns_change(struct devlink *devlink,
 	devlink_notify_unregister(devlink);
 	write_pnet(&devlink->_net, dest_net);
 	devlink_notify_register(devlink);
+	devlink_rel_nested_in_notify(devlink);
 }
 
 int devlink_reload(struct devlink *devlink, struct net *dest_net,

net/devlink/devl_internal.h

@@ -17,6 +17,8 @@
 
 #include "netlink_gen.h"
 
+struct devlink_rel;
+
 #define DEVLINK_REGISTERED XA_MARK_1
 
 #define DEVLINK_RELOAD_STATS_ARRAY_SIZE \
@@ -55,6 +57,7 @@ struct devlink {
 	u8 reload_failed:1;
 	refcount_t refcount;
 	struct rcu_work rwork;
+	struct devlink_rel *rel;
 	char priv[] __aligned(NETDEV_ALIGN);
 };
 
@@ -92,6 +95,20 @@ static inline bool devl_is_registered(struct devlink *devlink)
 	return xa_get_mark(&devlinks, devlink->index, DEVLINK_REGISTERED);
 }
 
+typedef void devlink_rel_notify_cb_t(struct devlink *devlink, u32 obj_index);
+typedef void devlink_rel_cleanup_cb_t(struct devlink *devlink, u32 obj_index,
+				      u32 rel_index);
+
+void devlink_rel_nested_in_clear(u32 rel_index);
+int devlink_rel_nested_in_add(u32 *rel_index, u32 devlink_index,
+			      u32 obj_index, devlink_rel_notify_cb_t *notify_cb,
+			      devlink_rel_cleanup_cb_t *cleanup_cb,
+			      struct devlink *devlink);
+void devlink_rel_nested_in_notify(struct devlink *devlink);
+int devlink_rel_devlink_handle_put(struct sk_buff *msg, struct devlink *devlink,
+				   u32 rel_index, int attrtype,
+				   bool *msg_updated);
+
 /* Netlink */
 #define DEVLINK_NL_FLAG_NEED_PORT		BIT(0)
 #define DEVLINK_NL_FLAG_NEED_DEVLINK_OR_PORT	BIT(1)