sysfs: add sysfs_link_change_owner()

Add a helper to change the owner of a sysfs link.
This function will be used to correctly account for kobject ownership
changes, e.g. when moving network devices between network namespaces.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index a788402..7e15ebf 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -312,6 +312,8 @@ static inline void sysfs_enable_ns(struct kernfs_node *kn)
 
 int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
 			    kgid_t kgid);
+int sysfs_link_change_owner(struct kobject *kobj, struct kobject *targ,
+			    const char *name, kuid_t kuid, kgid_t kgid);
 
 #else /* CONFIG_SYSFS */
 
@@ -532,6 +534,14 @@ static inline int sysfs_file_change_owner(struct kobject *kobj,
 	return 0;
 }
 
+static inline int sysfs_link_change_owner(struct kobject *kobj,
+					  struct kobject *targ,
+					  const char *name, kuid_t kuid,
+					  kgid_t kgid)
+{
+	return 0;
+}
+
 #endif /* CONFIG_SYSFS */
 
 static inline int __must_check sysfs_create_file(struct kobject *kobj,