The hotplug operations

struct kset_hotplug_ops {
        int (*filter)(struct kset *kset, 
                      struct kobject *kobj);
        char *(*name)(struct kset *kset, 
                      struct kobject *kobj);
        int (*hotplug)(struct kset *kset, 
                       struct kobject *kobj, 
                       char **envp,
                       int num_envp,
                       char *buffer,
                       int buffer_size);
};

These functions are:
filter() - Decide whether an event should be generated
name() - Set subsystem name for /sbin/hotplug
hotplug() - Set environment variables for /sbin/hotplug