// SPDX-License-Identifier: GPL-2.0
  #include <linux/export.h>
  #include <linux/icmpv6.h>
  #include <linux/mutex.h>
  #include <linux/netdevice.h>
  #include <linux/spinlock.h>
  
  #include <net/ipv6.h>
  
  #if IS_ENABLED(CONFIG_IPV6)
  
  static ip6_icmp_send_t __rcu *ip6_icmp_send;
  
  int inet6_register_icmp_sender(ip6_icmp_send_t *fn)
  {
  	return (cmpxchg((ip6_icmp_send_t **)&ip6_icmp_send, NULL, fn) == NULL) ?
  		0 : -EBUSY;
  }
  EXPORT_SYMBOL(inet6_register_icmp_sender);
  
  int inet6_unregister_icmp_sender(ip6_icmp_send_t *fn)
  {
  	int ret;
  
  	ret = (cmpxchg((ip6_icmp_send_t **)&ip6_icmp_send, fn, NULL) == fn) ?
  	      0 : -EINVAL;
  
  	synchronize_net();
  
  	return ret;
  }
  EXPORT_SYMBOL(inet6_unregister_icmp_sender);
  
  void icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info)
  {
  	ip6_icmp_send_t *send;
  
  	rcu_read_lock();
  	send = rcu_dereference(ip6_icmp_send);
  
  	if (!send)
  		goto out;
  	send(skb, type, code, info, NULL);
  out:
  	rcu_read_unlock();
  }
  EXPORT_SYMBOL(icmpv6_send);
  #endif