+/*
+ * Use these carefully. If you implement a network device and it
+ * needs per network namespace operations use device pernet operations,
+ * otherwise use pernet subsys operations.
+ *
+ * This is critically important. Most of the network code cleanup
+ * runs with the assumption that dev_remove_pack has been called so no
+ * new packets will arrive during and after the cleanup functions have
+ * been called. dev_remove_pack is not per namespace so instead the
+ * guarantee of no more packets arriving in a network namespace is
+ * provided by ensuring that all network devices and all sockets have
+ * left the network namespace before the cleanup methods are called.
+ *
+ * For the longest time the ipv4 icmp code was registered as a pernet
+ * device which caused kernel oops, and panics during network
+ * namespace cleanup. So please don't get this wrong.
+ */