IPN notes on the code

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Data Stuctures

  • ipn_network_table: hash table, used to search networks by inode number (and dentry address)
  • struct ipn_network: (from the slab ipn_network_cache + kalloc of connport)
    • connport array of ipn_node (port number to node mapping)
    • connectqueue/unconnectqueue lists of ipn_node (connectqueue: faster than scanning the array for broadcast, unconnectqueue, currently unused, can be used for future "close network")
    • msgpool_cache: cache for messages (struct msgpool_item). It is not global as MTU can be different.
  • struct msgpool_item: the kernel copy of the message waiting to be delivered. The message is always copied once. msgpool_item(s) are pointed by msgitem elements. Each receipient has two queues of pending msgs (normal and oob): these are actually queues of msgitem elements each one pointing to the correspondent msgpoll_item where the payload is stored. msgpool_item has a reference count to clean up the contents when there are no more receipients. There is a slab (ipnxxxx) for each MTU size (all networks with the same MTU share the same slab).
  • struct ipn_node: (from the slab ipn_node_cache). It is logically an extension of the struct sock (ipn sock contains a pointer to it). When a permanent node is released, ipn_node is kept and ipn_sock is freed.
    • msgqueue, oobmsgqueue: lists of struct msgitem for pending msgs
    • dev: net_device (for grab and tap)
    • pbp (temporary structurure for pre-bind-parameters)


IPN has several synchronization needs:

  • frequent operations (send/recv) should work fast
  • open/close operations may be slower
  • it is better to have a safe solution first, maybe it will be optimized in the future.
  • integrate with existing synchronization methods for tap and grab

IPN uses more synchronization means:

  • ipn_glob_mutex: this mutex serializes bind/connect/release
  • (ipn_network)->ipnn_mutex: this protects the membership tables (connport, connectqueue, unconnectqueue) and it serializes the call to the protocol functions.
  • (ipn_network)->msglock: this spinlock protects the access to the msgqueue.
  • ipn_table_lock: This spinlock protects the ipn_network_table. It is actually commented out, as all the access to the ipn_network_table are protected by ipn_global_mutex. It has been included ready for further optimizations.

Last Updated: 2007.12.18

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