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net: Add comment about pernet_operations methods and synchronization
Make locking scheme be visible for users, and provide a comment what for we are need exit_batch() methods, and when it should be used. Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -312,6 +312,20 @@ struct net *get_net_ns_by_id(struct net *net, int id);
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struct pernet_operations {
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struct list_head list;
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/*
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* Below methods are called without any exclusive locks.
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* More than one net may be constructed and destructed
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* in parallel on several cpus. Every pernet_operations
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* have to keep in mind all other pernet_operations and
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* to introduce a locking, if they share common resources.
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*
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* Exit methods using blocking RCU primitives, such as
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* synchronize_rcu(), should be implemented via exit_batch.
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* Then, destruction of a group of net requires single
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* synchronize_rcu() related to these pernet_operations,
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* instead of separate synchronize_rcu() for every net.
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* Please, avoid synchronize_rcu() at all, where it's possible.
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*/
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int (*init)(struct net *net);
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void (*exit)(struct net *net);
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void (*exit_batch)(struct list_head *net_exit_list);
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