From dec827d174d7f76c457238800183ca864a639365 Mon Sep 17 00:00:00 2001 From: Pavel Emelyanov Date: Tue, 15 Apr 2008 00:36:08 -0700 Subject: [NETNS]: The generic per-net pointers. Add the elastic array of void * pointer to the struct net. The access rules are simple: 1. register the ops with register_pernet_gen_device to get the id of your private pointer 2. call net_assign_generic() to put the private data on the struct net (most preferably this should be done in the ->init callback of the ops registered) 3. do not store any private reference on the net_generic array; 4. do not change this pointer while the net is alive; 5. use the net_generic() to get the pointer. When adding a new pointer, I copy the old array, replace it with a new one and schedule the old for kfree after an RCU grace period. Since the net_generic explores the net->gen array inside rcu read section and once set the net->gen->ptr[x] pointer never changes, this grants us a safe access to generic pointers. Quoting Paul: "... RCU is protecting -only- the net_generic structure that net_generic() is traversing, and the [pointer] returned by net_generic() is protected by a reference counter in the upper-level struct net." Signed-off-by: Pavel Emelyanov Acked-by: Paul E. McKenney Signed-off-by: David S. Miller --- include/net/netns/generic.h | 49 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) create mode 100644 include/net/netns/generic.h (limited to 'include/net/netns/generic.h') diff --git a/include/net/netns/generic.h b/include/net/netns/generic.h new file mode 100644 index 000000000000..0c04fd2a700b --- /dev/null +++ b/include/net/netns/generic.h @@ -0,0 +1,49 @@ +/* + * generic net pointers + */ + +#ifndef __NET_GENERIC_H__ +#define __NET_GENERIC_H__ + +#include + +/* + * Generic net pointers are to be used by modules to put some private + * stuff on the struct net without explicit struct net modification + * + * The rules are simple: + * 1. register the ops with register_pernet_gen_device to get the id + * of your private pointer; + * 2. call net_assign_generic() to put the private data on the struct + * net (most preferably this should be done in the ->init callback + * of the ops registered); + * 3. do not change this pointer while the net is alive; + * 4. do not try to have any private reference on the net_generic object. + * + * After accomplishing all of the above, the private pointer can be + * accessed with the net_generic() call. + */ + +struct net_generic { + unsigned int len; + struct rcu_head rcu; + + void *ptr[0]; +}; + +static inline void *net_generic(struct net *net, int id) +{ + struct net_generic *ng; + void *ptr; + + rcu_read_lock(); + ng = rcu_dereference(net->gen); + BUG_ON(id == 0 || id > ng->len); + ptr = ng->ptr[id - 1]; + rcu_read_unlock(); + + return ptr; +} + +extern int net_assign_generic(struct net *net, int id, void *data); +#endif -- cgit