dec827d174
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 <xemul@openvz.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
50 lines
1.2 KiB
C
50 lines
1.2 KiB
C
/*
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* generic net pointers
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*/
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#ifndef __NET_GENERIC_H__
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#define __NET_GENERIC_H__
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#include <linux/rcupdate.h>
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/*
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* Generic net pointers are to be used by modules to put some private
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* stuff on the struct net without explicit struct net modification
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*
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* The rules are simple:
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* 1. register the ops with register_pernet_gen_device to get the id
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* of your private pointer;
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* 2. call net_assign_generic() to put the private data on the struct
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* net (most preferably this should be done in the ->init callback
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* of the ops registered);
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* 3. do not change this pointer while the net is alive;
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* 4. do not try to have any private reference on the net_generic object.
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*
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* After accomplishing all of the above, the private pointer can be
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* accessed with the net_generic() call.
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*/
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struct net_generic {
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unsigned int len;
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struct rcu_head rcu;
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void *ptr[0];
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};
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static inline void *net_generic(struct net *net, int id)
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{
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struct net_generic *ng;
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void *ptr;
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rcu_read_lock();
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ng = rcu_dereference(net->gen);
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BUG_ON(id == 0 || id > ng->len);
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ptr = ng->ptr[id - 1];
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rcu_read_unlock();
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return ptr;
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}
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extern int net_assign_generic(struct net *net, int id, void *data);
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#endif
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