mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-11-16 00:34:20 +08:00
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
/*
|
|
* generic net pointers
|
|
*/
|
|
|
|
#ifndef __NET_GENERIC_H__
|
|
#define __NET_GENERIC_H__
|
|
|
|
#include <linux/rcupdate.h>
|
|
|
|
/*
|
|
* 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
|