Commit dec827d1 authored by Pavel Emelyanov's avatar Pavel Emelyanov Committed by David S. Miller
Browse files

[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: default avatarPavel Emelyanov <xemul@openvz.org>
Acked-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c93cf61f

include/net/net_namespace.h

+2 −0
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ struct proc_dir_entry; 
struct net_device;

struct sock;

struct ctl_table_header;

struct net_generic;



struct net {

	atomic_t		count;		/* To decided when the network
@@ -61,6 +62,7 @@ struct net { 
#ifdef CONFIG_NETFILTER

	struct netns_xt		xt;

#endif

	struct net_generic	*gen;

};

include/net/netns/generic.h

0 → 100644
+49 −0
Original line number Diff line number Diff line 
/*

 * 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

net/core/net_namespace.c

+62 −0
Original line number Diff line number Diff line
@@ -7,6 +7,7 @@ 
#include <linux/sched.h>

#include <linux/idr.h>

#include <net/net_namespace.h>

#include <net/netns/generic.h>



/*

 *	Our network namespace constructor/destructor lists
@@ -21,6 +22,8 @@ LIST_HEAD(net_namespace_list); 
struct net init_net;

EXPORT_SYMBOL(init_net);



#define INITIAL_NET_GEN_PTRS	13 /* +1 for len +2 for rcu_head */



/*

 * setup_net runs the initializers for the network namespace object.

 */
@@ -29,10 +32,21 @@ static __net_init int setup_net(struct net *net) 
	/* Must be called with net_mutex held */

	struct pernet_operations *ops;

	int error;

	struct net_generic *ng;



	atomic_set(&net->count, 1);

	atomic_set(&net->use_count, 0);



	error = -ENOMEM;

	ng = kzalloc(sizeof(struct net_generic) +

			INITIAL_NET_GEN_PTRS * sizeof(void *), GFP_KERNEL);

	if (ng == NULL)

		goto out;



	ng->len = INITIAL_NET_GEN_PTRS;

	INIT_RCU_HEAD(&ng->rcu);

	rcu_assign_pointer(net->gen, ng);



	error = 0;

	list_for_each_entry(ops, &pernet_list, list) {

		if (ops->init) {
@@ -54,6 +68,7 @@ out_undo: 
	}



	rcu_barrier();

	kfree(ng);

	goto out;

}
@@ -386,3 +401,50 @@ void unregister_pernet_gen_device(int id, struct pernet_operations *ops) 
	mutex_unlock(&net_mutex);

}

EXPORT_SYMBOL_GPL(unregister_pernet_gen_device);



static void net_generic_release(struct rcu_head *rcu)

{

	struct net_generic *ng;



	ng = container_of(rcu, struct net_generic, rcu);

	kfree(ng);

}



int net_assign_generic(struct net *net, int id, void *data)

{

	struct net_generic *ng, *old_ng;



	BUG_ON(!mutex_is_locked(&net_mutex));

	BUG_ON(id == 0);



	ng = old_ng = net->gen;

	if (old_ng->len >= id)

		goto assign;



	ng = kzalloc(sizeof(struct net_generic) +

			id * sizeof(void *), GFP_KERNEL);

	if (ng == NULL)

		return -ENOMEM;



	/*

	 * Some synchronisation notes:

	 *

	 * The net_generic explores the net->gen array inside rcu

	 * read section. Besides once set the net->gen->ptr[x]

	 * pointer never changes (see rules in netns/generic.h).

	 *

	 * That said, we simply duplicate this array and schedule

	 * the old copy for kfree after a grace period.

	 */



	ng->len = id;

	INIT_RCU_HEAD(&ng->rcu);

	memcpy(&ng->ptr, &old_ng->ptr, old_ng->len);



	rcu_assign_pointer(net->gen, ng);

	call_rcu(&old_ng->rcu, net_generic_release);

assign:

	ng->ptr[id - 1] = data;

	return 0;

}

EXPORT_SYMBOL_GPL(net_assign_generic);

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