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

[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
......@@ -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;
};
......
/*
* 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
......@@ -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 @@ static __net_init int setup_net(struct net *net)
}
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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