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Message-ID: <47FF6B1B.5090106@fr.ibm.com>
Date: Fri, 11 Apr 2008 15:43:55 +0200
From: Daniel Lezcano <dlezcano@...ibm.com>
To: Pavel Emelyanov <xemul@...nvz.org>
CC: Linux Netdev List <netdev@...r.kernel.org>,
Denis Lunev <den@...nvz.org>,
Linux Containers <containers@...ts.osdl.org>,
Benjamin Thery <benjamin.thery@...l.net>
Subject: Re: [PATCH 2/14][NETNS]: Generic per-net pointers.
Pavel Emelyanov wrote:
> 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 change this pointer while the net is alive;
> 4. 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.
>
> Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>
>
> ---
> include/net/net_namespace.h | 2 +
> include/net/netns/generic.h | 49 ++++++++++++++++++++++++++++++++++
> net/core/net_namespace.c | 62 +++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 113 insertions(+), 0 deletions(-)
> create mode 100644 include/net/netns/generic.h
>
> diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
> index 6971fdb..e3d4eb4 100644
> --- a/include/net/net_namespace.h
> +++ b/include/net/net_namespace.h
> @@ -19,6 +19,7 @@ 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
> @@ -57,6 +58,7 @@ struct net {
> #ifdef CONFIG_NETFILTER
> struct netns_xt xt;
> #endif
> + struct net_generic *gen;
> };
>
>
> diff --git a/include/net/netns/generic.h b/include/net/netns/generic.h
> new file mode 100644
> index 0000000..e8a6d27
> --- /dev/null
> +++ b/include/net/netns/generic.h
> @@ -0,0 +1,49 @@
> +/*
> + * 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.
> + *
> + * 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
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index 7ef3bac..b384840 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -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);
Why do you need to allocate more than sizeof(struct net_generic) ?
> + 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;
> }
>
> @@ -384,3 +399,50 @@ 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;
shouldn't it be rcu_dereferenced ?
> + 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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