From dec827d174d7f76c457238800183ca864a639365 Mon Sep 17 00:00:00 2001 From: Pavel Emelyanov Date: Tue, 15 Apr 2008 00:36:08 -0700 Subject: [PATCH] [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: Pavel Emelyanov Acked-by: Paul E. McKenney Signed-off-by: David S. Miller --- include/net/net_namespace.h | 2 ++ include/net/netns/generic.h | 49 +++++++++++++++++++++++++++++ net/core/net_namespace.c | 62 +++++++++++++++++++++++++++++++++++++ 3 files changed, 113 insertions(+) create mode 100644 include/net/netns/generic.h diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h index 72fad1a095..f880b0f9f1 100644 --- a/include/net/net_namespace.h +++ b/include/net/net_namespace.h @@ -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; }; diff --git a/include/net/netns/generic.h b/include/net/netns/generic.h new file mode 100644 index 0000000000..0c04fd2a70 --- /dev/null +++ b/include/net/netns/generic.h @@ -0,0 +1,49 @@ +/* + * generic net pointers + */ + +#ifndef __NET_GENERIC_H__ +#define __NET_GENERIC_H__ + +#include + +/* + * 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 diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c index 2197d51aef..763674e1e5 100644 --- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -7,6 +7,7 @@ #include #include #include +#include /* * 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); -- 2.39.5