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authorPavel Emelyanov <xemul@openvz.org>2008-04-15 00:36:08 -0700
committerDavid S. Miller <davem@davemloft.net>2008-04-15 00:36:08 -0700
commitdec827d174d7f76c457238800183ca864a639365 (patch)
treeca7c04e35eda9956afef94678a2a863c3e75e2ed
parentc93cf61fd1d5378134f9b06703f7078067542e00 (diff)
[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 <xemul@openvz.org> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/net/net_namespace.h2
-rw-r--r--include/net/netns/generic.h49
-rw-r--r--net/core/net_namespace.c62
3 files changed, 113 insertions, 0 deletions
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 72fad1a0956..f880b0f9f10 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 00000000000..0c04fd2a700
--- /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;
+ * 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 2197d51aef3..763674e1e59 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);
+ 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);