3 files changed, 113 insertions, 0 deletions

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 72fad1a0956b..f880b0f9f107 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 000000000000..0c04fd2a700b
--- /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 2197d51aef3b..763674e1e593 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);