[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>
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 72fad1a..f880b0f 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -20,6 +20,7 @@
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 @@
#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..0c04fd2
--- /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