This patch opens the multilevel model patches.

The multilevel model idea is basically the same as for the flat one,
but in this case task may have many virtual pids - one id for each 
sub-namespace this task is visible in. The struct pid carries the 
list of pid_number-s and two hash tables are used to find this number
by numerical id and by struct pid.



The struct pid doesn't need the numerical ids any longer. Instead it
has a single linked list of struct pid_number-s which are hashed
for quick search and have the numerical id.

Signed-off-by: Pavel Emelianov <xemul@openvz.org>

---

 pid.h |   31 +++++++++++++++++++++++++++++++
 1 files changed, 31 insertions(+)

--- ./include/linux/pid.h.multdatast	2007-06-15 15:23:00.000000000 +0400
+++ ./include/linux/pid.h	2007-06-15 15:32:15.000000000 +0400
@@ -50,9 +50,33 @@ enum pid_type
  * id must be used.
  */
 
+/*
+ * multilevel pid namespaces
+ * each task may belong to any number of namespaces and thus struct pid do
+ * not carry the number any longer. instead if this struct pid has a list of
+ * pid_number-s each belonging to one namespace. two hashes are used to find
+ * the number - by the numerical id and by the struct pid this nr belongs to.
+ * this allows for creating namespaces of infinite nesting, but has slight
+ * performance problems.
+ */
+
+struct pid_number
+{
+	int nr;
+	struct pid_namespace *ns;
+	struct pid *pid;
+
+	struct hlist_node pid_chain;
+	struct hlist_node nr_chain;
+	struct pid_number *next;
+};
+
 struct pid
 {
 	atomic_t count;
+#ifdef CONFIG_PID_NS_MULTILEVEL
+	struct pid_number *pid_nrs;
+#else
 	/* Try to keep pid_chain in the same cacheline as nr for find_pid */
 	int nr;
 	struct hlist_node pid_chain;
@@ -65,11 +89,18 @@ struct pid
 	struct pid_namespace *ns;
 	struct hlist_node vpid_chain;
 #endif
+#endif
 	/* lists of tasks that use this pid */
 	struct hlist_head tasks[PIDTYPE_MAX];
 	struct rcu_head rcu;
 };
 
+#ifdef CONFIG_PID_NS_MULTILEVEL
+/* small helper to iterate over the pid's numbers */
+#define for_each_pid_nr(nr, pid) \
+		for (nr = pid->pid_nrs; nr != NULL; nr = nr->next)
+#endif
+
 extern struct pid init_struct_pid;
 
 struct pid_link
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