This example subsystem exports debugging information as an aid to diagnosing
refcount leaks, etc, in the container framework.

Signed-off-by: Paul Menage <menage@google.com>
---

 include/linux/container_subsys.h |    4 +
 init/Kconfig                     |   10 ++++
 kernel/Makefile                  |    1 
 kernel/container_debug.c         |   97 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 112 insertions(+)

Index: container-2.6.22-rc6-mm1/include/linux/container_subsys.h
===================================================================
--- container-2.6.22-rc6-mm1.orig/include/linux/container_subsys.h
+++ container-2.6.22-rc6-mm1/include/linux/container_subsys.h
@@ -19,4 +19,8 @@ SUBSYS(cpuacct)
 
 /* */
 
+#ifdef CONFIG_CONTAINER_DEBUG
+SUBSYS(debug)
+#endif
+
 /* */
Index: container-2.6.22-rc6-mm1/init/Kconfig
===================================================================
--- container-2.6.22-rc6-mm1.orig/init/Kconfig
+++ container-2.6.22-rc6-mm1/init/Kconfig
@@ -303,6 +303,16 @@ config CONTAINERS
 
 	  Say N if unsure.
 
+config CONTAINER_DEBUG
+	bool "Example debug container subsystem"
+	depends on CONTAINERS
+	help
+	  This option enables a simple container subsystem that
+	  exports useful debugging information about the containers
+	  framework
+
+	  Say N if unsure
+
 config CPUSETS
 	bool "Cpuset support"
 	depends on SMP && CONTAINERS
Index: container-2.6.22-rc6-mm1/kernel/Makefile
===================================================================
--- container-2.6.22-rc6-mm1.orig/kernel/Makefile
+++ container-2.6.22-rc6-mm1/kernel/Makefile
@@ -38,6 +38,7 @@ obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
 obj-$(CONFIG_KEXEC) += kexec.o
 obj-$(CONFIG_COMPAT) += compat.o
 obj-$(CONFIG_CONTAINERS) += container.o
+obj-$(CONFIG_CONTAINER_DEBUG) += container_debug.o
 obj-$(CONFIG_CPUSETS) += cpuset.o
 obj-$(CONFIG_CONTAINER_CPUACCT) += cpu_acct.o
 obj-$(CONFIG_IKCONFIG) += configs.o
Index: container-2.6.22-rc6-mm1/kernel/container_debug.c
===================================================================
--- /dev/null
+++ container-2.6.22-rc6-mm1/kernel/container_debug.c
@@ -0,0 +1,97 @@
+/*
+ * kernel/ccontainer_debug.c - Example container subsystem that
+ * exposes debug info
+ *
+ * Copyright (C) Google Inc, 2007
+ *
+ * Developed by Paul Menage (menage@google.com)
+ *
+ */
+
+#include <linux/container.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/rcupdate.h>
+
+#include <asm/atomic.h>
+
+static struct container_subsys_state *debug_create(struct container_subsys *ss,
+						   struct container *cont)
+{
+	struct container_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
+
+	if (!css)
+		return ERR_PTR(-ENOMEM);
+
+	return css;
+}
+
+static void debug_destroy(struct container_subsys *ss, struct container *cont)
+{
+	kfree(cont->subsys[debug_subsys_id]);
+}
+
+static u64 container_refcount_read(struct container *cont, struct cftype *cft)
+{
+	return atomic_read(&cont->count);
+}
+
+static u64 taskcount_read(struct container *cont, struct cftype *cft)
+{
+	u64 count;
+
+	container_lock();
+	count = container_task_count(cont);
+	container_unlock();
+	return count;
+}
+
+static u64 current_css_group_read(struct container *cont, struct cftype *cft)
+{
+	return (u64)(long)current->containers;
+}
+
+static u64 current_css_group_refcount_read(struct container *cont,
+					   struct cftype *cft)
+{
+	u64 count;
+
+	rcu_read_lock();
+	count = atomic_read(&current->containers->ref.refcount);
+	rcu_read_unlock();
+	return count;
+}
+
+static struct cftype files[] =  {
+	{
+		.name = "container_refcount",
+		.read_uint = container_refcount_read,
+	},
+	{
+		.name = "taskcount",
+		.read_uint = taskcount_read,
+	},
+
+	{
+		.name = "current_css_group",
+		.read_uint = current_css_group_read,
+	},
+
+	{
+		.name = "current_css_group_refcount",
+		.read_uint = current_css_group_refcount_read,
+	},
+};
+
+static int debug_populate(struct container_subsys *ss, struct container *cont)
+{
+	return container_add_files(cont, ss, files, ARRAY_SIZE(files));
+}
+
+struct container_subsys debug_subsys = {
+	.name = "debug",
+	.create = debug_create,
+	.destroy = debug_destroy,
+	.populate = debug_populate,
+	.subsys_id = debug_subsys_id,
+};

--