4 files changed, 112 insertions, 0 deletions

diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index a568b8746f18..cbadc3b5dbc0 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -19,4 +19,8 @@ SUBSYS(cpuacct)
 
 /* */
 
+#ifdef CONFIG_CGROUP_DEBUG
+SUBSYS(debug)
+#endif
+
 /* */
diff --git a/init/Kconfig b/init/Kconfig
index b59a0a95a0e6..6687f805b38d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -278,6 +278,16 @@ config CGROUPS
 
           Say N if unsure.
 
+config CGROUP_DEBUG
+        bool "Example debug cgroup subsystem"
+        depends on CGROUPS
+        help
+          This option enables a simple cgroup subsystem that
+          exports useful debugging information about the cgroups
+          framework
+
+          Say N if unsure
+
 config CPUSETS
         bool "Cpuset support"
         depends on SMP && CGROUPS
diff --git a/kernel/Makefile b/kernel/Makefile
index 48a7fae00271..a50a6debe5fc 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -37,6 +37,7 @@ obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
 obj-$(CONFIG_KEXEC) += kexec.o
 obj-$(CONFIG_COMPAT) += compat.o
 obj-$(CONFIG_CGROUPS) += cgroup.o
+obj-$(CONFIG_CGROUP_DEBUG) += cgroup_debug.o
 obj-$(CONFIG_CPUSETS) += cpuset.o
 obj-$(CONFIG_CGROUP_CPUACCT) += cpu_acct.o
 obj-$(CONFIG_IKCONFIG) += configs.o
diff --git a/kernel/cgroup_debug.c b/kernel/cgroup_debug.c
new file mode 100644
index 000000000000..37301e877cb0
--- /dev/null
+++ b/kernel/cgroup_debug.c
@@ -0,0 +1,97 @@
+/*
+ * kernel/ccontainer_debug.c - Example cgroup subsystem that
+ * exposes debug info
+ *
+ * Copyright (C) Google Inc, 2007
+ *
+ * Developed by Paul Menage (menage@google.com)
+ *
+ */
+
+#include <linux/cgroup.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/rcupdate.h>
+
+#include <asm/atomic.h>
+
+static struct cgroup_subsys_state *debug_create(struct cgroup_subsys *ss,
+                                                   struct cgroup *cont)
+{
+        struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
+
+        if (!css)
+                return ERR_PTR(-ENOMEM);
+
+        return css;
+}
+
+static void debug_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
+{
+        kfree(cont->subsys[debug_subsys_id]);
+}
+
+static u64 cgroup_refcount_read(struct cgroup *cont, struct cftype *cft)
+{
+        return atomic_read(&cont->count);
+}
+
+static u64 taskcount_read(struct cgroup *cont, struct cftype *cft)
+{
+        u64 count;
+
+        cgroup_lock();
+        count = cgroup_task_count(cont);
+        cgroup_unlock();
+        return count;
+}
+
+static u64 current_css_set_read(struct cgroup *cont, struct cftype *cft)
+{
+        return (u64)(long)current->cgroups;
+}
+
+static u64 current_css_set_refcount_read(struct cgroup *cont,
+                                           struct cftype *cft)
+{
+        u64 count;
+
+        rcu_read_lock();
+        count = atomic_read(&current->cgroups->ref.refcount);
+        rcu_read_unlock();
+        return count;
+}
+
+static struct cftype files[] =  {
+        {
+                .name = "cgroup_refcount",
+                .read_uint = cgroup_refcount_read,
+        },
+        {
+                .name = "taskcount",
+                .read_uint = taskcount_read,
+        },
+
+        {
+                .name = "current_css_set",
+                .read_uint = current_css_set_read,
+        },
+
+        {
+                .name = "current_css_set_refcount",
+                .read_uint = current_css_set_refcount_read,
+        },
+};
+
+static int debug_populate(struct cgroup_subsys *ss, struct cgroup *cont)
+{
+        return cgroup_add_files(cont, ss, files, ARRAY_SIZE(files));
+}
+
+struct cgroup_subsys debug_subsys = {
+        .name = "debug",
+        .create = debug_create,
+        .destroy = debug_destroy,
+        .populate = debug_populate,
+        .subsys_id = debug_subsys_id,
+};