This patch removes all cpuset-specific knowlege from the container
system, replacing it with a generic API that can be used by multiple
subsystems. Cpusets is adapted to be a container subsystem.

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

---
 Documentation/containers.txt     |  415 +++++++++--
 Documentation/cpusets.txt        |   20 
 include/linux/container.h        |  156 +++-
 include/linux/container_subsys.h |   14 
 include/linux/cpuset.h           |   14 
 include/linux/mempolicy.h        |   12 
 include/linux/sched.h            |    4 
 kernel/container.c               | 1465 ++++++++++++++++++++++++++++-----------
 kernel/cpuset.c                  |  161 ++--
 kernel/exit.c                    |    2 
 kernel/fork.c                    |    9 
 mm/mempolicy.c                   |    2 
 12 files changed, 1712 insertions(+), 562 deletions(-)

Index: container-2.6.20-new/include/linux/container.h
===================================================================
--- container-2.6.20-new.orig/include/linux/container.h
+++ container-2.6.20-new/include/linux/container.h
@@ -9,33 +9,96 @@
  */
 
 #include <linux/sched.h>
+#include <linux/kref.h>
 #include <linux/cpumask.h>
 #include <linux/nodemask.h>
 
 #ifdef CONFIG_CONTAINERS
 
-extern int number_of_containers;	/* How many containers are defined in system? */
+#define SUBSYS(_x) _x ## _subsys_id,
+enum container_subsys_id {
+#include <linux/container_subsys.h>
+	CONTAINER_SUBSYS_COUNT
+};
+#undef SUBSYS
 
 extern int container_init_early(void);
 extern int container_init(void);
 extern void container_init_smp(void);
 extern void container_fork(struct task_struct *p);
-extern void container_exit(struct task_struct *p);
+extern void container_fork_callbacks(struct task_struct *p);
+extern void container_exit(struct task_struct *p, int run_callbacks);
 
 extern struct file_operations proc_container_operations;
 
 extern void container_lock(void);
 extern void container_unlock(void);
 
+struct containerfs_root;
+
+/* Per-subsystem/per-container state maintained by the system. */
+struct container_subsys_state {
+	/* The container that this subsystem is attached to. Useful
+	 * for subsystems that want to know about the container
+	 * hierarchy structure */
+	struct container *container;
+
+	/* State maintained by the container system to allow
+	 * subsystems to be "busy". Should be accessed via css_get()
+	 * and css_put() */
+
+	atomic_t refcnt;
+};
+
+/* A container_group is a structure holding pointers to a set of
+ * containers. This saves space in the task struct object and speeds
+ * up fork()/exit(), since a single inc/dec can bump the reference
+ * count on the entire container set for a task. */
+
+struct container_group {
+
+	/* Reference count */
+	struct kref ref;
+
+	/* List running through all container groups */
+	struct list_head list;
+
+	/* Set of subsystem states, one for each subsystem. NULL for
+	 * subsystems that aren't part of this hierarchy. These
+	 * pointers reduce the number of dereferences required to get
+	 * from a task to its state for a given container, but result
+	 * in increased space usage if tasks are in wildly different
+	 * groupings across different hierarchies. This array is
+	 * mostly immutable after creation - a newly registered
+	 * subsystem can result in a pointer in this array
+	 * transitioning from NULL to non-NULL */
+	struct container_subsys_state *subsys[CONTAINER_SUBSYS_COUNT];
+
+};
+
+/*
+ * Call css_get() to hold a reference on the container;
+ *
+ */
+
+static inline void css_get(struct container_subsys_state *css)
+{
+	atomic_inc(&css->refcnt);
+}
+/*
+ * css_put() should be called to release a reference taken by
+ * css_get()
+ */
+
+static inline void css_put(struct container_subsys_state *css)
+{
+	atomic_dec(&css->refcnt);
+}
+
 struct container {
 	unsigned long flags;		/* "unsigned long" so bitops work */
 
 	/*
-	 * Count is atomic so can incr (fork) or decr (exit) without a lock.
-	 */
-	atomic_t count;			/* count tasks using this container */
-
-	/*
 	 * We link our 'sibling' struct into our parent's 'children'.
 	 * Our children link their 'sibling' into our 'children'.
 	 */
@@ -43,11 +106,13 @@ struct container {
 	struct list_head children;	/* my children */
 
 	struct container *parent;	/* my parent */
-	struct dentry *dentry;		/* container fs entry */
+	struct dentry *dentry;	  	/* container fs entry */
 
-#ifdef CONFIG_CPUSETS
-	struct cpuset *cpuset;
-#endif
+	/* Private pointers for each registered subsystem */
+	struct container_subsys_state *subsys[CONTAINER_SUBSYS_COUNT];
+
+	struct containerfs_root *root;
+	struct container *top_container;
 };
 
 /* struct cftype:
@@ -64,8 +129,11 @@ struct container {
  */
 
 struct inode;
+#define MAX_CFTYPE_NAME 64
 struct cftype {
-	char *name;
+	/* By convention, the name should begin with the name of the
+	 * subsystem, followed by a period */
+	char name[MAX_CFTYPE_NAME];
 	int private;
 	int (*open) (struct inode *inode, struct file *file);
 	ssize_t (*read) (struct container *cont, struct cftype *cft,
@@ -77,10 +145,72 @@ struct cftype {
 	int (*release) (struct inode *inode, struct file *file);
 };
 
+/* Add a new file to the given container directory. Should only be
+ * called by subsystems from within a populate() method */
 int container_add_file(struct container *cont, const struct cftype *cft);
 
 int container_is_removed(const struct container *cont);
-void container_set_release_agent_path(const char *path);
+
+int container_path(const struct container *cont, char *buf, int buflen);
+
+int container_task_count(const struct container *cont);
+
+/* Return true if the container is a descendant of the current container */
+int container_is_descendant(const struct container *cont);
+
+/* Container subsystem type. See Documentation/containers.txt for details */
+
+struct container_subsys {
+	int (*create)(struct container_subsys *ss,
+		      struct container *cont);
+	void (*destroy)(struct container_subsys *ss, struct container *cont);
+	int (*can_attach)(struct container_subsys *ss,
+			  struct container *cont, struct task_struct *tsk);
+	void (*attach)(struct container_subsys *ss, struct container *cont,
+			struct container *old_cont, struct task_struct *tsk);
+	void (*fork)(struct container_subsys *ss, struct task_struct *task);
+	void (*exit)(struct container_subsys *ss, struct task_struct *task);
+	int (*populate)(struct container_subsys *ss,
+			struct container *cont);
+	void (*bind)(struct container_subsys *ss, struct container *root);
+	int subsys_id;
+	int active;
+	int early_init;
+#define MAX_CONTAINER_TYPE_NAMELEN 32
+	const char *name;
+
+	/* Protected by RCU */
+	struct containerfs_root *root;
+
+	struct list_head sibling;
+
+	void *private;
+};
+
+#define SUBSYS(_x) extern struct container_subsys _x ## _subsys;
+#include <linux/container_subsys.h>
+#undef SUBSYS
+
+int container_clone(struct task_struct *tsk, struct container_subsys *ss);
+
+static inline struct container_subsys_state *container_subsys_state(
+	struct container *cont, int subsys_id)
+{
+	return cont->subsys[subsys_id];
+}
+
+static inline struct container* task_container(struct task_struct *task,
+					       int subsys_id)
+{
+	return rcu_dereference(
+		task->containers->subsys[subsys_id]->container);
+}
+
+static inline struct container_subsys_state *task_subsys_state(
+	struct task_struct *task, int subsys_id)
+{
+	return rcu_dereference(task->containers->subsys[subsys_id]);
+}
 
 int container_path(const struct container *cont, char *buf, int buflen);
 
Index: container-2.6.20-new/include/linux/cpuset.h
===================================================================
--- container-2.6.20-new.orig/include/linux/cpuset.h
+++ container-2.6.20-new/include/linux/cpuset.h
@@ -74,14 +74,7 @@ static inline int cpuset_do_slab_mem_spr
 
 extern void cpuset_track_online_nodes(void);
 
-extern int cpuset_can_attach_task(struct container *cont,
-				  struct task_struct *tsk);
-extern void cpuset_attach_task(struct container *cont,
-			       struct container *oldcont,
-			       struct task_struct *tsk);
-extern int cpuset_populate_dir(struct container *cont);
-extern int cpuset_create(struct container *cont);
-extern void cpuset_destroy(struct container *cont);
+extern int current_cpuset_is_being_rebound(void);
 
 #else /* !CONFIG_CPUSETS */
 
@@ -152,6 +145,11 @@ static inline int cpuset_do_slab_mem_spr
 
 static inline void cpuset_track_online_nodes(void) {}
 
+static inline int current_cpuset_is_being_rebound(void)
+{
+	return 0;
+}
+
 #endif /* !CONFIG_CPUSETS */
 
 #endif /* _LINUX_CPUSET_H */
Index: container-2.6.20-new/kernel/container.c
===================================================================
--- container-2.6.20-new.orig/kernel/container.c
+++ container-2.6.20-new/kernel/container.c
@@ -55,7 +55,6 @@
 #include <linux/time.h>
 #include <linux/backing-dev.h>
 #include <linux/sort.h>
-#include <linux/cpuset.h>
 
 #include <asm/uaccess.h>
 #include <asm/atomic.h>
@@ -63,17 +62,59 @@
 
 #define CONTAINER_SUPER_MAGIC		0x27e0eb
 
-/*
- * Tracks how many containers are currently defined in system.
- * When there is only one container (the root container) we can
- * short circuit some hooks.
+/* Generate an array of container subsystem pointers */
+#define SUBSYS(_x) &_x ## _subsys,
+
+static struct container_subsys *subsys[] = {
+#include <linux/container_subsys.h>
+};
+
+/* A containerfs_root represents the root of a container hierarchy,
+ * and may be associated with a superblock to form an active
+ * hierarchy */
+struct containerfs_root {
+	struct super_block *sb;
+
+	/* The bitmask of subsystems attached to this hierarchy */
+	unsigned long subsys_bits;
+
+	/* A list running through the attached subsystems */
+	struct list_head subsys_list;
+
+	/* The root container for this hierarchy */
+