[PATCH 3/6] containers: Add generic multi-subsystem API to containers

[Paul Menage]

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@xxxxxxxxxx>

---
 Documentation/containers.txt |  273 ++++++++++---
 Documentation/cpusets.txt    |   20 
 include/linux/container.h    |  137 ++++++
 include/linux/cpuset.h       |   16 
 include/linux/mempolicy.h    |   12 
 include/linux/sched.h        |    4 
 init/Kconfig                 |   12 
 kernel/container.c           |  903 +++++++++++++++++++++++++++++++++----------
 kernel/cpuset.c              |  173 +++++---
 mm/mempolicy.c               |    2 
 10 files changed, 1215 insertions(+), 337 deletions(-)

Index: container-2.6.20-rc1/include/linux/container.h
===================================================================
--- container-2.6.20-rc1.orig/include/linux/container.h
+++ container-2.6.20-rc1/include/linux/container.h
@@ -14,8 +14,6 @@
 
 #ifdef CONFIG_CONTAINERS
 
-extern int number_of_containers;	/* How many containers are defined in system? */
-
 extern int container_init_early(void);
 extern int container_init(void);
 extern void container_init_smp(void);
@@ -30,6 +28,68 @@ extern void container_unlock(void);
 extern void container_manage_lock(void);
 extern void container_manage_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() */
+	spinlock_t refcnt_lock;
+	atomic_t refcnt;
+};
+
+/*
+ * Call css_get() to hold a reference on the container; following a
+ * return of 0, this container subsystem state object is guaranteed
+ * not to be destroyed until css_put() is called on it.  A non-zero
+ * return code indicates that a reference could not be taken.
+ *
+ */
+
+static inline int css_get(struct container_subsys_state *css)
+{
+	int retval = 0;
+	unsigned long flags;
+	/* Synchronize with container_rmdir() */
+	spin_lock_irqsave(&css->refcnt_lock, flags);
+	if (atomic_read(&css->refcnt) >= 0) {
+		/* Container is still alive */
+		atomic_inc(&css->refcnt);
+	} else {
+		/* Container removal is in progress */
+		retval = -EINVAL;
+	}
+	spin_unlock_irqrestore(&css->refcnt_lock, flags);
+	return retval;
+}
+
+/*
+ * If you are holding current->alloc_lock then it's impossible for you
+ * to be moved out of your container, and hence it's impossible for
+ * your container to be destroyed. Therefore doing a simple
+ * atomic_inc() on a css is safe.
+ */
+
+static inline void css_get_current(struct container_subsys_state *css)
+{
+	atomic_inc(&css->refcnt);
+}
+
+/*
+ * css_put() should be called to release a reference taken by
+ * css_get() or css_get_current()
+ */
+
+static inline void css_put(struct container_subsys_state *css) {
+	atomic_dec(&css->refcnt);
+}
+
 struct container {
 	unsigned long flags;		/* "unsigned long" so bitops work */
 
@@ -46,11 +106,15 @@ 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 */
+
+	/* Private pointers for each registered subsystem */
+	struct container_subsys_state *subsys[CONFIG_MAX_CONTAINER_SUBSYS];
+
+	int hierarchy;
 
-#ifdef CONFIG_CPUSETS
-	struct cpuset *cpuset;
-#endif
+	struct containerfs_root *root;
+	struct container *top_container;
 };
 
 /* struct cftype:
@@ -67,8 +131,11 @@ 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,
@@ -83,7 +150,61 @@ struct cftype {
 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);
+
+/* 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 (*post_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);
+
+	int subsys_id;
+#define MAX_CONTAINER_TYPE_NAMELEN 32
+	const char *name;
+
+	/* Protected by RCU */
+	int hierarchy;
+
+	struct list_head sibling;
+};
+
+int container_register_subsys(struct container_subsys *subsys);
+void container_set_release_agent_path(struct container_subsys *ss,
+				      const char *path);
+
+static inline struct container_subsys_state *container_subsys_state(
+	struct container *cont,
+	struct container_subsys *ss)
+{
+	return cont->subsys[ss->subsys_id];
+}
+
+static inline struct container* task_container(struct task_struct *task,
+					       struct container_subsys *ss)
+{
+	return rcu_dereference(task->container[ss->hierarchy]);
+}
+
+static inline struct container_subsys_state *task_subsys_state(
+	struct task_struct *task,
+	struct container_subsys *ss)
+{
+	return container_subsys_state(task_container(task, ss), ss);
+}
 
 int container_path(const struct container *cont, char *buf, int buflen);
 
Index: container-2.6.20-rc1/include/linux/cpuset.h
===================================================================
--- container-2.6.20-rc1.orig/include/linux/cpuset.h
+++ container-2.6.20-rc1/include/linux/cpuset.h
@@ -70,16 +70,7 @@ 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 task_struct *tsk);
-extern void cpuset_post_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 */
 
@@ -147,6 +138,11 @@ 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-rc1/kernel/container.c
===================================================================
--- container-2.6.20-rc1.orig/kernel/container.c
+++ container-2.6.20-rc1/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>
@@ -63,12 +62,58 @@
 
 #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.
+static struct container_subsys *subsys[CONFIG_MAX_CONTAINER_SUBSYS];
+static int subsys_count = 0;
+
+/* 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 */
+	struct container top_container;
+
+	/* Tracks how many containers are currently defined in hierarchy.*/
+	int number_of_containers;
+
+	/* The path to use for release notifications. No locking
+	 * between setting and use - so if userspace updates this
+	 * while subcontainers exist, you could miss a
+	 * notification. We ensure that it's always a valid
+	 * NUL-terminated string */
+	char release_agent_path[PATH_MAX];
+};
+
+/* The set of hierarchies in use. Hierarchy 0 is the "dummy
+ * container", reserved for the subsystems that are otherwise
+ * unattached - it never has more than a single container, and all
+ * tasks are part of that container. */
+
+static struct containerfs_root rootnode[CONFIG_MAX_CONTAINER_HIERARCHIES];
+
+/* dummytop is a shorthand for the dummy hierarchy's top container */
+#define dummytop (&rootnode[0].top_container)
+
+/* This flag indicates whether tasks in the fork and exit paths should
+ * take callback_mutex and check for fork/exit handlers to call. This
+ * avoids us having to take locks in the fork/exit path if none of the
+ * subsystems need to be called.
+ *
+ * It is protected via RCU, with the invariant that a process in an
+ * rcu_read_lock() section will never see this as 0 if there are
+ * actually registered subsystems with a fork or exit
+ * handler. (Sometimes it may be 1 without there being any registered
+ * subsystems with such a handler, but such periods are safe and of
+ * short duration).
  */
-int number_of_containers __read_mostly;
+static int need_forkexit_callback = 0;
 
 /* bits in struct container flags field */
 typedef enum {
@@ -87,27 +132,18 @@ static inline int notify_on_release(cons
 	return test_bit(CONT_NOTIFY_ON_RELEASE, &cont->flags);
 }
 
-static struct container top_container = {
-	.count = ATOMIC_INIT(0),
-	.sibling = LIST_HEAD_INIT(top_container.sibling),
-	.children = LIST_HEAD_INIT(top_container.children),
-};
+#define for_each_subsys(_hierarchy, _ss) list_for_each_entry(_ss, &rootnode[_hierarchy].subsys_list, sibling)
 
-/* The path to use for release notifications. No locking between
- * setting and use - so if userspace updates this while subcontainers
- * exist, you could miss a notification */
-static char release_agent_path[PATH_MAX] = "/sbin/container_release_agent";
-
-void container_set_release_agent_path(const char *path)
+void container_set_release_agent_path(struct container_subsys *ss,
+				      const char *path)
 {
+	struct containerfs_root *root;
 	container_manage_lock();
-	strcpy(release_agent_path, path);
+	root = &rootnode[ss->hierarchy];
+	strcpy(root->release_agent_path, path);
 	container_manage_unlock();
 }
 
-static struct vfsmount *container_mount;
-static struct super_block *container_sb;
-
 /*
  * We have two global container mutexes below.  They can nest.
  * It is ok to first take manage_mutex, then nest callback_mutex.  We also
@@ -189,11 +225,71 @@ static struct super_block *container_sb;
  * update of a tasks container pointer by attach_task() and the
  * access of task->container->mems_generation via that pointer in
  * the routine container_update_task_memory_state().
+ *
+ * Some container subsystems and other external code also use these
+ * mutexes, exposed through the container_lock()/container_unlock()
+ * and container_manage_lock()/container_manage_unlock() functions.
+ *
+ * E.g. the out of memory (OOM) code needs to prevent containers from
+ * being changed while it scans the tasklist looking for a task in an
+ * overlapping container. The tasklist_lock is a spinlock, so must be
+ * taken inside callback_mutex.
+ *
+ * Some container subsystems (including cpusets) also use
+ * callback_mutex as a primary lock for synchronizing access to
+ * subsystem state. Deciding on best practices of when to use
+ * fine-grained locks vs container_lock()/container_unlock() is still
+ * a TODO.
+ *
  */
 
 static DEFINE_MUTEX(manage_mutex);
 static DEFINE_MUTEX(callback_mutex);
 
+/**
+ * container_lock - lock out any changes to container structures
+ *
+ */
+
+void container_lock(void)
+{
+	mutex_lock(&callback_mutex);
+}
+
+/**
+ * container_unlock - release lock on container changes
+ *
+ * Undo the lock taken in a previous container_lock() call.
+ */
+
+void container_unlock(void)
+{
+	mutex_unlock(&callback_mutex);
+}
+
+/**
+ * container_manage_lock() - lock out anyone else considering making
+ * changes to container structures. This is a more heavy-weight lock
+ * than the callback_mutex taken by container_lock() */
+
+void container_manage_lock(void)
+{
+	mutex_lock(&manage_mutex);
+}
+
+/**
+ * container_manage_unlock
+ *
+ * Undo the lock taken in a previous container_manage_lock() call.
+ */
+
+void container_manage_unlock(void)
+{
+	mutex_unlock(&manage_mutex);
+}
+
+
+
 /*
  * A couple of forward declarations required, due to cyclic reference loop:
  *  container_mkdir -> container_create -> container_populate_dir -> container_add_file
@@ -202,15 +298,18 @@ static DEFINE_MUTEX(callback_mutex);
 
 static int container_mkdir(struct inode *dir, struct dentry *dentry, int mode);
 static int container_rmdir(struct inode *unused_dir, struct dentry *dentry);
+static int container_populate_dir(struct container *cont);
+static struct inode_operations container_dir_inode_operations;
+struct file_operations proc_containerstats_operations;
 
 static struct backing_dev_info container_backing_dev_info = {
 	.ra_pages = 0,		/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
 };
 
-static struct inode *container_new_inode(mode_t mode)
+static struct inode *container_new_inode(mode_t mode, struct super_block *sb)
 {
-	struct inode *inode = new_inode(container_sb);
+	struct inode *inode = new_inode(sb);
 
 	if (inode) {
 		inode->i_mode = mode;
@@ -282,32 +381,102 @@ static void container_d_remove_dir(struc
 	remove_dir(dentry);
 }
 
+/*
+ * Release the last use of a hierarchy.  Will never be called when
+ * there are active subcontainers since each subcontainer bumps the
+ * value of sb->s_active.
+ */
+
+static void container_put_super(struct super_block *sb) {
+
+	struct containerfs_root *root = sb->s_fs_info;
+	int hierarchy = root->top_container.hierarchy;
+	int i;
+	struct container *cont = &root->top_container;
+	struct task_struct *g, *p;
+
+	root->sb = NULL;
+	sb->s_fs_info = NULL;
+
+	mutex_lock(&manage_mutex);
+
+	BUG_ON(root->number_of_containers != 1);
+	BUG_ON(!list_empty(&cont->children));
+	BUG_ON(!list_empty(&cont->sibling));
+	BUG_ON(!root->subsys_bits);
+
+	mutex_lock(&callback_mutex);
+
+	/* Remove all tasks from this container hierarchy */
+	read_lock(&tasklist_lock);
+	do_each_thread(g, p) {
+		task_lock(p);
+		BUG_ON(!p->container[hierarchy]);
+		BUG_ON(p->container[hierarchy] != cont);
+		rcu_assign_pointer(p->container[hierarchy], NULL);
+		task_unlock(p);
+	} while_each_thread(g, p);
+	read_unlock(&tasklist_lock);
+	atomic_set(&cont->count, 1);
+
+	/* Remove all subsystems from this hierarchy */
+	for (i = 0; i < subsys_count; i++) {
+		if (root->subsys_bits & (1 << i)) {
+			struct container_subsys *ss = subsys[i];
+			BUG_ON(cont->subsys[i] != dummytop->subsys[i]);
+			BUG_ON(cont->subsys[i]->container != cont);
+			dummytop->subsys[i]->container = dummytop;
+			cont->subsys[i] = NULL;
+			rcu_assign_pointer(subsys[i]->hierarchy, 0);
+			list_del(&ss->sibling);
+		} else {
+			BUG_ON(cont->subsys[i]);
+		}
+	}
+	root->subsys_bits = 0;
+	mutex_unlock(&callback_mutex);
+	synchronize_rcu();
+
+	mutex_unlock(&manage_mutex);
+}
+
+static int container_show_options(struct seq_file *seq, struct vfsmount *vfs) {
+	struct containerfs_root *root = vfs->mnt_sb->s_fs_info;
+	struct container_subsys *ss;
+	for_each_subsys(root->top_container.hierarchy, ss) {
+		seq_printf(seq, ",%s", ss->name);
+	}
+	return 0;
+}
+
 static struct super_operations container_ops = {
 	.statfs = simple_statfs,
 	.drop_inode = generic_delete_inode,
+	.put_super = container_put_super,
+	.show_options = container_show_options,
 };
 
-static int container_fill_super(struct super_block *sb, void *unused_data,
-							int unused_silent)
+static int container_fill_super(struct super_block *sb, void *options,
+				int unused_silent)
 {
 	struct inode *inode;
 	struct dentry *root;
+	struct containerfs_root *hroot = options;
 
 	sb->s_blocksize = PAGE_CACHE_SIZE;
 	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
 	sb->s_magic = CONTAINER_SUPER_MAGIC;
 	sb->s_op = &container_ops;
-	container_sb = sb;
 
-	inode = container_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR);
-	if (inode) {
-		inode->i_op = &simple_dir_inode_operations;
-		inode->i_fop = &simple_dir_operations;
-		/* directories start off with i_nlink == 2 (for "." entry) */
-		inode->i_nlink++;
-	} else {
+	inode = container_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
+	if (!inode)
 		return -ENOMEM;
-	}
+
+	inode->i_op = &simple_dir_inode_operations;
+	inode->i_fop = &simple_dir_operations;
+	inode->i_op = &container_dir_inode_operations;
+	/* directories start off with i_nlink == 2 (for "." entry) */
+	inc_nlink(inode);
 
 	root = d_alloc_root(inode);
 	if (!root) {
@@ -315,6 +484,13 @@ static int container_fill_super(struct s
 		return -ENOMEM;
 	}
 	sb->s_root = root;
+	root->d_fsdata = &hroot->top_container;
+	hroot->top_container.dentry = root;
+
+	strcpy(hroot->release_agent_path, "");
+	sb->s_fs_info = hroot;
+	hroot->sb = sb;
+
 	return 0;
 }
 
@@ -322,7 +498,130 @@ static int container_get_sb(struct file_
 			 int flags, const char *unused_dev_name,
 			 void *data, struct vfsmount *mnt)
 {
-	return get_sb_single(fs_type, flags, data, container_fill_super, mnt);
+	int i;
+	struct container_subsys *ss;
+	char *token, *o = data ?: "all";
+	unsigned long subsys_bits = 0;
+	int ret = 0;
+	struct containerfs_root *root = NULL;
+	int hierarchy;
+
+	mutex_lock(&manage_mutex);
+
+	/* First find the desired set of resource controllers */
+	while ((token = strsep(&o, ",")) != NULL) {
+		if (!*token) {
+			ret = -EINVAL;
+			goto out_unlock;
+		}
+		if (!strcmp(token, "all")) {
+			subsys_bits = (1 << subsys_count) - 1;
+		} else {
+			for (i = 0; i < subsys_count; i++) {
+				ss = subsys[i];
+				if (!strcmp(token, ss->name)) {
+					subsys_bits |= 1 << i;
+					break;
+				}
+			}
+			if (i == subsys_count) {
+				ret = -ENOENT;
+				goto out_unlock;
+			}
+		}
+	}
+
+	/* See if we already have a hierarchy containing this set */
+
+	for (i = 1; i < CONFIG_MAX_CONTAINER_HIERARCHIES; i++) {
+		root = &rootnode[i];
+		/* We match - use this hieracrchy */
+		if (root->subsys_bits == subsys_bits) break;
+		/* We clash - fail */
+		if (root->subsys_bits & subsys_bits) {
+			ret = -EBUSY;
+			goto out_unlock;
+		}
+	}
+
+	if (i == CONFIG_MAX_CONTAINER_HIERARCHIES) {
+		/* No existing hierarchy matched this set - but we
+		 * know that all the subsystems are free */
+		for (i = 1; i < CONFIG_MAX_CONTAINER_HIERARCHIES; i++) {
+			root = &rootnode[i];
+			if (!root->sb && !root->subsys_bits) break;
+		}
+	}
+
+	if (i == CONFIG_MAX_CONTAINER_HIERARCHIES) {
+		ret = -ENOSPC;
+		goto out_unlock;
+	}
+
+	hierarchy = i;
+
+	if (!root->sb) {
+		/* We need a new superblock for this container combination */
+		struct container *cont = &root->top_container;
+		struct container_subsys *ss;
+		struct task_struct *p, *g;
+
+		BUG_ON(root->subsys_bits);
+		root->subsys_bits = subsys_bits;
+		ret = get_sb_nodev(fs_type, flags, root,
+				   container_fill_super, mnt);
+		if (ret)
+			goto out_unlock;
+
+		BUG_ON(!list_empty(&cont->sibling));
+		BUG_ON(!list_empty(&cont->children));
+		BUG_ON(root->number_of_containers != 1);
+
+		mutex_lock(&callback_mutex);
+
+		/* Add all tasks into this container hierarchy */
+		atomic_set(&cont->count, 1);
+		read_lock(&tasklist_lock);
+		do_each_thread(g, p) {
+			task_lock(p);
+			BUG_ON(p->container[hierarchy]);
+			rcu_assign_pointer(p->container[hierarchy], cont);
+			if (!(p->flags & PF_EXITING)) {
+				atomic_inc(&cont->count);
+			}
+			task_unlock(p);
+		} while_each_thread(g, p);
+		read_unlock(&tasklist_lock);
+
+		/* Move all the relevant subsystems into the hierarchy. */
+		for (i = 0; i < subsys_count; i++) {
+			if (!(subsys_bits & (1 << i))) continue;
+
+			ss = subsys[i];
+
+			BUG_ON(cont->subsys[i]);
+			BUG_ON(dummytop->subsys[i]->container != dummytop);
+			cont->subsys[i] = dummytop->subsys[i];
+			cont->subsys[i]->container = cont;
+			list_add(&ss->sibling, &root->subsys_list);
+			rcu_assign_pointer(subsys[i]->hierarchy,
+					   hierarchy);
+		}
+		mutex_unlock(&callback_mutex);
+		synchronize_rcu();
+
+		container_populate_dir(cont);
+
+	} else {
+		/* Reuse the existing superblock */
+		ret = simple_set_mnt(mnt, root->sb);
+		if (!ret)
+			atomic_inc(&root->sb->s_active);
+	}
+
+ out_unlock:
+	mutex_unlock(&manage_mutex);
+	return ret;
 }
 
 static struct file_system_type container_fs_type = {
@@ -401,7 +700,7 @@ int container_path(const struct containe
  * the time manage_mutex is held.
  */
 
-static void container_release_agent(const char *pathbuf)
+static void container_release_agent(int hierarchy, const char *pathbuf)
 {
 	char *argv[3], *envp[3];
 	int i;
@@ -410,7 +709,7 @@ static void container_release_agent(cons
 		return;
 
 	i = 0;
-	argv[i++] = release_agent_path;
+	argv[i++] = rootnode[hierarchy].release_agent_path;
 	argv[i++] = (char *)pathbuf;
 	argv[i] = NULL;
 
@@ -487,7 +786,7 @@ static int update_flag(container_flagbit
 
 
 /*
- * Attack task specified by pid in 'pidbuf' to container 'cont', possibly
+ * Attach task specified by pid in 'pidbuf' to container 'cont', possibly
  * writing the path of the old container in 'ppathbuf' if it needs to be
  * notified on release.
  *
@@ -501,6 +800,8 @@ static int attach_task(struct container 
 	struct task_struct *tsk;
 	struct container *oldcont;
 	int retval = 0;
+	struct container_subsys *ss;
+	int h = cont->hierarchy;
 
 	if (sscanf(pidbuf, "%d", &pid) != 1)
 		return -EIO;
@@ -527,37 +828,45 @@ static int attach_task(struct container 
 		get_task_struct(tsk);
 	}
 
-#ifdef CONFIG_CPUSETS
-	retval = cpuset_can_attach_task(cont, tsk);
-#endif
-	if (retval) {
-		put_task_struct(tsk);
-		return retval;
+	for_each_subsys(h, ss) {
+		if (ss->can_attach) {
+			retval = ss->can_attach(ss, cont, tsk);
+			if (retval) {
+				put_task_struct(tsk);
+				return retval;
+			}
+		}
 	}
 
 	mutex_lock(&callback_mutex);
 
 	task_lock(tsk);
-	oldcont = tsk->container;
+	oldcont = tsk->container[h];
 	if (!oldcont) {
 		task_unlock(tsk);
 		mutex_unlock(&callback_mutex);
 		put_task_struct(tsk);
 		return -ESRCH;
 	}
+        BUG_ON(oldcont == dummytop);
+
 	atomic_inc(&cont->count);
-	rcu_assign_pointer(tsk->container, cont);
+	rcu_assign_pointer(tsk->container[h], cont);
 	task_unlock(tsk);
 
-#ifdef CONFIG_CPUSETS
-	cpuset_attach_task(cont, tsk);
-#endif
+	for_each_subsys(h, ss) {
+		if (ss->attach) {
+			ss->attach(ss, cont, oldcont, tsk);
+		}
+	}
 
 	mutex_unlock(&callback_mutex);
 
-#ifdef CONFIG_CPUSETS
-	cpuset_post_attach_task(cont, oldcont, tsk);
-#endif
+	for_each_subsys(h, ss) {
+		if (ss->post_attach) {
+			ss->post_attach(ss, cont, oldcont, tsk);
+		}
+	}
 
 	put_task_struct(tsk);
 	synchronize_rcu();
@@ -616,13 +925,14 @@ static ssize_t container_common_file_wri
 		break;
 	case FILE_RELEASE_AGENT:
 	{
-		if (nbytes < sizeof(release_agent_path)) {
+		struct containerfs_root *root = &rootnode[cont->hierarchy];
+		if (nbytes < sizeof(root->release_agent_path)) {
 			/* We never write anything other than '\0'
 			 * into the last char of release_agent_path,
 			 * so it always remains a NUL-terminated
 			 * string */
-			strncpy(release_agent_path, buffer, nbytes);
-			release_agent_path[nbytes] = 0;
+			strncpy(root->release_agent_path, buffer, nbytes);
+			root->release_agent_path[nbytes] = 0;
 		} else {
 			retval = -ENOSPC;
 		}
@@ -637,7 +947,7 @@ static ssize_t container_common_file_wri
 		retval = nbytes;
 out2:
 	mutex_unlock(&manage_mutex);
-	container_release_agent(pathbuf);
+	container_release_agent(cont->hierarchy, pathbuf);
 out1:
 	kfree(buffer);
 	return retval;
@@ -683,11 +993,14 @@ static ssize_t container_common_file_rea
 		break;
 	case FILE_RELEASE_AGENT:
 	{
+		struct containerfs_root *root;
 		size_t n;
 		container_manage_lock();
-		n = strnlen(release_agent_path, sizeof(release_agent_path));
+		root = &rootnode[cont->hierarchy];
+		n = strnlen(root->release_agent_path,
+			    sizeof(root->release_agent_path));
 		n = min(n, (size_t) PAGE_SIZE);
-		strncpy(s, release_agent_path, n);
+		strncpy(s, root->release_agent_path, n);
 		container_manage_unlock();
 		s += n;
 		break;
@@ -780,7 +1093,7 @@ static struct inode_operations container
 	.rename = container_rename,
 };
 
-static int container_create_file(struct dentry *dentry, int mode)
+static int container_create_file(struct dentry *dentry, int mode, struct super_block *sb)
 {
 	struct inode *inode;
 
@@ -789,7 +1102,7 @@ static int container_create_file(struct 
 	if (dentry->d_inode)
 		return -EEXIST;
 
-	inode = container_new_inode(mode);
+	inode = container_new_inode(mode, sb);
 	if (!inode)
 		return -ENOMEM;
 
@@ -798,7 +1111,7 @@ static int container_create_file(struct 
 		inode->i_fop = &simple_dir_operations;
 
 		/* start off with i_nlink == 2 (for "." entry) */
-		inode->i_nlink++;
+		inc_nlink(inode);
 	} else if (S_ISREG(mode)) {
 		inode->i_size = 0;
 		inode->i_fop = &container_file_operations;
@@ -828,10 +1141,10 @@ static int container_create_dir(struct c
 	dentry = container_get_dentry(parent, name);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);
-	error = container_create_file(dentry, S_IFDIR | mode);
+	error = container_create_file(dentry, S_IFDIR | mode, cont->root->sb);
 	if (!error) {
 		dentry->d_fsdata = cont;
-		parent->d_inode->i_nlink++;
+		inc_nlink(parent->d_inode);
 		cont->dentry = dentry;
 	}
 	dput(dentry);
@@ -848,7 +1161,7 @@ int container_add_file(struct container 
 	mutex_lock(&dir->d_inode->i_mutex);
 	dentry = container_get_dentry(dir, cft->name);
 	if (!IS_ERR(dentry)) {
-		error = container_create_file(dentry, 0644 | S_IFREG);
+		error = container_create_file(dentry, 0644 | S_IFREG, cont->root->sb);
 		if (!error)
 			dentry->d_fsdata = (void *)cft;
 		dput(dentry);
@@ -894,7 +1207,7 @@ static int pid_array_load(pid_t *pidarra
 	read_lock(&tasklist_lock);
 
 	do_each_thread(g, p) {
-		if (p->container == cont) {
+		if (p->container[cont->hierarchy] == cont) {
 			pidarray[n++] = p->pid;
 			if (unlikely(n == npids))
 				goto array_full;
@@ -1037,21 +1350,33 @@ static struct cftype cft_release_agent =
 static int container_populate_dir(struct container *cont)
 {
 	int err;
+	struct container_subsys *ss;
 
 	if ((err = container_add_file(cont, &cft_notify_on_release)) < 0)
 		return err;
 	if ((err = container_add_file(cont, &cft_tasks)) < 0)
 		return err;
-	if ((cont == &top_container) &&
+	if ((cont == cont->top_container) &&
 	    (err = container_add_file(cont, &cft_release_agent)) < 0)
 		return err;
-#ifdef CONFIG_CPUSETS
-	if ((err = cpuset_populate_dir(cont)) < 0)
-		return err;
-#endif
+
+	for_each_subsys(cont->hierarchy, ss) {
+		if (ss->populate && (err = ss->populate(ss, cont)) < 0)
+			return err;
+	}
+
 	return 0;
 }
 
+static void init_container_css(struct container_subsys *ss,
+			       struct container *cont)
+{
+	struct container_subsys_state *css = cont->subsys[ss->subsys_id];
+	css->container = cont;
+	spin_lock_init(&css->refcnt_lock);
+	atomic_set(&css->refcnt, 0);
+}
+
 /*
  *	container_create - create a container
  *	parent:	container that will be parent of the new container.
@@ -1064,13 +1389,24 @@ static int container_populate_dir(struct
 static long container_create(struct container *parent, const char *name, int mode)
 {
 	struct container *cont;
-	int err;
+	struct containerfs_root *root = parent->root;
+	int err = 0;
+	struct container_subsys *ss;
+	struct super_block *sb = root->sb;
 
-	cont = kmalloc(sizeof(*cont), GFP_KERNEL);
+	cont = kzalloc(sizeof(*cont), GFP_KERNEL);
 	if (!cont)
 		return -ENOMEM;
 
+	/* Grab a reference on the superblock so the hierarchy doesn't
+	 * get deleted on unmount if there are child containers.  This
+	 * can be done outside manage_mutex, since the sb can't
+	 * disappear while someone has an open control file on the
+	 * fs */
+	atomic_inc(&sb->s_active);
+
 	mutex_lock(&manage_mutex);
+
 	cont->flags = 0;
 	if (notify_on_release(parent))
 		set_bit(CONT_NOTIFY_ON_RELEASE, &cont->flags);
@@ -1079,16 +1415,19 @@ static long container_create(struct cont
 	INIT_LIST_HEAD(&cont->children);
 
 	cont->parent = parent;
-
-#ifdef CONFIG_CPUSETS
-	err = cpuset_create(cont);
-	if (err)
-		goto err_unlock_free;
-#endif
+	cont->root = parent->root;
+	cont->hierarchy = parent->hierarchy;
+	cont->top_container = parent->top_container;
+
+	for_each_subsys(cont->hierarchy, ss) {
+		err = ss->create(ss, cont);
+		if (err) goto err_destroy;
+		init_container_css(ss, cont);
+	}
 
 	mutex_lock(&callback_mutex);
 	list_add(&cont->sibling, &cont->parent->children);
-	number_of_containers++;
+	root->number_of_containers++;
 	mutex_unlock(&callback_mutex);
 
 	err = container_create_dir(cont, name, mode);
@@ -1107,15 +1446,23 @@ static long container_create(struct cont
 	return 0;
 
  err_remove:
-#ifdef CONFIG_CPUSETS
-	cpuset_destroy(cont);
-#endif
+
 	mutex_lock(&callback_mutex);
 	list_del(&cont->sibling);
-	number_of_containers--;
+	root->number_of_containers--;
 	mutex_unlock(&callback_mutex);
- err_unlock_free:
+
+ err_destroy:
+
+	for_each_subsys(cont->hierarchy, ss) {
+		if (cont->subsys[ss->subsys_id])
+			ss->destroy(ss, cont);
+	}
+
 	mutex_unlock(&manage_mutex);
+
+	deactivate_super(sb);
+
 	kfree(cont);
 	return err;
 }
@@ -1128,23 +1475,18 @@ static int container_mkdir(struct inode 
 	return container_create(c_parent, dentry->d_name.name, mode | S_IFDIR);
 }
 
-/*
- * Locking note on the strange update_flag() call below:
- *
- * If the container being removed is marked cpu_exclusive, then simulate
- * turning cpu_exclusive off, which will call update_cpu_domains().
- * The lock_cpu_hotplug() call in update_cpu_domains() must not be
- * made while holding callback_mutex.  Elsewhere the kernel nests
- * callback_mutex inside lock_cpu_hotplug() calls.  So the reverse
- * nesting would risk an ABBA deadlock.
- */
-
 static int container_rmdir(struct inode *unused_dir, struct dentry *dentry)
 {
 	struct container *cont = dentry->d_fsdata;
 	struct dentry *d;
 	struct container *parent;
 	char *pathbuf = NULL;
+	struct container_subsys *ss;
+	struct super_block *sb;
+	struct containerfs_root *root;
+	unsigned long flags;
+	int css_busy = 0;
+	int hierarchy;
 
 	/* the vfs holds both inode->i_mutex already */
 
@@ -1157,7 +1499,41 @@ static int container_rmdir(struct inode 
 		mutex_unlock(&manage_mutex);
 		return -EBUSY;
 	}
+
+	hierarchy = cont->hierarchy;
 	parent = cont->parent;
+	root = cont->root;
+	sb = root->sb;
+
+	local_irq_save(flags);
+	/* Check each container, locking the refcnt lock and testing
+	 * the refcnt. This will lock out any calls to css_get() */
+	for_each_subsys(hierarchy, ss) {
+		struct container_subsys_state *css;
+		css = cont->subsys[ss->subsys_id];
+		spin_lock(&css->refcnt_lock);
+		css_busy += atomic_read(&css->refcnt);
+	}
+	/* Go through and release all the locks; if we weren't busy,
+	 * the set the refcount to -1 to prevent css_get() from adding
+	 * a refcount */
+	for_each_subsys(hierarchy, ss) {
+		struct container_subsys_state *css;
+		css = cont->subsys[ss->subsys_id];
+		if (!css_busy) atomic_dec(&css->refcnt);
+		spin_unlock(&css->refcnt_lock);
+	}
+	local_irq_restore(flags);
+	if (css_busy) {
+		mutex_unlock(&manage_mutex);
+		return -EBUSY;
+	}
+
+	for_each_subsys(hierarchy, ss) {
+		if (cont->subsys[ss->subsys_id])
+			ss->destroy(ss, cont);
+	}
+
 	mutex_lock(&callback_mutex);
 	set_bit(CONT_REMOVED, &cont->flags);
 	list_del(&cont->sibling);	/* delete my sibling from parent->children */
@@ -1165,67 +1541,143 @@ static int container_rmdir(struct inode 
 	d = dget(cont->dentry);
 	cont->dentry = NULL;
 	spin_unlock(&d->d_lock);
+
 	container_d_remove_dir(d);
 	dput(d);
-	number_of_containers--;
+	root->number_of_containers--;
 	mutex_unlock(&callback_mutex);
-#ifdef CONFIG_CPUSETS
-	cpuset_destroy(cont);
-#endif
+
 	if (list_empty(&parent->children))
 		check_for_release(parent, &pathbuf);
+
 	mutex_unlock(&manage_mutex);
-	container_release_agent(pathbuf);
+	/* Drop the active superblock reference that we took when we
+	 * created the container */
+	deactivate_super(sb);
+	container_release_agent(hierarchy, pathbuf);
 	return 0;
 }
 
-/*
- * container_init_early - probably not needed yet, but will be needed
- * once cpusets are hooked into this code
- */
+
+/**
+ * container_init_early - initialize containers at system boot
+ *
+ * Description: Initialize the container housekeeping structures
+ **/
 
 int __init container_init_early(void)
 {
-	struct task_struct *tsk = current;
+	int i;
+
+	for (i = 0; i < CONFIG_MAX_CONTAINER_HIERARCHIES; i++) {
+		struct containerfs_root *root = &rootnode[i];
+		struct container *cont = &root->top_container;
+		INIT_LIST_HEAD(&root->subsys_list);
+		root->number_of_containers = 1;
+
+		cont->root = root;
+		cont->hierarchy = i;
+		INIT_LIST_HEAD(&cont->sibling);
+		INIT_LIST_HEAD(&cont->children);
+		cont->top_container = cont;
+		atomic_set(&cont->count, 1);
+	}
+	init_task.container[0] = &rootnode[0].top_container;
 
-	tsk->container = &top_container;
 	return 0;
 }
 
 /**
- * container_init - initialize containers at system boot
- *
- * Description: Initialize top_container and the container internal file system,
+ * container_init - register container filesystem and /proc file
  **/
 
 int __init container_init(void)
 {
-	struct dentry *root;
 	int err;
-
-	init_task.container = &top_container;
+	struct proc_dir_entry *entry;
 
 	err = register_filesystem(&container_fs_type);
 	if (err < 0)
 		goto out;
-	container_mount = kern_mount(&container_fs_type);
-	if (IS_ERR(container_mount)) {
-		printk(KERN_ERR "container: could not mount!\n");
-		err = PTR_ERR(container_mount);
-		container_mount = NULL;
-		goto out;
-	}
-	root = container_mount->mnt_sb->s_root;
-	root->d_fsdata = &top_container;
-	root->d_inode->i_nlink++;
-	top_container.dentry = root;
-	root->d_inode->i_op = &container_dir_inode_operations;
-	number_of_containers = 1;
-	err = container_populate_dir(&top_container);
+
+	entry = create_proc_entry("containers", 0, NULL);
+	if (entry)
+		entry->proc_fops = &proc_containerstats_operations;
+
 out:
 	return err;
 }
 
+int container_register_subsys(struct container_subsys *new_subsys) {
+	int retval = 0;
+	int i;
+
+	BUG_ON(new_subsys->hierarchy);
+	mutex_lock(&manage_mutex);
+	if (subsys_count == CONFIG_MAX_CONTAINER_SUBSYS) {
+		retval = -ENOSPC;
+		goto out;
+	}
+	/* Sanity check the subsystem */
+	if (!new_subsys->name ||
+	    (strlen(new_subsys->name) > MAX_CONTAINER_TYPE_NAMELEN) ||
+	    !new_subsys->create || !new_subsys->destroy) {
+		retval = -EINVAL;
+		goto out;
+	}
+	/* Check this isn't a duplicate */
+	for (i = 0; i < subsys_count; i++) {
+		if (!strcmp(subsys[i]->name, new_subsys->name)) {
+			retval = -EEXIST;
+			goto out;
+		}
+	}
+
+	/* Create the top container state for this subsystem */
+	new_subsys->subsys_id = subsys_count;
+	retval = new_subsys->create(new_subsys, dummytop);
+	if (retval) {
+		new_subsys->subsys_id = -1;
+		goto out;
+	}
+	init_container_css(new_subsys, dummytop);
+ 	mutex_lock(&callback_mutex);
+ 	/* If this is the first subsystem that requested a fork or
+ 	 * exit callback, tell our fork/exit hooks that they need to
+ 	 * grab callback_mutex on every invocation. If they are
+ 	 * running concurrently with this code, they will either not
+ 	 * see the change now and go straight on, or they will see it
+ 	 * and grab callback_mutex, which will deschedule them. Either
+ 	 * way once synchronize_rcu() returns we know that all current
+ 	 * and future forks will make the callbacks. */
+ 	if (!need_forkexit_callback &&
+ 	    (new_subsys->fork || new_subsys->exit)) {
+ 		need_forkexit_callback = 1;
+		if (system_state == SYSTEM_RUNNING)
+			synchronize_rcu();
+ 	}
+
+ 	/* If this subsystem requested that it be notified with fork
+ 	 * events, we should send it one now for every process in the
+ 	 * system */
+ 	if (new_subsys->fork) {
+ 		struct task_struct *g, *p;
+
+ 		read_lock(&tasklist_lock);
+ 		do_each_thread(g, p) {
+ 			new_subsys->fork(new_subsys, p);
+ 		} while_each_thread(g, p);
+ 		read_unlock(&tasklist_lock);
+ 	}
+
+	subsys[subsys_count++] = new_subsys;
+ 	mutex_unlock(&callback_mutex);
+ out:
+ 	mutex_unlock(&manage_mutex);
+ 	return retval;
+
+}
+
 /**
  * container_fork - attach newly forked task to its parents container.
  * @tsk: pointer to task_struct of forking parent process.
@@ -1246,10 +1698,39 @@ out:
 
 void container_fork(struct task_struct *child)
 {
+	int i, need_callback;
+
+	rcu_read_lock();
+	/* need_forkexit_callback will be true if we might need to do
+ 	 * a callback. If so then switch from RCU to mutex locking */
+	need_callback = rcu_dereference(need_forkexit_callback);
+	if (need_callback) {
+		rcu_read_unlock();
+		mutex_lock(&callback_mutex);
+	}
 	task_lock(current);
-	child->container = current->container;
-	atomic_inc(&child->container->count);
+        /* Add the child task to the same container as the parent in
+	 * each hierarchy. Skip hierarchy 0 since it's permanent */
+	for (i = 1; i < CONFIG_MAX_CONTAINER_HIERARCHIES; i++) {
+		struct container *cont = current->container[i];
+		if (!cont) continue;
+		child->container[i] = cont;
+		atomic_inc(&cont->count);
+	}
+	if (need_callback) {
+		for (i = 0; i < subsys_count; i++) {
+			struct container_subsys *ss = subsys[i];
+			if (ss->fork) {
+				ss->fork(ss, child);
+			}
+		}
+	}
 	task_unlock(current);
+	if (need_callback) {
+		mutex_unlock(&callback_mutex);
+	} else {
+		rcu_read_unlock();
+	}
 }
 
 /**
@@ -1314,71 +1795,49 @@ void container_fork(struct task_struct *
 void container_exit(struct task_struct *tsk)
 {
 	struct container *cont;
-
-	cont = tsk->container;
-	tsk->container = &top_container;	/* the_top_container_hack - see above */
-
-	if (notify_on_release(cont)) {
-		char *pathbuf = NULL;
-
-		mutex_lock(&manage_mutex);
-		if (atomic_dec_and_test(&cont->count))
-			check_for_release(cont, &pathbuf);
-		mutex_unlock(&manage_mutex);
-		container_release_agent(pathbuf);
+	int i;
+	rcu_read_lock();
+	if (rcu_dereference(need_forkexit_callback)) {
+		rcu_read_unlock();
+		mutex_lock(&callback_mutex);
+		for (i = 0; i < subsys_count; i++) {
+			struct container_subsys *ss = subsys[i];
+			if (ss->exit) {
+				ss->exit(ss, tsk);
+			}
+		}
+		mutex_unlock(&callback_mutex);
 	} else {
-		atomic_dec(&cont->count);
+		rcu_read_unlock();
 	}
-}
-
-/**
- * container_lock - lock out any changes to container structures
- *
- * The out of memory (oom) code needs to mutex_lock containers
- * from being changed while it scans the tasklist looking for a
- * task in an overlapping container.  Expose callback_mutex via this
- * container_lock() routine, so the oom code can lock it, before
- * locking the task list.  The tasklist_lock is a spinlock, so
- * must be taken inside callback_mutex.
- */
-
-void container_lock(void)
-{
-	mutex_lock(&callback_mutex);
-}
-
-/**
- * container_unlock - release lock on container changes
- *
- * Undo the lock taken in a previous container_lock() call.
- */
-
-void container_unlock(void)
-{
-	mutex_unlock(&callback_mutex);
-}
-
-void container_manage_lock(void)
-{
-	mutex_lock(&manage_mutex);
-}
-
-/**
- * container_manage_unlock - release lock on container changes
- *
- * Undo the lock taken in a previous container_manage_lock() call.
- */
 
-void container_manage_unlock(void)
-{
-	mutex_unlock(&manage_mutex);
+	/* For each hierarchy, remove the task from its current
+	 * container in that hierarchy and attach it to the top
+	 * container instead. Skip hierarchy 0 since it never has
+	 * subcontainers */
+	for (i = 1; i < CONFIG_MAX_CONTAINER_HIERARCHIES; i++) {
+		cont = tsk->container[i];
+		if (!cont) continue;
+		/* the_top_container_hack - see above */
+		tsk->container[i] = cont->top_container;
+		if (notify_on_release(cont)) {
+			char *pathbuf = NULL;
+			int hierarchy;
+			mutex_lock(&manage_mutex);
+			hierarchy = cont->hierarchy;
+			if (atomic_dec_and_test(&cont->count))
+				check_for_release(cont, &pathbuf);
+			mutex_unlock(&manage_mutex);
+			container_release_agent(hierarchy, pathbuf);
+		} else {
+			atomic_dec(&cont->count);
+		}
+	}
 }
 
-
-
 /*
  * proc_container_show()
- *  - Print tasks container path into seq_file.
+ *  - Print task's container paths into seq_file, one line for each hierarchy
  *  - Used for /proc/<pid>/container.
  *  - No need to task_lock(tsk) on this tsk->container reference, as it
  *    doesn't really matter if tsk->container changes after we read it,
@@ -1387,12 +1846,15 @@ void container_manage_unlock(void)
  *    the_top_container_hack in container_exit(), which sets an exiting tasks
  *    container to top_container.
  */
+
+/* TODO: Use a proper seq_file iterator */
 static int proc_container_show(struct seq_file *m, void *v)
 {
 	struct pid *pid;
 	struct task_struct *tsk;
 	char *buf;
 	int retval;
+	int i;
 
 	retval = -ENOMEM;
 	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
@@ -1405,14 +1867,26 @@ static int proc_container_show(struct se
 	if (!tsk)
 		goto out_free;
 
-	retval = -EINVAL;
+	retval = 0;
+
 	mutex_lock(&manage_mutex);
 
-	retval = container_path(tsk->container, buf, PAGE_SIZE);
-	if (retval < 0)
-		goto out_unlock;
-	seq_puts(m, buf);
-	seq_putc(m, '\n');
+	for (i = 1; i < CONFIG_MAX_CONTAINER_HIERARCHIES; i++) {
+		struct containerfs_root *root = &rootnode[i];
+		struct container_subsys *ss;
+		int count = 0;
+		/* Skip this hierarchy if it has no active subsystems */
+		if (!root->subsys_bits) continue;
+		for_each_subsys(i, ss) {
+			seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
+		}
+		seq_putc(m, ':');
+		retval = container_path(tsk->container[i], buf, PAGE_SIZE);
+		if (retval < 0)
+			goto out_unlock;
+		seq_puts(m, buf);
+		seq_putc(m, '\n');
+	}
 out_unlock:
 	mutex_unlock(&manage_mutex);
 	put_task_struct(tsk);
@@ -1434,3 +1908,48 @@ struct file_operations proc_container_op
 	.llseek		= seq_lseek,
 	.release	= single_release,
 };
+
+/* Display information about each subsystem and each hierarchy */
+static int proc_containerstats_show(struct seq_file *m, void *v)
+{
+	int i;
+	mutex_lock(&manage_mutex);
+	seq_puts(m, "Hierarchies:\n");
+	for (i = 0; i < CONFIG_MAX_CONTAINER_HIERARCHIES; i++) {
+		struct containerfs_root *root = &rootnode[i];
+		struct container_subsys *ss;
+		int first = 1;
+		seq_printf(m, "%d: topcount=%d bits=%lx containers=%d (",
+			   i, atomic_read(&root->top_container.count),
+			   root->subsys_bits, root->number_of_containers);
+		for_each_subsys(i, ss) {
+			seq_printf(m, "%s%s", first ? "" : ", ", ss->name);
+			first = false;
+		}
+		seq_putc(m, ')');
+		if (root->sb) {
+			seq_printf(m, " s_active=%d", atomic_read(&root->sb->s_active));
+		}
+		seq_putc(m, '\n');
+	}
+	seq_puts(m, "Subsystems:\n");
+	for (i = 0; i < subsys_count; i++) {
+		struct container_subsys *ss = subsys[i];
+		seq_printf(m, "%d: name=%s hierarchy=%d\n",
+			   i, ss->name, ss->hierarchy);
+	}
+	mutex_unlock(&manage_mutex);
+	return 0;
+}
+
+static int containerstats_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, proc_containerstats_show, 0);
+}
+
+struct file_operations proc_containerstats_operations = {
+	.open = containerstats_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+};
Index: container-2.6.20-rc1/kernel/cpuset.c
===================================================================
--- container-2.6.20-rc1.orig/kernel/cpuset.c
+++ container-2.6.20-rc1/kernel/cpuset.c
@@ -5,6 +5,7 @@
  *
  *  Copyright (C) 2003 BULL SA.
  *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
+ *  Copyright (C) 2006 Google, Inc
  *
  *  Portions derived from Patrick Mochel's sysfs code.
  *  sysfs is Copyright (c) 2001-3 Patrick Mochel
@@ -12,6 +13,7 @@
  *  2003-10-10 Written by Simon Derr.
  *  2003-10-22 Updates by Stephen Hemminger.
  *  2004 May-July Rework by Paul Jackson.
+ *  2006 Rework by Paul Menage to use generic containers
  *
  *  This file is subject to the terms and conditions of the GNU General Public
  *  License.  See the file COPYING in the main directory of the Linux
@@ -61,6 +63,10 @@
  */
 int number_of_cpusets __read_mostly;
 
+/* Retrieve the cpuset from a container */
+static struct container_subsys cpuset_subsys;
+struct cpuset;
+
 /* See "Frequency meter" comments, below. */
 
 struct fmeter {
@@ -71,11 +77,12 @@ struct fmeter {
 };
 
 struct cpuset {
+	struct container_subsys_state css;
+
 	unsigned long flags;		/* "unsigned long" so bitops work */
 	cpumask_t cpus_allowed;		/* CPUs allowed to tasks in cpuset */
 	nodemask_t mems_allowed;	/* Memory Nodes allowed to tasks */
 
-	struct container *container;    /* Task container */
 	struct cpuset *parent;		/* my parent */
 
 	/*
@@ -87,6 +94,26 @@ struct cpuset {
 	struct fmeter fmeter;		/* memory_pressure filter */
 };
 
+/* Update the cpuset for a container */
+static inline void set_container_cs(struct container *cont, struct cpuset *cs)
+{
+	cont->subsys[cpuset_subsys.subsys_id] = &cs->css;
+}
+
+/* Retrieve the cpuset for a container */
+static inline struct cpuset *container_cs(struct container *cont)
+{
+	return container_of(container_subsys_state(cont, &cpuset_subsys),
+			    struct cpuset, css);
+}
+
+/* Retrieve the cpuset for a task */
+static inline struct cpuset *task_cs(struct task_struct *task)
+{
+	return container_cs(task_container(task, &cpuset_subsys));
+}
+
+
 /* bits in struct cpuset flags field */
 typedef enum {
 	CS_CPU_EXCLUSIVE,
@@ -158,12 +185,16 @@ static int cpuset_get_sb(struct file_sys
 {
 	struct file_system_type *container_fs = get_fs_type("container");
 	int ret = -ENODEV;
-	container_set_release_agent_path("/sbin/cpuset_release_agent");
 	if (container_fs) {
 		ret = container_fs->get_sb(container_fs, flags,
 					   unused_dev_name,
-					   data, mnt);
+					   "cpuset", mnt);
 		put_filesystem(container_fs);
+		if (!ret) {
+			container_set_release_agent_path(
+				&cpuset_subsys,
+				"/sbin/cpuset_release_agent");
+		}
 	}
 	return ret;
 }
@@ -270,20 +301,19 @@ void cpuset_update_task_memory_state(voi
 	struct task_struct *tsk = current;
 	struct cpuset *cs;
 
-	if (tsk->container->cpuset == &top_cpuset) {
+	if (task_cs(tsk) == &top_cpuset) {
 		/* Don't need rcu for top_cpuset.  It's never freed. */
 		my_cpusets_mem_gen = top_cpuset.mems_generation;
 	} else {
 		rcu_read_lock();
-		cs = rcu_dereference(tsk->container->cpuset);
-		my_cpusets_mem_gen = cs->mems_generation;
+		my_cpusets_mem_gen = task_cs(current)->mems_generation;
 		rcu_read_unlock();
 	}
 
 	if (my_cpusets_mem_gen != tsk->cpuset_mems_generation) {
 		container_lock();
 		task_lock(tsk);
-		cs = tsk->container->cpuset; /* Maybe changed when task not locked */
+		cs = task_cs(tsk); /* Maybe changed when task not locked */
 		guarantee_online_mems(cs, &tsk->mems_allowed);
 		tsk->cpuset_mems_generation = cs->mems_generation;
 		if (is_spread_page(cs))
@@ -342,9 +372,8 @@ static int validate_change(const struct 
 	struct cpuset *c, *par;
 
 	/* Each of our child cpusets must be a subset of us */
-	list_for_each_entry(cont, &cur->container->children, sibling) {
-		c = cont->cpuset;
-		if (!is_cpuset_subset(c, trial))
+	list_for_each_entry(cont, &cur->css.container->children, sibling) {
+		if (!is_cpuset_subset(container_cs(cont), trial))
 			return -EBUSY;
 	}
 
@@ -359,8 +388,8 @@ static int validate_change(const struct 
 		return -EACCES;
 
 	/* If either I or some sibling (!= me) is exclusive, we can't overlap */
-	list_for_each_entry(cont, &par->container->children, sibling) {
-		c = cont->cpuset;
+	list_for_each_entry(cont, &par->css.container->children, sibling) {
+		c = container_cs(cont);
 		if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
 		    c != cur &&
 		    cpus_intersects(trial->cpus_allowed, c->cpus_allowed))
@@ -402,8 +431,8 @@ static void update_cpu_domains(struct cp
 	 * children
 	 */
 	pspan = par->cpus_allowed;
-	list_for_each_entry(cont, &par->container->children, sibling) {
-		c = cont->cpuset;
+	list_for_each_entry(cont, &par->css.container->children, sibling) {
+		c = container_cs(cont);
 		if (is_cpu_exclusive(c))
 			cpus_andnot(pspan, pspan, c->cpus_allowed);
 	}
@@ -420,8 +449,8 @@ static void update_cpu_domains(struct cp
 		 * Get all cpus from current cpuset's cpus_allowed not part
 		 * of exclusive children
 		 */
-		list_for_each_entry(cont, &cur->container->children, sibling) {
-			c = cont->cpuset;
+		list_for_each_entry(cont, &cur->css.container->children, sibling) {
+			c = container_cs(cont);
 			if (is_cpu_exclusive(c))
 				cpus_andnot(cspan, cspan, c->cpus_allowed);
 		}
@@ -509,7 +538,7 @@ static void cpuset_migrate_mm(struct mm_
 	do_migrate_pages(mm, from, to, MPOL_MF_MOVE_ALL);
 
 	container_lock();
-	guarantee_online_mems(tsk->container->cpuset, &tsk->mems_allowed);
+	guarantee_online_mems(task_cs(tsk),&tsk->mems_allowed);
 	container_unlock();
 }
 
@@ -527,6 +556,8 @@ static void cpuset_migrate_mm(struct mm_
  * their mempolicies to the cpusets new mems_allowed.
  */
 
+static void *cpuset_being_rebound;
+
 static int update_nodemask(struct cpuset *cs, char *buf)
 {
 	struct cpuset trialcs;
@@ -544,7 +575,7 @@ static int update_nodemask(struct cpuset
 		return -EACCES;
 
 	trialcs = *cs;
-	cont = cs->container;
+	cont = cs->css.container;
 	retval = nodelist_parse(buf, trialcs.mems_allowed);
 	if (retval < 0)
 		goto done;
@@ -567,7 +598,7 @@ static int update_nodemask(struct cpuset
 	cs->mems_generation = cpuset_mems_generation++;
 	container_unlock();
 
-	set_cpuset_being_rebound(cs);		/* causes mpol_copy() rebind */
+	cpuset_being_rebound = cs;		/* causes mpol_copy() rebind */
 
 	fudge = 10;				/* spare mmarray[] slots */
 	fudge += cpus_weight(cs->cpus_allowed);	/* imagine one fork-bomb/cpu */
@@ -581,13 +612,13 @@ static int update_nodemask(struct cpuset
 	 * enough mmarray[] w/o using GFP_ATOMIC.
 	 */
 	while (1) {
-		ntasks = atomic_read(&cs->container->count);  /* guess */
+		ntasks = atomic_read(&cs->css.container->count);  /* guess */
 		ntasks += fudge;
 		mmarray = kmalloc(ntasks * sizeof(*mmarray), GFP_KERNEL);
 		if (!mmarray)
 			goto done;
 		write_lock_irq(&tasklist_lock);		/* block fork */
-		if (atomic_read(&cs->container->count) <= ntasks)
+		if (atomic_read(&cs->css.container->count) <= ntasks)
 			break;				/* got enough */
 		write_unlock_irq(&tasklist_lock);	/* try again */
 		kfree(mmarray);
@@ -604,7 +635,7 @@ static int update_nodemask(struct cpuset
 				"Cpuset mempolicy rebind incomplete.\n");
 			continue;
 		}
-		if (p->container != cont)
+		if (task_cs(p) != cs)
 			continue;
 		mm = get_task_mm(p);
 		if (!mm)
@@ -638,12 +669,17 @@ static int update_nodemask(struct cpuset
 
 	/* We're done rebinding vma's to this cpusets new mems_allowed. */
 	kfree(mmarray);
-	set_cpuset_being_rebound(NULL);
+	cpuset_being_rebound = NULL;
 	retval = 0;
 done:
 	return retval;
 }
 
+int current_cpuset_is_being_rebound(void)
+{
+	return task_cs(current) == cpuset_being_rebound;
+}
+
 /*
  * Call with manage_mutex held.
  */
@@ -794,9 +830,10 @@ static int fmeter_getrate(struct fmeter 
 	return val;
 }
 
-int cpuset_can_attach_task(struct container *cont, struct task_struct *tsk)
+int cpuset_can_attach(struct container_subsys *ss,
+		      struct container *cont, struct task_struct *tsk)
 {
-	struct cpuset *cs = cont->cpuset;
+	struct cpuset *cs = container_cs(cont);
 
 	if (cpus_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
 		return -ENOSPC;
@@ -804,22 +841,23 @@ int cpuset_can_attach_task(struct contai
 	return security_task_setscheduler(tsk, 0, NULL);
 }
 
-void cpuset_attach_task(struct container *cont, struct task_struct *tsk)
+void cpuset_attach(struct container_subsys *ss, struct container *cont,
+		   struct container *old_cont, struct task_struct *tsk)
 {
 	cpumask_t cpus;
-	struct cpuset *cs = cont->cpuset;
-	guarantee_online_cpus(cs, &cpus);
+	guarantee_online_cpus(container_cs(cont), &cpus);
 	set_cpus_allowed(tsk, cpus);
 }
 
-void cpuset_post_attach_task(struct container *cont,
-			     struct container *oldcont,
-			     struct task_struct *tsk)
+void cpuset_post_attach(struct container_subsys *ss,
+			struct container *cont,
+			struct container *oldcont,
+			struct task_struct *tsk)
 {
 	nodemask_t from, to;
 	struct mm_struct *mm;
-	struct cpuset *cs = cont->cpuset;
-	struct cpuset *oldcs = oldcont->cpuset;
+	struct cpuset *cs = container_cs(cont);
+	struct cpuset *oldcs = container_cs(oldcont);
 
 	from = oldcs->mems_allowed;
 	to = cs->mems_allowed;
@@ -853,7 +891,7 @@ static ssize_t cpuset_common_file_write(
 					const char __user *userbuf,
 					size_t nbytes, loff_t *unused_ppos)
 {
-	struct cpuset *cs = cont->cpuset;
+	struct cpuset *cs = container_cs(cont);
 	cpuset_filetype_t type = cft->private;
 	char *buffer;
 	int retval = 0;
@@ -963,7 +1001,7 @@ static ssize_t cpuset_common_file_read(s
 				       char __user *buf,
 				       size_t nbytes, loff_t *ppos)
 {
-	struct cpuset *cs = cont->cpuset;
+	struct cpuset *cs = container_cs(cont);
 	cpuset_filetype_t type = cft->private;
 	char *page;
 	ssize_t retval = 0;
@@ -1081,7 +1119,7 @@ static struct cftype cft_spread_slab = {
 	.private = FILE_SPREAD_SLAB,
 };
 
-int cpuset_populate_dir(struct container *cont)
+int cpuset_populate(struct container_subsys *ss, struct container *cont)
 {
 	int err;
 
@@ -1116,11 +1154,19 @@ int cpuset_populate_dir(struct container
  *	Must be called with the mutex on the parent inode held
  */
 
-int cpuset_create(struct container *cont)
+int cpuset_create(struct container_subsys *ss, struct container *cont)
 {
 	struct cpuset *cs;
-	struct cpuset *parent = cont->parent->cpuset;
+	struct cpuset *parent;
 
+	if (!cont->parent) {
+		/* This is early initialization for the top container */
+		set_container_cs(cont, &top_cpuset);
+		top_cpuset.css.container = cont;
+		top_cpuset.mems_generation = cpuset_mems_generation++;
+		return 0;
+	}
+	parent = container_cs(cont->parent);
 	cs = kmalloc(sizeof(*cs), GFP_KERNEL);
 	if (!cs)
 		return -ENOMEM;
@@ -1137,8 +1183,8 @@ int cpuset_create(struct container *cont
 	fmeter_init(&cs->fmeter);
 
 	cs->parent = parent;
-	cont->cpuset = cs;
-	cs->container = cont;
+	set_container_cs(cont, cs);
+	cs->css.container = cont;
 	number_of_cpusets++;
 	return 0;
 }
@@ -1154,9 +1200,9 @@ int cpuset_create(struct container *cont
  * nesting would risk an ABBA deadlock.
  */
 
-void cpuset_destroy(struct container *cont)
+void cpuset_destroy(struct container_subsys *ss, struct container *cont)
 {
-	struct cpuset *cs = cont->cpuset;
+	struct cpuset *cs = container_cs(cont);
 
 	cpuset_update_task_memory_state();
 	if (is_cpu_exclusive(cs)) {
@@ -1164,8 +1210,20 @@ void cpuset_destroy(struct container *co
 		BUG_ON(retval);
 	}
 	number_of_cpusets--;
+	kfree(cs);
 }
 
+static struct container_subsys cpuset_subsys = {
+	.name = "cpuset",
+	.create = cpuset_create,
+	.destroy  = cpuset_destroy,
+	.can_attach = cpuset_can_attach,
+	.attach = cpuset_attach,
+	.post_attach = cpuset_post_attach,
+	.populate = cpuset_populate,
+	.subsys_id = -1,
+};
+
 /*
  * cpuset_init_early - just enough so that the calls to
  * cpuset_update_task_memory_state() in early init code
@@ -1174,13 +1232,13 @@ void cpuset_destroy(struct container *co
 
 int __init cpuset_init_early(void)
 {
-	struct container *cont = current->container;
-	cont->cpuset = &top_cpuset;
-	top_cpuset.container = cont;
-	cont->cpuset->mems_generation = cpuset_mems_generation++;
+	if (container_register_subsys(&cpuset_subsys) < 0)
+		panic("Couldn't register cpuset subsystem");
+	top_cpuset.mems_generation = cpuset_mems_generation++;
 	return 0;
 }
 
+
 /**
  * cpuset_init - initialize cpusets at system boot
  *
@@ -1190,6 +1248,7 @@ int __init cpuset_init_early(void)
 int __init cpuset_init(void)
 {
 	int err = 0;
+
 	top_cpuset.cpus_allowed = CPU_MASK_ALL;
 	top_cpuset.mems_allowed = NODE_MASK_ALL;
 
@@ -1231,8 +1290,8 @@ static void guarantee_online_cpus_mems_i
 	struct cpuset *c;
 
 	/* Each of our child cpusets mems must be online */
-	list_for_each_entry(cont, &cur->container->children, sibling) {
-		c = cont->cpuset;
+	list_for_each_entry(cont, &cur->css.container->children, sibling) {
+		c = container_cs(cont);
 		guarantee_online_cpus_mems_in_subtree(c);
 		if (!cpus_empty(c->cpus_allowed))
 			guarantee_online_cpus(c, &c->cpus_allowed);
@@ -1330,7 +1389,7 @@ cpumask_t cpuset_cpus_allowed(struct tas
 
 	container_lock();
 	task_lock(tsk);
-	guarantee_online_cpus(tsk->container->cpuset, &mask);
+	guarantee_online_cpus(task_cs(tsk), &mask);
 	task_unlock(tsk);
 	container_unlock();
 
@@ -1358,7 +1417,7 @@ nodemask_t cpuset_mems_allowed(struct ta
 
 	container_lock();
 	task_lock(tsk);
-	guarantee_online_mems(tsk->container->cpuset, &mask);
+	guarantee_online_mems(task_cs(tsk), &mask);
 	task_unlock(tsk);
 	container_unlock();
 
@@ -1479,7 +1538,7 @@ int __cpuset_zone_allowed_softwall(struc
 	container_lock();
 
 	task_lock(current);
-	cs = nearest_exclusive_ancestor(current->container->cpuset);
+	cs = nearest_exclusive_ancestor(task_cs(current));
 	task_unlock(current);
 
 	allowed = node_isset(node, cs->mems_allowed);
@@ -1581,7 +1640,7 @@ int cpuset_excl_nodes_overlap(const stru
 		task_unlock(current);
 		goto done;
 	}
-	cs1 = nearest_exclusive_ancestor(current->container->cpuset);
+	cs1 = nearest_exclusive_ancestor(task_cs(current));
 	task_unlock(current);
 
 	task_lock((struct task_struct *)p);
@@ -1589,7 +1648,7 @@ int cpuset_excl_nodes_overlap(const stru
 		task_unlock((struct task_struct *)p);
 		goto done;
 	}
-	cs2 = nearest_exclusive_ancestor(p->container->cpuset);
+	cs2 = nearest_exclusive_ancestor(task_cs((struct task_struct *)p));
 	task_unlock((struct task_struct *)p);
 
 	overlap = nodes_intersects(cs1->mems_allowed, cs2->mems_allowed);
@@ -1625,11 +1684,8 @@ int cpuset_memory_pressure_enabled __rea
 
 void __cpuset_memory_pressure_bump(void)
 {
-	struct cpuset *cs;
-
 	task_lock(current);
-	cs = current->container->cpuset;
-	fmeter_markevent(&cs->fmeter);
+	fmeter_markevent(&task_cs(current)->fmeter);
 	task_unlock(current);
 }
 
@@ -1666,7 +1722,8 @@ static int proc_cpuset_show(struct seq_f
 	retval = -EINVAL;
 	container_manage_lock();
 
-	retval = container_path(tsk->container, buf, PAGE_SIZE);
+	retval = container_path(tsk->container[cpuset_subsys.hierarchy],
+				buf, PAGE_SIZE);
 	if (retval < 0)
 		goto out_unlock;
 	seq_puts(m, buf);
Index: container-2.6.20-rc1/Documentation/containers.txt
===================================================================
--- container-2.6.20-rc1.orig/Documentation/containers.txt
+++ container-2.6.20-rc1/Documentation/containers.txt
@@ -21,8 +21,11 @@ CONTENTS:
 2. Usage Examples and Syntax
   2.1 Basic Usage
   2.2 Attaching processes
-3. Questions
-4. Contact
+3. Kernel API
+  3.1 Overview
+  3.2 Synchronization
+  3.3 Subsystem API
+4. Questions
 
 1. Containers
 ==========
@@ -30,14 +33,18 @@ CONTENTS:
 1.1 What are containers ?
 ----------------------
 
-Containers provide a mechanism for aggregating sets of tasks, and all
-their children, into hierarchical groups.
-
-Each task has a pointer to a container.  Multiple tasks may reference
-the same container. User level code may create and destroy containers
-by name in the container virtual file system, specify and query to
-which container a task is assigned, and list the task pids assigned to
-a container.
+Containers provide a mechanism for aggregating/partitioning sets of
+tasks, and all their future children, into hierarchical groups. A
+container associates a set of tasks with a set of parameters for one
+or more "subsystems" (typically resource controllers).
+
+At any one time there may be up to CONFIG_MAX_CONTAINER_HIERARCHIES
+active hierachies of task containers.  Each task has a pointer to a
+container in each active hierarchy.  Multiple tasks may reference
+(i.e. be members of) the same container. User level code may create
+and destroy containers by name in an instance of the container virtual
+file system, specify and query to which container a task is assigned,
+and list the task pids assigned to a container.
 
 On their own, the only use for containers is for simple job
 tracking. The intention is that other subsystems, such as cpusets (see
@@ -51,9 +58,9 @@ resources which processes in a container
 There are multiple efforts to provide process aggregations in the
 Linux kernel, mainly for resource tracking purposes. Such efforts
 include cpusets, CKRM/ResGroups, and UserBeanCounters. These all
-require the basic notion of a grouping of processes, with newly forked
-processes ending in the same group (container) as their parent
-process.
+require the basic notion of a grouping/partitioning of processes, with
+newly forked processes ending in the same group (container) as their
+parent process.
 
 The kernel container patch provides the minimum essential kernel
 mechanisms required to efficiently implement such groups. It has
@@ -67,27 +74,46 @@ desired.
 
 Containers extends the kernel as follows:
 
- - Each task in the system is attached to a container, via a pointer
-   in the task structure to a reference counted container structure.
- - The hierarchy of containers can be mounted at /dev/container (or
-   elsewhere), for browsing and manipulation from user space.
+ - Each task in the system has set of reference-counted container
+   pointers, one for each active hierarchy
+ - A container hierarchy filesystem can be mounted  for browsing and
+   manipulation from user space.
  - You can list all the tasks (by pid) attached to any container.
 
 The implementation of containers requires a few, simple hooks
 into the rest of the kernel, none in performance critical paths:
 
- - in init/main.c, to initialize the root container at system boot.
- - in fork and exit, to attach and detach a task from its container.
-
-In addition a new file system, of type "container" may be mounted,
-typically at /dev/container, to enable browsing and modifying the containers
-presently known to the kernel.  No new system calls are added for
-containers - all support for querying and modifying containers is via
-this container file system.
+ - in init/main.c, to initialize the root containers at system boot.
+ - in fork and exit, to attach and detach a task from its containers.
 
-Each task under /proc has an added file named 'container', displaying
-the container name, as the path relative to the root of the container file
-system.
+In addition a new file system, of type "container" may be mounted, to
+enable browsing and modifying the containers presently known to the
+kernel.  When mounting a container hierarchy, you may specify a
+comma-separated list of subsystems to mount as the filesystem mount
+options.  By default, mounting the container filesystem attempts to
+mount a hierarchy containing all registered subsystems.
+
+If an active hierarchy with exactly the same set of subsystems already
+exists, it will be reused for the new mount. If no existing hierarchy
+matches, and any of the requested subsystems are in use in an existing
+hierarchy, the mount will fail with -EBUSY. Otherwise, a new hierarchy
+is created, associated with the requested subsystems.
+
+It's not currently possible to bind a new subsystem to an active
+container hierarchy, or to unbind a subsystem from an active container
+hierarchy.
+
+When a container filesystem is unmounted, if there are any
+subcontainers created below the top-level container, that hierarchy
+will remain active even though unmounted; if there are no
+subcontainers then the hierarchy will be deactivated.
+
+No new system calls are added for containers - all support for
+querying and modifying containers is via this container file system.
+
+Each task under /proc has an added file named 'container' displaying,
+for each active hierarchy, the subsystem names and the container name
+as the path relative to the root of the container file system.
 
 Each container is represented by a directory in the container file system
 containing the following files describing that container:
@@ -119,23 +145,27 @@ for containers, with a minimum of additi
 1.4 What does notify_on_release do ?
 ------------------------------------
 
-If the notify_on_release flag is enabled (1) in a container, then whenever
-the last task in the container leaves (exits or attaches to some other
-container) and the last child container of that container is removed, then
-the kernel runs the command /sbin/container_release_agent, supplying the
-pathname (relative to the mount point of the container file system) of the
-abandoned container.  This enables automatic removal of abandoned containers.
-The default value of notify_on_release in the root container at system
-boot is disabled (0).  The default value of other containers at creation
-is the current value of their parents notify_on_release setting.
+If the notify_on_release flag is enabled (1) in a container, then
+whenever the last task in the container leaves (exits or attaches to
+some other container) and the last child container of that container
+is removed, then the kernel runs the command specified by the contents
+of the "release_agent" file in that hierarchy's root directory,
+supplying the pathname (relative to the mount point of the container
+file system) of the abandoned container.  This enables automatic
+removal of abandoned containers.  The default value of
+notify_on_release in the root container at system boot is disabled
+(0).  The default value of other containers at creation is the current
+value of their parents notify_on_release setting. The default value of
+a container hierarchy's release_agent path is empty.
 
 1.5 How do I use containers ?
 --------------------------
 
-To start a new job that is to be contained within a container, the steps are:
+To start a new job that is to be contained within a container, using
+the "cpuset" container subsystem, the steps are something like:
 
  1) mkdir /dev/container
- 2) mount -t container container /dev/container
+ 2) mount -t container -ocpuset cpuset /dev/container
  3) Create the new container by doing mkdir's and write's (or echo's) in
     the /dev/container virtual file system.
  4) Start a task that will be the "founding father" of the new job.
@@ -147,7 +177,7 @@ For example, the following sequence of c
 named "Charlie", containing just CPUs 2 and 3, and Memory Node 1,
 and then start a subshell 'sh' in that container:
 
-  mount -t container none /dev/container
+  mount -t container cpuset -ocpuset /dev/container
   cd /dev/container
   mkdir Charlie
   cd Charlie
@@ -157,11 +187,6 @@ and then start a subshell 'sh' in that c
   # The next line should display '/Charlie'
   cat /proc/self/container
 
-In the future, a C library interface to containers will likely be
-available.  For now, the only way to query or modify containers is
-via the container file system, using the various cd, mkdir, echo, cat,
-rmdir commands from the shell, or their equivalent from C.
-
 2. Usage Examples and Syntax
 ============================
 
@@ -171,8 +196,15 @@ rmdir commands from the shell, or their 
 Creating, modifying, using the containers can be done through the container
 virtual filesystem.
 
-To mount it, type:
-# mount -t container none /dev/container
+To mount a container hierarchy will all available subsystems, type:
+# mount -t container xxx /dev/container
+
+The "xxx" is not interpreted by the container code, but will appear in
+/proc/mounts so may be any useful identifying string that you like.
+
+To mount a container hierarchy with just the cpuset and numtasks
+subsystems, type:
+# mount -t container -o cpuset,numtasks hier1 /dev/container
 
 Then under /dev/container you can find a tree that corresponds to the
 tree of the containers in the system. For instance, /dev/container
@@ -187,7 +219,8 @@ Now you want to do something with this c
 
 In this directory you can find several files:
 # ls
-notify_on_release  tasks
+notify_on_release release_agent tasks
+(plus whatever files are added by the attached subsystems)
 
 Now attach your shell to this container:
 # /bin/echo $$ > tasks
@@ -214,8 +247,150 @@ If you have several tasks to attach, you
 	...
 # /bin/echo PIDn > tasks
 
+3. Kernel API
+=============
+
+3.1 Overview
+------------
+
+Each kernel subsystem that wants to hook into the generic container
+system needs to create a container_subsys object. This contains
+various methods, which are callbacks from the container system, along
+with a subsystem id which will be assigned by the container system.
+
+Other fields in the container_subsys object include:
+
+- subsys_id: a unique array index for the subsystem, indicating which
+  entry in container->subsys[] this subsystem should be
+  managing. Initialized by container_register_subsys(); prior to this
+  it should be initialized to -1
+
+- hierarchy: an index indicating which hierarchy, if any, this
+  subsystem is currently attached to. If this is -1, then the
+  subsystem is not attached to any hierarchy, and all tasks should be
+  considered to be members of the subsystem's top_container. It should
+  be initialized to -1.
+
+- name: should be initialized to a unique subsystem name prior to
+  calling container_register_subsystem. Should be no longer than
+  MAX_CONTAINER_TYPE_NAMELEN
+
+Each container object created by the system has an array of pointers,
+indexed by subsystem id; this pointer is entirely managed by the
+subsystem; the generic container code will never touch this pointer.
+
+3.2 Synchronization
+-------------------
+
+There are two global mutexes used by the container system. The first
+is the manage_mutex, which should be taken by anything that wants to
+modify a container; The second if the callback_mutex, which should be
+taken by holders of the manage_mutex at the point when they actually
+make changes, and by callbacks from lower-level subsystems that want
+to ensure that no container changes occur.  Note that memory
+allocations cannot be made while holding callback_mutex.
+
+The callback_mutex nests inside the manage_mutex.
+
+In general, the pattern of use is:
+
+1) take manage_mutex
+2) verify that the change is valid and do any necessary allocations\
+3) take callback_mutex
+4) make changes
+5) release callback_mutex
+6) release manage_mutex
+
+See kernel/container.c for more details.
+
+Subsystems can take/release the manage_mutex via the functions
+container_manage_lock()/container_manage_unlock(), and can
+take/release the callback_mutex via the functions
+container_lock()/container_unlock().
+
+Accessing a task's container pointer may be done in the following ways:
+- while holding manage_mutex
+- while holding callback_mutex
+- while holding the task's alloc_lock (via task_lock())
+- inside an rcu_read_lock() section via rcu_dereference()
+
+3.3 Subsystem API
+--------------------------
+
+Each subsystem should call container_register_subsys() with a pointer
+to its subsystem object. This will store the new subsystem id in the
+subsystem subsys_id field and return 0, or a negative error.  There's
+currently no facility for deregestering a subsystem nor for
+registering a subsystem after any containers (other than the default
+"top_container") have been created.
+
+Each subsystem may export the following methods. The only mandatory
+methods are create/destroy. Any others that are null are presumed to
+be successful no-ops.
+
+int create(struct container *cont)
+LL=manage_mutex
+
+The subsystem should set its subsystem pointer for the passed
+container, returning 0 on success or a negative error code. On
+success, the subsystem pointer should point to a structure of type
+container_subsys_state (typically embedded in a larger
+subsystem-specific object), which will be initialized by the container
+system.
+
+void destroy(struct container *cont)
+LL=manage_mutex
+
+The container system is about to destroy the passed container; the
+subsystem should do any necessary cleanup
+
+int can_attach(struct container_subsys *ss, struct container *cont,
+	       struct task_struct *task)
+LL=manage_mutex
+
+Called prior to moving a task into a container; if the subsystem
+returns an error, this will abort the attach operation.  Note that
+this isn't called on a fork.
+
+void attach(struct container_subsys *ss, struct container *cont,
+	    struct container *old_cont, struct task_struct *task)
+LL=manage_mutex & callback_mutex
+
+Called during the attach operation.  The subsystem should do any
+necessary work that can be accomplished without memory allocations or
+sleeping.
+
+void post_attach(struct container_subsys *ss, struct container *cont,
+		 struct container *old_cont, struct task_struct *task)
+LL=manage_mutex
+
+Called after the task has been attached to the container, to allow any
+post-attachment activity that requires memory allocations or blocking.
+
+void fork(struct container_subsy *ss, struct task_struct *task)
+LL=callback_mutex, maybe read_lock(tasklist_lock)
+
+Called when a task is forked into a container. Also called during
+registration for all existing tasks.
+
+void exit(struct container_subsys *ss, struct task_struct *task)
+LL=callback_mutex
+
+Called during task exit
+
+int populate(struct container_subsys *ss, struct container *cont)
+LL=none
+
+Called after creation of a container to allow a subsystem to populate
+the container directory with file entries.  The subsystem should make
+calls to container_add_file() with objects of type cftype (see
+include/linux/container.h for details).  Called during
+container_register_subsys() to populate the root container.  Note that
+although this method can return an error code, the error code is
+currently not always handled well.
+
 
-3. Questions
+4. Questions
 ============
 
 Q: what's up with this '/bin/echo' ?
Index: container-2.6.20-rc1/include/linux/mempolicy.h
===================================================================
--- container-2.6.20-rc1.orig/include/linux/mempolicy.h
+++ container-2.6.20-rc1/include/linux/mempolicy.h
@@ -148,14 +148,6 @@ extern void mpol_rebind_task(struct task
 					const nodemask_t *new);
 extern void mpol_rebind_mm(struct mm_struct *mm, nodemask_t *new);
 extern void mpol_fix_fork_child_flag(struct task_struct *p);
-#define set_cpuset_being_rebound(x) (cpuset_being_rebound = (x))
-
-#ifdef CONFIG_CPUSETS
-#define current_cpuset_is_being_rebound() \
- (cpuset_being_rebound == current->container->cpuset)
-#else
-#define current_cpuset_is_being_rebound() 0
-#endif
 
 extern struct mempolicy default_policy;
 extern struct zonelist *huge_zonelist(struct vm_area_struct *vma,
@@ -173,8 +165,6 @@ static inline void check_highest_zone(en
 int do_migrate_pages(struct mm_struct *mm,
 	const nodemask_t *from_nodes, const nodemask_t *to_nodes, int flags);
 
-extern void *cpuset_being_rebound;	/* Trigger mpol_copy vma rebind */
-
 #else
 
 struct mempolicy {};
@@ -253,8 +243,6 @@ static inline void mpol_fix_fork_child_f
 {
 }
 
-#define set_cpuset_being_rebound(x) do {} while (0)
-
 static inline struct zonelist *huge_zonelist(struct vm_area_struct *vma,
 		unsigned long addr)
 {
Index: container-2.6.20-rc1/include/linux/sched.h
===================================================================
--- container-2.6.20-rc1.orig/include/linux/sched.h
+++ container-2.6.20-rc1/include/linux/sched.h
@@ -1030,7 +1030,7 @@ struct task_struct {
 	int cpuset_mem_spread_rotor;
 #endif
 #ifdef CONFIG_CONTAINERS
-	struct container *container;
+	struct container *container[CONFIG_MAX_CONTAINER_HIERARCHIES];
 #endif
 	struct robust_list_head __user *robust_list;
 #ifdef CONFIG_COMPAT
@@ -1469,7 +1469,7 @@ static inline int thread_group_empty(str
 /*
  * Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring
  * subscriptions and synchronises with wait4().  Also used in procfs.  Also
- * pins the final release of task.io_context.  Also protects ->container.
+ * pins the final release of task.io_context.  Also protects ->container[].
  *
  * Nests both inside and outside of read_lock(&tasklist_lock).
  * It must not be nested with write_lock_irq(&tasklist_lock),
Index: container-2.6.20-rc1/mm/mempolicy.c
===================================================================
--- container-2.6.20-rc1.orig/mm/mempolicy.c
+++ container-2.6.20-rc1/mm/mempolicy.c
@@ -1309,7 +1309,6 @@ EXPORT_SYMBOL(alloc_pages_current);
  * keeps mempolicies cpuset relative after its cpuset moves.  See
  * further kernel/cpuset.c update_nodemask().
  */
-void *cpuset_being_rebound;
 
 /* Slow path of a mempolicy copy */
 struct mempolicy *__mpol_copy(struct mempolicy *old)
@@ -1908,4 +1907,3 @@ out:
 		m->version = (vma != priv->tail_vma) ? vma->vm_start : 0;
 	return 0;
 }
-
Index: container-2.6.20-rc1/init/Kconfig
===================================================================
--- container-2.6.20-rc1.orig/init/Kconfig
+++ container-2.6.20-rc1/init/Kconfig
@@ -241,6 +241,18 @@ config IKCONFIG_PROC
 config CONTAINERS
 	bool
 
+config MAX_CONTAINER_SUBSYS
+	int "Number of container subsystems to support"
+	depends on CONTAINERS
+	range 1 255
+	default 8
+
+config MAX_CONTAINER_HIERARCHIES
+	int "Number of container hierarchies to support"
+	depends on CONTAINERS
+	range 2 255
+	default 4
+
 config CPUSETS
 	bool "Cpuset support"
 	depends on SMP
Index: container-2.6.20-rc1/Documentation/cpusets.txt
===================================================================
--- container-2.6.20-rc1.orig/Documentation/cpusets.txt
+++ container-2.6.20-rc1/Documentation/cpusets.txt
@@ -466,7 +466,7 @@ than stress the kernel.
 To start a new job that is to be contained within a cpuset, the steps are:
 
  1) mkdir /dev/cpuset
- 2) mount -t container none /dev/cpuset
+ 2) mount -t container -ocpuset cpuset /dev/cpuset
  3) Create the new cpuset by doing mkdir's and write's (or echo's) in
     the /dev/cpuset virtual file system.
  4) Start a task that will be the "founding father" of the new job.
@@ -478,7 +478,7 @@ For example, the following sequence of c
 named "Charlie", containing just CPUs 2 and 3, and Memory Node 1,
 and then start a subshell 'sh' in that cpuset:
 
-  mount -t container none /dev/cpuset
+  mount -t container -ocpuset cpuset /dev/cpuset
   cd /dev/cpuset
   mkdir Charlie
   cd Charlie
@@ -488,7 +488,7 @@ and then start a subshell 'sh' in that c
   sh
   # The subshell 'sh' is now running in cpuset Charlie
   # The next line should display '/Charlie'
-  cat /proc/self/container
+  cat /proc/self/cpuset
 
 In the future, a C library interface to cpusets will likely be
 available.  For now, the only way to query or modify cpusets is
@@ -510,7 +510,7 @@ Creating, modifying, using the cpusets c
 virtual filesystem.
 
 To mount it, type:
-# mount -t container none /dev/cpuset
+# mount -t container -o cpuset cpuset /dev/cpuset
 
 Then under /dev/cpuset you can find a tree that corresponds to the
 tree of the cpusets in the system. For instance, /dev/cpuset
@@ -550,6 +550,18 @@ To remove a cpuset, just use rmdir:
 This will fail if the cpuset is in use (has cpusets inside, or has
 processes attached).
 
+Note that for legacy reasons, the "cpuset" filesystem exists as a
+wrapper around the container filesystem.
+
+The command
+
+mount -t cpuset X /dev/cpuset
+
+is equivalent to
+
+mount -t container -ocpuset X /dev/cpuset
+echo "/sbin/cpuset_release_agent" > /dev/cpuset/release_agent
+
 2.2 Adding/removing cpus
 ------------------------
 

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