9 files changed, 1994 insertions, 1 deletions

diff --git a/Documentation/cgroups.txt b/Documentation/cgroups.txt
new file mode 100644
index 000000000000..4717887fd75d
--- /dev/null
+++ b/Documentation/cgroups.txt
@@ -0,0 +1,526 @@
+                                CGROUPS
+                                -------
+
+Written by Paul Menage <menage@google.com> based on Documentation/cpusets.txt
+
+Original copyright statements from cpusets.txt:
+Portions Copyright (C) 2004 BULL SA.
+Portions Copyright (c) 2004-2006 Silicon Graphics, Inc.
+Modified by Paul Jackson <pj@sgi.com>
+Modified by Christoph Lameter <clameter@sgi.com>
+
+CONTENTS:
+=========
+
+1. Control Groups
+  1.1 What are cgroups ?
+  1.2 Why are cgroups needed ?
+  1.3 How are cgroups implemented ?
+  1.4 What does notify_on_release do ?
+  1.5 How do I use cgroups ?
+2. Usage Examples and Syntax
+  2.1 Basic Usage
+  2.2 Attaching processes
+3. Kernel API
+  3.1 Overview
+  3.2 Synchronization
+  3.3 Subsystem API
+4. Questions
+
+1. Control Groups
+==========
+
+1.1 What are cgroups ?
+----------------------
+
+Control Groups provide a mechanism for aggregating/partitioning sets of
+tasks, and all their future children, into hierarchical groups with
+specialized behaviour.
+
+Definitions:
+
+A *cgroup* associates a set of tasks with a set of parameters for one
+or more subsystems.
+
+A *subsystem* is a module that makes use of the task grouping
+facilities provided by cgroups to treat groups of tasks in
+particular ways. A subsystem is typically a "resource controller" that
+schedules a resource or applies per-cgroup limits, but it may be
+anything that wants to act on a group of processes, e.g. a
+virtualization subsystem.
+
+A *hierarchy* is a set of cgroups arranged in a tree, such that
+every task in the system is in exactly one of the cgroups in the
+hierarchy, and a set of subsystems; each subsystem has system-specific
+state attached to each cgroup in the hierarchy.  Each hierarchy has
+an instance of the cgroup virtual filesystem associated with it.
+
+At any one time there may be multiple active hierachies of task
+cgroups. Each hierarchy is a partition of all tasks in the system.
+
+User level code may create and destroy cgroups by name in an
+instance of the cgroup virtual file system, specify and query to
+which cgroup a task is assigned, and list the task pids assigned to
+a cgroup. Those creations and assignments only affect the hierarchy
+associated with that instance of the cgroup file system.
+
+On their own, the only use for cgroups is for simple job
+tracking. The intention is that other subsystems hook into the generic
+cgroup support to provide new attributes for cgroups, such as
+accounting/limiting the resources which processes in a cgroup can
+access. For example, cpusets (see Documentation/cpusets.txt) allows
+you to associate a set of CPUs and a set of memory nodes with the
+tasks in each cgroup.
+
+1.2 Why are cgroups needed ?
+----------------------------
+
+There are multiple efforts to provide process aggregations in the
+Linux kernel, mainly for resource tracking purposes. Such efforts
+include cpusets, CKRM/ResGroups, UserBeanCounters, and virtual server
+namespaces. These all require the basic notion of a
+grouping/partitioning of processes, with newly forked processes ending
+in the same group (cgroup) as their parent process.
+
+The kernel cgroup patch provides the minimum essential kernel
+mechanisms required to efficiently implement such groups. It has
+minimal impact on the system fast paths, and provides hooks for
+specific subsystems such as cpusets to provide additional behaviour as
+desired.
+
+Multiple hierarchy support is provided to allow for situations where
+the division of tasks into cgroups is distinctly different for
+different subsystems - having parallel hierarchies allows each
+hierarchy to be a natural division of tasks, without having to handle
+complex combinations of tasks that would be present if several
+unrelated subsystems needed to be forced into the same tree of
+cgroups.
+
+At one extreme, each resource controller or subsystem could be in a
+separate hierarchy; at the other extreme, all subsystems
+would be attached to the same hierarchy.
+
+As an example of a scenario (originally proposed by vatsa@in.ibm.com)
+that can benefit from multiple hierarchies, consider a large
+university server with various users - students, professors, system
+tasks etc. The resource planning for this server could be along the
+following lines:
+
+       CPU :           Top cpuset
+                       /       \
+               CPUSet1         CPUSet2
+                  |              |
+               (Profs)         (Students)
+
+               In addition (system tasks) are attached to topcpuset (so
+               that they can run anywhere) with a limit of 20%
+
+       Memory : Professors (50%), students (30%), system (20%)
+
+       Disk : Prof (50%), students (30%), system (20%)
+
+       Network : WWW browsing (20%), Network File System (60%), others (20%)
+                               / \
+                       Prof (15%) students (5%)
+
+Browsers like firefox/lynx go into the WWW network class, while (k)nfsd go
+into NFS network class.
+
+At the same time firefox/lynx will share an appropriate CPU/Memory class
+depending on who launched it (prof/student).
+
+With the ability to classify tasks differently for different resources
+(by putting those resource subsystems in different hierarchies) then
+the admin can easily set up a script which receives exec notifications
+and depending on who is launching the browser he can
+
+       # echo browser_pid > /mnt/<restype>/<userclass>/tasks
+
+With only a single hierarchy, he now would potentially have to create
+a separate cgroup for every browser launched and associate it with
+approp network and other resource class.  This may lead to
+proliferation of such cgroups.
+
+Also lets say that the administrator would like to give enhanced network
+access temporarily to a student's browser (since it is night and the user
+wants to do online gaming :)  OR give one of the students simulation
+apps enhanced CPU power,
+
+With ability to write pids directly to resource classes, its just a
+matter of :
+
+       # echo pid > /mnt/network/<new_class>/tasks
+       (after some time)
+       # echo pid > /mnt/network/<orig_class>/tasks
+
+Without this ability, he would have to split the cgroup into
+multiple separate ones and then associate the new cgroups with the
+new resource classes.
+
+
+
+1.3 How are cgroups implemented ?
+---------------------------------
+
+Control Groups extends the kernel as follows:
+
+ - Each task in the system has a reference-counted pointer to a
+   css_set.
+
+ - A css_set contains a set of reference-counted pointers to
+   cgroup_subsys_state objects, one for each cgroup subsystem
+   registered in the system. There is no direct link from a task to
+   the cgroup of which it's a member in each hierarchy, but this
+   can be determined by following pointers through the
+   cgroup_subsys_state objects. This is because accessing the
+   subsystem state is something that's expected to happen frequently
+   and in performance-critical code, whereas operations that require a
+   task's actual cgroup assignments (in particular, moving between
+   cgroups) are less common.
+
+ - A cgroup hierarchy filesystem can be mounted  for browsing and
+   manipulation from user space.
+
+ - You can list all the tasks (by pid) attached to any cgroup.
+
+The implementation of cgroups requires a few, simple hooks
+into the rest of the kernel, none in performance critical paths:
+
+ - in init/main.c, to initialize the root cgroups and initial
+   css_set at system boot.
+
+ - in fork and exit, to attach and detach a task from its css_set.
+
+In addition a new file system, of type "cgroup" may be mounted, to
+enable browsing and modifying the cgroups presently known to the
+kernel.  When mounting a cgroup hierarchy, you may specify a
+comma-separated list of subsystems to mount as the filesystem mount
+options.  By default, mounting the cgroup 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 activated, associated with the requested subsystems.
+
+It's not currently possible to bind a new subsystem to an active
+cgroup hierarchy, or to unbind a subsystem from an active cgroup
+hierarchy. This may be possible in future, but is fraught with nasty
+error-recovery issues.
+
+When a cgroup filesystem is unmounted, if there are any
+child cgroups created below the top-level cgroup, that hierarchy
+will remain active even though unmounted; if there are no
+child cgroups then the hierarchy will be deactivated.
+
+No new system calls are added for cgroups - all support for
+querying and modifying cgroups is via this cgroup file system.
+
+Each task under /proc has an added file named 'cgroup' displaying,
+for each active hierarchy, the subsystem names and the cgroup name
+as the path relative to the root of the cgroup file system.
+
+Each cgroup is represented by a directory in the cgroup file system
+containing the following files describing that cgroup:
+
+ - tasks: list of tasks (by pid) attached to that cgroup
+ - notify_on_release flag: run /sbin/cgroup_release_agent on exit?
+
+Other subsystems such as cpusets may add additional files in each
+cgroup dir
+
+New cgroups are created using the mkdir system call or shell
+command.  The properties of a cgroup, such as its flags, are
+modified by writing to the appropriate file in that cgroups
+directory, as listed above.
+
+The named hierarchical structure of nested cgroups allows partitioning
+a large system into nested, dynamically changeable, "soft-partitions".
+
+The attachment of each task, automatically inherited at fork by any
+children of that task, to a cgroup allows organizing the work load
+on a system into related sets of tasks.  A task may be re-attached to
+any other cgroup, if allowed by the permissions on the necessary
+cgroup file system directories.
+
+When a task is moved from one cgroup to another, it gets a new
+css_set pointer - if there's an already existing css_set with the
+desired collection of cgroups then that group is reused, else a new
+css_set is allocated. Note that the current implementation uses a
+linear search to locate an appropriate existing css_set, so isn't
+very efficient. A future version will use a hash table for better
+performance.
+
+The use of a Linux virtual file system (vfs) to represent the
+cgroup hierarchy provides for a familiar permission and name space
+for cgroups, with a minimum of additional kernel code.
+
+1.4 What does notify_on_release do ?
+------------------------------------
+
+*** notify_on_release is disabled in the current patch set. It will be
+*** reactivated in a future patch in a less-intrusive manner
+
+If the notify_on_release flag is enabled (1) in a cgroup, then
+whenever the last task in the cgroup leaves (exits or attaches to
+some other cgroup) and the last child cgroup of that cgroup
+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 cgroup
+file system) of the abandoned cgroup.  This enables automatic
+removal of abandoned cgroups.  The default value of
+notify_on_release in the root cgroup at system boot is disabled
+(0).  The default value of other cgroups at creation is the current
+value of their parents notify_on_release setting. The default value of
+a cgroup hierarchy's release_agent path is empty.
+
+1.5 How do I use cgroups ?
+--------------------------
+
+To start a new job that is to be contained within a cgroup, using
+the "cpuset" cgroup subsystem, the steps are something like:
+
+ 1) mkdir /dev/cgroup
+ 2) mount -t cgroup -ocpuset cpuset /dev/cgroup
+ 3) Create the new cgroup by doing mkdir's and write's (or echo's) in
+    the /dev/cgroup virtual file system.
+ 4) Start a task that will be the "founding father" of the new job.
+ 5) Attach that task to the new cgroup by writing its pid to the
+    /dev/cgroup tasks file for that cgroup.
+ 6) fork, exec or clone the job tasks from this founding father task.
+
+For example, the following sequence of commands will setup a cgroup
+named "Charlie", containing just CPUs 2 and 3, and Memory Node 1,
+and then start a subshell 'sh' in that cgroup:
+
+  mount -t cgroup cpuset -ocpuset /dev/cgroup
+  cd /dev/cgroup
+  mkdir Charlie
+  cd Charlie
+  /bin/echo 2-3 > cpus
+  /bin/echo 1 > mems
+  /bin/echo $$ > tasks
+  sh
+  # The subshell 'sh' is now running in cgroup Charlie
+  # The next line should display '/Charlie'
+  cat /proc/self/cgroup
+
+2. Usage Examples and Syntax
+============================
+
+2.1 Basic Usage
+---------------
+
+Creating, modifying, using the cgroups can be done through the cgroup
+virtual filesystem.
+
+To mount a cgroup hierarchy will all available subsystems, type:
+# mount -t cgroup xxx /dev/cgroup
+
+The "xxx" is not interpreted by the cgroup code, but will appear in
+/proc/mounts so may be any useful identifying string that you like.
+
+To mount a cgroup hierarchy with just the cpuset and numtasks
+subsystems, type:
+# mount -t cgroup -o cpuset,numtasks hier1 /dev/cgroup
+
+To change the set of subsystems bound to a mounted hierarchy, just
+remount with different options:
+
+# mount -o remount,cpuset,ns  /dev/cgroup
+
+Note that changing the set of subsystems is currently only supported
+when the hierarchy consists of a single (root) cgroup. Supporting
+the ability to arbitrarily bind/unbind subsystems from an existing
+cgroup hierarchy is intended to be implemented in the future.
+
+Then under /dev/cgroup you can find a tree that corresponds to the
+tree of the cgroups in the system. For instance, /dev/cgroup
+is the cgroup that holds the whole system.
+
+If you want to create a new cgroup under /dev/cgroup:
+# cd /dev/cgroup
+# mkdir my_cgroup
+
+Now you want to do something with this cgroup.
+# cd my_cgroup
+
+In this directory you can find several files:
+# ls
+notify_on_release release_agent tasks
+(plus whatever files are added by the attached subsystems)
+
+Now attach your shell to this cgroup:
+# /bin/echo $$ > tasks
+
+You can also create cgroups inside your cgroup by using mkdir in this
+directory.
+# mkdir my_sub_cs
+
+To remove a cgroup, just use rmdir:
+# rmdir my_sub_cs
+
+This will fail if the cgroup is in use (has cgroups inside, or
+has processes attached, or is held alive by other subsystem-specific
+reference).
+
+2.2 Attaching processes
+-----------------------
+
+# /bin/echo PID > tasks
+
+Note that it is PID, not PIDs. You can only attach ONE task at a time.
+If you have several tasks to attach, you have to do it one after another:
+
+# /bin/echo PID1 > tasks
+# /bin/echo PID2 > tasks
+        ...
+# /bin/echo PIDn > tasks
+
+3. Kernel API
+=============
+
+3.1 Overview
+------------
+
+Each kernel subsystem that wants to hook into the generic cgroup
+system needs to create a cgroup_subsys object. This contains
+various methods, which are callbacks from the cgroup system, along
+with a subsystem id which will be assigned by the cgroup system.
+
+Other fields in the cgroup_subsys object include:
+
+- subsys_id: a unique array index for the subsystem, indicating which
+  entry in cgroup->subsys[] this subsystem should be
+  managing. Initialized by cgroup_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_cgroup. It should
+  be initialized to -1.
+
+- name: should be initialized to a unique subsystem name prior to
+  calling cgroup_register_subsystem. Should be no longer than
+  MAX_CGROUP_TYPE_NAMELEN
+
+Each cgroup object created by the system has an array of pointers,
+indexed by subsystem id; this pointer is entirely managed by the
+subsystem; the generic cgroup code will never touch this pointer.
+
+3.2 Synchronization
+-------------------
+
+There is a global mutex, cgroup_mutex, used by the cgroup
+system. This should be taken by anything that wants to modify a
+cgroup. It may also be taken to prevent cgroups from being
+modified, but more specific locks may be more appropriate in that
+situation.
+
+See kernel/cgroup.c for more details.
+
+Subsystems can take/release the cgroup_mutex via the functions
+cgroup_lock()/cgroup_unlock(), and can
+take/release the callback_mutex via the functions
+cgroup_lock()/cgroup_unlock().
+
+Accessing a task's cgroup pointer may be done in the following ways:
+- while holding cgroup_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:
+
+- add an entry in linux/cgroup_subsys.h
+- define a cgroup_subsys object called <name>_subsys
+
+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.
+
+struct cgroup_subsys_state *create(struct cgroup *cont)
+LL=cgroup_mutex
+
+Called to create a subsystem state object for a cgroup. The
+subsystem should allocate its subsystem state object for the passed
+cgroup, returning a pointer to the new object on success or a
+negative error code. On success, the subsystem pointer should point to
+a structure of type cgroup_subsys_state (typically embedded in a
+larger subsystem-specific object), which will be initialized by the
+cgroup system. Note that this will be called at initialization to
+create the root subsystem state for this subsystem; this case can be
+identified by the passed cgroup object having a NULL parent (since
+it's the root of the hierarchy) and may be an appropriate place for
+initialization code.
+
+void destroy(struct cgroup *cont)
+LL=cgroup_mutex
+
+The cgroup system is about to destroy the passed cgroup; the
+subsystem should do any necessary cleanup
+
+int can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
+               struct task_struct *task)
+LL=cgroup_mutex
+
+Called prior to moving a task into a cgroup; if the subsystem
+returns an error, this will abort the attach operation.  If a NULL
+task is passed, then a successful result indicates that *any*
+unspecified task can be moved into the cgroup. Note that this isn't
+called on a fork. If this method returns 0 (success) then this should
+remain valid while the caller holds cgroup_mutex.
+
+void attach(struct cgroup_subsys *ss, struct cgroup *cont,
+            struct cgroup *old_cont, struct task_struct *task)
+LL=cgroup_mutex
+
+
+Called after the task has been attached to the cgroup, to allow any
+post-attachment activity that requires memory allocations or blocking.
+
+void fork(struct cgroup_subsy *ss, struct task_struct *task)
+LL=callback_mutex, maybe read_lock(tasklist_lock)
+
+Called when a task is forked into a cgroup. Also called during
+registration for all existing tasks.
+
+void exit(struct cgroup_subsys *ss, struct task_struct *task)
+LL=callback_mutex
+
+Called during task exit
+
+int populate(struct cgroup_subsys *ss, struct cgroup *cont)
+LL=none
+
+Called after creation of a cgroup to allow a subsystem to populate
+the cgroup directory with file entries.  The subsystem should make
+calls to cgroup_add_file() with objects of type cftype (see
+include/linux/cgroup.h for details).  Note that although this
+method can return an error code, the error code is currently not
+always handled well.
+
+void bind(struct cgroup_subsys *ss, struct cgroup *root)
+LL=callback_mutex
+
+Called when a cgroup subsystem is rebound to a different hierarchy
+and root cgroup. Currently this will only involve movement between
+the default hierarchy (which never has sub-cgroups) and a hierarchy
+that is being created/destroyed (and hence has no sub-cgroups).
+
+4. Questions
+============
+
+Q: what's up with this '/bin/echo' ?
+A: bash's builtin 'echo' command does not check calls to write() against
+   errors. If you use it in the cgroup file system, you won't be
+   able to tell whether a command succeeded or failed.
+
+Q: When I attach processes, only the first of the line gets really attached !
+A: We can only return one error code per call to write(). So you should also
+   put only ONE pid.
+
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
new file mode 100644
index 000000000000..60735dcf427a
--- /dev/null
+++ b/include/linux/cgroup.h
@@ -0,0 +1,214 @@
+#ifndef _LINUX_CGROUP_H
+#define _LINUX_CGROUP_H
+/*
+ *  cgroup interface
+ *
+ *  Copyright (C) 2003 BULL SA
+ *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
+ *
+ */
+
+#include <linux/sched.h>
+#include <linux/kref.h>
+#include <linux/cpumask.h>
+#include <linux/nodemask.h>
+#include <linux/rcupdate.h>
+
+#ifdef CONFIG_CGROUPS
+
+struct cgroupfs_root;
+struct cgroup_subsys;
+struct inode;
+
+extern int cgroup_init_early(void);
+extern int cgroup_init(void);
+extern void cgroup_init_smp(void);
+extern void cgroup_lock(void);
+extern void cgroup_unlock(void);
+
+/* Per-subsystem/per-cgroup state maintained by the system. */
+struct cgroup_subsys_state {
+        /* The cgroup that this subsystem is attached to. Useful
+         * for subsystems that want to know about the cgroup
+         * hierarchy structure */
+        struct cgroup *cgroup;
+
+        /* State maintained by the cgroup system to allow
+         * subsystems to be "busy". Should be accessed via css_get()
+         * and css_put() */
+
+        atomic_t refcnt;
+
+        unsigned long flags;
+};
+
+/* bits in struct cgroup_subsys_state flags field */
+enum {
+        CSS_ROOT, /* This CSS is the root of the subsystem */
+};
+
+/*
+ * Call css_get() to hold a reference on the cgroup;
+ *
+ */
+
+static inline void css_get(struct cgroup_subsys_state *css)
+{
+        /* We don't need to reference count the root state */
+        if (!test_bit(CSS_ROOT, &css->flags))
+                atomic_inc(&css->refcnt);
+}
+/*
+ * css_put() should be called to release a reference taken by
+ * css_get()
+ */
+
+static inline void css_put(struct cgroup_subsys_state *css)
+{
+        if (!test_bit(CSS_ROOT, &css->flags))
+                atomic_dec(&css->refcnt);
+}
+
+struct cgroup {
+        unsigned long flags;            /* "unsigned long" so bitops work */
+
+        /* count users of this cgroup. >0 means busy, but doesn't
+         * necessarily indicate the number of tasks in the
+         * cgroup */
+        atomic_t count;
+
+        /*
+         * We link our 'sibling' struct into our parent's 'children'.
+         * Our children link their 'sibling' into our 'children'.
+         */
+        struct list_head sibling;       /* my parent's children */
+        struct list_head children;      /* my children */
+
+        struct cgroup *parent;  /* my parent */
+        struct dentry *dentry;          /* cgroup fs entry */
+
+        /* Private pointers for each registered subsystem */
+        struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
+
+        struct cgroupfs_root *root;
+        struct cgroup *top_cgroup;
+};
+
+/* struct cftype:
+ *
+ * The files in the cgroup filesystem mostly have a very simple read/write
+ * handling, some common function will take care of it. Nevertheless some cases
+ * (read tasks) are special and therefore I define this structure for every
+ * kind of file.
+ *
+ *
+ * When reading/writing to a file:
+ *      - the cgroup to use in file->f_dentry->d_parent->d_fsdata
+ *      - the 'cftype' of the file is file->f_dentry->d_fsdata
+ */
+
+#define MAX_CFTYPE_NAME 64
+struct cftype {
+        /* 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 cgroup *cont, struct cftype *cft,
+                         struct file *file,
+                         char __user *buf, size_t nbytes, loff_t *ppos);
+        /*
+         * read_uint() is a shortcut for the common case of returning a
+         * single integer. Use it in place of read()
+         */
+        u64 (*read_uint) (struct cgroup *cont, struct cftype *cft);
+        ssize_t (*write) (struct cgroup *cont, struct cftype *cft,
+                          struct file *file,
+                          const char __user *buf, size_t nbytes, loff_t *ppos);
+        int (*release) (struct inode *inode, struct file *file);
+};
+
+/* Add a new file to the given cgroup directory. Should only be
+ * called by subsystems from within a populate() method */
+int cgroup_add_file(struct cgroup *cont, struct cgroup_subsys *subsys,
+                       const struct cftype *cft);
+
+/* Add a set of new files to the given cgroup directory. Should
+ * only be called by subsystems from within a populate() method */
+int cgroup_add_files(struct cgroup *cont,
+                        struct cgroup_subsys *subsys,
+                        const struct cftype cft[],
+                        int count);
+
+int cgroup_is_removed(const struct cgroup *cont);
+
+int cgroup_path(const struct cgroup *cont, char *buf, int buflen);
+
+/* Return true if the cgroup is a descendant of the current cgroup */
+int cgroup_is_descendant(const struct cgroup *cont);
+
+/* Control Group subsystem type. See Documentation/cgroups.txt for details */
+
+struct cgroup_subsys {
+        struct cgroup_subsys_state *(*create)(struct cgroup_subsys *ss,
+                                                  struct cgroup *cont);
+        void (*destroy)(struct cgroup_subsys *ss, struct cgroup *cont);
+        int (*can_attach)(struct cgroup_subsys *ss,
+                          struct cgroup *cont, struct task_struct *tsk);
+        void (*attach)(struct cgroup_subsys *ss, struct cgroup *cont,
+                        struct cgroup *old_cont, struct task_struct *tsk);
+        void (*fork)(struct cgroup_subsys *ss, struct task_struct *task);
+        void (*exit)(struct cgroup_subsys *ss, struct task_struct *task);
+        int (*populate)(struct cgroup_subsys *ss,
+                        struct cgroup *cont);
+        void (*bind)(struct cgroup_subsys *ss, struct cgroup *root);
+        int subsys_id;
+        int active;
+        int early_init;
+#define MAX_CGROUP_TYPE_NAMELEN 32
+        const char *name;
+
+        /* Protected by RCU */
+        struct cgroupfs_root *root;
+
+        struct list_head sibling;
+
+        void *private;
+};
+
+#define SUBSYS(_x) extern struct cgroup_subsys _x ## _subsys;
+#include <linux/cgroup_subsys.h>
+#undef SUBSYS
+
+static inline struct cgroup_subsys_state *cgroup_subsys_state(
+        struct cgroup *cont, int subsys_id)
+{
+        return cont->subsys[subsys_id];
+}
+
+static inline struct cgroup_subsys_state *task_subsys_state(
+        struct task_struct *task, int subsys_id)
+{
+        return rcu_dereference(task->cgroups.subsys[subsys_id]);
+}
+
+static inline struct cgroup* task_cgroup(struct task_struct *task,
+                                               int subsys_id)
+{
+        return task_subsys_state(task, subsys_id)->cgroup;
+}
+
+int cgroup_path(const struct cgroup *cont, char *buf, int buflen);
+
+#else /* !CONFIG_CGROUPS */
+
+static inline int cgroup_init_early(void) { return 0; }
+static inline int cgroup_init(void) { return 0; }
+static inline void cgroup_init_smp(void) {}
+
+static inline void cgroup_lock(void) {}
+static inline void cgroup_unlock(void) {}
+
+#endif /* !CONFIG_CGROUPS */
+
+#endif /* _LINUX_CGROUP_H */
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
new file mode 100644
index 000000000000..f8eddbbcad9a
--- /dev/null
+++ b/include/linux/cgroup_subsys.h
@@ -0,0 +1,10 @@
+/* Add subsystem definitions of the form SUBSYS(<name>) in this
+ * file. Surround each one by a line of comment markers so that
+ * patches don't collide
+ */
+
+/* */
+
+/* */
+
+/* */
diff --git a/include/linux/magic.h b/include/linux/magic.h
index 722d4755060f..1fa0c2ce4dec 100644
--- a/include/linux/magic.h
+++ b/include/linux/magic.h
@@ -37,6 +37,7 @@
 
 #define SMB_SUPER_MAGIC         0x517B
 #define USBDEVICE_SUPER_MAGIC   0x9fa2
+#define CGROUP_SUPER_MAGIC      0x27e0eb
 
 #define FUTEXFS_SUPER_MAGIC     0xBAD1DEA
 #define INOTIFYFS_SUPER_MAGIC   0x2BAD1DEA
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 10a83d8d5775..af2ed4bae678 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -894,6 +894,34 @@ struct sched_entity {
 #endif
 };
 
+#ifdef CONFIG_CGROUPS
+
+#define SUBSYS(_x) _x ## _subsys_id,
+enum cgroup_subsys_id {
+#include <linux/cgroup_subsys.h>
+        CGROUP_SUBSYS_COUNT
+};
+#undef SUBSYS
+
+/* A css_set is a structure holding pointers to a set of
+ * cgroup_subsys_state objects.
+ */
+
+struct css_set {
+
+        /* 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 cgroup, but result
+         * in increased space usage if tasks are in wildly different
+         * groupings across different hierarchies. This array is
+         * immutable after creation */
+        struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
+
+};
+
+#endif /* CONFIG_CGROUPS */
+
 struct task_struct {
         volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */
         void *stack;
@@ -1130,6 +1158,9 @@ struct task_struct {
         int cpuset_mems_generation;
         int cpuset_mem_spread_rotor;
 #endif
+#ifdef CONFIG_CGROUPS
+        struct css_set cgroups;
+#endif
 #ifdef CONFIG_FUTEX
         struct robust_list_head __user *robust_list;
 #ifdef CONFIG_COMPAT
@@ -1625,7 +1656,8 @@ static inline int thread_group_empty(struct task_struct *p)
 /*
  * 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 ->cpuset.
+ * pins the final release of task.io_context.  Also protects ->cpuset and
+ * ->cgroup.subsys[].
  *
  * Nests both inside and outside of read_lock(&tasklist_lock).
  * It must not be nested with write_lock_irq(&tasklist_lock),
diff --git a/init/Kconfig b/init/Kconfig
index a29a688c47d3..51b3d14f44f1 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -270,6 +270,14 @@ config LOG_BUF_SHIFT
                      13 =>  8 KB
                      12 =>  4 KB
 
+config CGROUPS
+        bool "Control Group support"
+        help
+          This option will let you use process cgroup subsystems
+          such as Cpusets
+
+          Say N if unsure.
+
 config CPUSETS
         bool "Cpuset support"
         depends on SMP
diff --git a/init/main.c b/init/main.c
index 9def935ab13a..0dd0e7a1f632 100644
--- a/init/main.c
+++ b/init/main.c
@@ -39,6 +39,7 @@
 #include <linux/writeback.h>
 #include <linux/cpu.h>
 #include <linux/cpuset.h>
+#include <linux/cgroup.h>
 #include <linux/efi.h>
 #include <linux/tick.h>
 #include <linux/interrupt.h>
@@ -523,6 +524,7 @@ asmlinkage void __init start_kernel(void)
          */
         unwind_init();
         lockdep_init();
+        cgroup_init_early();
 
         local_irq_disable();
         early_boot_irqs_off();
@@ -640,6 +642,7 @@ asmlinkage void __init start_kernel(void)
 #ifdef CONFIG_PROC_FS
         proc_root_init();
 #endif
+        cgroup_init();
         cpuset_init();
         taskstats_init_early();
         delayacct_init();
diff --git a/kernel/Makefile b/kernel/Makefile
index 001bd3b65dd1..ea8c8a12e19a 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -36,6 +36,7 @@ obj-$(CONFIG_PM) += power/
 obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
 obj-$(CONFIG_KEXEC) += kexec.o
 obj-$(CONFIG_COMPAT) += compat.o
+obj-$(CONFIG_CGROUPS) += cgroup.o
 obj-$(CONFIG_CPUSETS) += cpuset.o
 obj-$(CONFIG_IKCONFIG) += configs.o
 obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
new file mode 100644
index 000000000000..6ba857bec71b
--- /dev/null
+++ b/kernel/cgroup.c
@@ -0,0 +1,1198 @@
+/*
+ *  kernel/cgroup.c
+ *
+ *  Generic process-grouping system.
+ *
+ *  Based originally on the cpuset system, extracted by Paul Menage
+ *  Copyright (C) 2006 Google, Inc
+ *
+ *  Copyright notices from the original cpuset code:
+ *  --------------------------------------------------
+ *  Copyright (C) 2003 BULL SA.
+ *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
+ *
+ *  Portions derived from Patrick Mochel's sysfs code.
+ *  sysfs is Copyright (c) 2001-3 Patrick Mochel
+ *
+ *  2003-10-10 Written by Simon Derr.
+ *  2003-10-22 Updates by Stephen Hemminger.
+ *  2004 May-July Rework by Paul Jackson.
+ *  ---------------------------------------------------
+ *
+ *  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
+ *  distribution for more details.
+ */
+
+#include <linux/cgroup.h>
+#include <linux/errno.h>
+#include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/mm.h>
+#include <linux/mutex.h>
+#include <linux/mount.h>
+#include <linux/pagemap.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include <linux/magic.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+
+#include <asm/atomic.h>
+
+/* Generate an array of cgroup subsystem pointers */
+#define SUBSYS(_x) &_x ## _subsys,
+
+static struct cgroup_subsys *subsys[] = {
+#include <linux/cgroup_subsys.h>
+};
+
+/*
+ * A cgroupfs_root represents the root of a cgroup hierarchy,
+ * and may be associated with a superblock to form an active
+ * hierarchy
+ */
+struct cgroupfs_root {
+        struct super_block *sb;
+
+        /*
+         * The bitmask of subsystems intended to be attached to this
+         * hierarchy
+         */
+        unsigned long subsys_bits;
+
+        /* The bitmask of subsystems currently attached to this hierarchy */
+        unsigned long actual_subsys_bits;
+
+        /* A list running through the attached subsystems */
+        struct list_head subsys_list;
+
+        /* The root cgroup for this hierarchy */
+        struct cgroup top_cgroup;
+
+        /* Tracks how many cgroups are currently defined in hierarchy.*/
+        int number_of_cgroups;
+
+        /* A list running through the mounted hierarchies */
+        struct list_head root_list;
+
+        /* Hierarchy-specific flags */
+        unsigned long flags;
+};
+
+
+/*
+ * The "rootnode" hierarchy is the "dummy hierarchy", reserved for the
+ * subsystems that are otherwise unattached - it never has more than a
+ * single cgroup, and all tasks are part of that cgroup.
+ */
+static struct cgroupfs_root rootnode;
+
+/* The list of hierarchy roots */
+
+static LIST_HEAD(roots);
+
+/* dummytop is a shorthand for the dummy hierarchy's top cgroup */
+#define dummytop (&rootnode.top_cgroup)
+
+/* 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 do extra work in the fork/exit path if none of the
+ * subsystems need to be called.
+ */
+static int need_forkexit_callback;
+
+/* bits in struct cgroup flags field */
+enum {
+        CONT_REMOVED,
+};
+
+/* convenient tests for these bits */
+inline int cgroup_is_removed(const struct cgroup *cont)
+{
+        return test_bit(CONT_REMOVED, &cont->flags);
+}
+
+/* bits in struct cgroupfs_root flags field */
+enum {
+        ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
+};
+
+/*
+ * for_each_subsys() allows you to iterate on each subsystem attached to
+ * an active hierarchy
+ */
+#define for_each_subsys(_root, _ss) \
+list_for_each_entry(_ss, &_root->subsys_list, sibling)
+
+/* for_each_root() allows you to iterate across the active hierarchies */
+#define for_each_root(_root) \
+list_for_each_entry(_root, &roots, root_list)
+
+/*
+ * There is one global cgroup mutex. We also require taking
+ * task_lock() when dereferencing a task's cgroup subsys pointers.
+ * See "The task_lock() exception", at the end of this comment.
+ *
+ * A task must hold cgroup_mutex to modify cgroups.
+ *
+ * Any task can increment and decrement the count field without lock.
+ * So in general, code holding cgroup_mutex can't rely on the count
+ * field not changing.  However, if the count goes to zero, then only
+ * attach_task() can increment it again.  Because a count of zero
+ * means that no tasks are currently attached, therefore there is no
+ * way a task attached to that cgroup can fork (the other way to
+ * increment the count).  So code holding cgroup_mutex can safely
+ * assume that if the count is zero, it will stay zero. Similarly, if
+ * a task holds cgroup_mutex on a cgroup with zero count, it
+ * knows that the cgroup won't be removed, as cgroup_rmdir()
+ * needs that mutex.
+ *
+ * The cgroup_common_file_write handler for operations that modify
+ * the cgroup hierarchy holds cgroup_mutex across the entire operation,
+ * single threading all such cgroup modifications across the system.
+ *
+ * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
+ * (usually) take cgroup_mutex.  These are the two most performance
+ * critical pieces of code here.  The exception occurs on cgroup_exit(),
+ * when a task in a notify_on_release cgroup exits.  Then cgroup_mutex
+ * is taken, and if the cgroup count is zero, a usermode call made
+ * to /sbin/cgroup_release_agent with the name of the cgroup (path
+ * relative to the root of cgroup file system) as the argument.
+ *
+ * A cgroup can only be deleted if both its 'count' of using tasks
+ * is zero, and its list of 'children' cgroups is empty.  Since all
+ * tasks in the system use _some_ cgroup, and since there is always at
+ * least one task in the system (init, pid == 1), therefore, top_cgroup
+ * always has either children cgroups and/or using tasks.  So we don't
+ * need a special hack to ensure that top_cgroup cannot be deleted.
+ *
+ *      The task_lock() exception
+ *
+ * The need for this exception arises from the action of
+ * attach_task(), which overwrites one tasks cgroup pointer with
+ * another.  It does so using cgroup_mutexe, however there are
+ * several performance critical places that need to reference
+ * task->cgroup without the expense of grabbing a system global
+ * mutex.  Therefore except as noted below, when dereferencing or, as
+ * in attach_task(), modifying a task'ss cgroup pointer we use
+ * task_lock(), which acts on a spinlock (task->alloc_lock) already in
+ * the task_struct routinely used for such matters.
+ *
+ * P.S.  One more locking exception.  RCU is used to guard the
+ * update of a tasks cgroup pointer by attach_task()
+ */
+
+static DEFINE_MUTEX(cgroup_mutex);
+
+/**
+ * cgroup_lock - lock out any changes to cgroup structures
+ *
+ */
+
+void cgroup_lock(void)
+{
+        mutex_lock(&cgroup_mutex);
+}
+
+/**
+ * cgroup_unlock - release lock on cgroup changes
+ *
+ * Undo the lock taken in a previous cgroup_lock() call.
+ */
+
+void cgroup_unlock(void)
+{
+        mutex_unlock(&cgroup_mutex);
+}
+
+/*
+ * A couple of forward declarations required, due to cyclic reference loop:
+ * cgroup_mkdir -> cgroup_create -> cgroup_populate_dir ->
+ * cgroup_add_file -> cgroup_create_file -> cgroup_dir_inode_operations
+ * -> cgroup_mkdir.
+ */
+
+static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode);
+static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
+static int cgroup_populate_dir(struct cgroup *cont);
+static struct inode_operations cgroup_dir_inode_operations;
+
+static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
+{
+        struct inode *inode = new_inode(sb);
+        static struct backing_dev_info cgroup_backing_dev_info = {
+                .capabilities   = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+        };
+
+        if (inode) {
+                inode->i_mode = mode;
+                inode->i_uid = current->fsuid;
+                inode->i_gid = current->fsgid;
+                inode->i_blocks = 0;
+                inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
+                inode->i_mapping->backing_dev_info = &cgroup_backing_dev_info;
+        }
+        return inode;
+}
+
+static void cgroup_diput(struct dentry *dentry, struct inode *inode)
+{
+        /* is dentry a directory ? if so, kfree() associated cgroup */
+        if (S_ISDIR(inode->i_mode)) {
+                struct cgroup *cont = dentry->d_fsdata;
+                BUG_ON(!(cgroup_is_removed(cont)));
+                kfree(cont);
+        }
+        iput(inode);
+}
+
+static void remove_dir(struct dentry *d)
+{
+        struct dentry *parent = dget(d->d_parent);
+
+        d_delete(d);
+        simple_rmdir(parent->d_inode, d);
+        dput(parent);
+}
+
+static void cgroup_clear_directory(struct dentry *dentry)
+{
+        struct list_head *node;
+
+        BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
+        spin_lock(&dcache_lock);
+        node = dentry->d_subdirs.next;
+        while (node != &dentry->d_subdirs) {
+                struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
+                list_del_init(node);
+                if (d->d_inode) {
+                        /* This should never be called on a cgroup
+                         * directory with child cgroups */
+                        BUG_ON(d->d_inode->i_mode & S_IFDIR);
+                        d = dget_locked(d);
+                        spin_unlock(&dcache_lock);
+                        d_delete(d);
+                        simple_unlink(dentry->d_inode, d);
+                        dput(d);
+                        spin_lock(&dcache_lock);
+                }
+                node = dentry->d_subdirs.next;
+        }
+        spin_unlock(&dcache_lock);
+}
+
+/*
+ * NOTE : the dentry must have been dget()'ed
+ */
+static void cgroup_d_remove_dir(struct dentry *dentry)
+{
+        cgroup_clear_directory(dentry);
+
+        spin_lock(&dcache_lock);
+        list_del_init(&dentry->d_u.d_child);
+        spin_unlock(&dcache_lock);
+        remove_dir(dentry);
+}
+
+static int rebind_subsystems(struct cgroupfs_root *root,
+                              unsigned long final_bits)
+{
+        unsigned long added_bits, removed_bits;
+        struct cgroup *cont = &root->top_cgroup;
+        int i;
+
+        removed_bits = root->actual_subsys_bits & ~final_bits;
+        added_bits = final_bits & ~root->actual_subsys_bits;
+        /* Check that any added subsystems are currently free */
+        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+                unsigned long long bit = 1ull << i;
+                struct cgroup_subsys *ss = subsys[i];
+                if (!(bit & added_bits))
+                        continue;
+                if (ss->root != &rootnode) {
+                        /* Subsystem isn't free */
+                        return -EBUSY;
+                }
+        }
+
+        /* Currently we don't handle adding/removing subsystems when
+         * any child cgroups exist. This is theoretically supportable
+         * but involves complex error handling, so it's being left until
+         * later */
+        if (!list_empty(&cont->children))
+                return -EBUSY;
+
+        /* Process each subsystem */
+        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+                struct cgroup_subsys *ss = subsys[i];
+                unsigned long bit = 1UL << i;
+                if (bit & added_bits) {
+                        /* We're binding this subsystem to this hierarchy */
+                        BUG_ON(cont->subsys[i]);
+                        BUG_ON(!dummytop->subsys[i]);
+                        BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
+                        cont->subsys[i] = dummytop->subsys[i];
+                        cont->subsys[i]->cgroup = cont;
+                        list_add(&ss->sibling, &root->subsys_list);
+                        rcu_assign_pointer(ss->root, root);
+                        if (ss->bind)
+                                ss->bind(ss, cont);
+
+                } else if (bit & removed_bits) {
+                        /* We're removing this subsystem */
+                        BUG_ON(cont->subsys[i] != dummytop->subsys[i]);
+                        BUG_ON(cont->subsys[i]->cgroup != cont);
+                        if (ss->bind)
+                                ss->bind(ss, dummytop);
+                        dummytop->subsys[i]->cgroup = dummytop;
+                        cont->subsys[i] = NULL;
+                        rcu_assign_pointer(subsys[i]->root, &rootnode);
+                        list_del(&ss->sibling);
+                } else if (bit & final_bits) {
+                        /* Subsystem state should already exist */
+                        BUG_ON(!cont->subsys[i]);
+                } else {
+                        /* Subsystem state shouldn't exist */
+                        BUG_ON(cont->subsys[i]);
+                }
+        }
+        root->subsys_bits = root->actual_subsys_bits = final_bits;
+        synchronize_rcu();
+
+        return 0;
+}
+
+static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
+{
+        struct cgroupfs_root *root = vfs->mnt_sb->s_fs_info;
+        struct cgroup_subsys *ss;
+
+        mutex_lock(&cgroup_mutex);
+        for_each_subsys(root, ss)
+                seq_printf(seq, ",%s", ss->name);
+        if (test_bit(ROOT_NOPREFIX, &root->flags))
+                seq_puts(seq, ",noprefix");
+        mutex_unlock(&cgroup_mutex);
+        return 0;
+}
+
+struct cgroup_sb_opts {
+        unsigned long subsys_bits;
+        unsigned long flags;
+};
+
+/* Convert a hierarchy specifier into a bitmask of subsystems and
+ * flags. */
+static int parse_cgroupfs_options(char *data,
+                                     struct cgroup_sb_opts *opts)
+{
+        char *token, *o = data ?: "all";
+
+        opts->subsys_bits = 0;
+        opts->flags = 0;
+
+        while ((token = strsep(&o, ",")) != NULL) {
+                if (!*token)
+                        return -EINVAL;
+                if (!strcmp(token, "all")) {
+                        opts->subsys_bits = (1 << CGROUP_SUBSYS_COUNT) - 1;
+                } else if (!strcmp(token, "noprefix")) {
+                        set_bit(ROOT_NOPREFIX, &opts->flags);
+                } else {
+                        struct cgroup_subsys *ss;
+                        int i;
+                        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+                                ss = subsys[i];
+                                if (!strcmp(token, ss->name)) {
+                                        set_bit(i, &opts->subsys_bits);
+                                        break;
+                                }
+                        }
+                        if (i == CGROUP_SUBSYS_COUNT)
+                                return -ENOENT;
+                }
+        }
+
+        /* We can't have an empty hierarchy */
+        if (!opts->subsys_bits)
+                return -EINVAL;
+
+        return 0;
+}
+
+static int cgroup_remount(struct super_block *sb, int *flags, char *data)
+{
+        int ret = 0;
+        struct cgroupfs_root *root = sb->s_fs_info;
+        struct cgroup *cont = &root->top_cgroup;
+        struct cgroup_sb_opts opts;
+
+        mutex_lock(&cont->dentry->d_inode->i_mutex);
+        mutex_lock(&cgroup_mutex);
+
+        /* See what subsystems are wanted */
+        ret = parse_cgroupfs_options(data, &opts);
+        if (ret)
+                goto out_unlock;
+
+        /* Don't allow flags to change at remount */
+        if (opts.flags != root->flags) {
+                ret = -EINVAL;
+                goto out_unlock;
+        }
+
+        ret = rebind_subsystems(root, opts.subsys_bits);
+
+        /* (re)populate subsystem files */
+        if (!ret)
+                cgroup_populate_dir(cont);
+
+ out_unlock:
+        mutex_unlock(&cgroup_mutex);
+        mutex_unlock(&cont->dentry->d_inode->i_mutex);
+        return ret;
+}
+
+static struct super_operations cgroup_ops = {
+        .statfs = simple_statfs,
+        .drop_inode = generic_delete_inode,
+        .show_options = cgroup_show_options,
+        .remount_fs = cgroup_remount,
+};
+
+static void init_cgroup_root(struct cgroupfs_root *root)
+{
+        struct cgroup *cont = &root->top_cgroup;
+        INIT_LIST_HEAD(&root->subsys_list);
+        INIT_LIST_HEAD(&root->root_list);
+        root->number_of_cgroups = 1;
+        cont->root = root;
+        cont->top_cgroup = cont;
+        INIT_LIST_HEAD(&cont->sibling);
+        INIT_LIST_HEAD(&cont->children);
+}
+
+static int cgroup_test_super(struct super_block *sb, void *data)
+{
+        struct cgroupfs_root *new = data;
+        struct cgroupfs_root *root = sb->s_fs_info;
+
+        /* First check subsystems */
+        if (new->subsys_bits != root->subsys_bits)
+            return 0;
+
+        /* Next check flags */
+        if (new->flags != root->flags)
+                return 0;
+
+        return 1;
+}
+
+static int cgroup_set_super(struct super_block *sb, void *data)
+{
+        int ret;
+        struct cgroupfs_root *root = data;
+
+        ret = set_anon_super(sb, NULL);
+        if (ret)
+                return ret;
+
+        sb->s_fs_info = root;
+        root->sb = sb;
+
+        sb->s_blocksize = PAGE_CACHE_SIZE;
+        sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
+        sb->s_magic = CGROUP_SUPER_MAGIC;
+        sb->s_op = &cgroup_ops;
+
+        return 0;
+}
+
+static int cgroup_get_rootdir(struct super_block *sb)
+{
+        struct inode *inode =
+                cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
+        struct dentry *dentry;
+
+        if (!inode)
+                return -ENOMEM;
+
+        inode->i_op = &simple_dir_inode_operations;
+        inode->i_fop = &simple_dir_operations;
+        inode->i_op = &cgroup_dir_inode_operations;
+        /* directories start off with i_nlink == 2 (for "." entry) */
+        inc_nlink(inode);
+        dentry = d_alloc_root(inode);
+        if (!dentry) {
+                iput(inode);
+                return -ENOMEM;
+        }
+        sb->s_root = dentry;
+        return 0;
+}
+
+static int cgroup_get_sb(struct file_system_type *fs_type,
+                         int flags, const char *unused_dev_name,
+                         void *data, struct vfsmount *mnt)
+{
+        struct cgroup_sb_opts opts;
+        int ret = 0;
+        struct super_block *sb;
+        struct cgroupfs_root *root;
+
+        /* First find the desired set of subsystems */
+        ret = parse_cgroupfs_options(data, &opts);
+        if (ret)
+                return ret;
+
+        root = kzalloc(sizeof(*root), GFP_KERNEL);
+        if (!root)
+                return -ENOMEM;
+
+        init_cgroup_root(root);
+        root->subsys_bits = opts.subsys_bits;
+        root->flags = opts.flags;
+
+        sb = sget(fs_type, cgroup_test_super, cgroup_set_super, root);
+
+        if (IS_ERR(sb)) {
+                kfree(root);
+                return PTR_ERR(sb);
+        }
+
+        if (sb->s_fs_info != root) {
+                /* Reusing an existing superblock */
+                BUG_ON(sb->s_root == NULL);
+                kfree(root);
+                root = NULL;
+        } else {
+                /* New superblock */
+                struct cgroup *cont = &root->top_cgroup;
+
+                BUG_ON(sb->s_root != NULL);
+
+                ret = cgroup_get_rootdir(sb);
+                if (ret)
+                        goto drop_new_super;
+
+                mutex_lock(&cgroup_mutex);
+
+                ret = rebind_subsystems(root, root->subsys_bits);
+                if (ret == -EBUSY) {
+                        mutex_unlock(&cgroup_mutex);
+                        goto drop_new_super;
+                }
+
+                /* EBUSY should be the only error here */
+                BUG_ON(ret);
+
+                list_add(&root->root_list, &roots);
+
+                sb->s_root->d_fsdata = &root->top_cgroup;
+                root->top_cgroup.dentry = sb->s_root;
+
+                BUG_ON(!list_empty(&cont->sibling));
+                BUG_ON(!list_empty(&cont->children));
+                BUG_ON(root->number_of_cgroups != 1);
+
+                /*
+                 * I believe that it's safe to nest i_mutex inside
+                 * cgroup_mutex in this case, since no-one else can
+                 * be accessing this directory yet. But we still need
+                 * to teach lockdep that this is the case - currently
+                 * a cgroupfs remount triggers a lockdep warning
+                 */
+                mutex_lock(&cont->dentry->d_inode->i_mutex);
+                cgroup_populate_dir(cont);
+                mutex_unlock(&cont->dentry->d_inode->i_mutex);
+                mutex_unlock(&cgroup_mutex);
+        }
+
+        return simple_set_mnt(mnt, sb);
+
+ drop_new_super:
+        up_write(&sb->s_umount);
+        deactivate_super(sb);
+        return ret;
+}
+
+static void cgroup_kill_sb(struct super_block *sb) {
+        struct cgroupfs_root *root = sb->s_fs_info;
+        struct cgroup *cont = &root->top_cgroup;
+        int ret;
+
+        BUG_ON(!root);
+
+        BUG_ON(root->number_of_cgroups != 1);
+        BUG_ON(!list_empty(&cont->children));
+        BUG_ON(!list_empty(&cont->sibling));
+
+        mutex_lock(&cgroup_mutex);
+
+        /* Rebind all subsystems back to the default hierarchy */
+        ret = rebind_subsystems(root, 0);
+        /* Shouldn't be able to fail ... */
+        BUG_ON(ret);
+
+        if (!list_empty(&root->root_list))
+                list_del(&root->root_list);
+        mutex_unlock(&cgroup_mutex);
+
+        kfree(root);
+        kill_litter_super(sb);
+}
+
+static struct file_system_type cgroup_fs_type = {
+        .name = "cgroup",
+        .get_sb = cgroup_get_sb,
+        .kill_sb = cgroup_kill_sb,
+};
+
+static inline struct cgroup *__d_cont(struct dentry *dentry)
+{
+        return dentry->d_fsdata;
+}
+
+static inline struct cftype *__d_cft(struct dentry *dentry)
+{
+        return dentry->d_fsdata;
+}
+
+/*
+ * Called with cgroup_mutex held.  Writes path of cgroup into buf.
+ * Returns 0 on success, -errno on error.
+ */
+int cgroup_path(const struct cgroup *cont, char *buf, int buflen)
+{
+        char *start;
+
+        if (cont == dummytop) {
+                /*
+                 * Inactive subsystems have no dentry for their root
+                 * cgroup
+                 */
+                strcpy(buf, "/");
+                return 0;
+        }
+
+        start = buf + buflen;
+
+        *--start = '\0';
+        for (;;) {
+                int len = cont->dentry->d_name.len;
+                if ((start -= len) < buf)
+                        return -ENAMETOOLONG;
+                memcpy(start, cont->dentry->d_name.name, len);
+                cont = cont->parent;
+                if (!cont)
+                        break;
+                if (!cont->parent)
+                        continue;
+                if (--start < buf)
+                        return -ENAMETOOLONG;
+                *start = '/';
+        }
+        memmove(buf, start, buf + buflen - start);
+        return 0;
+}
+
+/* The various types of files and directories in a cgroup file system */
+
+enum cgroup_filetype {
+        FILE_ROOT,
+        FILE_DIR,
+        FILE_TASKLIST,
+};
+
+static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
+                                                size_t nbytes, loff_t *ppos)
+{
+        struct cftype *cft = __d_cft(file->f_dentry);
+        struct cgroup *cont = __d_cont(file->f_dentry->d_parent);
+
+        if (!cft)
+                return -ENODEV;
+        if (!cft->write)
+                return -EINVAL;
+
+        return cft->write(cont, cft, file, buf, nbytes, ppos);
+}
+
+static ssize_t cgroup_read_uint(struct cgroup *cont, struct cftype *cft,
+                                   struct file *file,
+                                   char __user *buf, size_t nbytes,
+                                   loff_t *ppos)
+{
+        char tmp[64];
+        u64 val = cft->read_uint(cont, cft);
+        int len = sprintf(tmp, "%llu\n", (unsigned long long) val);
+
+        return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
+}
+
+static ssize_t cgroup_file_read(struct file *file, char __user *buf,
+                                   size_t nbytes, loff_t *ppos)
+{
+        struct cftype *cft = __d_cft(file->f_dentry);
+        struct cgroup *cont = __d_cont(file->f_dentry->d_parent);
+
+        if (!cft)
+                return -ENODEV;
+
+        if (cft->read)
+                return cft->read(cont, cft, file, buf, nbytes, ppos);
+        if (cft->read_uint)
+                return cgroup_read_uint(cont, cft, file, buf, nbytes, ppos);
+        return -EINVAL;
+}
+
+static int cgroup_file_open(struct inode *inode, struct file *file)
+{
+        int err;
+        struct cftype *cft;
+
+        err = generic_file_open(inode, file);
+        if (err)
+                return err;
+
+        cft = __d_cft(file->f_dentry);
+        if (!cft)
+                return -ENODEV;
+        if (cft->open)
+                err = cft->open(inode, file);
+        else
+                err = 0;
+
+        return err;
+}
+
+static int cgroup_file_release(struct inode *inode, struct file *file)
+{
+        struct cftype *cft = __d_cft(file->f_dentry);
+        if (cft->release)
+                return cft->release(inode, file);
+        return 0;
+}
+
+/*
+ * cgroup_rename - Only allow simple rename of directories in place.
+ */
+static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
+                            struct inode *new_dir, struct dentry *new_dentry)
+{
+        if (!S_ISDIR(old_dentry->d_inode->i_mode))
+                return -ENOTDIR;
+        if (new_dentry->d_inode)
+                return -EEXIST;
+        if (old_dir != new_dir)
+                return -EIO;
+        return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
+}
+
+static struct file_operations cgroup_file_operations = {
+        .read = cgroup_file_read,
+        .write = cgroup_file_write,
+        .llseek = generic_file_llseek,
+        .open = cgroup_file_open,
+        .release = cgroup_file_release,
+};
+
+static struct inode_operations cgroup_dir_inode_operations = {
+        .lookup = simple_lookup,
+        .mkdir = cgroup_mkdir,
+        .rmdir = cgroup_rmdir,
+        .rename = cgroup_rename,
+};
+
+static int cgroup_create_file(struct dentry *dentry, int mode,
+                                struct super_block *sb)
+{
+        static struct dentry_operations cgroup_dops = {
+                .d_iput = cgroup_diput,
+        };
+
+        struct inode *inode;
+
+        if (!dentry)
+                return -ENOENT;
+        if (dentry->d_inode)
+                return -EEXIST;
+
+        inode = cgroup_new_inode(mode, sb);
+        if (!inode)
+                return -ENOMEM;
+
+        if (S_ISDIR(mode)) {
+                inode->i_op = &cgroup_dir_inode_operations;
+                inode->i_fop = &simple_dir_operations;
+
+                /* start off with i_nlink == 2 (for "." entry) */
+                inc_nlink(inode);
+
+                /* start with the directory inode held, so that we can
+                 * populate it without racing with another mkdir */
+                mutex_lock(&inode->i_mutex);
+        } else if (S_ISREG(mode)) {
+                inode->i_size = 0;
+                inode->i_fop = &cgroup_file_operations;
+        }
+        dentry->d_op = &cgroup_dops;
+        d_instantiate(dentry, inode);
+        dget(dentry);   /* Extra count - pin the dentry in core */
+        return 0;
+}
+
+/*
+ *      cgroup_create_dir - create a directory for an object.
+ *      cont:   the cgroup we create the directory for.
+ *              It must have a valid ->parent field
+ *              And we are going to fill its ->dentry field.
+ *      dentry: dentry of the new container
+ *      mode:   mode to set on new directory.
+ */
+static int cgroup_create_dir(struct cgroup *cont, struct dentry *dentry,
+                                int mode)
+{
+        struct dentry *parent;
+        int error = 0;
+
+        parent = cont->parent->dentry;
+        error = cgroup_create_file(dentry, S_IFDIR | mode, cont->root->sb);
+        if (!error) {
+                dentry->d_fsdata = cont;
+                inc_nlink(parent->d_inode);
+                cont->dentry = dentry;
+                dget(dentry);
+        }
+        dput(dentry);
+
+        return error;
+}
+
+int cgroup_add_file(struct cgroup *cont,
+                       struct cgroup_subsys *subsys,
+                       const struct cftype *cft)
+{
+        struct dentry *dir = cont->dentry;
+        struct dentry *dentry;
+        int error;
+
+        char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
+        if (subsys && !test_bit(ROOT_NOPREFIX, &cont->root->flags)) {
+                strcpy(name, subsys->name);
+                strcat(name, ".");
+        }
+        strcat(name, cft->name);
+        BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
+        dentry = lookup_one_len(name, dir, strlen(name));
+        if (!IS_ERR(dentry)) {
+                error = cgroup_create_file(dentry, 0644 | S_IFREG,
+                                                cont->root->sb);
+                if (!error)
+                        dentry->d_fsdata = (void *)cft;
+                dput(dentry);
+        } else
+                error = PTR_ERR(dentry);
+        return error;
+}
+
+int cgroup_add_files(struct cgroup *cont,
+                        struct cgroup_subsys *subsys,
+                        const struct cftype cft[],
+                        int count)
+{
+        int i, err;
+        for (i = 0; i < count; i++) {
+                err = cgroup_add_file(cont, subsys, &cft[i]);
+                if (err)
+                        return err;
+        }
+        return 0;
+}
+
+static int cgroup_populate_dir(struct cgroup *cont)
+{
+        int err;
+        struct cgroup_subsys *ss;
+
+        /* First clear out any existing files */
+        cgroup_clear_directory(cont->dentry);
+
+        for_each_subsys(cont->root, ss) {
+                if (ss->populate && (err = ss->populate(ss, cont)) < 0)
+                        return err;
+        }
+
+        return 0;
+}
+
+static void init_cgroup_css(struct cgroup_subsys_state *css,
+                               struct cgroup_subsys *ss,
+                               struct cgroup *cont)
+{
+        css->cgroup = cont;
+        atomic_set(&css->refcnt, 0);
+        css->flags = 0;
+        if (cont == dummytop)
+                set_bit(CSS_ROOT, &css->flags);
+        BUG_ON(cont->subsys[ss->subsys_id]);
+        cont->subsys[ss->subsys_id] = css;
+}
+
+/*
+ *      cgroup_create - create a cgroup
+ *      parent: cgroup that will be parent of the new cgroup.
+ *      name:           name of the new cgroup. Will be strcpy'ed.
+ *      mode:           mode to set on new inode
+ *
+ *      Must be called with the mutex on the parent inode held
+ */
+
+static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
+                             int mode)
+{
+        struct cgroup *cont;
+        struct cgroupfs_root *root = parent->root;
+        int err = 0;
+        struct cgroup_subsys *ss;
+        struct super_block *sb = root->sb;
+
+        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 cgroups.  This
+         * can be done outside cgroup_mutex, since the sb can't
+         * disappear while someone has an open control file on the
+         * fs */
+        atomic_inc(&sb->s_active);
+
+        mutex_lock(&cgroup_mutex);
+
+        cont->flags = 0;
+        INIT_LIST_HEAD(&cont->sibling);
+        INIT_LIST_HEAD(&cont->children);
+
+        cont->parent = parent;
+        cont->root = parent->root;
+        cont->top_cgroup = parent->top_cgroup;
+
+        for_each_subsys(root, ss) {
+                struct cgroup_subsys_state *css = ss->create(ss, cont);
+                if (IS_ERR(css)) {
+                        err = PTR_ERR(css);
+                        goto err_destroy;
+                }
+                init_cgroup_css(css, ss, cont);
+        }
+
+        list_add(&cont->sibling, &cont->parent->children);
+        root->number_of_cgroups++;
+
+        err = cgroup_create_dir(cont, dentry, mode);
+        if (err < 0)
+                goto err_remove;
+
+        /* The cgroup directory was pre-locked for us */
+        BUG_ON(!mutex_is_locked(&cont->dentry->d_inode->i_mutex));
+
+        err = cgroup_populate_dir(cont);
+        /* If err < 0, we have a half-filled directory - oh well ;) */
+
+        mutex_unlock(&cgroup_mutex);
+        mutex_unlock(&cont->dentry->d_inode->i_mutex);
+
+        return 0;
+
+ err_remove:
+
+        list_del(&cont->sibling);
+        root->number_of_cgroups--;
+
+ err_destroy:
+
+        for_each_subsys(root, ss) {
+                if (cont->subsys[ss->subsys_id])
+                        ss->destroy(ss, cont);
+        }
+
+        mutex_unlock(&cgroup_mutex);
+
+        /* Release the reference count that we took on the superblock */
+        deactivate_super(sb);
+
+        kfree(cont);
+        return err;
+}
+
+static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode)
+{
+        struct cgroup *c_parent = dentry->d_parent->d_fsdata;
+
+        /* the vfs holds inode->i_mutex already */
+        return cgroup_create(c_parent, dentry, mode | S_IFDIR);
+}
+
+static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
+{
+        struct cgroup *cont = dentry->d_fsdata;
+        struct dentry *d;
+        struct cgroup *parent;
+        struct cgroup_subsys *ss;
+        struct super_block *sb;
+        struct cgroupfs_root *root;
+        int css_busy = 0;
+
+        /* the vfs holds both inode->i_mutex already */
+
+        mutex_lock(&cgroup_mutex);
+        if (atomic_read(&cont->count) != 0) {
+                mutex_unlock(&cgroup_mutex);
+                return -EBUSY;
+        }
+        if (!list_empty(&cont->children)) {
+                mutex_unlock(&cgroup_mutex);
+                return -EBUSY;
+        }
+
+        parent = cont->parent;
+        root = cont->root;
+        sb = root->sb;
+
+        /* Check the reference count on each subsystem. Since we
+         * already established that there are no tasks in the
+         * cgroup, if the css refcount is also 0, then there should
+         * be no outstanding references, so the subsystem is safe to
+         * destroy */
+        for_each_subsys(root, ss) {
+                struct cgroup_subsys_state *css;
+                css = cont->subsys[ss->subsys_id];
+                if (atomic_read(&css->refcnt)) {
+                        css_busy = 1;
+                        break;
+                }
+        }
+        if (css_busy) {
+                mutex_unlock(&cgroup_mutex);
+                return -EBUSY;
+        }
+
+        for_each_subsys(root, ss) {
+                if (cont->subsys[ss->subsys_id])
+                        ss->destroy(ss, cont);
+        }
+
+        set_bit(CONT_REMOVED, &cont->flags);
+        /* delete my sibling from parent->children */
+        list_del(&cont->sibling);
+        spin_lock(&cont->dentry->d_lock);
+        d = dget(cont->dentry);
+        cont->dentry = NULL;
+        spin_unlock(&d->d_lock);
+
+        cgroup_d_remove_dir(d);
+        dput(d);
+        root->number_of_cgroups--;
+
+        mutex_unlock(&cgroup_mutex);
+        /* Drop the active superblock reference that we took when we
+         * created the cgroup */
+        deactivate_super(sb);
+        return 0;
+}
+
+static void cgroup_init_subsys(struct cgroup_subsys *ss)
+{
+        struct task_struct *g, *p;
+        struct cgroup_subsys_state *css;
+        printk(KERN_ERR "Initializing cgroup subsys %s\n", ss->name);
+
+        /* Create the top cgroup state for this subsystem */
+        ss->root = &rootnode;
+        css = ss->create(ss, dummytop);
+        /* We don't handle early failures gracefully */
+        BUG_ON(IS_ERR(css));
+        init_cgroup_css(css, ss, dummytop);
+
+        /* Update all tasks to contain a subsys pointer to this state
+         * - since the subsystem is newly registered, all tasks are in
+         * the subsystem's top cgroup. */
+
+        /* If this subsystem requested that it be notified with fork
+         * events, we should send it one now for every process in the
+         * system */
+
+        read_lock(&tasklist_lock);
+        init_task.cgroups.subsys[ss->subsys_id] = css;
+        if (ss->fork)
+                ss->fork(ss, &init_task);
+
+        do_each_thread(g, p) {
+                printk(KERN_INFO "Setting task %p css to %p (%d)\n", css, p, p->pid);
+                p->cgroups.subsys[ss->subsys_id] = css;
+                if (ss->fork)
+                        ss->fork(ss, p);
+        } while_each_thread(g, p);
+        read_unlock(&tasklist_lock);
+
+        need_forkexit_callback |= ss->fork || ss->exit;
+
+        ss->active = 1;
+}
+
+/**
+ * cgroup_init_early - initialize cgroups at system boot, and
+ * initialize any subsystems that request early init.
+ */
+int __init cgroup_init_early(void)
+{
+        int i;
+        init_cgroup_root(&rootnode);
+        list_add(&rootnode.root_list, &roots);
+
+        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+                struct cgroup_subsys *ss = subsys[i];
+
+                BUG_ON(!ss->name);
+                BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);
+                BUG_ON(!ss->create);
+                BUG_ON(!ss->destroy);
+                if (ss->subsys_id != i) {
+                        printk(KERN_ERR "Subsys %s id == %d\n",
+                               ss->name, ss->subsys_id);
+                        BUG();
+                }
+
+                if (ss->early_init)
+                        cgroup_init_subsys(ss);
+        }
+        return 0;
+}
+
+/**
+ * cgroup_init - register cgroup filesystem and /proc file, and
+ * initialize any subsystems that didn't request early init.
+ */
+int __init cgroup_init(void)
+{
+        int err;
+        int i;
+
+        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+                struct cgroup_subsys *ss = subsys[i];
+                if (!ss->early_init)
+                        cgroup_init_subsys(ss);
+        }
+
+        err = register_filesystem(&cgroup_fs_type);
+        if (err < 0)
+                goto out;
+
+out:
+        return err;
+}