#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/cpumask.h>
  #include <linux/nodemask.h>
  #include <linux/rcupdate.h>
  #include <linux/rculist.h>
  #include <linux/cgroupstats.h>
  #include <linux/prio_heap.h>
  #include <linux/rwsem.h>
  #include <linux/idr.h>
  #include <linux/workqueue.h>
  #include <linux/xattr.h>
  #include <linux/fs.h>
  #include <linux/percpu-refcount.h>
  #include <linux/seq_file.h>
  
  #ifdef CONFIG_CGROUPS
  
  struct cgroupfs_root;
  struct cgroup_subsys;
  struct inode;
  struct cgroup;
  
  extern int cgroup_init_early(void);
  extern int cgroup_init(void);
  extern void cgroup_fork(struct task_struct *p);
  extern void cgroup_post_fork(struct task_struct *p);
  extern void cgroup_exit(struct task_struct *p, int run_callbacks);
  extern int cgroupstats_build(struct cgroupstats *stats,
  				struct dentry *dentry);
  extern int cgroup_load_subsys(struct cgroup_subsys *ss);
  extern void cgroup_unload_subsys(struct cgroup_subsys *ss);
  
  extern int proc_cgroup_show(struct seq_file *, void *);
  
  /*
   * Define the enumeration of all cgroup subsystems.
   *
   * We define ids for builtin subsystems and then modular ones.
   */
  #define SUBSYS(_x) _x ## _subsys_id,
  enum cgroup_subsys_id {
  #define IS_SUBSYS_ENABLED(option) IS_BUILTIN(option)
  #include <linux/cgroup_subsys.h>
  #undef IS_SUBSYS_ENABLED
  	CGROUP_BUILTIN_SUBSYS_COUNT,
  
  	__CGROUP_SUBSYS_TEMP_PLACEHOLDER = CGROUP_BUILTIN_SUBSYS_COUNT - 1,
  
  #define IS_SUBSYS_ENABLED(option) IS_MODULE(option)
  #include <linux/cgroup_subsys.h>
  #undef IS_SUBSYS_ENABLED
  	CGROUP_SUBSYS_COUNT,
  };
  #undef SUBSYS
  
  /* Per-subsystem/per-cgroup state maintained by the system. */
  struct cgroup_subsys_state {
  	/* the cgroup that this css is attached to */
  	struct cgroup *cgroup;
  
  	/* the cgroup subsystem that this css is attached to */
  	struct cgroup_subsys *ss;
  
  	/* reference count - access via css_[try]get() and css_put() */
  	struct percpu_ref refcnt;
  
  	/* the parent css */
  	struct cgroup_subsys_state *parent;
  
  	unsigned long flags;
  
  	/* percpu_ref killing and RCU release */
  	struct rcu_head rcu_head;
  	struct work_struct destroy_work;
  };
  
  /* bits in struct cgroup_subsys_state flags field */
  enum {
  	CSS_ROOT	= (1 << 0), /* this CSS is the root of the subsystem */
  	CSS_ONLINE	= (1 << 1), /* between ->css_online() and ->css_offline() */
  };
  
  /**
   * css_get - obtain a reference on the specified css
   * @css: target css
   *
   * The caller must already have a reference.
   */
  static inline void css_get(struct cgroup_subsys_state *css)
  {
  	/* We don't need to reference count the root state */
  	if (!(css->flags & CSS_ROOT))
  		percpu_ref_get(&css->refcnt);
  }
  
  /**
   * css_tryget - try to obtain a reference on the specified css
   * @css: target css
   *
   * Obtain a reference on @css if it's alive.  The caller naturally needs to
   * ensure that @css is accessible but doesn't have to be holding a
   * reference on it - IOW, RCU protected access is good enough for this
   * function.  Returns %true if a reference count was successfully obtained;
   * %false otherwise.
   */
  static inline bool css_tryget(struct cgroup_subsys_state *css)
  {
  	if (css->flags & CSS_ROOT)
  		return true;
  	return percpu_ref_tryget(&css->refcnt);
  }
  
  /**
   * css_put - put a css reference
   * @css: target css
   *
   * Put a reference obtained via css_get() and css_tryget().
   */
  static inline void css_put(struct cgroup_subsys_state *css)
  {
  	if (!(css->flags & CSS_ROOT))
  		percpu_ref_put(&css->refcnt);
  }
  
  /* bits in struct cgroup flags field */
  enum {
  	/* Control Group is dead */
  	CGRP_DEAD,
  	/*
  	 * Control Group has previously had a child cgroup or a task,
  	 * but no longer (only if CGRP_NOTIFY_ON_RELEASE is set)
  	 */
  	CGRP_RELEASABLE,
  	/* Control Group requires release notifications to userspace */
  	CGRP_NOTIFY_ON_RELEASE,
  	/*
  	 * Clone the parent's configuration when creating a new child
  	 * cpuset cgroup.  For historical reasons, this option can be
  	 * specified at mount time and thus is implemented here.
  	 */
  	CGRP_CPUSET_CLONE_CHILDREN,
  	/* see the comment above CGRP_ROOT_SANE_BEHAVIOR for details */
  	CGRP_SANE_BEHAVIOR,
  };
  
  struct cgroup_name {
  	struct rcu_head rcu_head;
  	char name[];
  };
  
  struct cgroup {
  	unsigned long flags;		/* "unsigned long" so bitops work */
  
  	/*
  	 * idr allocated in-hierarchy ID.
  	 *
  	 * The ID of the root cgroup is always 0, and a new cgroup
  	 * will be assigned with a smallest available ID.
  	 *
  	 * Allocating/Removing ID must be protected by cgroup_mutex.
  	 */
  	int id;
  
  	/* the number of attached css's */
  	int nr_css;
  
  	/*
  	 * 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 list_head files;		/* my files */
  
  	struct cgroup *parent;		/* my parent */
  	struct dentry *dentry;		/* cgroup fs entry, RCU protected */
  
  	/*
  	 * Monotonically increasing unique serial number which defines a
  	 * uniform order among all cgroups.  It's guaranteed that all
  	 * ->children lists are in the ascending order of ->serial_nr.
  	 * It's used to allow interrupting and resuming iterations.
  	 */
  	u64 serial_nr;
  
  	/*
  	 * This is a copy of dentry->d_name, and it's needed because
  	 * we can't use dentry->d_name in cgroup_path().
  	 *
  	 * You must acquire rcu_read_lock() to access cgrp->name, and
  	 * the only place that can change it is rename(), which is
  	 * protected by parent dir's i_mutex.
  	 *
  	 * Normally you should use cgroup_name() wrapper rather than
  	 * access it directly.
  	 */
  	struct cgroup_name __rcu *name;
  
  	/* Private pointers for each registered subsystem */
  	struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];
  
  	struct cgroupfs_root *root;
  
  	/*
  	 * List of cgrp_cset_links pointing at css_sets with tasks in this
  	 * cgroup.  Protected by css_set_lock.
  	 */
  	struct list_head cset_links;
  
  	/*
  	 * Linked list running through all cgroups that can
  	 * potentially be reaped by the release agent. Protected by
  	 * release_list_lock
  	 */
  	struct list_head release_list;
  
  	/*
  	 * list of pidlists, up to two for each namespace (one for procs, one
  	 * for tasks); created on demand.
  	 */
  	struct list_head pidlists;
  	struct mutex pidlist_mutex;
  
  	/* dummy css with NULL ->ss, points back to this cgroup */
  	struct cgroup_subsys_state dummy_css;
  
  	/* For css percpu_ref killing and RCU-protected deletion */
  	struct rcu_head rcu_head;
  	struct work_struct destroy_work;
  
  	/* directory xattrs */
  	struct simple_xattrs xattrs;
  };
  
  #define MAX_CGROUP_ROOT_NAMELEN 64
  
  /* cgroupfs_root->flags */
  enum {
  	/*
  	 * Unfortunately, cgroup core and various controllers are riddled
  	 * with idiosyncrasies and pointless options.  The following flag,
  	 * when set, will force sane behavior - some options are forced on,
  	 * others are disallowed, and some controllers will change their
  	 * hierarchical or other behaviors.
  	 *
  	 * The set of behaviors affected by this flag are still being
  	 * determined and developed and the mount option for this flag is
  	 * prefixed with __DEVEL__.  The prefix will be dropped once we
  	 * reach the point where all behaviors are compatible with the
  	 * planned unified hierarchy, which will automatically turn on this
  	 * flag.
  	 *
  	 * The followings are the behaviors currently affected this flag.
  	 *
  	 * - Mount options "noprefix" and "clone_children" are disallowed.
  	 *   Also, cgroupfs file cgroup.clone_children is not created.
  	 *
  	 * - When mounting an existing superblock, mount options should
  	 *   match.
  	 *
  	 * - Remount is disallowed.
  	 *
  	 * - rename(2) is disallowed.
  	 *
  	 * - "tasks" is removed.  Everything should be at process
  	 *   granularity.  Use "cgroup.procs" instead.
  	 *
  	 * - "cgroup.procs" is not sorted.  pids will be unique unless they
  	 *   got recycled inbetween reads.
  	 *
  	 * - "release_agent" and "notify_on_release" are removed.
  	 *   Replacement notification mechanism will be implemented.
  	 *
  	 * - cpuset: tasks will be kept in empty cpusets when hotplug happens
  	 *   and take masks of ancestors with non-empty cpus/mems, instead of
  	 *   being moved to an ancestor.
  	 *
  	 * - cpuset: a task can be moved into an empty cpuset, and again it
  	 *   takes masks of ancestors.
  	 *
  	 * - memcg: use_hierarchy is on by default and the cgroup file for
  	 *   the flag is not created.
  	 *
  	 * - blkcg: blk-throttle becomes properly hierarchical.
  	 */
  	CGRP_ROOT_SANE_BEHAVIOR	= (1 << 0),
  
  	CGRP_ROOT_NOPREFIX	= (1 << 1), /* mounted subsystems have no named prefix */
  	CGRP_ROOT_XATTR		= (1 << 2), /* supports extended attributes */
  
  	/* mount options live below bit 16 */
  	CGRP_ROOT_OPTION_MASK	= (1 << 16) - 1,
  
  	CGRP_ROOT_SUBSYS_BOUND	= (1 << 16), /* subsystems finished binding */
  };
  
  /*
   * A cgroupfs_root represents the root of a cgroup hierarchy, and may be
   * associated with a superblock to form an active hierarchy.  This is
   * internal to cgroup core.  Don't access directly from controllers.
   */
  struct cgroupfs_root {
  	struct super_block *sb;
  
  	/* The bitmask of subsystems attached to this hierarchy */
  	unsigned long subsys_mask;
  
  	/* Unique id for this hierarchy. */
  	int hierarchy_id;
  
  	/* 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 active hierarchies */
  	struct list_head root_list;
  
  	/* Hierarchy-specific flags */
  	unsigned long flags;
  
  	/* IDs for cgroups in this hierarchy */
  	struct idr cgroup_idr;
  
  	/* The path to use for release notifications. */
  	char release_agent_path[PATH_MAX];
  
  	/* The name for this hierarchy - may be empty */
  	char name[MAX_CGROUP_ROOT_NAMELEN];
  };
  
  /*
   * A css_set is a structure holding pointers to a set of
   * cgroup_subsys_state objects. This saves space in the task struct
   * object and speeds up fork()/exit(), since a single inc/dec and a
   * list_add()/del() can bump the reference count on the entire cgroup
   * set for a task.
   */
  
  struct css_set {
  
  	/* Reference count */
  	atomic_t refcount;
  
  	/*
  	 * List running through all cgroup groups in the same hash
  	 * slot. Protected by css_set_lock
  	 */
  	struct hlist_node hlist;
  
  	/*
  	 * List running through all tasks using this cgroup
  	 * group. Protected by css_set_lock
  	 */
  	struct list_head tasks;
  
  	/*
  	 * List of cgrp_cset_links pointing at cgroups referenced from this
  	 * css_set.  Protected by css_set_lock.
  	 */
  	struct list_head cgrp_links;
  
  	/*
  	 * Set of subsystem states, one for each subsystem. This array
  	 * is immutable after creation apart from the init_css_set
  	 * during subsystem registration (at boot time) and modular subsystem
  	 * loading/unloading.
  	 */
  	struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
  
  	/* For RCU-protected deletion */
  	struct rcu_head rcu_head;
  };
  
  /*
   * struct cftype: handler definitions for cgroup control files
   *
   * When reading/writing to a file:
   *	- the cgroup to use is file->f_dentry->d_parent->d_fsdata
   *	- the 'cftype' of the file is file->f_dentry->d_fsdata
   */
  
  /* cftype->flags */
  enum {
  	CFTYPE_ONLY_ON_ROOT	= (1 << 0),	/* only create on root cgrp */
  	CFTYPE_NOT_ON_ROOT	= (1 << 1),	/* don't create on root cgrp */
  	CFTYPE_INSANE		= (1 << 2),	/* don't create if sane_behavior */
  	CFTYPE_NO_PREFIX	= (1 << 3),	/* (DON'T USE FOR NEW FILES) no subsys prefix */
  };
  
  #define MAX_CFTYPE_NAME		64
  
  struct cftype {
  	/*
  	 * By convention, the name should begin with the name of the
  	 * subsystem, followed by a period.  Zero length string indicates
  	 * end of cftype array.
  	 */
  	char name[MAX_CFTYPE_NAME];
  	int private;
  	/*
  	 * If not 0, file mode is set to this value, otherwise it will
  	 * be figured out automatically
  	 */
  	umode_t mode;
  
  	/*
  	 * If non-zero, defines the maximum length of string that can
  	 * be passed to write_string; defaults to 64
  	 */
  	size_t max_write_len;
  
  	/* CFTYPE_* flags */
  	unsigned int flags;
  
  	/*
  	 * The subsys this file belongs to.  Initialized automatically
  	 * during registration.  NULL for cgroup core files.
  	 */
  	struct cgroup_subsys *ss;
  
  	/*
  	 * read_u64() is a shortcut for the common case of returning a
  	 * single integer. Use it in place of read()
  	 */
  	u64 (*read_u64)(struct cgroup_subsys_state *css, struct cftype *cft);
  	/*
  	 * read_s64() is a signed version of read_u64()
  	 */
  	s64 (*read_s64)(struct cgroup_subsys_state *css, struct cftype *cft);
  
  	/* generic seq_file read interface */
  	int (*seq_show)(struct seq_file *sf, void *v);
  
  	/* optional ops, implement all or none */
  	void *(*seq_start)(struct seq_file *sf, loff_t *ppos);
  	void *(*seq_next)(struct seq_file *sf, void *v, loff_t *ppos);
  	void (*seq_stop)(struct seq_file *sf, void *v);
  
  	/*
  	 * write_u64() is a shortcut for the common case of accepting
  	 * a single integer (as parsed by simple_strtoull) from
  	 * userspace. Use in place of write(); return 0 or error.
  	 */
  	int (*write_u64)(struct cgroup_subsys_state *css, struct cftype *cft,
  			 u64 val);
  	/*
  	 * write_s64() is a signed version of write_u64()
  	 */
  	int (*write_s64)(struct cgroup_subsys_state *css, struct cftype *cft,
  			 s64 val);
  
  	/*
  	 * write_string() is passed a nul-terminated kernelspace
  	 * buffer of maximum length determined by max_write_len.
  	 * Returns 0 or -ve error code.
  	 */
  	int (*write_string)(struct cgroup_subsys_state *css, struct cftype *cft,
  			    const char *buffer);
  	/*
  	 * trigger() callback can be used to get some kick from the
  	 * userspace, when the actual string written is not important
  	 * at all. The private field can be used to determine the
  	 * kick type for multiplexing.
  	 */
  	int (*trigger)(struct cgroup_subsys_state *css, unsigned int event);
  };
  
  /*
   * cftype_sets describe cftypes belonging to a subsystem and are chained at
   * cgroup_subsys->cftsets.  Each cftset points to an array of cftypes
   * terminated by zero length name.
   */
  struct cftype_set {
  	struct list_head		node;	/* chained at subsys->cftsets */
  	struct cftype			*cfts;
  };
  
  /*
   * cgroupfs file entry, pointed to from leaf dentry->d_fsdata.  Don't
   * access directly.
   */
  struct cfent {
  	struct list_head		node;
  	struct dentry			*dentry;
  	struct cftype			*type;
  	struct cgroup_subsys_state	*css;
  
  	/* file xattrs */
  	struct simple_xattrs		xattrs;
  };
  
  /* seq_file->private points to the following, only ->priv is public */
  struct cgroup_open_file {
  	struct cfent			*cfe;
  	void				*priv;
  };
  
  /*
   * See the comment above CGRP_ROOT_SANE_BEHAVIOR for details.  This
   * function can be called as long as @cgrp is accessible.
   */
  static inline bool cgroup_sane_behavior(const struct cgroup *cgrp)
  {
  	return cgrp->root->flags & CGRP_ROOT_SANE_BEHAVIOR;
  }
  
  /* Caller should hold rcu_read_lock() */
  static inline const char *cgroup_name(const struct cgroup *cgrp)
  {
  	return rcu_dereference(cgrp->name)->name;
  }
  
  static inline struct cgroup_subsys_state *seq_css(struct seq_file *seq)
  {
  	struct cgroup_open_file *of = seq->private;
  	return of->cfe->css;
  }
  
  static inline struct cftype *seq_cft(struct seq_file *seq)
  {
  	struct cgroup_open_file *of = seq->private;
  	return of->cfe->type;
  }
  
  int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
  int cgroup_rm_cftypes(struct cftype *cfts);
  
  bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor);
  
  int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
  int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
  
  int cgroup_task_count(const struct cgroup *cgrp);
  
  /*
   * Control Group taskset, used to pass around set of tasks to cgroup_subsys
   * methods.
   */
  struct cgroup_taskset;
  struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset);
  struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset);
  struct cgroup_subsys_state *cgroup_taskset_cur_css(struct cgroup_taskset *tset,
  						   int subsys_id);
  int cgroup_taskset_size(struct cgroup_taskset *tset);
  
  /**
   * cgroup_taskset_for_each - iterate cgroup_taskset
   * @task: the loop cursor
   * @skip_css: skip if task's css matches this, %NULL to iterate through all
   * @tset: taskset to iterate
   */
  #define cgroup_taskset_for_each(task, skip_css, tset)			\
  	for ((task) = cgroup_taskset_first((tset)); (task);		\
  	     (task) = cgroup_taskset_next((tset)))			\
  		if (!(skip_css) ||					\
  		    cgroup_taskset_cur_css((tset),			\
  			(skip_css)->ss->subsys_id) != (skip_css))
  
  /*
   * Control Group subsystem type.
   * See Documentation/cgroups/cgroups.txt for details
   */
  
  struct cgroup_subsys {
  	struct cgroup_subsys_state *(*css_alloc)(struct cgroup_subsys_state *parent_css);
  	int (*css_online)(struct cgroup_subsys_state *css);
  	void (*css_offline)(struct cgroup_subsys_state *css);
  	void (*css_free)(struct cgroup_subsys_state *css);
  
  	int (*can_attach)(struct cgroup_subsys_state *css,
  			  struct cgroup_taskset *tset);
  	void (*cancel_attach)(struct cgroup_subsys_state *css,
  			      struct cgroup_taskset *tset);
  	void (*attach)(struct cgroup_subsys_state *css,
  		       struct cgroup_taskset *tset);
  	void (*fork)(struct task_struct *task);
  	void (*exit)(struct cgroup_subsys_state *css,
  		     struct cgroup_subsys_state *old_css,
  		     struct task_struct *task);
  	void (*bind)(struct cgroup_subsys_state *root_css);
  
  	int subsys_id;
  	int disabled;
  	int early_init;
  
  	/*
  	 * If %false, this subsystem is properly hierarchical -
  	 * configuration, resource accounting and restriction on a parent
  	 * cgroup cover those of its children.  If %true, hierarchy support
  	 * is broken in some ways - some subsystems ignore hierarchy
  	 * completely while others are only implemented half-way.
  	 *
  	 * It's now disallowed to create nested cgroups if the subsystem is
  	 * broken and cgroup core will emit a warning message on such
  	 * cases.  Eventually, all subsystems will be made properly
  	 * hierarchical and this will go away.
  	 */
  	bool broken_hierarchy;
  	bool warned_broken_hierarchy;
  
  #define MAX_CGROUP_TYPE_NAMELEN 32
  	const char *name;
  
  	/* link to parent, protected by cgroup_lock() */
  	struct cgroupfs_root *root;
  
  	/* list of cftype_sets */
  	struct list_head cftsets;
  
  	/* base cftypes, automatically [de]registered with subsys itself */
  	struct cftype *base_cftypes;
  	struct cftype_set base_cftset;
  
  	/* should be defined only by modular subsystems */
  	struct module *module;
  };
  
  #define SUBSYS(_x) extern struct cgroup_subsys _x ## _subsys;
  #define IS_SUBSYS_ENABLED(option) IS_BUILTIN(option)
  #include <linux/cgroup_subsys.h>
  #undef IS_SUBSYS_ENABLED
  #undef SUBSYS
  
  /**
   * css_parent - find the parent css
   * @css: the target cgroup_subsys_state
   *
   * Return the parent css of @css.  This function is guaranteed to return
   * non-NULL parent as long as @css isn't the root.
   */
  static inline
  struct cgroup_subsys_state *css_parent(struct cgroup_subsys_state *css)
  {
  	return css->parent;
  }
  
  /**
   * task_css_set_check - obtain a task's css_set with extra access conditions
   * @task: the task to obtain css_set for
   * @__c: extra condition expression to be passed to rcu_dereference_check()
   *
   * A task's css_set is RCU protected, initialized and exited while holding
   * task_lock(), and can only be modified while holding both cgroup_mutex
   * and task_lock() while the task is alive.  This macro verifies that the
   * caller is inside proper critical section and returns @task's css_set.
   *
   * The caller can also specify additional allowed conditions via @__c, such
   * as locks used during the cgroup_subsys::attach() methods.
   */
  #ifdef CONFIG_PROVE_RCU
  extern struct mutex cgroup_mutex;
  #define task_css_set_check(task, __c)					\
  	rcu_dereference_check((task)->cgroups,				\
  		lockdep_is_held(&(task)->alloc_lock) ||			\
  		lockdep_is_held(&cgroup_mutex) || (__c))
  #else
  #define task_css_set_check(task, __c)					\
  	rcu_dereference((task)->cgroups)
  #endif
  
  /**
   * task_css_check - obtain css for (task, subsys) w/ extra access conds
   * @task: the target task
   * @subsys_id: the target subsystem ID
   * @__c: extra condition expression to be passed to rcu_dereference_check()
   *
   * Return the cgroup_subsys_state for the (@task, @subsys_id) pair.  The
   * synchronization rules are the same as task_css_set_check().
   */
  #define task_css_check(task, subsys_id, __c)				\
  	task_css_set_check((task), (__c))->subsys[(subsys_id)]
  
  /**
   * task_css_set - obtain a task's css_set
   * @task: the task to obtain css_set for
   *
   * See task_css_set_check().
   */
  static inline struct css_set *task_css_set(struct task_struct *task)
  {
  	return task_css_set_check(task, false);
  }
  
  /**
   * task_css - obtain css for (task, subsys)
   * @task: the target task
   * @subsys_id: the target subsystem ID
   *
   * See task_css_check().
   */
  static inline struct cgroup_subsys_state *task_css(struct task_struct *task,
  						   int subsys_id)
  {
  	return task_css_check(task, subsys_id, false);
  }
  
  static inline struct cgroup *task_cgroup(struct task_struct *task,
  					 int subsys_id)
  {
  	return task_css(task, subsys_id)->cgroup;
  }
  
  struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
  					   struct cgroup_subsys_state *parent);
  
  struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss);
  
  /**
   * css_for_each_child - iterate through children of a css
   * @pos: the css * to use as the loop cursor
   * @parent: css whose children to walk
   *
   * Walk @parent's children.  Must be called under rcu_read_lock().  A child
   * css which hasn't finished ->css_online() or already has finished
   * ->css_offline() may show up during traversal and it's each subsystem's
   * responsibility to verify that each @pos is alive.
   *
   * If a subsystem synchronizes against the parent in its ->css_online() and
   * before starting iterating, a css which finished ->css_online() is
   * guaranteed to be visible in the future iterations.
   *
   * It is allowed to temporarily drop RCU read lock during iteration.  The
   * caller is responsible for ensuring that @pos remains accessible until
   * the start of the next iteration by, for example, bumping the css refcnt.
   */
  #define css_for_each_child(pos, parent)					\
  	for ((pos) = css_next_child(NULL, (parent)); (pos);		\
  	     (pos) = css_next_child((pos), (parent)))
  
  struct cgroup_subsys_state *
  css_next_descendant_pre(struct cgroup_subsys_state *pos,
  			struct cgroup_subsys_state *css);
  
  struct cgroup_subsys_state *
  css_rightmost_descendant(struct cgroup_subsys_state *pos);
  
  /**
   * css_for_each_descendant_pre - pre-order walk of a css's descendants
   * @pos: the css * to use as the loop cursor
   * @root: css whose descendants to walk
   *
   * Walk @root's descendants.  @root is included in the iteration and the
   * first node to be visited.  Must be called under rcu_read_lock().  A
   * descendant css which hasn't finished ->css_online() or already has
   * finished ->css_offline() may show up during traversal and it's each
   * subsystem's responsibility to verify that each @pos is alive.
   *
   * If a subsystem synchronizes against the parent in its ->css_online() and
   * before starting iterating, and synchronizes against @pos on each
   * iteration, any descendant css which finished ->css_online() is
   * guaranteed to be visible in the future iterations.
   *
   * In other words, the following guarantees that a descendant can't escape
   * state updates of its ancestors.
   *
   * my_online(@css)
   * {
   *	Lock @css's parent and @css;
   *	Inherit state from the parent;
   *	Unlock both.
   * }
   *
   * my_update_state(@css)
   * {
   *	css_for_each_descendant_pre(@pos, @css) {
   *		Lock @pos;
   *		if (@pos == @css)
   *			Update @css's state;
   *		else
   *			Verify @pos is alive and inherit state from its parent;
   *		Unlock @pos;
   *	}
   * }
   *
   * As long as the inheriting step, including checking the parent state, is
   * enclosed inside @pos locking, double-locking the parent isn't necessary
   * while inheriting.  The state update to the parent is guaranteed to be
   * visible by walking order and, as long as inheriting operations to the
   * same @pos are atomic to each other, multiple updates racing each other
   * still result in the correct state.  It's guaranateed that at least one
   * inheritance happens for any css after the latest update to its parent.
   *
   * If checking parent's state requires locking the parent, each inheriting
   * iteration should lock and unlock both @pos->parent and @pos.
   *
   * Alternatively, a subsystem may choose to use a single global lock to
   * synchronize ->css_online() and ->css_offline() against tree-walking
   * operations.
   *
   * It is allowed to temporarily drop RCU read lock during iteration.  The
   * caller is responsible for ensuring that @pos remains accessible until
   * the start of the next iteration by, for example, bumping the css refcnt.
   */
  #define css_for_each_descendant_pre(pos, css)				\
  	for ((pos) = css_next_descendant_pre(NULL, (css)); (pos);	\
  	     (pos) = css_next_descendant_pre((pos), (css)))
  
  struct cgroup_subsys_state *
  css_next_descendant_post(struct cgroup_subsys_state *pos,
  			 struct cgroup_subsys_state *css);
  
  /**
   * css_for_each_descendant_post - post-order walk of a css's descendants
   * @pos: the css * to use as the loop cursor
   * @css: css whose descendants to walk
   *
   * Similar to css_for_each_descendant_pre() but performs post-order
   * traversal instead.  @root is included in the iteration and the last
   * node to be visited.  Note that the walk visibility guarantee described
   * in pre-order walk doesn't apply the same to post-order walks.
   */
  #define css_for_each_descendant_post(pos, css)				\
  	for ((pos) = css_next_descendant_post(NULL, (css)); (pos);	\
  	     (pos) = css_next_descendant_post((pos), (css)))
  
  /* A css_task_iter should be treated as an opaque object */
  struct css_task_iter {
  	struct cgroup_subsys_state	*origin_css;
  	struct list_head		*cset_link;
  	struct list_head		*task;
  };
  
  void css_task_iter_start(struct cgroup_subsys_state *css,
  			 struct css_task_iter *it);
  struct task_struct *css_task_iter_next(struct css_task_iter *it);
  void css_task_iter_end(struct css_task_iter *it);
  
  int css_scan_tasks(struct cgroup_subsys_state *css,
  		   bool (*test)(struct task_struct *, void *),
  		   void (*process)(struct task_struct *, void *),
  		   void *data, struct ptr_heap *heap);
  
  int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
  int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);
  
  struct cgroup_subsys_state *css_from_dir(struct dentry *dentry,
  					 struct cgroup_subsys *ss);
  
  #else /* !CONFIG_CGROUPS */
  
  static inline int cgroup_init_early(void) { return 0; }
  static inline int cgroup_init(void) { return 0; }
  static inline void cgroup_fork(struct task_struct *p) {}
  static inline void cgroup_post_fork(struct task_struct *p) {}
  static inline void cgroup_exit(struct task_struct *p, int callbacks) {}
  
  static inline int cgroupstats_build(struct cgroupstats *stats,
  					struct dentry *dentry)
  {
  	return -EINVAL;
  }
  
  /* No cgroups - nothing to do */
  static inline int cgroup_attach_task_all(struct task_struct *from,
  					 struct task_struct *t)
  {
  	return 0;
  }
  
  #endif /* !CONFIG_CGROUPS */
  
  #endif /* _LINUX_CGROUP_H */