1 #ifndef _LINUX_CGROUP_H
2 #define _LINUX_CGROUP_H
6 * Copyright (C) 2003 BULL SA
7 * Copyright (C) 2004-2006 Silicon Graphics, Inc.
11 #include <linux/sched.h>
12 #include <linux/cpumask.h>
13 #include <linux/nodemask.h>
14 #include <linux/rcupdate.h>
15 #include <linux/rculist.h>
16 #include <linux/cgroupstats.h>
17 #include <linux/prio_heap.h>
18 #include <linux/rwsem.h>
19 #include <linux/idr.h>
20 #include <linux/workqueue.h>
21 #include <linux/xattr.h>
32 extern int cgroup_init_early(void);
33 extern int cgroup_init(void);
34 extern void cgroup_fork(struct task_struct *p);
35 extern void cgroup_post_fork(struct task_struct *p);
36 extern void cgroup_exit(struct task_struct *p, int run_callbacks);
37 extern int cgroupstats_build(struct cgroupstats *stats,
38 struct dentry *dentry);
39 extern int cgroup_load_subsys(struct cgroup_subsys *ss);
40 extern void cgroup_unload_subsys(struct cgroup_subsys *ss);
42 extern const struct file_operations proc_cgroup_operations;
45 * Define the enumeration of all cgroup subsystems.
47 * We define ids for builtin subsystems and then modular ones.
49 #define SUBSYS(_x) _x ## _subsys_id,
50 enum cgroup_subsys_id {
51 #define IS_SUBSYS_ENABLED(option) IS_BUILTIN(option)
52 #include <linux/cgroup_subsys.h>
53 #undef IS_SUBSYS_ENABLED
54 CGROUP_BUILTIN_SUBSYS_COUNT,
56 __CGROUP_SUBSYS_TEMP_PLACEHOLDER = CGROUP_BUILTIN_SUBSYS_COUNT - 1,
58 #define IS_SUBSYS_ENABLED(option) IS_MODULE(option)
59 #include <linux/cgroup_subsys.h>
60 #undef IS_SUBSYS_ENABLED
65 /* Per-subsystem/per-cgroup state maintained by the system. */
66 struct cgroup_subsys_state {
68 * The cgroup that this subsystem is attached to. Useful
69 * for subsystems that want to know about the cgroup
72 struct cgroup *cgroup;
75 * State maintained by the cgroup system to allow subsystems
76 * to be "busy". Should be accessed via css_get(),
77 * css_tryget() and css_put().
83 /* ID for this css, if possible */
84 struct css_id __rcu *id;
86 /* Used to put @cgroup->dentry on the last css_put() */
87 struct work_struct dput_work;
90 /* bits in struct cgroup_subsys_state flags field */
92 CSS_ROOT = (1 << 0), /* this CSS is the root of the subsystem */
93 CSS_ONLINE = (1 << 1), /* between ->css_online() and ->css_offline() */
96 /* Caller must verify that the css is not for root cgroup */
97 static inline void __css_get(struct cgroup_subsys_state *css, int count)
99 atomic_add(count, &css->refcnt);
103 * Call css_get() to hold a reference on the css; it can be used
104 * for a reference obtained via:
105 * - an existing ref-counted reference to the css
106 * - task->cgroups for a locked task
109 static inline void css_get(struct cgroup_subsys_state *css)
111 /* We don't need to reference count the root state */
112 if (!(css->flags & CSS_ROOT))
117 * Call css_tryget() to take a reference on a css if your existing
118 * (known-valid) reference isn't already ref-counted. Returns false if
119 * the css has been destroyed.
122 extern bool __css_tryget(struct cgroup_subsys_state *css);
123 static inline bool css_tryget(struct cgroup_subsys_state *css)
125 if (css->flags & CSS_ROOT)
127 return __css_tryget(css);
131 * css_put() should be called to release a reference taken by
132 * css_get() or css_tryget()
135 extern void __css_put(struct cgroup_subsys_state *css);
136 static inline void css_put(struct cgroup_subsys_state *css)
138 if (!(css->flags & CSS_ROOT))
142 /* bits in struct cgroup flags field */
144 /* Control Group is dead */
147 * Control Group has previously had a child cgroup or a task,
148 * but no longer (only if CGRP_NOTIFY_ON_RELEASE is set)
151 /* Control Group requires release notifications to userspace */
152 CGRP_NOTIFY_ON_RELEASE,
154 * Clone the parent's configuration when creating a new child
155 * cpuset cgroup. For historical reasons, this option can be
156 * specified at mount time and thus is implemented here.
158 CGRP_CPUSET_CLONE_CHILDREN,
159 /* see the comment above CGRP_ROOT_SANE_BEHAVIOR for details */
164 struct rcu_head rcu_head;
169 unsigned long flags; /* "unsigned long" so bitops work */
172 * count users of this cgroup. >0 means busy, but doesn't
173 * necessarily indicate the number of tasks in the cgroup
177 int id; /* ida allocated in-hierarchy ID */
180 * We link our 'sibling' struct into our parent's 'children'.
181 * Our children link their 'sibling' into our 'children'.
183 struct list_head sibling; /* my parent's children */
184 struct list_head children; /* my children */
185 struct list_head files; /* my files */
187 struct cgroup *parent; /* my parent */
188 struct dentry *dentry; /* cgroup fs entry, RCU protected */
191 * This is a copy of dentry->d_name, and it's needed because
192 * we can't use dentry->d_name in cgroup_path().
194 * You must acquire rcu_read_lock() to access cgrp->name, and
195 * the only place that can change it is rename(), which is
196 * protected by parent dir's i_mutex.
198 * Normally you should use cgroup_name() wrapper rather than
199 * access it directly.
201 struct cgroup_name __rcu *name;
203 /* Private pointers for each registered subsystem */
204 struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
206 struct cgroupfs_root *root;
209 * List of cg_cgroup_links pointing at css_sets with
210 * tasks in this cgroup. Protected by css_set_lock
212 struct list_head css_sets;
214 struct list_head allcg_node; /* cgroupfs_root->allcg_list */
215 struct list_head cft_q_node; /* used during cftype add/rm */
218 * Linked list running through all cgroups that can
219 * potentially be reaped by the release agent. Protected by
222 struct list_head release_list;
225 * list of pidlists, up to two for each namespace (one for procs, one
226 * for tasks); created on demand.
228 struct list_head pidlists;
229 struct mutex pidlist_mutex;
231 /* For RCU-protected deletion */
232 struct rcu_head rcu_head;
233 struct work_struct free_work;
235 /* List of events which userspace want to receive */
236 struct list_head event_list;
237 spinlock_t event_list_lock;
239 /* directory xattrs */
240 struct simple_xattrs xattrs;
243 #define MAX_CGROUP_ROOT_NAMELEN 64
245 /* cgroupfs_root->flags */
248 * Unfortunately, cgroup core and various controllers are riddled
249 * with idiosyncrasies and pointless options. The following flag,
250 * when set, will force sane behavior - some options are forced on,
251 * others are disallowed, and some controllers will change their
252 * hierarchical or other behaviors.
254 * The set of behaviors affected by this flag are still being
255 * determined and developed and the mount option for this flag is
256 * prefixed with __DEVEL__. The prefix will be dropped once we
257 * reach the point where all behaviors are compatible with the
258 * planned unified hierarchy, which will automatically turn on this
261 * The followings are the behaviors currently affected this flag.
263 * - Mount options "noprefix" and "clone_children" are disallowed.
264 * Also, cgroupfs file cgroup.clone_children is not created.
266 * - When mounting an existing superblock, mount options should
269 * - Remount is disallowed.
271 * - memcg: use_hierarchy is on by default and the cgroup file for
272 * the flag is not created.
274 * The followings are planned changes.
276 * - release_agent will be disallowed once replacement notification
277 * mechanism is implemented.
279 CGRP_ROOT_SANE_BEHAVIOR = (1 << 0),
281 CGRP_ROOT_NOPREFIX = (1 << 1), /* mounted subsystems have no named prefix */
282 CGRP_ROOT_XATTR = (1 << 2), /* supports extended attributes */
286 * A cgroupfs_root represents the root of a cgroup hierarchy, and may be
287 * associated with a superblock to form an active hierarchy. This is
288 * internal to cgroup core. Don't access directly from controllers.
290 struct cgroupfs_root {
291 struct super_block *sb;
294 * The bitmask of subsystems intended to be attached to this
297 unsigned long subsys_mask;
299 /* Unique id for this hierarchy. */
302 /* The bitmask of subsystems currently attached to this hierarchy */
303 unsigned long actual_subsys_mask;
305 /* A list running through the attached subsystems */
306 struct list_head subsys_list;
308 /* The root cgroup for this hierarchy */
309 struct cgroup top_cgroup;
311 /* Tracks how many cgroups are currently defined in hierarchy.*/
312 int number_of_cgroups;
314 /* A list running through the active hierarchies */
315 struct list_head root_list;
317 /* All cgroups on this root, cgroup_mutex protected */
318 struct list_head allcg_list;
320 /* Hierarchy-specific flags */
323 /* IDs for cgroups in this hierarchy */
324 struct ida cgroup_ida;
326 /* The path to use for release notifications. */
327 char release_agent_path[PATH_MAX];
329 /* The name for this hierarchy - may be empty */
330 char name[MAX_CGROUP_ROOT_NAMELEN];
334 * A css_set is a structure holding pointers to a set of
335 * cgroup_subsys_state objects. This saves space in the task struct
336 * object and speeds up fork()/exit(), since a single inc/dec and a
337 * list_add()/del() can bump the reference count on the entire cgroup
343 /* Reference count */
347 * List running through all cgroup groups in the same hash
348 * slot. Protected by css_set_lock
350 struct hlist_node hlist;
353 * List running through all tasks using this cgroup
354 * group. Protected by css_set_lock
356 struct list_head tasks;
359 * List of cg_cgroup_link objects on link chains from
360 * cgroups referenced from this css_set. Protected by
363 struct list_head cg_links;
366 * Set of subsystem states, one for each subsystem. This array
367 * is immutable after creation apart from the init_css_set
368 * during subsystem registration (at boot time) and modular subsystem
371 struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
373 /* For RCU-protected deletion */
374 struct rcu_head rcu_head;
378 * cgroup_map_cb is an abstract callback API for reporting map-valued
382 struct cgroup_map_cb {
383 int (*fill)(struct cgroup_map_cb *cb, const char *key, u64 value);
388 * struct cftype: handler definitions for cgroup control files
390 * When reading/writing to a file:
391 * - the cgroup to use is file->f_dentry->d_parent->d_fsdata
392 * - the 'cftype' of the file is file->f_dentry->d_fsdata
396 #define CFTYPE_ONLY_ON_ROOT (1U << 0) /* only create on root cg */
397 #define CFTYPE_NOT_ON_ROOT (1U << 1) /* don't create on root cg */
398 #define CFTYPE_INSANE (1U << 2) /* don't create if sane_behavior */
400 #define MAX_CFTYPE_NAME 64
404 * By convention, the name should begin with the name of the
405 * subsystem, followed by a period. Zero length string indicates
406 * end of cftype array.
408 char name[MAX_CFTYPE_NAME];
411 * If not 0, file mode is set to this value, otherwise it will
412 * be figured out automatically
417 * If non-zero, defines the maximum length of string that can
418 * be passed to write_string; defaults to 64
420 size_t max_write_len;
425 int (*open)(struct inode *inode, struct file *file);
426 ssize_t (*read)(struct cgroup *cgrp, struct cftype *cft,
428 char __user *buf, size_t nbytes, loff_t *ppos);
430 * read_u64() is a shortcut for the common case of returning a
431 * single integer. Use it in place of read()
433 u64 (*read_u64)(struct cgroup *cgrp, struct cftype *cft);
435 * read_s64() is a signed version of read_u64()
437 s64 (*read_s64)(struct cgroup *cgrp, struct cftype *cft);
439 * read_map() is used for defining a map of key/value
440 * pairs. It should call cb->fill(cb, key, value) for each
441 * entry. The key/value pairs (and their ordering) should not
442 * change between reboots.
444 int (*read_map)(struct cgroup *cont, struct cftype *cft,
445 struct cgroup_map_cb *cb);
447 * read_seq_string() is used for outputting a simple sequence
450 int (*read_seq_string)(struct cgroup *cont, struct cftype *cft,
453 ssize_t (*write)(struct cgroup *cgrp, struct cftype *cft,
455 const char __user *buf, size_t nbytes, loff_t *ppos);
458 * write_u64() is a shortcut for the common case of accepting
459 * a single integer (as parsed by simple_strtoull) from
460 * userspace. Use in place of write(); return 0 or error.
462 int (*write_u64)(struct cgroup *cgrp, struct cftype *cft, u64 val);
464 * write_s64() is a signed version of write_u64()
466 int (*write_s64)(struct cgroup *cgrp, struct cftype *cft, s64 val);
469 * write_string() is passed a nul-terminated kernelspace
470 * buffer of maximum length determined by max_write_len.
471 * Returns 0 or -ve error code.
473 int (*write_string)(struct cgroup *cgrp, struct cftype *cft,
476 * trigger() callback can be used to get some kick from the
477 * userspace, when the actual string written is not important
478 * at all. The private field can be used to determine the
479 * kick type for multiplexing.
481 int (*trigger)(struct cgroup *cgrp, unsigned int event);
483 int (*release)(struct inode *inode, struct file *file);
486 * register_event() callback will be used to add new userspace
487 * waiter for changes related to the cftype. Implement it if
488 * you want to provide this functionality. Use eventfd_signal()
489 * on eventfd to send notification to userspace.
491 int (*register_event)(struct cgroup *cgrp, struct cftype *cft,
492 struct eventfd_ctx *eventfd, const char *args);
494 * unregister_event() callback will be called when userspace
495 * closes the eventfd or on cgroup removing.
496 * This callback must be implemented, if you want provide
497 * notification functionality.
499 void (*unregister_event)(struct cgroup *cgrp, struct cftype *cft,
500 struct eventfd_ctx *eventfd);
504 * cftype_sets describe cftypes belonging to a subsystem and are chained at
505 * cgroup_subsys->cftsets. Each cftset points to an array of cftypes
506 * terminated by zero length name.
509 struct list_head node; /* chained at subsys->cftsets */
513 struct cgroup_scanner {
515 int (*test_task)(struct task_struct *p, struct cgroup_scanner *scan);
516 void (*process_task)(struct task_struct *p,
517 struct cgroup_scanner *scan);
518 struct ptr_heap *heap;
523 * See the comment above CGRP_ROOT_SANE_BEHAVIOR for details. This
524 * function can be called as long as @cgrp is accessible.
526 static inline bool cgroup_sane_behavior(const struct cgroup *cgrp)
528 return cgrp->root->flags & CGRP_ROOT_SANE_BEHAVIOR;
531 /* Caller should hold rcu_read_lock() */
532 static inline const char *cgroup_name(const struct cgroup *cgrp)
534 return rcu_dereference(cgrp->name)->name;
537 int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
538 int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
540 int cgroup_is_removed(const struct cgroup *cgrp);
541 bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor);
543 int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
545 int cgroup_task_count(const struct cgroup *cgrp);
548 * Control Group taskset, used to pass around set of tasks to cgroup_subsys
551 struct cgroup_taskset;
552 struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset);
553 struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset);
554 struct cgroup *cgroup_taskset_cur_cgroup(struct cgroup_taskset *tset);
555 int cgroup_taskset_size(struct cgroup_taskset *tset);
558 * cgroup_taskset_for_each - iterate cgroup_taskset
559 * @task: the loop cursor
560 * @skip_cgrp: skip if task's cgroup matches this, %NULL to iterate through all
561 * @tset: taskset to iterate
563 #define cgroup_taskset_for_each(task, skip_cgrp, tset) \
564 for ((task) = cgroup_taskset_first((tset)); (task); \
565 (task) = cgroup_taskset_next((tset))) \
566 if (!(skip_cgrp) || \
567 cgroup_taskset_cur_cgroup((tset)) != (skip_cgrp))
570 * Control Group subsystem type.
571 * See Documentation/cgroups/cgroups.txt for details
574 struct cgroup_subsys {
575 struct cgroup_subsys_state *(*css_alloc)(struct cgroup *cgrp);
576 int (*css_online)(struct cgroup *cgrp);
577 void (*css_offline)(struct cgroup *cgrp);
578 void (*css_free)(struct cgroup *cgrp);
580 int (*can_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
581 void (*cancel_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
582 void (*attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
583 void (*fork)(struct task_struct *task);
584 void (*exit)(struct cgroup *cgrp, struct cgroup *old_cgrp,
585 struct task_struct *task);
586 void (*bind)(struct cgroup *root);
592 * True if this subsys uses ID. ID is not available before cgroup_init()
593 * (not available in early_init time.)
598 * If %false, this subsystem is properly hierarchical -
599 * configuration, resource accounting and restriction on a parent
600 * cgroup cover those of its children. If %true, hierarchy support
601 * is broken in some ways - some subsystems ignore hierarchy
602 * completely while others are only implemented half-way.
604 * It's now disallowed to create nested cgroups if the subsystem is
605 * broken and cgroup core will emit a warning message on such
606 * cases. Eventually, all subsystems will be made properly
607 * hierarchical and this will go away.
609 bool broken_hierarchy;
610 bool warned_broken_hierarchy;
612 #define MAX_CGROUP_TYPE_NAMELEN 32
616 * Link to parent, and list entry in parent's children.
617 * Protected by cgroup_lock()
619 struct cgroupfs_root *root;
620 struct list_head sibling;
621 /* used when use_id == true */
625 /* list of cftype_sets */
626 struct list_head cftsets;
628 /* base cftypes, automatically [de]registered with subsys itself */
629 struct cftype *base_cftypes;
630 struct cftype_set base_cftset;
632 /* should be defined only by modular subsystems */
633 struct module *module;
636 #define SUBSYS(_x) extern struct cgroup_subsys _x ## _subsys;
637 #define IS_SUBSYS_ENABLED(option) IS_BUILTIN(option)
638 #include <linux/cgroup_subsys.h>
639 #undef IS_SUBSYS_ENABLED
642 static inline struct cgroup_subsys_state *cgroup_subsys_state(
643 struct cgroup *cgrp, int subsys_id)
645 return cgrp->subsys[subsys_id];
649 * function to get the cgroup_subsys_state which allows for extra
650 * rcu_dereference_check() conditions, such as locks used during the
651 * cgroup_subsys::attach() methods.
653 #ifdef CONFIG_PROVE_RCU
654 extern struct mutex cgroup_mutex;
655 #define task_subsys_state_check(task, subsys_id, __c) \
656 rcu_dereference_check((task)->cgroups->subsys[(subsys_id)], \
657 lockdep_is_held(&(task)->alloc_lock) || \
658 lockdep_is_held(&cgroup_mutex) || (__c))
660 #define task_subsys_state_check(task, subsys_id, __c) \
661 rcu_dereference((task)->cgroups->subsys[(subsys_id)])
664 static inline struct cgroup_subsys_state *
665 task_subsys_state(struct task_struct *task, int subsys_id)
667 return task_subsys_state_check(task, subsys_id, false);
670 static inline struct cgroup* task_cgroup(struct task_struct *task,
673 return task_subsys_state(task, subsys_id)->cgroup;
677 * cgroup_for_each_child - iterate through children of a cgroup
678 * @pos: the cgroup * to use as the loop cursor
679 * @cgroup: cgroup whose children to walk
681 * Walk @cgroup's children. Must be called under rcu_read_lock(). A child
682 * cgroup which hasn't finished ->css_online() or already has finished
683 * ->css_offline() may show up during traversal and it's each subsystem's
684 * responsibility to verify that each @pos is alive.
686 * If a subsystem synchronizes against the parent in its ->css_online() and
687 * before starting iterating, a cgroup which finished ->css_online() is
688 * guaranteed to be visible in the future iterations.
690 #define cgroup_for_each_child(pos, cgroup) \
691 list_for_each_entry_rcu(pos, &(cgroup)->children, sibling)
693 struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
694 struct cgroup *cgroup);
695 struct cgroup *cgroup_rightmost_descendant(struct cgroup *pos);
698 * cgroup_for_each_descendant_pre - pre-order walk of a cgroup's descendants
699 * @pos: the cgroup * to use as the loop cursor
700 * @cgroup: cgroup whose descendants to walk
702 * Walk @cgroup's descendants. Must be called under rcu_read_lock(). A
703 * descendant cgroup which hasn't finished ->css_online() or already has
704 * finished ->css_offline() may show up during traversal and it's each
705 * subsystem's responsibility to verify that each @pos is alive.
707 * If a subsystem synchronizes against the parent in its ->css_online() and
708 * before starting iterating, and synchronizes against @pos on each
709 * iteration, any descendant cgroup which finished ->css_offline() is
710 * guaranteed to be visible in the future iterations.
712 * In other words, the following guarantees that a descendant can't escape
713 * state updates of its ancestors.
717 * Lock @cgrp->parent and @cgrp;
718 * Inherit state from @cgrp->parent;
722 * my_update_state(@cgrp)
725 * Update @cgrp's state;
728 * cgroup_for_each_descendant_pre(@pos, @cgrp) {
730 * Verify @pos is alive and inherit state from @pos->parent;
735 * As long as the inheriting step, including checking the parent state, is
736 * enclosed inside @pos locking, double-locking the parent isn't necessary
737 * while inheriting. The state update to the parent is guaranteed to be
738 * visible by walking order and, as long as inheriting operations to the
739 * same @pos are atomic to each other, multiple updates racing each other
740 * still result in the correct state. It's guaranateed that at least one
741 * inheritance happens for any cgroup after the latest update to its
744 * If checking parent's state requires locking the parent, each inheriting
745 * iteration should lock and unlock both @pos->parent and @pos.
747 * Alternatively, a subsystem may choose to use a single global lock to
748 * synchronize ->css_online() and ->css_offline() against tree-walking
751 #define cgroup_for_each_descendant_pre(pos, cgroup) \
752 for (pos = cgroup_next_descendant_pre(NULL, (cgroup)); (pos); \
753 pos = cgroup_next_descendant_pre((pos), (cgroup)))
755 struct cgroup *cgroup_next_descendant_post(struct cgroup *pos,
756 struct cgroup *cgroup);
759 * cgroup_for_each_descendant_post - post-order walk of a cgroup's descendants
760 * @pos: the cgroup * to use as the loop cursor
761 * @cgroup: cgroup whose descendants to walk
763 * Similar to cgroup_for_each_descendant_pre() but performs post-order
764 * traversal instead. Note that the walk visibility guarantee described in
765 * pre-order walk doesn't apply the same to post-order walks.
767 #define cgroup_for_each_descendant_post(pos, cgroup) \
768 for (pos = cgroup_next_descendant_post(NULL, (cgroup)); (pos); \
769 pos = cgroup_next_descendant_post((pos), (cgroup)))
771 /* A cgroup_iter should be treated as an opaque object */
773 struct list_head *cg_link;
774 struct list_head *task;
778 * To iterate across the tasks in a cgroup:
780 * 1) call cgroup_iter_start to initialize an iterator
782 * 2) call cgroup_iter_next() to retrieve member tasks until it
783 * returns NULL or until you want to end the iteration
785 * 3) call cgroup_iter_end() to destroy the iterator.
787 * Or, call cgroup_scan_tasks() to iterate through every task in a
788 * cgroup - cgroup_scan_tasks() holds the css_set_lock when calling
789 * the test_task() callback, but not while calling the process_task()
792 void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it);
793 struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
794 struct cgroup_iter *it);
795 void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
796 int cgroup_scan_tasks(struct cgroup_scanner *scan);
797 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
798 int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);
801 * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works
802 * if cgroup_subsys.use_id == true. It can be used for looking up and scanning.
803 * CSS ID is assigned at cgroup allocation (create) automatically
804 * and removed when subsys calls free_css_id() function. This is because
805 * the lifetime of cgroup_subsys_state is subsys's matter.
807 * Looking up and scanning function should be called under rcu_read_lock().
808 * Taking cgroup_mutex is not necessary for following calls.
809 * But the css returned by this routine can be "not populated yet" or "being
810 * destroyed". The caller should check css and cgroup's status.
814 * Typically Called at ->destroy(), or somewhere the subsys frees
815 * cgroup_subsys_state.
817 void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css);
819 /* Find a cgroup_subsys_state which has given ID */
821 struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id);
823 /* Returns true if root is ancestor of cg */
824 bool css_is_ancestor(struct cgroup_subsys_state *cg,
825 const struct cgroup_subsys_state *root);
827 /* Get id and depth of css */
828 unsigned short css_id(struct cgroup_subsys_state *css);
829 unsigned short css_depth(struct cgroup_subsys_state *css);
830 struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id);
832 #else /* !CONFIG_CGROUPS */
834 static inline int cgroup_init_early(void) { return 0; }
835 static inline int cgroup_init(void) { return 0; }
836 static inline void cgroup_fork(struct task_struct *p) {}
837 static inline void cgroup_post_fork(struct task_struct *p) {}
838 static inline void cgroup_exit(struct task_struct *p, int callbacks) {}
840 static inline void cgroup_lock(void) {}
841 static inline void cgroup_unlock(void) {}
842 static inline int cgroupstats_build(struct cgroupstats *stats,
843 struct dentry *dentry)
848 /* No cgroups - nothing to do */
849 static inline int cgroup_attach_task_all(struct task_struct *from,
850 struct task_struct *t)
855 #endif /* !CONFIG_CGROUPS */
857 #endif /* _LINUX_CGROUP_H */