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/rwsem.h>
18 #include <linux/idr.h>
19 #include <linux/workqueue.h>
21 #include <linux/percpu-refcount.h>
22 #include <linux/seq_file.h>
23 #include <linux/kernfs.h>
24 #include <linux/wait.h>
33 extern int cgroup_init_early(void);
34 extern int cgroup_init(void);
35 extern void cgroup_fork(struct task_struct
*p
);
36 extern void cgroup_post_fork(struct task_struct
*p
);
37 extern void cgroup_exit(struct task_struct
*p
);
38 extern int cgroupstats_build(struct cgroupstats
*stats
,
39 struct dentry
*dentry
);
41 extern int proc_cgroup_show(struct seq_file
*, void *);
43 /* define the enumeration of all cgroup subsystems */
44 #define SUBSYS(_x) _x ## _cgrp_id,
45 enum cgroup_subsys_id
{
46 #include <linux/cgroup_subsys.h>
52 * Per-subsystem/per-cgroup state maintained by the system. This is the
53 * fundamental structural building block that controllers deal with.
55 * Fields marked with "PI:" are public and immutable and may be accessed
56 * directly without synchronization.
58 struct cgroup_subsys_state
{
59 /* PI: the cgroup that this css is attached to */
60 struct cgroup
*cgroup
;
62 /* PI: the cgroup subsystem that this css is attached to */
63 struct cgroup_subsys
*ss
;
65 /* reference count - access via css_[try]get() and css_put() */
66 struct percpu_ref refcnt
;
68 /* PI: the parent css */
69 struct cgroup_subsys_state
*parent
;
71 /* siblings list anchored at the parent's ->children */
72 struct list_head sibling
;
73 struct list_head children
;
76 * PI: Subsys-unique ID. 0 is unused and root is always 1. The
77 * matching css can be looked up using css_from_id().
84 * Monotonically increasing unique serial number which defines a
85 * uniform order among all csses. It's guaranteed that all
86 * ->children lists are in the ascending order of ->serial_nr and
87 * used to allow interrupting and resuming iterations.
91 /* percpu_ref killing and RCU release */
92 struct rcu_head rcu_head
;
93 struct work_struct destroy_work
;
96 /* bits in struct cgroup_subsys_state flags field */
98 CSS_NO_REF
= (1 << 0), /* no reference counting for this css */
99 CSS_ONLINE
= (1 << 1), /* between ->css_online() and ->css_offline() */
100 CSS_RELEASED
= (1 << 2), /* refcnt reached zero, released */
104 * css_get - obtain a reference on the specified css
107 * The caller must already have a reference.
109 static inline void css_get(struct cgroup_subsys_state
*css
)
111 if (!(css
->flags
& CSS_NO_REF
))
112 percpu_ref_get(&css
->refcnt
);
116 * css_tryget - try to obtain a reference on the specified css
119 * Obtain a reference on @css unless it already has reached zero and is
120 * being released. This function doesn't care whether @css is on or
121 * offline. The caller naturally needs to ensure that @css is accessible
122 * but doesn't have to be holding a reference on it - IOW, RCU protected
123 * access is good enough for this function. Returns %true if a reference
124 * count was successfully obtained; %false otherwise.
126 static inline bool css_tryget(struct cgroup_subsys_state
*css
)
128 if (!(css
->flags
& CSS_NO_REF
))
129 return percpu_ref_tryget(&css
->refcnt
);
134 * css_tryget_online - try to obtain a reference on the specified css if online
137 * Obtain a reference on @css if it's online. The caller naturally needs
138 * to ensure that @css is accessible but doesn't have to be holding a
139 * reference on it - IOW, RCU protected access is good enough for this
140 * function. Returns %true if a reference count was successfully obtained;
143 static inline bool css_tryget_online(struct cgroup_subsys_state
*css
)
145 if (!(css
->flags
& CSS_NO_REF
))
146 return percpu_ref_tryget_live(&css
->refcnt
);
151 * css_put - put a css reference
154 * Put a reference obtained via css_get() and css_tryget_online().
156 static inline void css_put(struct cgroup_subsys_state
*css
)
158 if (!(css
->flags
& CSS_NO_REF
))
159 percpu_ref_put(&css
->refcnt
);
162 /* bits in struct cgroup flags field */
165 * Control Group has previously had a child cgroup or a task,
166 * but no longer (only if CGRP_NOTIFY_ON_RELEASE is set)
169 /* Control Group requires release notifications to userspace */
170 CGRP_NOTIFY_ON_RELEASE
,
172 * Clone the parent's configuration when creating a new child
173 * cpuset cgroup. For historical reasons, this option can be
174 * specified at mount time and thus is implemented here.
176 CGRP_CPUSET_CLONE_CHILDREN
,
180 /* self css with NULL ->ss, points back to this cgroup */
181 struct cgroup_subsys_state self
;
183 unsigned long flags
; /* "unsigned long" so bitops work */
186 * idr allocated in-hierarchy ID.
188 * ID 0 is not used, the ID of the root cgroup is always 1, and a
189 * new cgroup will be assigned with a smallest available ID.
191 * Allocating/Removing ID must be protected by cgroup_mutex.
196 * If this cgroup contains any tasks, it contributes one to
197 * populated_cnt. All children with non-zero popuplated_cnt of
198 * their own contribute one. The count is zero iff there's no task
199 * in this cgroup or its subtree.
203 struct kernfs_node
*kn
; /* cgroup kernfs entry */
204 struct kernfs_node
*populated_kn
; /* kn for "cgroup.subtree_populated" */
207 * The bitmask of subsystems enabled on the child cgroups.
208 * ->subtree_control is the one configured through
209 * "cgroup.subtree_control" while ->child_subsys_mask is the
210 * effective one which may have more subsystems enabled.
211 * Controller knobs are made available iff it's enabled in
214 unsigned int subtree_control
;
215 unsigned int child_subsys_mask
;
217 /* Private pointers for each registered subsystem */
218 struct cgroup_subsys_state __rcu
*subsys
[CGROUP_SUBSYS_COUNT
];
220 struct cgroup_root
*root
;
223 * List of cgrp_cset_links pointing at css_sets with tasks in this
224 * cgroup. Protected by css_set_lock.
226 struct list_head cset_links
;
229 * On the default hierarchy, a css_set for a cgroup with some
230 * susbsys disabled will point to css's which are associated with
231 * the closest ancestor which has the subsys enabled. The
232 * following lists all css_sets which point to this cgroup's css
233 * for the given subsystem.
235 struct list_head e_csets
[CGROUP_SUBSYS_COUNT
];
238 * Linked list running through all cgroups that can
239 * potentially be reaped by the release agent. Protected by
242 struct list_head release_list
;
245 * list of pidlists, up to two for each namespace (one for procs, one
246 * for tasks); created on demand.
248 struct list_head pidlists
;
249 struct mutex pidlist_mutex
;
251 /* used to wait for offlining of csses */
252 wait_queue_head_t offline_waitq
;
255 #define MAX_CGROUP_ROOT_NAMELEN 64
257 /* cgroup_root->flags */
259 CGRP_ROOT_SANE_BEHAVIOR
= (1 << 0), /* __DEVEL__sane_behavior specified */
260 CGRP_ROOT_NOPREFIX
= (1 << 1), /* mounted subsystems have no named prefix */
261 CGRP_ROOT_XATTR
= (1 << 2), /* supports extended attributes */
265 * A cgroup_root represents the root of a cgroup hierarchy, and may be
266 * associated with a kernfs_root to form an active hierarchy. This is
267 * internal to cgroup core. Don't access directly from controllers.
270 struct kernfs_root
*kf_root
;
272 /* The bitmask of subsystems attached to this hierarchy */
273 unsigned int subsys_mask
;
275 /* Unique id for this hierarchy. */
278 /* The root cgroup. Root is destroyed on its release. */
281 /* Number of cgroups in the hierarchy, used only for /proc/cgroups */
284 /* A list running through the active hierarchies */
285 struct list_head root_list
;
287 /* Hierarchy-specific flags */
290 /* IDs for cgroups in this hierarchy */
291 struct idr cgroup_idr
;
293 /* The path to use for release notifications. */
294 char release_agent_path
[PATH_MAX
];
296 /* The name for this hierarchy - may be empty */
297 char name
[MAX_CGROUP_ROOT_NAMELEN
];
301 * A css_set is a structure holding pointers to a set of
302 * cgroup_subsys_state objects. This saves space in the task struct
303 * object and speeds up fork()/exit(), since a single inc/dec and a
304 * list_add()/del() can bump the reference count on the entire cgroup
310 /* Reference count */
314 * List running through all cgroup groups in the same hash
315 * slot. Protected by css_set_lock
317 struct hlist_node hlist
;
320 * Lists running through all tasks using this cgroup group.
321 * mg_tasks lists tasks which belong to this cset but are in the
322 * process of being migrated out or in. Protected by
323 * css_set_rwsem, but, during migration, once tasks are moved to
324 * mg_tasks, it can be read safely while holding cgroup_mutex.
326 struct list_head tasks
;
327 struct list_head mg_tasks
;
330 * List of cgrp_cset_links pointing at cgroups referenced from this
331 * css_set. Protected by css_set_lock.
333 struct list_head cgrp_links
;
335 /* the default cgroup associated with this css_set */
336 struct cgroup
*dfl_cgrp
;
339 * Set of subsystem states, one for each subsystem. This array is
340 * immutable after creation apart from the init_css_set during
341 * subsystem registration (at boot time).
343 struct cgroup_subsys_state
*subsys
[CGROUP_SUBSYS_COUNT
];
346 * List of csets participating in the on-going migration either as
347 * source or destination. Protected by cgroup_mutex.
349 struct list_head mg_preload_node
;
350 struct list_head mg_node
;
353 * If this cset is acting as the source of migration the following
354 * two fields are set. mg_src_cgrp is the source cgroup of the
355 * on-going migration and mg_dst_cset is the destination cset the
356 * target tasks on this cset should be migrated to. Protected by
359 struct cgroup
*mg_src_cgrp
;
360 struct css_set
*mg_dst_cset
;
363 * On the default hierarhcy, ->subsys[ssid] may point to a css
364 * attached to an ancestor instead of the cgroup this css_set is
365 * associated with. The following node is anchored at
366 * ->subsys[ssid]->cgroup->e_csets[ssid] and provides a way to
367 * iterate through all css's attached to a given cgroup.
369 struct list_head e_cset_node
[CGROUP_SUBSYS_COUNT
];
371 /* For RCU-protected deletion */
372 struct rcu_head rcu_head
;
376 * struct cftype: handler definitions for cgroup control files
378 * When reading/writing to a file:
379 * - the cgroup to use is file->f_dentry->d_parent->d_fsdata
380 * - the 'cftype' of the file is file->f_dentry->d_fsdata
385 CFTYPE_ONLY_ON_ROOT
= (1 << 0), /* only create on root cgrp */
386 CFTYPE_NOT_ON_ROOT
= (1 << 1), /* don't create on root cgrp */
387 CFTYPE_NO_PREFIX
= (1 << 3), /* (DON'T USE FOR NEW FILES) no subsys prefix */
389 /* internal flags, do not use outside cgroup core proper */
390 __CFTYPE_ONLY_ON_DFL
= (1 << 16), /* only on default hierarchy */
391 __CFTYPE_NOT_ON_DFL
= (1 << 17), /* not on default hierarchy */
394 #define MAX_CFTYPE_NAME 64
398 * By convention, the name should begin with the name of the
399 * subsystem, followed by a period. Zero length string indicates
400 * end of cftype array.
402 char name
[MAX_CFTYPE_NAME
];
405 * If not 0, file mode is set to this value, otherwise it will
406 * be figured out automatically
411 * The maximum length of string, excluding trailing nul, that can
412 * be passed to write. If < PAGE_SIZE-1, PAGE_SIZE-1 is assumed.
414 size_t max_write_len
;
420 * Fields used for internal bookkeeping. Initialized automatically
421 * during registration.
423 struct cgroup_subsys
*ss
; /* NULL for cgroup core files */
424 struct list_head node
; /* anchored at ss->cfts */
425 struct kernfs_ops
*kf_ops
;
428 * read_u64() is a shortcut for the common case of returning a
429 * single integer. Use it in place of read()
431 u64 (*read_u64
)(struct cgroup_subsys_state
*css
, struct cftype
*cft
);
433 * read_s64() is a signed version of read_u64()
435 s64 (*read_s64
)(struct cgroup_subsys_state
*css
, struct cftype
*cft
);
437 /* generic seq_file read interface */
438 int (*seq_show
)(struct seq_file
*sf
, void *v
);
440 /* optional ops, implement all or none */
441 void *(*seq_start
)(struct seq_file
*sf
, loff_t
*ppos
);
442 void *(*seq_next
)(struct seq_file
*sf
, void *v
, loff_t
*ppos
);
443 void (*seq_stop
)(struct seq_file
*sf
, void *v
);
446 * write_u64() is a shortcut for the common case of accepting
447 * a single integer (as parsed by simple_strtoull) from
448 * userspace. Use in place of write(); return 0 or error.
450 int (*write_u64
)(struct cgroup_subsys_state
*css
, struct cftype
*cft
,
453 * write_s64() is a signed version of write_u64()
455 int (*write_s64
)(struct cgroup_subsys_state
*css
, struct cftype
*cft
,
459 * write() is the generic write callback which maps directly to
460 * kernfs write operation and overrides all other operations.
461 * Maximum write size is determined by ->max_write_len. Use
462 * of_css/cft() to access the associated css and cft.
464 ssize_t (*write
)(struct kernfs_open_file
*of
,
465 char *buf
, size_t nbytes
, loff_t off
);
467 #ifdef CONFIG_DEBUG_LOCK_ALLOC
468 struct lock_class_key lockdep_key
;
472 extern struct cgroup_root cgrp_dfl_root
;
473 extern struct css_set init_css_set
;
476 * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
477 * @cgrp: the cgroup of interest
479 * The default hierarchy is the v2 interface of cgroup and this function
480 * can be used to test whether a cgroup is on the default hierarchy for
481 * cases where a subsystem should behave differnetly depending on the
484 * The set of behaviors which change on the default hierarchy are still
485 * being determined and the mount option is prefixed with __DEVEL__.
487 * List of changed behaviors:
489 * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
490 * and "name" are disallowed.
492 * - When mounting an existing superblock, mount options should match.
494 * - Remount is disallowed.
496 * - rename(2) is disallowed.
498 * - "tasks" is removed. Everything should be at process granularity. Use
499 * "cgroup.procs" instead.
501 * - "cgroup.procs" is not sorted. pids will be unique unless they got
502 * recycled inbetween reads.
504 * - "release_agent" and "notify_on_release" are removed. Replacement
505 * notification mechanism will be implemented.
507 * - "cgroup.clone_children" is removed.
509 * - "cgroup.subtree_populated" is available. Its value is 0 if the cgroup
510 * and its descendants contain no task; otherwise, 1. The file also
511 * generates kernfs notification which can be monitored through poll and
512 * [di]notify when the value of the file changes.
514 * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
515 * take masks of ancestors with non-empty cpus/mems, instead of being
516 * moved to an ancestor.
518 * - cpuset: a task can be moved into an empty cpuset, and again it takes
519 * masks of ancestors.
521 * - memcg: use_hierarchy is on by default and the cgroup file for the flag
524 * - blkcg: blk-throttle becomes properly hierarchical.
526 * - debug: disallowed on the default hierarchy.
528 static inline bool cgroup_on_dfl(const struct cgroup
*cgrp
)
530 return cgrp
->root
== &cgrp_dfl_root
;
533 /* no synchronization, the result can only be used as a hint */
534 static inline bool cgroup_has_tasks(struct cgroup
*cgrp
)
536 return !list_empty(&cgrp
->cset_links
);
539 /* returns ino associated with a cgroup, 0 indicates unmounted root */
540 static inline ino_t
cgroup_ino(struct cgroup
*cgrp
)
543 return cgrp
->kn
->ino
;
548 /* cft/css accessors for cftype->write() operation */
549 static inline struct cftype
*of_cft(struct kernfs_open_file
*of
)
554 struct cgroup_subsys_state
*of_css(struct kernfs_open_file
*of
);
556 /* cft/css accessors for cftype->seq_*() operations */
557 static inline struct cftype
*seq_cft(struct seq_file
*seq
)
559 return of_cft(seq
->private);
562 static inline struct cgroup_subsys_state
*seq_css(struct seq_file
*seq
)
564 return of_css(seq
->private);
568 * Name / path handling functions. All are thin wrappers around the kernfs
569 * counterparts and can be called under any context.
572 static inline int cgroup_name(struct cgroup
*cgrp
, char *buf
, size_t buflen
)
574 return kernfs_name(cgrp
->kn
, buf
, buflen
);
577 static inline char * __must_check
cgroup_path(struct cgroup
*cgrp
, char *buf
,
580 return kernfs_path(cgrp
->kn
, buf
, buflen
);
583 static inline void pr_cont_cgroup_name(struct cgroup
*cgrp
)
585 pr_cont_kernfs_name(cgrp
->kn
);
588 static inline void pr_cont_cgroup_path(struct cgroup
*cgrp
)
590 pr_cont_kernfs_path(cgrp
->kn
);
593 char *task_cgroup_path(struct task_struct
*task
, char *buf
, size_t buflen
);
595 int cgroup_add_dfl_cftypes(struct cgroup_subsys
*ss
, struct cftype
*cfts
);
596 int cgroup_add_legacy_cftypes(struct cgroup_subsys
*ss
, struct cftype
*cfts
);
597 int cgroup_rm_cftypes(struct cftype
*cfts
);
599 bool cgroup_is_descendant(struct cgroup
*cgrp
, struct cgroup
*ancestor
);
602 * Control Group taskset, used to pass around set of tasks to cgroup_subsys
605 struct cgroup_taskset
;
606 struct task_struct
*cgroup_taskset_first(struct cgroup_taskset
*tset
);
607 struct task_struct
*cgroup_taskset_next(struct cgroup_taskset
*tset
);
610 * cgroup_taskset_for_each - iterate cgroup_taskset
611 * @task: the loop cursor
612 * @tset: taskset to iterate
614 #define cgroup_taskset_for_each(task, tset) \
615 for ((task) = cgroup_taskset_first((tset)); (task); \
616 (task) = cgroup_taskset_next((tset)))
619 * Control Group subsystem type.
620 * See Documentation/cgroups/cgroups.txt for details
623 struct cgroup_subsys
{
624 struct cgroup_subsys_state
*(*css_alloc
)(struct cgroup_subsys_state
*parent_css
);
625 int (*css_online
)(struct cgroup_subsys_state
*css
);
626 void (*css_offline
)(struct cgroup_subsys_state
*css
);
627 void (*css_free
)(struct cgroup_subsys_state
*css
);
628 void (*css_reset
)(struct cgroup_subsys_state
*css
);
630 int (*can_attach
)(struct cgroup_subsys_state
*css
,
631 struct cgroup_taskset
*tset
);
632 void (*cancel_attach
)(struct cgroup_subsys_state
*css
,
633 struct cgroup_taskset
*tset
);
634 void (*attach
)(struct cgroup_subsys_state
*css
,
635 struct cgroup_taskset
*tset
);
636 void (*fork
)(struct task_struct
*task
);
637 void (*exit
)(struct cgroup_subsys_state
*css
,
638 struct cgroup_subsys_state
*old_css
,
639 struct task_struct
*task
);
640 void (*bind
)(struct cgroup_subsys_state
*root_css
);
646 * If %false, this subsystem is properly hierarchical -
647 * configuration, resource accounting and restriction on a parent
648 * cgroup cover those of its children. If %true, hierarchy support
649 * is broken in some ways - some subsystems ignore hierarchy
650 * completely while others are only implemented half-way.
652 * It's now disallowed to create nested cgroups if the subsystem is
653 * broken and cgroup core will emit a warning message on such
654 * cases. Eventually, all subsystems will be made properly
655 * hierarchical and this will go away.
657 bool broken_hierarchy
;
658 bool warned_broken_hierarchy
;
660 /* the following two fields are initialized automtically during boot */
662 #define MAX_CGROUP_TYPE_NAMELEN 32
665 /* link to parent, protected by cgroup_lock() */
666 struct cgroup_root
*root
;
668 /* idr for css->id */
672 * List of cftypes. Each entry is the first entry of an array
673 * terminated by zero length name.
675 struct list_head cfts
;
678 * Base cftypes which are automatically registered. The two can
679 * point to the same array.
681 struct cftype
*dfl_cftypes
; /* for the default hierarchy */
682 struct cftype
*legacy_cftypes
; /* for the legacy hierarchies */
685 * A subsystem may depend on other subsystems. When such subsystem
686 * is enabled on a cgroup, the depended-upon subsystems are enabled
687 * together if available. Subsystems enabled due to dependency are
688 * not visible to userland until explicitly enabled. The following
689 * specifies the mask of subsystems that this one depends on.
691 unsigned int depends_on
;
694 #define SUBSYS(_x) extern struct cgroup_subsys _x ## _cgrp_subsys;
695 #include <linux/cgroup_subsys.h>
699 * task_css_set_check - obtain a task's css_set with extra access conditions
700 * @task: the task to obtain css_set for
701 * @__c: extra condition expression to be passed to rcu_dereference_check()
703 * A task's css_set is RCU protected, initialized and exited while holding
704 * task_lock(), and can only be modified while holding both cgroup_mutex
705 * and task_lock() while the task is alive. This macro verifies that the
706 * caller is inside proper critical section and returns @task's css_set.
708 * The caller can also specify additional allowed conditions via @__c, such
709 * as locks used during the cgroup_subsys::attach() methods.
711 #ifdef CONFIG_PROVE_RCU
712 extern struct mutex cgroup_mutex
;
713 extern struct rw_semaphore css_set_rwsem
;
714 #define task_css_set_check(task, __c) \
715 rcu_dereference_check((task)->cgroups, \
716 lockdep_is_held(&cgroup_mutex) || \
717 lockdep_is_held(&css_set_rwsem) || \
718 ((task)->flags & PF_EXITING) || (__c))
720 #define task_css_set_check(task, __c) \
721 rcu_dereference((task)->cgroups)
725 * task_css_check - obtain css for (task, subsys) w/ extra access conds
726 * @task: the target task
727 * @subsys_id: the target subsystem ID
728 * @__c: extra condition expression to be passed to rcu_dereference_check()
730 * Return the cgroup_subsys_state for the (@task, @subsys_id) pair. The
731 * synchronization rules are the same as task_css_set_check().
733 #define task_css_check(task, subsys_id, __c) \
734 task_css_set_check((task), (__c))->subsys[(subsys_id)]
737 * task_css_set - obtain a task's css_set
738 * @task: the task to obtain css_set for
740 * See task_css_set_check().
742 static inline struct css_set
*task_css_set(struct task_struct
*task
)
744 return task_css_set_check(task
, false);
748 * task_css - obtain css for (task, subsys)
749 * @task: the target task
750 * @subsys_id: the target subsystem ID
752 * See task_css_check().
754 static inline struct cgroup_subsys_state
*task_css(struct task_struct
*task
,
757 return task_css_check(task
, subsys_id
, false);
761 * task_css_is_root - test whether a task belongs to the root css
762 * @task: the target task
763 * @subsys_id: the target subsystem ID
765 * Test whether @task belongs to the root css on the specified subsystem.
766 * May be invoked in any context.
768 static inline bool task_css_is_root(struct task_struct
*task
, int subsys_id
)
770 return task_css_check(task
, subsys_id
, true) ==
771 init_css_set
.subsys
[subsys_id
];
774 static inline struct cgroup
*task_cgroup(struct task_struct
*task
,
777 return task_css(task
, subsys_id
)->cgroup
;
780 struct cgroup_subsys_state
*css_next_child(struct cgroup_subsys_state
*pos
,
781 struct cgroup_subsys_state
*parent
);
783 struct cgroup_subsys_state
*css_from_id(int id
, struct cgroup_subsys
*ss
);
786 * css_for_each_child - iterate through children of a css
787 * @pos: the css * to use as the loop cursor
788 * @parent: css whose children to walk
790 * Walk @parent's children. Must be called under rcu_read_lock().
792 * If a subsystem synchronizes ->css_online() and the start of iteration, a
793 * css which finished ->css_online() is guaranteed to be visible in the
794 * future iterations and will stay visible until the last reference is put.
795 * A css which hasn't finished ->css_online() or already finished
796 * ->css_offline() may show up during traversal. It's each subsystem's
797 * responsibility to synchronize against on/offlining.
799 * It is allowed to temporarily drop RCU read lock during iteration. The
800 * caller is responsible for ensuring that @pos remains accessible until
801 * the start of the next iteration by, for example, bumping the css refcnt.
803 #define css_for_each_child(pos, parent) \
804 for ((pos) = css_next_child(NULL, (parent)); (pos); \
805 (pos) = css_next_child((pos), (parent)))
807 struct cgroup_subsys_state
*
808 css_next_descendant_pre(struct cgroup_subsys_state
*pos
,
809 struct cgroup_subsys_state
*css
);
811 struct cgroup_subsys_state
*
812 css_rightmost_descendant(struct cgroup_subsys_state
*pos
);
815 * css_for_each_descendant_pre - pre-order walk of a css's descendants
816 * @pos: the css * to use as the loop cursor
817 * @root: css whose descendants to walk
819 * Walk @root's descendants. @root is included in the iteration and the
820 * first node to be visited. Must be called under rcu_read_lock().
822 * If a subsystem synchronizes ->css_online() and the start of iteration, a
823 * css which finished ->css_online() is guaranteed to be visible in the
824 * future iterations and will stay visible until the last reference is put.
825 * A css which hasn't finished ->css_online() or already finished
826 * ->css_offline() may show up during traversal. It's each subsystem's
827 * responsibility to synchronize against on/offlining.
829 * For example, the following guarantees that a descendant can't escape
830 * state updates of its ancestors.
834 * Lock @css's parent and @css;
835 * Inherit state from the parent;
839 * my_update_state(@css)
841 * css_for_each_descendant_pre(@pos, @css) {
844 * Update @css's state;
846 * Verify @pos is alive and inherit state from its parent;
851 * As long as the inheriting step, including checking the parent state, is
852 * enclosed inside @pos locking, double-locking the parent isn't necessary
853 * while inheriting. The state update to the parent is guaranteed to be
854 * visible by walking order and, as long as inheriting operations to the
855 * same @pos are atomic to each other, multiple updates racing each other
856 * still result in the correct state. It's guaranateed that at least one
857 * inheritance happens for any css after the latest update to its parent.
859 * If checking parent's state requires locking the parent, each inheriting
860 * iteration should lock and unlock both @pos->parent and @pos.
862 * Alternatively, a subsystem may choose to use a single global lock to
863 * synchronize ->css_online() and ->css_offline() against tree-walking
866 * It is allowed to temporarily drop RCU read lock during iteration. The
867 * caller is responsible for ensuring that @pos remains accessible until
868 * the start of the next iteration by, for example, bumping the css refcnt.
870 #define css_for_each_descendant_pre(pos, css) \
871 for ((pos) = css_next_descendant_pre(NULL, (css)); (pos); \
872 (pos) = css_next_descendant_pre((pos), (css)))
874 struct cgroup_subsys_state
*
875 css_next_descendant_post(struct cgroup_subsys_state
*pos
,
876 struct cgroup_subsys_state
*css
);
879 * css_for_each_descendant_post - post-order walk of a css's descendants
880 * @pos: the css * to use as the loop cursor
881 * @css: css whose descendants to walk
883 * Similar to css_for_each_descendant_pre() but performs post-order
884 * traversal instead. @root is included in the iteration and the last
885 * node to be visited.
887 * If a subsystem synchronizes ->css_online() and the start of iteration, a
888 * css which finished ->css_online() is guaranteed to be visible in the
889 * future iterations and will stay visible until the last reference is put.
890 * A css which hasn't finished ->css_online() or already finished
891 * ->css_offline() may show up during traversal. It's each subsystem's
892 * responsibility to synchronize against on/offlining.
894 * Note that the walk visibility guarantee example described in pre-order
895 * walk doesn't apply the same to post-order walks.
897 #define css_for_each_descendant_post(pos, css) \
898 for ((pos) = css_next_descendant_post(NULL, (css)); (pos); \
899 (pos) = css_next_descendant_post((pos), (css)))
901 bool css_has_online_children(struct cgroup_subsys_state
*css
);
903 /* A css_task_iter should be treated as an opaque object */
904 struct css_task_iter
{
905 struct cgroup_subsys
*ss
;
907 struct list_head
*cset_pos
;
908 struct list_head
*cset_head
;
910 struct list_head
*task_pos
;
911 struct list_head
*tasks_head
;
912 struct list_head
*mg_tasks_head
;
915 void css_task_iter_start(struct cgroup_subsys_state
*css
,
916 struct css_task_iter
*it
);
917 struct task_struct
*css_task_iter_next(struct css_task_iter
*it
);
918 void css_task_iter_end(struct css_task_iter
*it
);
920 int cgroup_attach_task_all(struct task_struct
*from
, struct task_struct
*);
921 int cgroup_transfer_tasks(struct cgroup
*to
, struct cgroup
*from
);
923 struct cgroup_subsys_state
*css_tryget_online_from_dir(struct dentry
*dentry
,
924 struct cgroup_subsys
*ss
);
926 #else /* !CONFIG_CGROUPS */
928 static inline int cgroup_init_early(void) { return 0; }
929 static inline int cgroup_init(void) { return 0; }
930 static inline void cgroup_fork(struct task_struct
*p
) {}
931 static inline void cgroup_post_fork(struct task_struct
*p
) {}
932 static inline void cgroup_exit(struct task_struct
*p
) {}
934 static inline int cgroupstats_build(struct cgroupstats
*stats
,
935 struct dentry
*dentry
)
940 /* No cgroups - nothing to do */
941 static inline int cgroup_attach_task_all(struct task_struct
*from
,
942 struct task_struct
*t
)
947 #endif /* !CONFIG_CGROUPS */
949 #endif /* _LINUX_CGROUP_H */