#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/rwsem.h>
#include <linux/idr.h>
#include <linux/workqueue.h>
#include <linux/fs.h>
#include <linux/percpu-refcount.h>
#include <linux/seq_file.h>
#include <linux/kernfs.h>
#include <linux/wait.h>
#ifdef CONFIG_CGROUPS
struct cgroup_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);
extern int cgroupstats_build(struct cgroupstats *stats,
struct dentry *dentry);
extern int proc_cgroup_show(struct seq_file *, void *);
/* define the enumeration of all cgroup subsystems */
#define SUBSYS(_x) _x ## _cgrp_id,
enum cgroup_subsys_id {
#include <linux/cgroup_subsys.h>
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 int 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 {
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;
/*
* If this cgroup contains any tasks, it contributes one to
* populated_cnt. All children with non-zero popuplated_cnt of
* their own contribute one. The count is zero iff there's no task
* in this cgroup or its subtree.
*/
int populated_cnt;
atomic_t refcnt;
/*
* 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 kernfs_node *kn; /* cgroup kernfs entry */
struct kernfs_node *control_kn; /* kn for "cgroup.subtree_control" */
struct kernfs_node *populated_kn; /* kn for "cgroup.subtree_populated" */
/*
* 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;
/* the bitmask of subsystems enabled on the child cgroups */
unsigned int child_subsys_mask;
/* Private pointers for each registered subsystem */
struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];
struct cgroup_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;
/*
* On the default hierarchy, a css_set for a cgroup with some
* susbsys disabled will point to css's which are associated with
* the closest ancestor which has the subsys enabled. The
* following lists all css_sets which point to this cgroup's css
* for the given subsystem.
*/
struct list_head e_csets[CGROUP_SUBSYS_COUNT];
/*
* 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;
/* used to wait for offlining of csses */
wait_queue_head_t offline_waitq;
};
#define MAX_CGROUP_ROOT_NAMELEN 64
/* cgroup_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", "xattr", "clone_children",
* "release_agent" and "name" are disallowed.
*
* - 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.
*
* - "cgroup.clone_children" is removed.
*
* - "cgroup.subtree_populated" is available. Its value is 0 if
* the cgroup and its descendants contain no task; otherwise, 1.
* The file also generates kernfs notification which can be
* monitored through poll and [di]notify when the value of the
* file changes.
*
* - If mount is requested with sane_behavior but without any
* subsystem, the default unified hierarchy is mounted.
*
* - 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,
};
/*
* A cgroup_root represents the root of a cgroup hierarchy, and may be
* associated with a kernfs_root to form an active hierarchy. This is
* internal to cgroup core. Don't access directly from controllers.
*/
struct cgroup_root {
struct kernfs_root *kf_root;
/* The bitmask of subsystems attached to this hierarchy */
unsigned int subsys_mask;
/* Unique id for this hierarchy. */
int hierarchy_id;
/* The root cgroup. Root is destroyed on its release. */
struct cgroup cgrp;
/* Number of cgroups in the hierarchy, used only for /proc/cgroups */
atomic_t nr_cgrps;
/* A list running through the active hierarchies */
struct list_head root_list;
/* Hierarchy-specific flags */
unsigned int 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;
/*
* Lists running through all tasks using this cgroup group.
* mg_tasks lists tasks which belong to this cset but are in the
* process of being migrated out or in. Protected by
* css_set_rwsem, but, during migration, once tasks are moved to
* mg_tasks, it can be read safely while holding cgroup_mutex.
*/
struct list_head tasks;
struct list_head mg_tasks;
/*
* List of cgrp_cset_links pointing at cgroups referenced from this
* css_set. Protected by css_set_lock.
*/
struct list_head cgrp_links;
/* the default cgroup associated with this css_set */
struct cgroup *dfl_cgrp;
/*
* 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).
*/
struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
/*
* List of csets participating in the on-going migration either as
* source or destination. Protected by cgroup_mutex.
*/
struct list_head mg_preload_node;
struct list_head mg_node;
/*
* If this cset is acting as the source of migration the following
* two fields are set. mg_src_cgrp is the source cgroup of the
* on-going migration and mg_dst_cset is the destination cset the
* target tasks on this cset should be migrated to. Protected by
* cgroup_mutex.
*/
struct cgroup *mg_src_cgrp;
struct css_set *mg_dst_cset;
/*
* On the default hierarhcy, ->subsys[ssid] may point to a css
* attached to an ancestor instead of the cgroup this css_set is
* associated with. The following node is anchored at
* ->subsys[ssid]->cgroup->e_csets[ssid] and provides a way to
* iterate through all css's attached to a given cgroup.
*/
struct list_head e_cset_node[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 */
CFTYPE_ONLY_ON_DFL = (1 << 4), /* only on default hierarchy */
};
#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;
/*
* The maximum length of string, excluding trailing nul, that can
* be passed to write_string. If < PAGE_SIZE-1, PAGE_SIZE-1 is
* assumed.
*/
size_t max_write_len;
/* CFTYPE_* flags */
unsigned int flags;
/*
* Fields used for internal bookkeeping. Initialized automatically
* during registration.
*/
struct cgroup_subsys *ss; /* NULL for cgroup core files */
struct list_head node; /* anchored at ss->cfts */
struct kernfs_ops *kf_ops;
/*
* 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,
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);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lock_class_key lockdep_key;
#endif
};
extern struct cgroup_root cgrp_dfl_root;
static inline bool cgroup_on_dfl(const struct cgroup *cgrp)
{
return cgrp->root == &cgrp_dfl_root;
}
/*
* 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;
}
/* no synchronization, the result can only be used as a hint */
static inline bool cgroup_has_tasks(struct cgroup *cgrp)
{
return !list_empty(&cgrp->cset_links);
}
/* returns ino associated with a cgroup, 0 indicates unmounted root */
static inline ino_t cgroup_ino(struct cgroup *cgrp)
{
if (cgrp->kn)
return cgrp->kn->ino;
else
return 0;
}
static inline struct cftype *seq_cft(struct seq_file *seq)
{
struct kernfs_open_file *of = seq->private;
return of->kn->priv;
}
struct cgroup_subsys_state *seq_css(struct seq_file *seq);
/*
* Name / path handling functions. All are thin wrappers around the kernfs
* counterparts and can be called under any context.
*/
static inline int cgroup_name(struct cgroup *cgrp, char *buf, size_t buflen)
{
return kernfs_name(cgrp->kn, buf, buflen);
}
static inline char * __must_check cgroup_path(struct cgroup *cgrp, char *buf,
size_t buflen)
{
return kernfs_path(cgrp->kn, buf, buflen);
}
static inline void pr_cont_cgroup_name(struct cgroup *cgrp)
{
pr_cont_kernfs_name(cgrp->kn);
}
static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
{
pr_cont_kernfs_path(cgrp->kn);
}
char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
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);
/*
* 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);
/**
* cgroup_taskset_for_each - iterate cgroup_taskset
* @task: the loop cursor
* @tset: taskset to iterate
*/
#define cgroup_taskset_for_each(task, tset) \
for ((task) = cgroup_taskset_first((tset)); (task); \
(task) = cgroup_taskset_next((tset)))
/*
* 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 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;
/* the following two fields are initialized automtically during boot */
int id;
#define MAX_CGROUP_TYPE_NAMELEN 32
const char *name;
/* link to parent, protected by cgroup_lock() */
struct cgroup_root *root;
/*
* List of cftypes. Each entry is the first entry of an array
* terminated by zero length name.
*/
struct list_head cfts;
/* base cftypes, automatically registered with subsys itself */
struct cftype *base_cftypes;
};
#define SUBSYS(_x) extern struct cgroup_subsys _x ## _cgrp_subsys;
#include <linux/cgroup_subsys.h>
#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;
extern struct rw_semaphore css_set_rwsem;
#define task_css_set_check(task, __c) \
rcu_dereference_check((task)->cgroups, \
lockdep_is_held(&cgroup_mutex) || \
lockdep_is_held(&css_set_rwsem) || \
((task)->flags & PF_EXITING) || (__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 *ss;
struct list_head *cset_pos;
struct list_head *cset_head;
struct list_head *task_pos;
struct list_head *tasks_head;
struct list_head *mg_tasks_head;
};
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 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_tryget_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) {}
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 */
