linux/include/linux/cgroup.h
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   1#ifndef _LINUX_CGROUP_H
   2#define _LINUX_CGROUP_H
   3/*
   4 *  cgroup interface
   5 *
   6 *  Copyright (C) 2003 BULL SA
   7 *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
   8 *
   9 */
  10
  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>
  22
  23#ifdef CONFIG_CGROUPS
  24
  25struct cgroupfs_root;
  26struct cgroup_subsys;
  27struct inode;
  28struct cgroup;
  29struct css_id;
  30
  31extern int cgroup_init_early(void);
  32extern int cgroup_init(void);
  33extern void cgroup_lock(void);
  34extern int cgroup_lock_is_held(void);
  35extern bool cgroup_lock_live_group(struct cgroup *cgrp);
  36extern void cgroup_unlock(void);
  37extern void cgroup_fork(struct task_struct *p);
  38extern void cgroup_post_fork(struct task_struct *p);
  39extern void cgroup_exit(struct task_struct *p, int run_callbacks);
  40extern int cgroupstats_build(struct cgroupstats *stats,
  41                                struct dentry *dentry);
  42extern int cgroup_load_subsys(struct cgroup_subsys *ss);
  43extern void cgroup_unload_subsys(struct cgroup_subsys *ss);
  44
  45extern const struct file_operations proc_cgroup_operations;
  46
  47/* Define the enumeration of all builtin cgroup subsystems */
  48#define SUBSYS(_x) _x ## _subsys_id,
  49#define IS_SUBSYS_ENABLED(option) IS_ENABLED(option)
  50enum cgroup_subsys_id {
  51#include <linux/cgroup_subsys.h>
  52        CGROUP_SUBSYS_COUNT,
  53};
  54#undef IS_SUBSYS_ENABLED
  55#undef SUBSYS
  56
  57/* Per-subsystem/per-cgroup state maintained by the system. */
  58struct cgroup_subsys_state {
  59        /*
  60         * The cgroup that this subsystem is attached to. Useful
  61         * for subsystems that want to know about the cgroup
  62         * hierarchy structure
  63         */
  64        struct cgroup *cgroup;
  65
  66        /*
  67         * State maintained by the cgroup system to allow subsystems
  68         * to be "busy". Should be accessed via css_get(),
  69         * css_tryget() and css_put().
  70         */
  71
  72        atomic_t refcnt;
  73
  74        unsigned long flags;
  75        /* ID for this css, if possible */
  76        struct css_id __rcu *id;
  77
  78        /* Used to put @cgroup->dentry on the last css_put() */
  79        struct work_struct dput_work;
  80};
  81
  82/* bits in struct cgroup_subsys_state flags field */
  83enum {
  84        CSS_ROOT        = (1 << 0), /* this CSS is the root of the subsystem */
  85        CSS_ONLINE      = (1 << 1), /* between ->css_online() and ->css_offline() */
  86};
  87
  88/* Caller must verify that the css is not for root cgroup */
  89static inline void __css_get(struct cgroup_subsys_state *css, int count)
  90{
  91        atomic_add(count, &css->refcnt);
  92}
  93
  94/*
  95 * Call css_get() to hold a reference on the css; it can be used
  96 * for a reference obtained via:
  97 * - an existing ref-counted reference to the css
  98 * - task->cgroups for a locked task
  99 */
 100
 101static inline void css_get(struct cgroup_subsys_state *css)
 102{
 103        /* We don't need to reference count the root state */
 104        if (!(css->flags & CSS_ROOT))
 105                __css_get(css, 1);
 106}
 107
 108/*
 109 * Call css_tryget() to take a reference on a css if your existing
 110 * (known-valid) reference isn't already ref-counted. Returns false if
 111 * the css has been destroyed.
 112 */
 113
 114extern bool __css_tryget(struct cgroup_subsys_state *css);
 115static inline bool css_tryget(struct cgroup_subsys_state *css)
 116{
 117        if (css->flags & CSS_ROOT)
 118                return true;
 119        return __css_tryget(css);
 120}
 121
 122/*
 123 * css_put() should be called to release a reference taken by
 124 * css_get() or css_tryget()
 125 */
 126
 127extern void __css_put(struct cgroup_subsys_state *css);
 128static inline void css_put(struct cgroup_subsys_state *css)
 129{
 130        if (!(css->flags & CSS_ROOT))
 131                __css_put(css);
 132}
 133
 134/* bits in struct cgroup flags field */
 135enum {
 136        /* Control Group is dead */
 137        CGRP_REMOVED,
 138        /*
 139         * Control Group has previously had a child cgroup or a task,
 140         * but no longer (only if CGRP_NOTIFY_ON_RELEASE is set)
 141         */
 142        CGRP_RELEASABLE,
 143        /* Control Group requires release notifications to userspace */
 144        CGRP_NOTIFY_ON_RELEASE,
 145        /*
 146         * Clone the parent's configuration when creating a new child
 147         * cpuset cgroup.  For historical reasons, this option can be
 148         * specified at mount time and thus is implemented here.
 149         */
 150        CGRP_CPUSET_CLONE_CHILDREN,
 151};
 152
 153struct cgroup {
 154        unsigned long flags;            /* "unsigned long" so bitops work */
 155
 156        /*
 157         * count users of this cgroup. >0 means busy, but doesn't
 158         * necessarily indicate the number of tasks in the cgroup
 159         */
 160        atomic_t count;
 161
 162        int id;                         /* ida allocated in-hierarchy ID */
 163
 164        /*
 165         * We link our 'sibling' struct into our parent's 'children'.
 166         * Our children link their 'sibling' into our 'children'.
 167         */
 168        struct list_head sibling;       /* my parent's children */
 169        struct list_head children;      /* my children */
 170        struct list_head files;         /* my files */
 171
 172        struct cgroup *parent;          /* my parent */
 173        struct dentry *dentry;          /* cgroup fs entry, RCU protected */
 174
 175        /* Private pointers for each registered subsystem */
 176        struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
 177
 178        struct cgroupfs_root *root;
 179        struct cgroup *top_cgroup;
 180
 181        /*
 182         * List of cg_cgroup_links pointing at css_sets with
 183         * tasks in this cgroup. Protected by css_set_lock
 184         */
 185        struct list_head css_sets;
 186
 187        struct list_head allcg_node;    /* cgroupfs_root->allcg_list */
 188        struct list_head cft_q_node;    /* used during cftype add/rm */
 189
 190        /*
 191         * Linked list running through all cgroups that can
 192         * potentially be reaped by the release agent. Protected by
 193         * release_list_lock
 194         */
 195        struct list_head release_list;
 196
 197        /*
 198         * list of pidlists, up to two for each namespace (one for procs, one
 199         * for tasks); created on demand.
 200         */
 201        struct list_head pidlists;
 202        struct mutex pidlist_mutex;
 203
 204        /* For RCU-protected deletion */
 205        struct rcu_head rcu_head;
 206
 207        /* List of events which userspace want to receive */
 208        struct list_head event_list;
 209        spinlock_t event_list_lock;
 210
 211        /* directory xattrs */
 212        struct simple_xattrs xattrs;
 213};
 214
 215/*
 216 * A css_set is a structure holding pointers to a set of
 217 * cgroup_subsys_state objects. This saves space in the task struct
 218 * object and speeds up fork()/exit(), since a single inc/dec and a
 219 * list_add()/del() can bump the reference count on the entire cgroup
 220 * set for a task.
 221 */
 222
 223struct css_set {
 224
 225        /* Reference count */
 226        atomic_t refcount;
 227
 228        /*
 229         * List running through all cgroup groups in the same hash
 230         * slot. Protected by css_set_lock
 231         */
 232        struct hlist_node hlist;
 233
 234        /*
 235         * List running through all tasks using this cgroup
 236         * group. Protected by css_set_lock
 237         */
 238        struct list_head tasks;
 239
 240        /*
 241         * List of cg_cgroup_link objects on link chains from
 242         * cgroups referenced from this css_set. Protected by
 243         * css_set_lock
 244         */
 245        struct list_head cg_links;
 246
 247        /*
 248         * Set of subsystem states, one for each subsystem. This array
 249         * is immutable after creation apart from the init_css_set
 250         * during subsystem registration (at boot time) and modular subsystem
 251         * loading/unloading.
 252         */
 253        struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
 254
 255        /* For RCU-protected deletion */
 256        struct rcu_head rcu_head;
 257};
 258
 259/*
 260 * cgroup_map_cb is an abstract callback API for reporting map-valued
 261 * control files
 262 */
 263
 264struct cgroup_map_cb {
 265        int (*fill)(struct cgroup_map_cb *cb, const char *key, u64 value);
 266        void *state;
 267};
 268
 269/*
 270 * struct cftype: handler definitions for cgroup control files
 271 *
 272 * When reading/writing to a file:
 273 *      - the cgroup to use is file->f_dentry->d_parent->d_fsdata
 274 *      - the 'cftype' of the file is file->f_dentry->d_fsdata
 275 */
 276
 277/* cftype->flags */
 278#define CFTYPE_ONLY_ON_ROOT     (1U << 0)       /* only create on root cg */
 279#define CFTYPE_NOT_ON_ROOT      (1U << 1)       /* don't create on root cg */
 280
 281#define MAX_CFTYPE_NAME         64
 282
 283struct cftype {
 284        /*
 285         * By convention, the name should begin with the name of the
 286         * subsystem, followed by a period.  Zero length string indicates
 287         * end of cftype array.
 288         */
 289        char name[MAX_CFTYPE_NAME];
 290        int private;
 291        /*
 292         * If not 0, file mode is set to this value, otherwise it will
 293         * be figured out automatically
 294         */
 295        umode_t mode;
 296
 297        /*
 298         * If non-zero, defines the maximum length of string that can
 299         * be passed to write_string; defaults to 64
 300         */
 301        size_t max_write_len;
 302
 303        /* CFTYPE_* flags */
 304        unsigned int flags;
 305
 306        /* file xattrs */
 307        struct simple_xattrs xattrs;
 308
 309        int (*open)(struct inode *inode, struct file *file);
 310        ssize_t (*read)(struct cgroup *cgrp, struct cftype *cft,
 311                        struct file *file,
 312                        char __user *buf, size_t nbytes, loff_t *ppos);
 313        /*
 314         * read_u64() is a shortcut for the common case of returning a
 315         * single integer. Use it in place of read()
 316         */
 317        u64 (*read_u64)(struct cgroup *cgrp, struct cftype *cft);
 318        /*
 319         * read_s64() is a signed version of read_u64()
 320         */
 321        s64 (*read_s64)(struct cgroup *cgrp, struct cftype *cft);
 322        /*
 323         * read_map() is used for defining a map of key/value
 324         * pairs. It should call cb->fill(cb, key, value) for each
 325         * entry. The key/value pairs (and their ordering) should not
 326         * change between reboots.
 327         */
 328        int (*read_map)(struct cgroup *cont, struct cftype *cft,
 329                        struct cgroup_map_cb *cb);
 330        /*
 331         * read_seq_string() is used for outputting a simple sequence
 332         * using seqfile.
 333         */
 334        int (*read_seq_string)(struct cgroup *cont, struct cftype *cft,
 335                               struct seq_file *m);
 336
 337        ssize_t (*write)(struct cgroup *cgrp, struct cftype *cft,
 338                         struct file *file,
 339                         const char __user *buf, size_t nbytes, loff_t *ppos);
 340
 341        /*
 342         * write_u64() is a shortcut for the common case of accepting
 343         * a single integer (as parsed by simple_strtoull) from
 344         * userspace. Use in place of write(); return 0 or error.
 345         */
 346        int (*write_u64)(struct cgroup *cgrp, struct cftype *cft, u64 val);
 347        /*
 348         * write_s64() is a signed version of write_u64()
 349         */
 350        int (*write_s64)(struct cgroup *cgrp, struct cftype *cft, s64 val);
 351
 352        /*
 353         * write_string() is passed a nul-terminated kernelspace
 354         * buffer of maximum length determined by max_write_len.
 355         * Returns 0 or -ve error code.
 356         */
 357        int (*write_string)(struct cgroup *cgrp, struct cftype *cft,
 358                            const char *buffer);
 359        /*
 360         * trigger() callback can be used to get some kick from the
 361         * userspace, when the actual string written is not important
 362         * at all. The private field can be used to determine the
 363         * kick type for multiplexing.
 364         */
 365        int (*trigger)(struct cgroup *cgrp, unsigned int event);
 366
 367        int (*release)(struct inode *inode, struct file *file);
 368
 369        /*
 370         * register_event() callback will be used to add new userspace
 371         * waiter for changes related to the cftype. Implement it if
 372         * you want to provide this functionality. Use eventfd_signal()
 373         * on eventfd to send notification to userspace.
 374         */
 375        int (*register_event)(struct cgroup *cgrp, struct cftype *cft,
 376                        struct eventfd_ctx *eventfd, const char *args);
 377        /*
 378         * unregister_event() callback will be called when userspace
 379         * closes the eventfd or on cgroup removing.
 380         * This callback must be implemented, if you want provide
 381         * notification functionality.
 382         */
 383        void (*unregister_event)(struct cgroup *cgrp, struct cftype *cft,
 384                        struct eventfd_ctx *eventfd);
 385};
 386
 387/*
 388 * cftype_sets describe cftypes belonging to a subsystem and are chained at
 389 * cgroup_subsys->cftsets.  Each cftset points to an array of cftypes
 390 * terminated by zero length name.
 391 */
 392struct cftype_set {
 393        struct list_head                node;   /* chained at subsys->cftsets */
 394        struct cftype                   *cfts;
 395};
 396
 397struct cgroup_scanner {
 398        struct cgroup *cg;
 399        int (*test_task)(struct task_struct *p, struct cgroup_scanner *scan);
 400        void (*process_task)(struct task_struct *p,
 401                        struct cgroup_scanner *scan);
 402        struct ptr_heap *heap;
 403        void *data;
 404};
 405
 406int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 407int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 408
 409int cgroup_is_removed(const struct cgroup *cgrp);
 410
 411int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
 412
 413int cgroup_task_count(const struct cgroup *cgrp);
 414
 415/* Return true if cgrp is a descendant of the task's cgroup */
 416int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task);
 417
 418/*
 419 * Control Group taskset, used to pass around set of tasks to cgroup_subsys
 420 * methods.
 421 */
 422struct cgroup_taskset;
 423struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset);
 424struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset);
 425struct cgroup *cgroup_taskset_cur_cgroup(struct cgroup_taskset *tset);
 426int cgroup_taskset_size(struct cgroup_taskset *tset);
 427
 428/**
 429 * cgroup_taskset_for_each - iterate cgroup_taskset
 430 * @task: the loop cursor
 431 * @skip_cgrp: skip if task's cgroup matches this, %NULL to iterate through all
 432 * @tset: taskset to iterate
 433 */
 434#define cgroup_taskset_for_each(task, skip_cgrp, tset)                  \
 435        for ((task) = cgroup_taskset_first((tset)); (task);             \
 436             (task) = cgroup_taskset_next((tset)))                      \
 437                if (!(skip_cgrp) ||                                     \
 438                    cgroup_taskset_cur_cgroup((tset)) != (skip_cgrp))
 439
 440/*
 441 * Control Group subsystem type.
 442 * See Documentation/cgroups/cgroups.txt for details
 443 */
 444
 445struct cgroup_subsys {
 446        struct cgroup_subsys_state *(*css_alloc)(struct cgroup *cgrp);
 447        int (*css_online)(struct cgroup *cgrp);
 448        void (*css_offline)(struct cgroup *cgrp);
 449        void (*css_free)(struct cgroup *cgrp);
 450
 451        int (*can_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
 452        void (*cancel_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
 453        void (*attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
 454        void (*fork)(struct task_struct *task);
 455        void (*exit)(struct cgroup *cgrp, struct cgroup *old_cgrp,
 456                     struct task_struct *task);
 457        void (*bind)(struct cgroup *root);
 458
 459        int subsys_id;
 460        int active;
 461        int disabled;
 462        int early_init;
 463        /*
 464         * True if this subsys uses ID. ID is not available before cgroup_init()
 465         * (not available in early_init time.)
 466         */
 467        bool use_id;
 468
 469        /*
 470         * If %false, this subsystem is properly hierarchical -
 471         * configuration, resource accounting and restriction on a parent
 472         * cgroup cover those of its children.  If %true, hierarchy support
 473         * is broken in some ways - some subsystems ignore hierarchy
 474         * completely while others are only implemented half-way.
 475         *
 476         * It's now disallowed to create nested cgroups if the subsystem is
 477         * broken and cgroup core will emit a warning message on such
 478         * cases.  Eventually, all subsystems will be made properly
 479         * hierarchical and this will go away.
 480         */
 481        bool broken_hierarchy;
 482        bool warned_broken_hierarchy;
 483
 484#define MAX_CGROUP_TYPE_NAMELEN 32
 485        const char *name;
 486
 487        /*
 488         * Link to parent, and list entry in parent's children.
 489         * Protected by cgroup_lock()
 490         */
 491        struct cgroupfs_root *root;
 492        struct list_head sibling;
 493        /* used when use_id == true */
 494        struct idr idr;
 495        spinlock_t id_lock;
 496
 497        /* list of cftype_sets */
 498        struct list_head cftsets;
 499
 500        /* base cftypes, automatically [de]registered with subsys itself */
 501        struct cftype *base_cftypes;
 502        struct cftype_set base_cftset;
 503
 504        /* should be defined only by modular subsystems */
 505        struct module *module;
 506};
 507
 508#define SUBSYS(_x) extern struct cgroup_subsys _x ## _subsys;
 509#define IS_SUBSYS_ENABLED(option) IS_BUILTIN(option)
 510#include <linux/cgroup_subsys.h>
 511#undef IS_SUBSYS_ENABLED
 512#undef SUBSYS
 513
 514static inline struct cgroup_subsys_state *cgroup_subsys_state(
 515        struct cgroup *cgrp, int subsys_id)
 516{
 517        return cgrp->subsys[subsys_id];
 518}
 519
 520/*
 521 * function to get the cgroup_subsys_state which allows for extra
 522 * rcu_dereference_check() conditions, such as locks used during the
 523 * cgroup_subsys::attach() methods.
 524 */
 525#define task_subsys_state_check(task, subsys_id, __c)                   \
 526        rcu_dereference_check(task->cgroups->subsys[subsys_id],         \
 527                              lockdep_is_held(&task->alloc_lock) ||     \
 528                              cgroup_lock_is_held() || (__c))
 529
 530static inline struct cgroup_subsys_state *
 531task_subsys_state(struct task_struct *task, int subsys_id)
 532{
 533        return task_subsys_state_check(task, subsys_id, false);
 534}
 535
 536static inline struct cgroup* task_cgroup(struct task_struct *task,
 537                                               int subsys_id)
 538{
 539        return task_subsys_state(task, subsys_id)->cgroup;
 540}
 541
 542/**
 543 * cgroup_for_each_child - iterate through children of a cgroup
 544 * @pos: the cgroup * to use as the loop cursor
 545 * @cgroup: cgroup whose children to walk
 546 *
 547 * Walk @cgroup's children.  Must be called under rcu_read_lock().  A child
 548 * cgroup which hasn't finished ->css_online() or already has finished
 549 * ->css_offline() may show up during traversal and it's each subsystem's
 550 * responsibility to verify that each @pos is alive.
 551 *
 552 * If a subsystem synchronizes against the parent in its ->css_online() and
 553 * before starting iterating, a cgroup which finished ->css_online() is
 554 * guaranteed to be visible in the future iterations.
 555 */
 556#define cgroup_for_each_child(pos, cgroup)                              \
 557        list_for_each_entry_rcu(pos, &(cgroup)->children, sibling)
 558
 559struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
 560                                          struct cgroup *cgroup);
 561
 562/**
 563 * cgroup_for_each_descendant_pre - pre-order walk of a cgroup's descendants
 564 * @pos: the cgroup * to use as the loop cursor
 565 * @cgroup: cgroup whose descendants to walk
 566 *
 567 * Walk @cgroup's descendants.  Must be called under rcu_read_lock().  A
 568 * descendant cgroup which hasn't finished ->css_online() or already has
 569 * finished ->css_offline() may show up during traversal and it's each
 570 * subsystem's responsibility to verify that each @pos is alive.
 571 *
 572 * If a subsystem synchronizes against the parent in its ->css_online() and
 573 * before starting iterating, and synchronizes against @pos on each
 574 * iteration, any descendant cgroup which finished ->css_offline() is
 575 * guaranteed to be visible in the future iterations.
 576 *
 577 * In other words, the following guarantees that a descendant can't escape
 578 * state updates of its ancestors.
 579 *
 580 * my_online(@cgrp)
 581 * {
 582 *      Lock @cgrp->parent and @cgrp;
 583 *      Inherit state from @cgrp->parent;
 584 *      Unlock both.
 585 * }
 586 *
 587 * my_update_state(@cgrp)
 588 * {
 589 *      Lock @cgrp;
 590 *      Update @cgrp's state;
 591 *      Unlock @cgrp;
 592 *
 593 *      cgroup_for_each_descendant_pre(@pos, @cgrp) {
 594 *              Lock @pos;
 595 *              Verify @pos is alive and inherit state from @pos->parent;
 596 *              Unlock @pos;
 597 *      }
 598 * }
 599 *
 600 * As long as the inheriting step, including checking the parent state, is
 601 * enclosed inside @pos locking, double-locking the parent isn't necessary
 602 * while inheriting.  The state update to the parent is guaranteed to be
 603 * visible by walking order and, as long as inheriting operations to the
 604 * same @pos are atomic to each other, multiple updates racing each other
 605 * still result in the correct state.  It's guaranateed that at least one
 606 * inheritance happens for any cgroup after the latest update to its
 607 * parent.
 608 *
 609 * If checking parent's state requires locking the parent, each inheriting
 610 * iteration should lock and unlock both @pos->parent and @pos.
 611 *
 612 * Alternatively, a subsystem may choose to use a single global lock to
 613 * synchronize ->css_online() and ->css_offline() against tree-walking
 614 * operations.
 615 */
 616#define cgroup_for_each_descendant_pre(pos, cgroup)                     \
 617        for (pos = cgroup_next_descendant_pre(NULL, (cgroup)); (pos);   \
 618             pos = cgroup_next_descendant_pre((pos), (cgroup)))
 619
 620struct cgroup *cgroup_next_descendant_post(struct cgroup *pos,
 621                                           struct cgroup *cgroup);
 622
 623/**
 624 * cgroup_for_each_descendant_post - post-order walk of a cgroup's descendants
 625 * @pos: the cgroup * to use as the loop cursor
 626 * @cgroup: cgroup whose descendants to walk
 627 *
 628 * Similar to cgroup_for_each_descendant_pre() but performs post-order
 629 * traversal instead.  Note that the walk visibility guarantee described in
 630 * pre-order walk doesn't apply the same to post-order walks.
 631 */
 632#define cgroup_for_each_descendant_post(pos, cgroup)                    \
 633        for (pos = cgroup_next_descendant_post(NULL, (cgroup)); (pos);  \
 634             pos = cgroup_next_descendant_post((pos), (cgroup)))
 635
 636/* A cgroup_iter should be treated as an opaque object */
 637struct cgroup_iter {
 638        struct list_head *cg_link;
 639        struct list_head *task;
 640};
 641
 642/*
 643 * To iterate across the tasks in a cgroup:
 644 *
 645 * 1) call cgroup_iter_start to initialize an iterator
 646 *
 647 * 2) call cgroup_iter_next() to retrieve member tasks until it
 648 *    returns NULL or until you want to end the iteration
 649 *
 650 * 3) call cgroup_iter_end() to destroy the iterator.
 651 *
 652 * Or, call cgroup_scan_tasks() to iterate through every task in a
 653 * cgroup - cgroup_scan_tasks() holds the css_set_lock when calling
 654 * the test_task() callback, but not while calling the process_task()
 655 * callback.
 656 */
 657void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it);
 658struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
 659                                        struct cgroup_iter *it);
 660void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
 661int cgroup_scan_tasks(struct cgroup_scanner *scan);
 662int cgroup_attach_task(struct cgroup *, struct task_struct *);
 663int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
 664
 665/*
 666 * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works
 667 * if cgroup_subsys.use_id == true. It can be used for looking up and scanning.
 668 * CSS ID is assigned at cgroup allocation (create) automatically
 669 * and removed when subsys calls free_css_id() function. This is because
 670 * the lifetime of cgroup_subsys_state is subsys's matter.
 671 *
 672 * Looking up and scanning function should be called under rcu_read_lock().
 673 * Taking cgroup_mutex is not necessary for following calls.
 674 * But the css returned by this routine can be "not populated yet" or "being
 675 * destroyed". The caller should check css and cgroup's status.
 676 */
 677
 678/*
 679 * Typically Called at ->destroy(), or somewhere the subsys frees
 680 * cgroup_subsys_state.
 681 */
 682void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css);
 683
 684/* Find a cgroup_subsys_state which has given ID */
 685
 686struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id);
 687
 688/*
 689 * Get a cgroup whose id is greater than or equal to id under tree of root.
 690 * Returning a cgroup_subsys_state or NULL.
 691 */
 692struct cgroup_subsys_state *css_get_next(struct cgroup_subsys *ss, int id,
 693                struct cgroup_subsys_state *root, int *foundid);
 694
 695/* Returns true if root is ancestor of cg */
 696bool css_is_ancestor(struct cgroup_subsys_state *cg,
 697                     const struct cgroup_subsys_state *root);
 698
 699/* Get id and depth of css */
 700unsigned short css_id(struct cgroup_subsys_state *css);
 701unsigned short css_depth(struct cgroup_subsys_state *css);
 702struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id);
 703
 704#else /* !CONFIG_CGROUPS */
 705
 706static inline int cgroup_init_early(void) { return 0; }
 707static inline int cgroup_init(void) { return 0; }
 708static inline void cgroup_fork(struct task_struct *p) {}
 709static inline void cgroup_fork_callbacks(struct task_struct *p) {}
 710static inline void cgroup_post_fork(struct task_struct *p) {}
 711static inline void cgroup_exit(struct task_struct *p, int callbacks) {}
 712
 713static inline void cgroup_lock(void) {}
 714static inline void cgroup_unlock(void) {}
 715static inline int cgroupstats_build(struct cgroupstats *stats,
 716                                        struct dentry *dentry)
 717{
 718        return -EINVAL;
 719}
 720
 721/* No cgroups - nothing to do */
 722static inline int cgroup_attach_task_all(struct task_struct *from,
 723                                         struct task_struct *t)
 724{
 725        return 0;
 726}
 727
 728#endif /* !CONFIG_CGROUPS */
 729
 730#endif /* _LINUX_CGROUP_H */
 731
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