include/linux/blk-cgroup.h

   1 #ifndef _BLK_CGROUP_H
   2 #define _BLK_CGROUP_H
   3 /*
   4  * Common Block IO controller cgroup interface
   5  *
   6  * Based on ideas and code from CFQ, CFS and BFQ:
   7  * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
   8  *
   9  * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
  10  *                    Paolo Valente <paolo.valente@unimore.it>
  11  *
  12  * Copyright (C) 2009 Vivek Goyal <vgoyal@redhat.com>
  13  *                    Nauman Rafique <nauman@google.com>
  14  */
  15
  16 #include <linux/cgroup.h>
  17 #include <linux/u64_stats_sync.h>
  18 #include <linux/seq_file.h>
  19 #include <linux/radix-tree.h>
  20 #include <linux/blkdev.h>
  21 #include <linux/atomic.h>
  22
  23 /* Max limits for throttle policy */
  24 #define THROTL_IOPS_MAX         UINT_MAX
  25
  26 #ifdef CONFIG_BLK_CGROUP
  27
  28 enum blkg_rwstat_type {
  29         BLKG_RWSTAT_READ,
  30         BLKG_RWSTAT_WRITE,
  31         BLKG_RWSTAT_SYNC,
  32         BLKG_RWSTAT_ASYNC,
  33
  34         BLKG_RWSTAT_NR,
  35         BLKG_RWSTAT_TOTAL = BLKG_RWSTAT_NR,
  36 };
  37
  38 struct blkcg_gq;
  39
  40 struct blkcg {
  41         struct cgroup_subsys_state      css;
  42         spinlock_t                      lock;
  43
  44         struct radix_tree_root          blkg_tree;
  45         struct blkcg_gq                 *blkg_hint;
  46         struct hlist_head               blkg_list;
  47
  48         struct blkcg_policy_data        *pd[BLKCG_MAX_POLS];
  49
  50         struct list_head                all_blkcgs_node;
  51 #ifdef CONFIG_CGROUP_WRITEBACK
  52         struct list_head                cgwb_list;
  53 #endif
  54 };
  55
  56 struct blkg_stat {
  57         struct u64_stats_sync           syncp;
  58         uint64_t                        cnt;
  59 };
  60
  61 struct blkg_rwstat {
  62         struct u64_stats_sync           syncp;
  63         uint64_t                        cnt[BLKG_RWSTAT_NR];
  64 };
  65
  66 /*
  67  * A blkcg_gq (blkg) is association between a block cgroup (blkcg) and a
  68  * request_queue (q).  This is used by blkcg policies which need to track
  69  * information per blkcg - q pair.
  70  *
  71  * There can be multiple active blkcg policies and each has its private
  72  * data on each blkg, the size of which is determined by
  73  * blkcg_policy->pd_size.  blkcg core allocates and frees such areas
  74  * together with blkg and invokes pd_init/exit_fn() methods.
  75  *
  76  * Such private data must embed struct blkg_policy_data (pd) at the
  77  * beginning and pd_size can't be smaller than pd.
  78  */
  79 struct blkg_policy_data {
  80         /* the blkg and policy id this per-policy data belongs to */
  81         struct blkcg_gq                 *blkg;
  82         int                             plid;
  83 };
  84
  85 /*
  86  * Policies that need to keep per-blkcg data which is independent
  87  * from any request_queue associated to it must specify its size
  88  * with the cpd_size field of the blkcg_policy structure and
  89  * embed a blkcg_policy_data in it.  cpd_init() is invoked to let
  90  * each policy handle per-blkcg data.
  91  */
  92 struct blkcg_policy_data {
  93         /* the policy id this per-policy data belongs to */
  94         int                             plid;
  95 };
  96
  97 /* association between a blk cgroup and a request queue */
  98 struct blkcg_gq {
  99         /* Pointer to the associated request_queue */
 100         struct request_queue            *q;
 101         struct list_head                q_node;
 102         struct hlist_node               blkcg_node;
 103         struct blkcg                    *blkcg;
 104
 105         /*
 106          * Each blkg gets congested separately and the congestion state is
 107          * propagated to the matching bdi_writeback_congested.
 108          */
 109         struct bdi_writeback_congested  *wb_congested;
 110
 111         /* all non-root blkcg_gq's are guaranteed to have access to parent */
 112         struct blkcg_gq                 *parent;
 113
 114         /* request allocation list for this blkcg-q pair */
 115         struct request_list             rl;
 116
 117         /* reference count */
 118         atomic_t                        refcnt;
 119
 120         /* is this blkg online? protected by both blkcg and q locks */
 121         bool                            online;
 122
 123         struct blkg_policy_data         *pd[BLKCG_MAX_POLS];
 124
 125         struct rcu_head                 rcu_head;
 126 };
 127
 128 typedef void (blkcg_pol_init_cpd_fn)(const struct blkcg *blkcg);
 129 typedef void (blkcg_pol_init_pd_fn)(struct blkcg_gq *blkg);
 130 typedef void (blkcg_pol_online_pd_fn)(struct blkcg_gq *blkg);
 131 typedef void (blkcg_pol_offline_pd_fn)(struct blkcg_gq *blkg);
 132 typedef void (blkcg_pol_exit_pd_fn)(struct blkcg_gq *blkg);
 133 typedef void (blkcg_pol_reset_pd_stats_fn)(struct blkcg_gq *blkg);
 134
 135 struct blkcg_policy {
 136         int                             plid;
 137         /* policy specific private data size */
 138         size_t                          pd_size;
 139         /* policy specific per-blkcg data size */
 140         size_t                          cpd_size;
 141         /* cgroup files for the policy */
 142         struct cftype                   *cftypes;
 143
 144         /* operations */
 145         blkcg_pol_init_cpd_fn           *cpd_init_fn;
 146         blkcg_pol_init_pd_fn            *pd_init_fn;
 147         blkcg_pol_online_pd_fn          *pd_online_fn;
 148         blkcg_pol_offline_pd_fn         *pd_offline_fn;
 149         blkcg_pol_exit_pd_fn            *pd_exit_fn;
 150         blkcg_pol_reset_pd_stats_fn     *pd_reset_stats_fn;
 151 };
 152
 153 extern struct blkcg blkcg_root;
 154 extern struct cgroup_subsys_state * const blkcg_root_css;
 155
 156 struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, struct request_queue *q);
 157 struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
 158                                     struct request_queue *q);
 159 int blkcg_init_queue(struct request_queue *q);
 160 void blkcg_drain_queue(struct request_queue *q);
 161 void blkcg_exit_queue(struct request_queue *q);
 162
 163 /* Blkio controller policy registration */
 164 int blkcg_policy_register(struct blkcg_policy *pol);
 165 void blkcg_policy_unregister(struct blkcg_policy *pol);
 166 int blkcg_activate_policy(struct request_queue *q,
 167                           const struct blkcg_policy *pol);
 168 void blkcg_deactivate_policy(struct request_queue *q,
 169                              const struct blkcg_policy *pol);
 170
 171 void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
 172                        u64 (*prfill)(struct seq_file *,
 173                                      struct blkg_policy_data *, int),
 174                        const struct blkcg_policy *pol, int data,
 175                        bool show_total);
 176 u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v);
 177 u64 __blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
 178                          const struct blkg_rwstat *rwstat);
 179 u64 blkg_prfill_stat(struct seq_file *sf, struct blkg_policy_data *pd, int off);
 180 u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
 181                        int off);
 182
 183 u64 blkg_stat_recursive_sum(struct blkg_policy_data *pd, int off);
 184 struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkg_policy_data *pd,
 185                                              int off);
 186
 187 struct blkg_conf_ctx {
 188         struct gendisk                  *disk;
 189         struct blkcg_gq                 *blkg;
 190         u64                             v;
 191 };
 192
 193 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 194                    const char *input, struct blkg_conf_ctx *ctx);
 195 void blkg_conf_finish(struct blkg_conf_ctx *ctx);
 196
 197
 198 static inline struct blkcg *css_to_blkcg(struct cgroup_subsys_state *css)
 199 {
 200         return css ? container_of(css, struct blkcg, css) : NULL;
 201 }
 202
 203 static inline struct blkcg *task_blkcg(struct task_struct *tsk)
 204 {
 205         return css_to_blkcg(task_css(tsk, blkio_cgrp_id));
 206 }
 207
 208 static inline struct blkcg *bio_blkcg(struct bio *bio)
 209 {
 210         if (bio && bio->bi_css)
 211                 return css_to_blkcg(bio->bi_css);
 212         return task_blkcg(current);
 213 }
 214
 215 static inline struct cgroup_subsys_state *
 216 task_get_blkcg_css(struct task_struct *task)
 217 {
 218         return task_get_css(task, blkio_cgrp_id);
 219 }
 220
 221 /**
 222  * blkcg_parent - get the parent of a blkcg
 223  * @blkcg: blkcg of interest
 224  *
 225  * Return the parent blkcg of @blkcg.  Can be called anytime.
 226  */
 227 static inline struct blkcg *blkcg_parent(struct blkcg *blkcg)
 228 {
 229         return css_to_blkcg(blkcg->css.parent);
 230 }
 231
 232 /**
 233  * blkg_to_pdata - get policy private data
 234  * @blkg: blkg of interest
 235  * @pol: policy of interest
 236  *
 237  * Return pointer to private data associated with the @blkg-@pol pair.
 238  */
 239 static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
 240                                                   struct blkcg_policy *pol)
 241 {
 242         return blkg ? blkg->pd[pol->plid] : NULL;
 243 }
 244
 245 static inline struct blkcg_policy_data *blkcg_to_cpd(struct blkcg *blkcg,
 246                                                      struct blkcg_policy *pol)
 247 {
 248         return blkcg ? blkcg->pd[pol->plid] : NULL;
 249 }
 250
 251 /**
 252  * pdata_to_blkg - get blkg associated with policy private data
 253  * @pd: policy private data of interest
 254  *
 255  * @pd is policy private data.  Determine the blkg it's associated with.
 256  */
 257 static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd)
 258 {
 259         return pd ? pd->blkg : NULL;
 260 }
 261
 262 /**
 263  * blkg_path - format cgroup path of blkg
 264  * @blkg: blkg of interest
 265  * @buf: target buffer
 266  * @buflen: target buffer length
 267  *
 268  * Format the path of the cgroup of @blkg into @buf.
 269  */
 270 static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
 271 {
 272         char *p;
 273
 274         p = cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
 275         if (!p) {
 276                 strncpy(buf, "<unavailable>", buflen);
 277                 return -ENAMETOOLONG;
 278         }
 279
 280         memmove(buf, p, buf + buflen - p);
 281         return 0;
 282 }
 283
 284 /**
 285  * blkg_get - get a blkg reference
 286  * @blkg: blkg to get
 287  *
 288  * The caller should be holding an existing reference.
 289  */
 290 static inline void blkg_get(struct blkcg_gq *blkg)
 291 {
 292         WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0);
 293         atomic_inc(&blkg->refcnt);
 294 }
 295
 296 void __blkg_release_rcu(struct rcu_head *rcu);
 297
 298 /**
 299  * blkg_put - put a blkg reference
 300  * @blkg: blkg to put
 301  */
 302 static inline void blkg_put(struct blkcg_gq *blkg)
 303 {
 304         WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0);
 305         if (atomic_dec_and_test(&blkg->refcnt))
 306                 call_rcu(&blkg->rcu_head, __blkg_release_rcu);
 307 }
 308
 309 struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg, struct request_queue *q,
 310                                bool update_hint);
 311
 312 /**
 313  * blkg_for_each_descendant_pre - pre-order walk of a blkg's descendants
 314  * @d_blkg: loop cursor pointing to the current descendant
 315  * @pos_css: used for iteration
 316  * @p_blkg: target blkg to walk descendants of
 317  *
 318  * Walk @c_blkg through the descendants of @p_blkg.  Must be used with RCU
 319  * read locked.  If called under either blkcg or queue lock, the iteration
 320  * is guaranteed to include all and only online blkgs.  The caller may
 321  * update @pos_css by calling css_rightmost_descendant() to skip subtree.
 322  * @p_blkg is included in the iteration and the first node to be visited.
 323  */
 324 #define blkg_for_each_descendant_pre(d_blkg, pos_css, p_blkg)           \
 325         css_for_each_descendant_pre((pos_css), &(p_blkg)->blkcg->css)   \
 326                 if (((d_blkg) = __blkg_lookup(css_to_blkcg(pos_css),    \
 327                                               (p_blkg)->q, false)))
 328
 329 /**
 330  * blkg_for_each_descendant_post - post-order walk of a blkg's descendants
 331  * @d_blkg: loop cursor pointing to the current descendant
 332  * @pos_css: used for iteration
 333  * @p_blkg: target blkg to walk descendants of
 334  *
 335  * Similar to blkg_for_each_descendant_pre() but performs post-order
 336  * traversal instead.  Synchronization rules are the same.  @p_blkg is
 337  * included in the iteration and the last node to be visited.
 338  */
 339 #define blkg_for_each_descendant_post(d_blkg, pos_css, p_blkg)          \
 340         css_for_each_descendant_post((pos_css), &(p_blkg)->blkcg->css)  \
 341                 if (((d_blkg) = __blkg_lookup(css_to_blkcg(pos_css),    \
 342                                               (p_blkg)->q, false)))
 343
 344 /**
 345  * blk_get_rl - get request_list to use
 346  * @q: request_queue of interest
 347  * @bio: bio which will be attached to the allocated request (may be %NULL)
 348  *
 349  * The caller wants to allocate a request from @q to use for @bio.  Find
 350  * the request_list to use and obtain a reference on it.  Should be called
 351  * under queue_lock.  This function is guaranteed to return non-%NULL
 352  * request_list.
 353  */
 354 static inline struct request_list *blk_get_rl(struct request_queue *q,
 355                                               struct bio *bio)
 356 {
 357         struct blkcg *blkcg;
 358         struct blkcg_gq *blkg;
 359
 360         rcu_read_lock();
 361
 362         blkcg = bio_blkcg(bio);
 363
 364         /* bypass blkg lookup and use @q->root_rl directly for root */
 365         if (blkcg == &blkcg_root)
 366                 goto root_rl;
 367
 368         /*
 369          * Try to use blkg->rl.  blkg lookup may fail under memory pressure
 370          * or if either the blkcg or queue is going away.  Fall back to
 371          * root_rl in such cases.
 372          */
 373         blkg = blkg_lookup_create(blkcg, q);
 374         if (unlikely(IS_ERR(blkg)))
 375                 goto root_rl;
 376
 377         blkg_get(blkg);
 378         rcu_read_unlock();
 379         return &blkg->rl;
 380 root_rl:
 381         rcu_read_unlock();
 382         return &q->root_rl;
 383 }
 384
 385 /**
 386  * blk_put_rl - put request_list
 387  * @rl: request_list to put
 388  *
 389  * Put the reference acquired by blk_get_rl().  Should be called under
 390  * queue_lock.
 391  */
 392 static inline void blk_put_rl(struct request_list *rl)
 393 {
 394         if (rl->blkg->blkcg != &blkcg_root)
 395                 blkg_put(rl->blkg);
 396 }
 397
 398 /**
 399  * blk_rq_set_rl - associate a request with a request_list
 400  * @rq: request of interest
 401  * @rl: target request_list
 402  *
 403  * Associate @rq with @rl so that accounting and freeing can know the
 404  * request_list @rq came from.
 405  */
 406 static inline void blk_rq_set_rl(struct request *rq, struct request_list *rl)
 407 {
 408         rq->rl = rl;
 409 }
 410
 411 /**
 412  * blk_rq_rl - return the request_list a request came from
 413  * @rq: request of interest
 414  *
 415  * Return the request_list @rq is allocated from.
 416  */
 417 static inline struct request_list *blk_rq_rl(struct request *rq)
 418 {
 419         return rq->rl;
 420 }
 421
 422 struct request_list *__blk_queue_next_rl(struct request_list *rl,
 423                                          struct request_queue *q);
 424 /**
 425  * blk_queue_for_each_rl - iterate through all request_lists of a request_queue
 426  *
 427  * Should be used under queue_lock.
 428  */
 429 #define blk_queue_for_each_rl(rl, q)    \
 430         for ((rl) = &(q)->root_rl; (rl); (rl) = __blk_queue_next_rl((rl), (q)))
 431
 432 static inline void blkg_stat_init(struct blkg_stat *stat)
 433 {
 434         u64_stats_init(&stat->syncp);
 435 }
 436
 437 /**
 438  * blkg_stat_add - add a value to a blkg_stat
 439  * @stat: target blkg_stat
 440  * @val: value to add
 441  *
 442  * Add @val to @stat.  The caller is responsible for synchronizing calls to
 443  * this function.
 444  */
 445 static inline void blkg_stat_add(struct blkg_stat *stat, uint64_t val)
 446 {
 447         u64_stats_update_begin(&stat->syncp);
 448         stat->cnt += val;
 449         u64_stats_update_end(&stat->syncp);
 450 }
 451
 452 /**
 453  * blkg_stat_read - read the current value of a blkg_stat
 454  * @stat: blkg_stat to read
 455  *
 456  * Read the current value of @stat.  This function can be called without
 457  * synchroniztion and takes care of u64 atomicity.
 458  */
 459 static inline uint64_t blkg_stat_read(struct blkg_stat *stat)
 460 {
 461         unsigned int start;
 462         uint64_t v;
 463
 464         do {
 465                 start = u64_stats_fetch_begin_irq(&stat->syncp);
 466                 v = stat->cnt;
 467         } while (u64_stats_fetch_retry_irq(&stat->syncp, start));
 468
 469         return v;
 470 }
 471
 472 /**
 473  * blkg_stat_reset - reset a blkg_stat
 474  * @stat: blkg_stat to reset
 475  */
 476 static inline void blkg_stat_reset(struct blkg_stat *stat)
 477 {
 478         stat->cnt = 0;
 479 }
 480
 481 /**
 482  * blkg_stat_merge - merge a blkg_stat into another
 483  * @to: the destination blkg_stat
 484  * @from: the source
 485  *
 486  * Add @from's count to @to.
 487  */
 488 static inline void blkg_stat_merge(struct blkg_stat *to, struct blkg_stat *from)
 489 {
 490         blkg_stat_add(to, blkg_stat_read(from));
 491 }
 492
 493 static inline void blkg_rwstat_init(struct blkg_rwstat *rwstat)
 494 {
 495         u64_stats_init(&rwstat->syncp);
 496 }
 497
 498 /**
 499  * blkg_rwstat_add - add a value to a blkg_rwstat
 500  * @rwstat: target blkg_rwstat
 501  * @rw: mask of REQ_{WRITE|SYNC}
 502  * @val: value to add
 503  *
 504  * Add @val to @rwstat.  The counters are chosen according to @rw.  The
 505  * caller is responsible for synchronizing calls to this function.
 506  */
 507 static inline void blkg_rwstat_add(struct blkg_rwstat *rwstat,
 508                                    int rw, uint64_t val)
 509 {
 510         u64_stats_update_begin(&rwstat->syncp);
 511
 512         if (rw & REQ_WRITE)
 513                 rwstat->cnt[BLKG_RWSTAT_WRITE] += val;
 514         else
 515                 rwstat->cnt[BLKG_RWSTAT_READ] += val;
 516         if (rw & REQ_SYNC)
 517                 rwstat->cnt[BLKG_RWSTAT_SYNC] += val;
 518         else
 519                 rwstat->cnt[BLKG_RWSTAT_ASYNC] += val;
 520
 521         u64_stats_update_end(&rwstat->syncp);
 522 }
 523
 524 /**
 525  * blkg_rwstat_read - read the current values of a blkg_rwstat
 526  * @rwstat: blkg_rwstat to read
 527  *
 528  * Read the current snapshot of @rwstat and return it as the return value.
 529  * This function can be called without synchronization and takes care of
 530  * u64 atomicity.
 531  */
 532 static inline struct blkg_rwstat blkg_rwstat_read(struct blkg_rwstat *rwstat)
 533 {
 534         unsigned int start;
 535         struct blkg_rwstat tmp;
 536
 537         do {
 538                 start = u64_stats_fetch_begin_irq(&rwstat->syncp);
 539                 tmp = *rwstat;
 540         } while (u64_stats_fetch_retry_irq(&rwstat->syncp, start));
 541
 542         return tmp;
 543 }
 544
 545 /**
 546  * blkg_rwstat_total - read the total count of a blkg_rwstat
 547  * @rwstat: blkg_rwstat to read
 548  *
 549  * Return the total count of @rwstat regardless of the IO direction.  This
 550  * function can be called without synchronization and takes care of u64
 551  * atomicity.
 552  */
 553 static inline uint64_t blkg_rwstat_total(struct blkg_rwstat *rwstat)
 554 {
 555         struct blkg_rwstat tmp = blkg_rwstat_read(rwstat);
 556
 557         return tmp.cnt[BLKG_RWSTAT_READ] + tmp.cnt[BLKG_RWSTAT_WRITE];
 558 }
 559
 560 /**
 561  * blkg_rwstat_reset - reset a blkg_rwstat
 562  * @rwstat: blkg_rwstat to reset
 563  */
 564 static inline void blkg_rwstat_reset(struct blkg_rwstat *rwstat)
 565 {
 566         memset(rwstat->cnt, 0, sizeof(rwstat->cnt));
 567 }
 568
 569 /**
 570  * blkg_rwstat_merge - merge a blkg_rwstat into another
 571  * @to: the destination blkg_rwstat
 572  * @from: the source
 573  *
 574  * Add @from's counts to @to.
 575  */
 576 static inline void blkg_rwstat_merge(struct blkg_rwstat *to,
 577                                      struct blkg_rwstat *from)
 578 {
 579         struct blkg_rwstat v = blkg_rwstat_read(from);
 580         int i;
 581
 582         u64_stats_update_begin(&to->syncp);
 583         for (i = 0; i < BLKG_RWSTAT_NR; i++)
 584                 to->cnt[i] += v.cnt[i];
 585         u64_stats_update_end(&to->syncp);
 586 }
 587
 588 #else   /* CONFIG_BLK_CGROUP */
 589
 590 struct blkcg {
 591 };
 592
 593 struct blkg_policy_data {
 594 };
 595
 596 struct blkcg_policy_data {
 597 };
 598
 599 struct blkcg_gq {
 600 };
 601
 602 struct blkcg_policy {
 603 };
 604
 605 #define blkcg_root_css  ((struct cgroup_subsys_state *)ERR_PTR(-EINVAL))
 606
 607 static inline struct cgroup_subsys_state *
 608 task_get_blkcg_css(struct task_struct *task)
 609 {
 610         return NULL;
 611 }
 612
 613 #ifdef CONFIG_BLOCK
 614
 615 static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, void *key) { return NULL; }
 616 static inline int blkcg_init_queue(struct request_queue *q) { return 0; }
 617 static inline void blkcg_drain_queue(struct request_queue *q) { }
 618 static inline void blkcg_exit_queue(struct request_queue *q) { }
 619 static inline int blkcg_policy_register(struct blkcg_policy *pol) { return 0; }
 620 static inline void blkcg_policy_unregister(struct blkcg_policy *pol) { }
 621 static inline int blkcg_activate_policy(struct request_queue *q,
 622                                         const struct blkcg_policy *pol) { return 0; }
 623 static inline void blkcg_deactivate_policy(struct request_queue *q,
 624                                            const struct blkcg_policy *pol) { }
 625
 626 static inline struct blkcg *bio_blkcg(struct bio *bio) { return NULL; }
 627
 628 static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
 629                                                   struct blkcg_policy *pol) { return NULL; }
 630 static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd) { return NULL; }
 631 static inline char *blkg_path(struct blkcg_gq *blkg) { return NULL; }
 632 static inline void blkg_get(struct blkcg_gq *blkg) { }
 633 static inline void blkg_put(struct blkcg_gq *blkg) { }
 634
 635 static inline struct request_list *blk_get_rl(struct request_queue *q,
 636                                               struct bio *bio) { return &q->root_rl; }
 637 static inline void blk_put_rl(struct request_list *rl) { }
 638 static inline void blk_rq_set_rl(struct request *rq, struct request_list *rl) { }
 639 static inline struct request_list *blk_rq_rl(struct request *rq) { return &rq->q->root_rl; }
 640
 641 #define blk_queue_for_each_rl(rl, q)    \
 642         for ((rl) = &(q)->root_rl; (rl); (rl) = NULL)
 643
 644 #endif  /* CONFIG_BLOCK */
 645 #endif  /* CONFIG_BLK_CGROUP */
 646 #endif  /* _BLK_CGROUP_H */