block/blk-cgroup.h - kernel/common - Git at Google

 #ifndef _BLK_CGROUP_H
 #define _BLK_CGROUP_H
 /*
  * Common Block IO controller cgroup interface
  *
  * Based on ideas and code from CFQ, CFS and BFQ:
  * Copyright (C) 2003 Jens Axboe <[email protected]>
  *
  * Copyright (C) 2008 Fabio Checconi <[email protected]>
  *		      Paolo Valente <[email protected]>
  *
  * Copyright (C) 2009 Vivek Goyal <[email protected]>
  * 	              Nauman Rafique <[email protected]>
  */

 #include <linux/cgroup.h>
 #include <linux/u64_stats_sync.h>
 #include <linux/seq_file.h>
 #include <linux/radix-tree.h>
 #include <linux/blkdev.h>

 /* Max limits for throttle policy */
 #define THROTL_IOPS_MAX		UINT_MAX

 /* CFQ specific, out here for blkcg->cfq_weight */
 #define CFQ_WEIGHT_MIN		10
 #define CFQ_WEIGHT_MAX		1000
 #define CFQ_WEIGHT_DEFAULT	500

 #ifdef CONFIG_BLK_CGROUP

 enum blkg_rwstat_type {
 	BLKG_RWSTAT_READ,
 	BLKG_RWSTAT_WRITE,
 	BLKG_RWSTAT_SYNC,
 	BLKG_RWSTAT_ASYNC,

 	BLKG_RWSTAT_NR,
 	BLKG_RWSTAT_TOTAL = BLKG_RWSTAT_NR,
 };

 struct blkcg_gq;

 struct blkcg {
 	struct cgroup_subsys_state	css;
 	spinlock_t			lock;

 	struct radix_tree_root		blkg_tree;
 	struct blkcg_gq			*blkg_hint;
 	struct hlist_head		blkg_list;

 	/* for policies to test whether associated blkcg has changed */
 	uint64_t			id;

 	/* TODO: per-policy storage in blkcg */
 	unsigned int			cfq_weight;	/* belongs to cfq */
 };

 struct blkg_stat {
 	struct u64_stats_sync		syncp;
 	uint64_t			cnt;
 };

 struct blkg_rwstat {
 	struct u64_stats_sync		syncp;
 	uint64_t			cnt[BLKG_RWSTAT_NR];
 };

 /*
  * A blkcg_gq (blkg) is association between a block cgroup (blkcg) and a
  * request_queue (q).  This is used by blkcg policies which need to track
  * information per blkcg - q pair.
  *
  * There can be multiple active blkcg policies and each has its private
  * data on each blkg, the size of which is determined by
  * blkcg_policy->pd_size.  blkcg core allocates and frees such areas
  * together with blkg and invokes pd_init/exit_fn() methods.
  *
  * Such private data must embed struct blkg_policy_data (pd) at the
  * beginning and pd_size can't be smaller than pd.
  */
 struct blkg_policy_data {
 	/* the blkg this per-policy data belongs to */
 	struct blkcg_gq			*blkg;

 	/* used during policy activation */
 	struct list_head		alloc_node;
 };

 /* association between a blk cgroup and a request queue */
 struct blkcg_gq {
 	/* Pointer to the associated request_queue */
 	struct request_queue		*q;
 	struct list_head		q_node;
 	struct hlist_node		blkcg_node;
 	struct blkcg			*blkcg;
 	/* request allocation list for this blkcg-q pair */
 	struct request_list		rl;
 	/* reference count */
 	int				refcnt;

 	struct blkg_policy_data		*pd[BLKCG_MAX_POLS];

 	struct rcu_head			rcu_head;
 };

 typedef void (blkcg_pol_init_pd_fn)(struct blkcg_gq *blkg);
 typedef void (blkcg_pol_exit_pd_fn)(struct blkcg_gq *blkg);
 typedef void (blkcg_pol_reset_pd_stats_fn)(struct blkcg_gq *blkg);

 struct blkcg_policy {
 	int				plid;
 	/* policy specific private data size */
 	size_t				pd_size;
 	/* cgroup files for the policy */
 	struct cftype			*cftypes;

 	/* operations */
 	blkcg_pol_init_pd_fn		*pd_init_fn;
 	blkcg_pol_exit_pd_fn		*pd_exit_fn;
 	blkcg_pol_reset_pd_stats_fn	*pd_reset_stats_fn;
 };

 extern struct blkcg blkcg_root;

 struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, struct request_queue *q);
 struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
 				    struct request_queue *q);
 int blkcg_init_queue(struct request_queue *q);
 void blkcg_drain_queue(struct request_queue *q);
 void blkcg_exit_queue(struct request_queue *q);

 /* Blkio controller policy registration */
 int blkcg_policy_register(struct blkcg_policy *pol);
 void blkcg_policy_unregister(struct blkcg_policy *pol);
 int blkcg_activate_policy(struct request_queue *q,
 			  const struct blkcg_policy *pol);
 void blkcg_deactivate_policy(struct request_queue *q,
 			     const struct blkcg_policy *pol);

 void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
 		       u64 (*prfill)(struct seq_file *,
 				     struct blkg_policy_data *, int),
 		       const struct blkcg_policy *pol, int data,
 		       bool show_total);
 u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v);
 u64 __blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
 			 const struct blkg_rwstat *rwstat);
 u64 blkg_prfill_stat(struct seq_file *sf, struct blkg_policy_data *pd, int off);
 u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
 		       int off);

 struct blkg_conf_ctx {
 	struct gendisk			*disk;
 	struct blkcg_gq			*blkg;
 	u64				v;
 };

 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 		   const char *input, struct blkg_conf_ctx *ctx);
 void blkg_conf_finish(struct blkg_conf_ctx *ctx);


 static inline struct blkcg *cgroup_to_blkcg(struct cgroup *cgroup)
 {
 	return container_of(cgroup_subsys_state(cgroup, blkio_subsys_id),
 			    struct blkcg, css);
 }

 static inline struct blkcg *task_blkcg(struct task_struct *tsk)
 {
 	return container_of(task_subsys_state(tsk, blkio_subsys_id),
 			    struct blkcg, css);
 }

 static inline struct blkcg *bio_blkcg(struct bio *bio)
 {
 	if (bio && bio->bi_css)
 		return container_of(bio->bi_css, struct blkcg, css);
 	return task_blkcg(current);
 }

 /**
  * blkg_to_pdata - get policy private data
  * @blkg: blkg of interest
  * @pol: policy of interest
  *
  * Return pointer to private data associated with the @blkg-@pol pair.
  */
 static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
 						  struct blkcg_policy *pol)
 {
 	return blkg ? blkg->pd[pol->plid] : NULL;
 }

 /**
  * pdata_to_blkg - get blkg associated with policy private data
  * @pd: policy private data of interest
  *
  * @pd is policy private data.  Determine the blkg it's associated with.
  */
 static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd)
 {
 	return pd ? pd->blkg : NULL;
 }

 /**
  * blkg_path - format cgroup path of blkg
  * @blkg: blkg of interest
  * @buf: target buffer
  * @buflen: target buffer length
  *
  * Format the path of the cgroup of @blkg into @buf.
  */
 static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
 {
 	int ret;

 	rcu_read_lock();
 	ret = cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
 	rcu_read_unlock();
 	if (ret)
 		strncpy(buf, "<unavailable>", buflen);
 	return ret;
 }

 /**
  * blkg_get - get a blkg reference
  * @blkg: blkg to get
  *
  * The caller should be holding queue_lock and an existing reference.
  */
 static inline void blkg_get(struct blkcg_gq *blkg)
 {
 	lockdep_assert_held(blkg->q->queue_lock);
 	WARN_ON_ONCE(!blkg->refcnt);
 	blkg->refcnt++;
 }

 void __blkg_release(struct blkcg_gq *blkg);

 /**
  * blkg_put - put a blkg reference
  * @blkg: blkg to put
  *
  * The caller should be holding queue_lock.
  */
 static inline void blkg_put(struct blkcg_gq *blkg)
 {
 	lockdep_assert_held(blkg->q->queue_lock);
 	WARN_ON_ONCE(blkg->refcnt <= 0);
 	if (!--blkg->refcnt)
 		__blkg_release(blkg);
 }

 /**
  * blk_get_rl - get request_list to use
  * @q: request_queue of interest
  * @bio: bio which will be attached to the allocated request (may be %NULL)
  *
  * The caller wants to allocate a request from @q to use for @bio.  Find
  * the request_list to use and obtain a reference on it.  Should be called
  * under queue_lock.  This function is guaranteed to return non-%NULL
  * request_list.
  */
 static inline struct request_list *blk_get_rl(struct request_queue *q,
 					      struct bio *bio)
 {
 	struct blkcg *blkcg;
 	struct blkcg_gq *blkg;

 	rcu_read_lock();

 	blkcg = bio_blkcg(bio);

 	/* bypass blkg lookup and use @q->root_rl directly for root */
 	if (blkcg == &blkcg_root)
 		goto root_rl;

 	/*
 	 * Try to use blkg->rl.  blkg lookup may fail under memory pressure
 	 * or if either the blkcg or queue is going away.  Fall back to
 	 * root_rl in such cases.
 	 */
 	blkg = blkg_lookup_create(blkcg, q);
 	if (unlikely(IS_ERR(blkg)))
 		goto root_rl;

 	blkg_get(blkg);
 	rcu_read_unlock();
 	return &blkg->rl;
 root_rl:
 	rcu_read_unlock();
 	return &q->root_rl;
 }

 /**
  * blk_put_rl - put request_list
  * @rl: request_list to put
  *
  * Put the reference acquired by blk_get_rl().  Should be called under
  * queue_lock.
  */
 static inline void blk_put_rl(struct request_list *rl)
 {
 	/* root_rl may not have blkg set */
 	if (rl->blkg && rl->blkg->blkcg != &blkcg_root)
 		blkg_put(rl->blkg);
 }

 /**
  * blk_rq_set_rl - associate a request with a request_list
  * @rq: request of interest
  * @rl: target request_list
  *
  * Associate @rq with @rl so that accounting and freeing can know the
  * request_list @rq came from.
  */
 static inline void blk_rq_set_rl(struct request *rq, struct request_list *rl)
 {
 	rq->rl = rl;
 }

 /**
  * blk_rq_rl - return the request_list a request came from
  * @rq: request of interest
  *
  * Return the request_list @rq is allocated from.
  */
 static inline struct request_list *blk_rq_rl(struct request *rq)
 {
 	return rq->rl;
 }

 struct request_list *__blk_queue_next_rl(struct request_list *rl,
 					 struct request_queue *q);
 /**
  * blk_queue_for_each_rl - iterate through all request_lists of a request_queue
  *
  * Should be used under queue_lock.
  */
 #define blk_queue_for_each_rl(rl, q)	\
 	for ((rl) = &(q)->root_rl; (rl); (rl) = __blk_queue_next_rl((rl), (q)))

 /**
  * blkg_stat_add - add a value to a blkg_stat
  * @stat: target blkg_stat
  * @val: value to add
  *
  * Add @val to @stat.  The caller is responsible for synchronizing calls to
  * this function.
  */
 static inline void blkg_stat_add(struct blkg_stat *stat, uint64_t val)
 {
 	u64_stats_update_begin(&stat->syncp);
 	stat->cnt += val;
 	u64_stats_update_end(&stat->syncp);
 }

 /**
  * blkg_stat_read - read the current value of a blkg_stat
  * @stat: blkg_stat to read
  *
  * Read the current value of @stat.  This function can be called without
  * synchroniztion and takes care of u64 atomicity.
  */
 static inline uint64_t blkg_stat_read(struct blkg_stat *stat)
 {
 	unsigned int start;
 	uint64_t v;

 	do {
 		start = u64_stats_fetch_begin(&stat->syncp);
 		v = stat->cnt;
 	} while (u64_stats_fetch_retry(&stat->syncp, start));

 	return v;
 }

 /**
  * blkg_stat_reset - reset a blkg_stat
  * @stat: blkg_stat to reset
  */
 static inline void blkg_stat_reset(struct blkg_stat *stat)
 {
 	stat->cnt = 0;
 }

 /**
  * blkg_rwstat_add - add a value to a blkg_rwstat
  * @rwstat: target blkg_rwstat
  * @rw: mask of REQ_{WRITE|SYNC}
  * @val: value to add
  *
  * Add @val to @rwstat.  The counters are chosen according to @rw.  The
  * caller is responsible for synchronizing calls to this function.
  */
 static inline void blkg_rwstat_add(struct blkg_rwstat *rwstat,
 				   int rw, uint64_t val)
 {
 	u64_stats_update_begin(&rwstat->syncp);

 	if (rw & REQ_WRITE)
 		rwstat->cnt[BLKG_RWSTAT_WRITE] += val;
 	else
 		rwstat->cnt[BLKG_RWSTAT_READ] += val;
 	if (rw & REQ_SYNC)
 		rwstat->cnt[BLKG_RWSTAT_SYNC] += val;
 	else
 		rwstat->cnt[BLKG_RWSTAT_ASYNC] += val;

 	u64_stats_update_end(&rwstat->syncp);
 }

 /**
  * blkg_rwstat_read - read the current values of a blkg_rwstat
  * @rwstat: blkg_rwstat to read
  *
  * Read the current snapshot of @rwstat and return it as the return value.
  * This function can be called without synchronization and takes care of
  * u64 atomicity.
  */
 static inline struct blkg_rwstat blkg_rwstat_read(struct blkg_rwstat *rwstat)
 {
 	unsigned int start;
 	struct blkg_rwstat tmp;

 	do {
 		start = u64_stats_fetch_begin(&rwstat->syncp);
 		tmp = *rwstat;
 	} while (u64_stats_fetch_retry(&rwstat->syncp, start));

 	return tmp;
 }

 /**
  * blkg_rwstat_sum - read the total count of a blkg_rwstat
  * @rwstat: blkg_rwstat to read
  *
  * Return the total count of @rwstat regardless of the IO direction.  This
  * function can be called without synchronization and takes care of u64
  * atomicity.
  */
 static inline uint64_t blkg_rwstat_sum(struct blkg_rwstat *rwstat)
 {
 	struct blkg_rwstat tmp = blkg_rwstat_read(rwstat);

 	return tmp.cnt[BLKG_RWSTAT_READ] + tmp.cnt[BLKG_RWSTAT_WRITE];
 }

 /**
  * blkg_rwstat_reset - reset a blkg_rwstat
  * @rwstat: blkg_rwstat to reset
  */
 static inline void blkg_rwstat_reset(struct blkg_rwstat *rwstat)
 {
 	memset(rwstat->cnt, 0, sizeof(rwstat->cnt));
 }

 #else	/* CONFIG_BLK_CGROUP */

 struct cgroup;
 struct blkcg;

 struct blkg_policy_data {
 };

 struct blkcg_gq {
 };

 struct blkcg_policy {
 };

 static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, void *key) { return NULL; }
 static inline int blkcg_init_queue(struct request_queue *q) { return 0; }
 static inline void blkcg_drain_queue(struct request_queue *q) { }
 static inline void blkcg_exit_queue(struct request_queue *q) { }
 static inline int blkcg_policy_register(struct blkcg_policy *pol) { return 0; }
 static inline void blkcg_policy_unregister(struct blkcg_policy *pol) { }
 static inline int blkcg_activate_policy(struct request_queue *q,
 					const struct blkcg_policy *pol) { return 0; }
 static inline void blkcg_deactivate_policy(struct request_queue *q,
 					   const struct blkcg_policy *pol) { }

 static inline struct blkcg *cgroup_to_blkcg(struct cgroup *cgroup) { return NULL; }
 static inline struct blkcg *bio_blkcg(struct bio *bio) { return NULL; }

 static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
 						  struct blkcg_policy *pol) { return NULL; }
 static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd) { return NULL; }
 static inline char *blkg_path(struct blkcg_gq *blkg) { return NULL; }
 static inline void blkg_get(struct blkcg_gq *blkg) { }
 static inline void blkg_put(struct blkcg_gq *blkg) { }

 static inline struct request_list *blk_get_rl(struct request_queue *q,
 					      struct bio *bio) { return &q->root_rl; }
 static inline void blk_put_rl(struct request_list *rl) { }
 static inline void blk_rq_set_rl(struct request *rq, struct request_list *rl) { }
 static inline struct request_list *blk_rq_rl(struct request *rq) { return &rq->q->root_rl; }

 #define blk_queue_for_each_rl(rl, q)	\
 	for ((rl) = &(q)->root_rl; (rl); (rl) = NULL)

 #endif	/* CONFIG_BLK_CGROUP */
 #endif	/* _BLK_CGROUP_H */
	#ifndef _BLK_CGROUP_H
	#define _BLK_CGROUP_H
	/*
	* Common Block IO controller cgroup interface
	*
	* Based on ideas and code from CFQ, CFS and BFQ:
	* Copyright (C) 2003 Jens Axboe <[email protected]>
	*
	* Copyright (C) 2008 Fabio Checconi <[email protected]>
	* Paolo Valente <[email protected]>
	*
	* Copyright (C) 2009 Vivek Goyal <[email protected]>
	* Nauman Rafique <[email protected]>
	*/

	#include <linux/cgroup.h>
	#include <linux/u64_stats_sync.h>
	#include <linux/seq_file.h>
	#include <linux/radix-tree.h>
	#include <linux/blkdev.h>

	/* Max limits for throttle policy */
	#define THROTL_IOPS_MAX UINT_MAX

	/* CFQ specific, out here for blkcg->cfq_weight */
	#define CFQ_WEIGHT_MIN 10
	#define CFQ_WEIGHT_MAX 1000
	#define CFQ_WEIGHT_DEFAULT 500

	#ifdef CONFIG_BLK_CGROUP

	enum blkg_rwstat_type {
	BLKG_RWSTAT_READ,
	BLKG_RWSTAT_WRITE,
	BLKG_RWSTAT_SYNC,
	BLKG_RWSTAT_ASYNC,

	BLKG_RWSTAT_NR,
	BLKG_RWSTAT_TOTAL = BLKG_RWSTAT_NR,
	};

	struct blkcg_gq;

	struct blkcg {
	struct cgroup_subsys_state css;
	spinlock_t lock;

	struct radix_tree_root blkg_tree;
	struct blkcg_gq *blkg_hint;
	struct hlist_head blkg_list;

	/* for policies to test whether associated blkcg has changed */
	uint64_t id;

	/* TODO: per-policy storage in blkcg */
	unsigned int cfq_weight; /* belongs to cfq */
	};

	struct blkg_stat {
	struct u64_stats_sync syncp;
	uint64_t cnt;
	};

	struct blkg_rwstat {
	struct u64_stats_sync syncp;
	uint64_t cnt[BLKG_RWSTAT_NR];
	};

	/*
	* A blkcg_gq (blkg) is association between a block cgroup (blkcg) and a
	* request_queue (q). This is used by blkcg policies which need to track
	* information per blkcg - q pair.
	*
	* There can be multiple active blkcg policies and each has its private
	* data on each blkg, the size of which is determined by
	* blkcg_policy->pd_size. blkcg core allocates and frees such areas
	* together with blkg and invokes pd_init/exit_fn() methods.
	*
	* Such private data must embed struct blkg_policy_data (pd) at the
	* beginning and pd_size can't be smaller than pd.
	*/
	struct blkg_policy_data {
	/* the blkg this per-policy data belongs to */
	struct blkcg_gq *blkg;

	/* used during policy activation */
	struct list_head alloc_node;
	};

	/* association between a blk cgroup and a request queue */
	struct blkcg_gq {
	/* Pointer to the associated request_queue */
	struct request_queue *q;
	struct list_head q_node;
	struct hlist_node blkcg_node;
	struct blkcg *blkcg;
	/* request allocation list for this blkcg-q pair */
	struct request_list rl;
	/* reference count */
	int refcnt;

	struct blkg_policy_data *pd[BLKCG_MAX_POLS];

	struct rcu_head rcu_head;
	};

	typedef void (blkcg_pol_init_pd_fn)(struct blkcg_gq *blkg);
	typedef void (blkcg_pol_exit_pd_fn)(struct blkcg_gq *blkg);
	typedef void (blkcg_pol_reset_pd_stats_fn)(struct blkcg_gq *blkg);

	struct blkcg_policy {
	int plid;
	/* policy specific private data size */
	size_t pd_size;
	/* cgroup files for the policy */
	struct cftype *cftypes;

	/* operations */
	blkcg_pol_init_pd_fn *pd_init_fn;
	blkcg_pol_exit_pd_fn *pd_exit_fn;
	blkcg_pol_reset_pd_stats_fn *pd_reset_stats_fn;
	};

	extern struct blkcg blkcg_root;

	struct blkcg_gq blkg_lookup(struct blkcg blkcg, struct request_queue *q);
	struct blkcg_gq blkg_lookup_create(struct blkcg blkcg,
	struct request_queue *q);
	int blkcg_init_queue(struct request_queue *q);
	void blkcg_drain_queue(struct request_queue *q);
	void blkcg_exit_queue(struct request_queue *q);

	/* Blkio controller policy registration */
	int blkcg_policy_register(struct blkcg_policy *pol);
	void blkcg_policy_unregister(struct blkcg_policy *pol);
	int blkcg_activate_policy(struct request_queue *q,
	const struct blkcg_policy *pol);
	void blkcg_deactivate_policy(struct request_queue *q,
	const struct blkcg_policy *pol);

	void blkcg_print_blkgs(struct seq_file sf, struct blkcg blkcg,
	u64 (prfill)(struct seq_file ,
	struct blkg_policy_data *, int),
	const struct blkcg_policy *pol, int data,
	bool show_total);
	u64 __blkg_prfill_u64(struct seq_file sf, struct blkg_policy_data pd, u64 v);
	u64 __blkg_prfill_rwstat(struct seq_file sf, struct blkg_policy_data pd,
	const struct blkg_rwstat *rwstat);
	u64 blkg_prfill_stat(struct seq_file sf, struct blkg_policy_data pd, int off);
	u64 blkg_prfill_rwstat(struct seq_file sf, struct blkg_policy_data pd,
	int off);

	struct blkg_conf_ctx {
	struct gendisk *disk;
	struct blkcg_gq *blkg;
	u64 v;
	};

	int blkg_conf_prep(struct blkcg blkcg, const struct blkcg_policy pol,
	const char input, struct blkg_conf_ctx ctx);
	void blkg_conf_finish(struct blkg_conf_ctx *ctx);


	static inline struct blkcg cgroup_to_blkcg(struct cgroup cgroup)
	{
	return container_of(cgroup_subsys_state(cgroup, blkio_subsys_id),
	struct blkcg, css);
	}

	static inline struct blkcg task_blkcg(struct task_struct tsk)
	{
	return container_of(task_subsys_state(tsk, blkio_subsys_id),
	struct blkcg, css);
	}

	static inline struct blkcg bio_blkcg(struct bio bio)
	{
	if (bio && bio->bi_css)
	return container_of(bio->bi_css, struct blkcg, css);
	return task_blkcg(current);
	}

	/**
	* blkg_to_pdata - get policy private data
	* @blkg: blkg of interest
	* @pol: policy of interest
	*
	* Return pointer to private data associated with the @blkg-@pol pair.
	*/
	static inline struct blkg_policy_data blkg_to_pd(struct blkcg_gq blkg,
	struct blkcg_policy *pol)
	{
	return blkg ? blkg->pd[pol->plid] : NULL;
	}

	/**
	* pdata_to_blkg - get blkg associated with policy private data
	* @pd: policy private data of interest
	*
	* @pd is policy private data. Determine the blkg it's associated with.
	*/
	static inline struct blkcg_gq pd_to_blkg(struct blkg_policy_data pd)
	{
	return pd ? pd->blkg : NULL;
	}

	/**
	* blkg_path - format cgroup path of blkg
	* @blkg: blkg of interest
	* @buf: target buffer
	* @buflen: target buffer length
	*
	* Format the path of the cgroup of @blkg into @buf.
	*/
	static inline int blkg_path(struct blkcg_gq blkg, char buf, int buflen)
	{
	int ret;

	rcu_read_lock();
	ret = cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
	rcu_read_unlock();
	if (ret)
	strncpy(buf, "<unavailable>", buflen);
	return ret;
	}

	/**
	* blkg_get - get a blkg reference
	* @blkg: blkg to get
	*
	* The caller should be holding queue_lock and an existing reference.
	*/
	static inline void blkg_get(struct blkcg_gq *blkg)
	{
	lockdep_assert_held(blkg->q->queue_lock);
	WARN_ON_ONCE(!blkg->refcnt);
	blkg->refcnt++;
	}

	void __blkg_release(struct blkcg_gq *blkg);

	/**
	* blkg_put - put a blkg reference
	* @blkg: blkg to put
	*
	* The caller should be holding queue_lock.
	*/
	static inline void blkg_put(struct blkcg_gq *blkg)
	{
	lockdep_assert_held(blkg->q->queue_lock);
	WARN_ON_ONCE(blkg->refcnt <= 0);
	if (!--blkg->refcnt)
	__blkg_release(blkg);
	}

	/**
	* blk_get_rl - get request_list to use
	* @q: request_queue of interest
	* @bio: bio which will be attached to the allocated request (may be %NULL)
	*
	* The caller wants to allocate a request from @q to use for @bio. Find
	* the request_list to use and obtain a reference on it. Should be called
	* under queue_lock. This function is guaranteed to return non-%NULL
	* request_list.
	*/
	static inline struct request_list blk_get_rl(struct request_queue q,
	struct bio *bio)
	{
	struct blkcg *blkcg;
	struct blkcg_gq *blkg;

	rcu_read_lock();

	blkcg = bio_blkcg(bio);

	/* bypass blkg lookup and use @q->root_rl directly for root */
	if (blkcg == &blkcg_root)
	goto root_rl;

	/*
	* Try to use blkg->rl. blkg lookup may fail under memory pressure
	* or if either the blkcg or queue is going away. Fall back to
	* root_rl in such cases.
	*/
	blkg = blkg_lookup_create(blkcg, q);
	if (unlikely(IS_ERR(blkg)))
	goto root_rl;

	blkg_get(blkg);
	rcu_read_unlock();
	return &blkg->rl;
	root_rl:
	rcu_read_unlock();
	return &q->root_rl;
	}

	/**
	* blk_put_rl - put request_list
	* @rl: request_list to put
	*
	* Put the reference acquired by blk_get_rl(). Should be called under
	* queue_lock.
	*/
	static inline void blk_put_rl(struct request_list *rl)
	{
	/* root_rl may not have blkg set */
	if (rl->blkg && rl->blkg->blkcg != &blkcg_root)
	blkg_put(rl->blkg);
	}

	/**
	* blk_rq_set_rl - associate a request with a request_list
	* @rq: request of interest
	* @rl: target request_list
	*
	* Associate @rq with @rl so that accounting and freeing can know the
	* request_list @rq came from.
	*/
	static inline void blk_rq_set_rl(struct request rq, struct request_list rl)
	{
	rq->rl = rl;
	}

	/**
	* blk_rq_rl - return the request_list a request came from
	* @rq: request of interest
	*
	* Return the request_list @rq is allocated from.
	*/
	static inline struct request_list blk_rq_rl(struct request rq)
	{
	return rq->rl;
	}

	struct request_list __blk_queue_next_rl(struct request_list rl,
	struct request_queue *q);
	/**
	* blk_queue_for_each_rl - iterate through all request_lists of a request_queue
	*
	* Should be used under queue_lock.
	*/
	#define blk_queue_for_each_rl(rl, q) \
	for ((rl) = &(q)->root_rl; (rl); (rl) = __blk_queue_next_rl((rl), (q)))

	/**
	* blkg_stat_add - add a value to a blkg_stat
	* @stat: target blkg_stat
	* @val: value to add
	*
	* Add @val to @stat. The caller is responsible for synchronizing calls to
	* this function.
	*/
	static inline void blkg_stat_add(struct blkg_stat *stat, uint64_t val)
	{
	u64_stats_update_begin(&stat->syncp);
	stat->cnt += val;
	u64_stats_update_end(&stat->syncp);
	}

	/**
	* blkg_stat_read - read the current value of a blkg_stat
	* @stat: blkg_stat to read
	*
	* Read the current value of @stat. This function can be called without
	* synchroniztion and takes care of u64 atomicity.
	*/
	static inline uint64_t blkg_stat_read(struct blkg_stat *stat)
	{
	unsigned int start;
	uint64_t v;

	do {
	start = u64_stats_fetch_begin(&stat->syncp);
	v = stat->cnt;
	} while (u64_stats_fetch_retry(&stat->syncp, start));

	return v;
	}

	/**
	* blkg_stat_reset - reset a blkg_stat
	* @stat: blkg_stat to reset
	*/
	static inline void blkg_stat_reset(struct blkg_stat *stat)
	{
	stat->cnt = 0;
	}

	/**
	* blkg_rwstat_add - add a value to a blkg_rwstat
	* @rwstat: target blkg_rwstat
	* @rw: mask of REQ_{WRITE\|SYNC}
	* @val: value to add
	*
	* Add @val to @rwstat. The counters are chosen according to @rw. The
	* caller is responsible for synchronizing calls to this function.
	*/
	static inline void blkg_rwstat_add(struct blkg_rwstat *rwstat,
	int rw, uint64_t val)
	{
	u64_stats_update_begin(&rwstat->syncp);

	if (rw & REQ_WRITE)
	rwstat->cnt[BLKG_RWSTAT_WRITE] += val;
	else
	rwstat->cnt[BLKG_RWSTAT_READ] += val;
	if (rw & REQ_SYNC)
	rwstat->cnt[BLKG_RWSTAT_SYNC] += val;
	else
	rwstat->cnt[BLKG_RWSTAT_ASYNC] += val;

	u64_stats_update_end(&rwstat->syncp);
	}

	/**
	* blkg_rwstat_read - read the current values of a blkg_rwstat
	* @rwstat: blkg_rwstat to read
	*
	* Read the current snapshot of @rwstat and return it as the return value.
	* This function can be called without synchronization and takes care of
	* u64 atomicity.
	*/
	static inline struct blkg_rwstat blkg_rwstat_read(struct blkg_rwstat *rwstat)
	{
	unsigned int start;
	struct blkg_rwstat tmp;

	do {
	start = u64_stats_fetch_begin(&rwstat->syncp);
	tmp = *rwstat;
	} while (u64_stats_fetch_retry(&rwstat->syncp, start));

	return tmp;
	}

	/**
	* blkg_rwstat_sum - read the total count of a blkg_rwstat
	* @rwstat: blkg_rwstat to read
	*
	* Return the total count of @rwstat regardless of the IO direction. This
	* function can be called without synchronization and takes care of u64
	* atomicity.
	*/
	static inline uint64_t blkg_rwstat_sum(struct blkg_rwstat *rwstat)
	{
	struct blkg_rwstat tmp = blkg_rwstat_read(rwstat);

	return tmp.cnt[BLKG_RWSTAT_READ] + tmp.cnt[BLKG_RWSTAT_WRITE];
	}

	/**
	* blkg_rwstat_reset - reset a blkg_rwstat
	* @rwstat: blkg_rwstat to reset
	*/
	static inline void blkg_rwstat_reset(struct blkg_rwstat *rwstat)
	{
	memset(rwstat->cnt, 0, sizeof(rwstat->cnt));
	}

	#else /* CONFIG_BLK_CGROUP */

	struct cgroup;
	struct blkcg;

	struct blkg_policy_data {
	};

	struct blkcg_gq {
	};

	struct blkcg_policy {
	};

	static inline struct blkcg_gq blkg_lookup(struct blkcg blkcg, void *key) { return NULL; }
	static inline int blkcg_init_queue(struct request_queue *q) { return 0; }
	static inline void blkcg_drain_queue(struct request_queue *q) { }
	static inline void blkcg_exit_queue(struct request_queue *q) { }
	static inline int blkcg_policy_register(struct blkcg_policy *pol) { return 0; }
	static inline void blkcg_policy_unregister(struct blkcg_policy *pol) { }
	static inline int blkcg_activate_policy(struct request_queue *q,
	const struct blkcg_policy *pol) { return 0; }
	static inline void blkcg_deactivate_policy(struct request_queue *q,
	const struct blkcg_policy *pol) { }

	static inline struct blkcg cgroup_to_blkcg(struct cgroup cgroup) { return NULL; }
	static inline struct blkcg bio_blkcg(struct bio bio) { return NULL; }

	static inline struct blkg_policy_data blkg_to_pd(struct blkcg_gq blkg,
	struct blkcg_policy *pol) { return NULL; }
	static inline struct blkcg_gq pd_to_blkg(struct blkg_policy_data pd) { return NULL; }
	static inline char blkg_path(struct blkcg_gq blkg) { return NULL; }
	static inline void blkg_get(struct blkcg_gq *blkg) { }
	static inline void blkg_put(struct blkcg_gq *blkg) { }

	static inline struct request_list blk_get_rl(struct request_queue q,
	struct bio *bio) { return &q->root_rl; }
	static inline void blk_put_rl(struct request_list *rl) { }
	static inline void blk_rq_set_rl(struct request rq, struct request_list rl) { }
	static inline struct request_list blk_rq_rl(struct request rq) { return &rq->q->root_rl; }

	#define blk_queue_for_each_rl(rl, q) \
	for ((rl) = &(q)->root_rl; (rl); (rl) = NULL)

	#endif /* CONFIG_BLK_CGROUP */
	#endif /* _BLK_CGROUP_H */