[linux-block.git] / block / 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 <axboe@kernel.dk>
 *
 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
 *		      Paolo Valente <paolo.valente@unimore.it>
 *
 * Copyright (C) 2009 Vivek Goyal <vgoyal@redhat.com>
 * 	              Nauman Rafique <nauman@google.com>
 */

#include <linux/cgroup.h>
#include <linux/u64_stats_sync.h>
#include <linux/seq_file.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 {
	struct cgroup_subsys_state	css;
	spinlock_t			lock;
	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;
	/* 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_ops {
	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;
};

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

extern struct blkcg blkcg_root;

struct blkcg *cgroup_to_blkcg(struct cgroup *cgroup);
struct blkcg *bio_blkcg(struct bio *bio);
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);


/**
 * 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);
}

/**
 * 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 blkg_policy_data {
};

struct blkcg_gq {
};

struct blkcg_policy {
};

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 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 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) { }

#endif	/* CONFIG_BLK_CGROUP */
#endif	/* _BLK_CGROUP_H */
Commit	Line	Data
	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
	20	/* Max limits for throttle policy */
	21	#define THROTL_IOPS_MAX UINT_MAX
	22
	23	/* CFQ specific, out here for blkcg->cfq_weight */
	24	#define CFQ_WEIGHT_MIN 10
	25	#define CFQ_WEIGHT_MAX 1000
	26	#define CFQ_WEIGHT_DEFAULT 500
	27
	28	#ifdef CONFIG_BLK_CGROUP
	29
	30	enum blkg_rwstat_type {
	31	BLKG_RWSTAT_READ,
	32	BLKG_RWSTAT_WRITE,
	33	BLKG_RWSTAT_SYNC,
	34	BLKG_RWSTAT_ASYNC,
	35
	36	BLKG_RWSTAT_NR,
	37	BLKG_RWSTAT_TOTAL = BLKG_RWSTAT_NR,
	38	};
	39
	40	struct blkcg {
	41	struct cgroup_subsys_state css;
	42	spinlock_t lock;
	43	struct hlist_head blkg_list;
	44
	45	/* for policies to test whether associated blkcg has changed */
	46	uint64_t id;
	47
	48	/* TODO: per-policy storage in blkcg */
	49	unsigned int cfq_weight; /* belongs to cfq */
	50	};
	51
	52	struct blkg_stat {
	53	struct u64_stats_sync syncp;
	54	uint64_t cnt;
	55	};
	56
	57	struct blkg_rwstat {
	58	struct u64_stats_sync syncp;
	59	uint64_t cnt[BLKG_RWSTAT_NR];
	60	};
	61
	62	/*
	63	* A blkcg_gq (blkg) is association between a block cgroup (blkcg) and a
	64	* request_queue (q). This is used by blkcg policies which need to track
	65	* information per blkcg - q pair.
	66	*
	67	* There can be multiple active blkcg policies and each has its private
	68	* data on each blkg, the size of which is determined by
	69	* blkcg_policy->pd_size. blkcg core allocates and frees such areas
	70	* together with blkg and invokes pd_init/exit_fn() methods.
	71	*
	72	* Such private data must embed struct blkg_policy_data (pd) at the
	73	* beginning and pd_size can't be smaller than pd.
	74	*/
	75	struct blkg_policy_data {
	76	/* the blkg this per-policy data belongs to */
	77	struct blkcg_gq *blkg;
	78
	79	/* used during policy activation */
	80	struct list_head alloc_node;
	81	};
	82
	83	/* association between a blk cgroup and a request queue */
	84	struct blkcg_gq {
	85	/* Pointer to the associated request_queue */
	86	struct request_queue *q;
	87	struct list_head q_node;
	88	struct hlist_node blkcg_node;
	89	struct blkcg *blkcg;
	90	/* reference count */
	91	int refcnt;
	92
	93	struct blkg_policy_data *pd[BLKCG_MAX_POLS];
	94
	95	struct rcu_head rcu_head;
	96	};
	97
	98	typedef void (blkcg_pol_init_pd_fn)(struct blkcg_gq *blkg);
	99	typedef void (blkcg_pol_exit_pd_fn)(struct blkcg_gq *blkg);
	100	typedef void (blkcg_pol_reset_pd_stats_fn)(struct blkcg_gq *blkg);
	101
	102	struct blkcg_policy_ops {
	103	blkcg_pol_init_pd_fn *pd_init_fn;
	104	blkcg_pol_exit_pd_fn *pd_exit_fn;
	105	blkcg_pol_reset_pd_stats_fn *pd_reset_stats_fn;
	106	};
	107
	108	struct blkcg_policy {
	109	struct blkcg_policy_ops ops;
	110	int plid;
	111	/* policy specific private data size */
	112	size_t pd_size;
	113	/* cgroup files for the policy */
	114	struct cftype *cftypes;
	115	};
	116
	117	extern struct blkcg blkcg_root;
	118
	119	struct blkcg cgroup_to_blkcg(struct cgroup cgroup);
	120	struct blkcg bio_blkcg(struct bio bio);
	121	struct blkcg_gq blkg_lookup(struct blkcg blkcg, struct request_queue *q);
	122	struct blkcg_gq blkg_lookup_create(struct blkcg blkcg,
	123	struct request_queue *q);
	124	int blkcg_init_queue(struct request_queue *q);
	125	void blkcg_drain_queue(struct request_queue *q);
	126	void blkcg_exit_queue(struct request_queue *q);
	127
	128	/* Blkio controller policy registration */
	129	int blkcg_policy_register(struct blkcg_policy *pol);
	130	void blkcg_policy_unregister(struct blkcg_policy *pol);
	131	int blkcg_activate_policy(struct request_queue *q,
	132	const struct blkcg_policy *pol);
	133	void blkcg_deactivate_policy(struct request_queue *q,
	134	const struct blkcg_policy *pol);
	135
	136	void blkcg_print_blkgs(struct seq_file sf, struct blkcg blkcg,
	137	u64 (prfill)(struct seq_file ,
	138	struct blkg_policy_data *, int),
	139	const struct blkcg_policy *pol, int data,
	140	bool show_total);
	141	u64 __blkg_prfill_u64(struct seq_file sf, struct blkg_policy_data pd, u64 v);
	142	u64 __blkg_prfill_rwstat(struct seq_file sf, struct blkg_policy_data pd,
	143	const struct blkg_rwstat *rwstat);
	144	u64 blkg_prfill_stat(struct seq_file sf, struct blkg_policy_data pd, int off);
	145	u64 blkg_prfill_rwstat(struct seq_file sf, struct blkg_policy_data pd,
	146	int off);
	147
	148	struct blkg_conf_ctx {
	149	struct gendisk *disk;
	150	struct blkcg_gq *blkg;
	151	u64 v;
	152	};
	153
	154	int blkg_conf_prep(struct blkcg blkcg, const struct blkcg_policy pol,
	155	const char input, struct blkg_conf_ctx ctx);
	156	void blkg_conf_finish(struct blkg_conf_ctx *ctx);
	157
	158
	159	/**
	160	* blkg_to_pdata - get policy private data
	161	* @blkg: blkg of interest
	162	* @pol: policy of interest
	163	*
	164	* Return pointer to private data associated with the @blkg-@pol pair.
	165	*/
	166	static inline struct blkg_policy_data blkg_to_pd(struct blkcg_gq blkg,
	167	struct blkcg_policy *pol)
	168	{
	169	return blkg ? blkg->pd[pol->plid] : NULL;
	170	}
	171
	172	/**
	173	* pdata_to_blkg - get blkg associated with policy private data
	174	* @pd: policy private data of interest
	175	*
	176	* @pd is policy private data. Determine the blkg it's associated with.
	177	*/
	178	static inline struct blkcg_gq pd_to_blkg(struct blkg_policy_data pd)
	179	{
	180	return pd ? pd->blkg : NULL;
	181	}
	182
	183	/**
	184	* blkg_path - format cgroup path of blkg
	185	* @blkg: blkg of interest
	186	* @buf: target buffer
	187	* @buflen: target buffer length
	188	*
	189	* Format the path of the cgroup of @blkg into @buf.
	190	*/
	191	static inline int blkg_path(struct blkcg_gq blkg, char buf, int buflen)
	192	{
	193	int ret;
	194
	195	rcu_read_lock();
	196	ret = cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
	197	rcu_read_unlock();
	198	if (ret)
	199	strncpy(buf, "<unavailable>", buflen);
	200	return ret;
	201	}
	202
	203	/**
	204	* blkg_get - get a blkg reference
	205	* @blkg: blkg to get
	206	*
	207	* The caller should be holding queue_lock and an existing reference.
	208	*/
	209	static inline void blkg_get(struct blkcg_gq *blkg)
	210	{
	211	lockdep_assert_held(blkg->q->queue_lock);
	212	WARN_ON_ONCE(!blkg->refcnt);
	213	blkg->refcnt++;
	214	}
	215
	216	void __blkg_release(struct blkcg_gq *blkg);
	217
	218	/**
	219	* blkg_put - put a blkg reference
	220	* @blkg: blkg to put
	221	*
	222	* The caller should be holding queue_lock.
	223	*/
	224	static inline void blkg_put(struct blkcg_gq *blkg)
	225	{
	226	lockdep_assert_held(blkg->q->queue_lock);
	227	WARN_ON_ONCE(blkg->refcnt <= 0);
	228	if (!--blkg->refcnt)
	229	__blkg_release(blkg);
	230	}
	231
	232	/**
	233	* blkg_stat_add - add a value to a blkg_stat
	234	* @stat: target blkg_stat
	235	* @val: value to add
	236	*
	237	* Add @val to @stat. The caller is responsible for synchronizing calls to
	238	* this function.
	239	*/
	240	static inline void blkg_stat_add(struct blkg_stat *stat, uint64_t val)
	241	{
	242	u64_stats_update_begin(&stat->syncp);
	243	stat->cnt += val;
	244	u64_stats_update_end(&stat->syncp);
	245	}
	246
	247	/**
	248	* blkg_stat_read - read the current value of a blkg_stat
	249	* @stat: blkg_stat to read
	250	*
	251	* Read the current value of @stat. This function can be called without
	252	* synchroniztion and takes care of u64 atomicity.
	253	*/
	254	static inline uint64_t blkg_stat_read(struct blkg_stat *stat)
	255	{
	256	unsigned int start;
	257	uint64_t v;
	258
	259	do {
	260	start = u64_stats_fetch_begin(&stat->syncp);
	261	v = stat->cnt;
	262	} while (u64_stats_fetch_retry(&stat->syncp, start));
	263
	264	return v;
	265	}
	266
	267	/**
	268	* blkg_stat_reset - reset a blkg_stat
	269	* @stat: blkg_stat to reset
	270	*/
	271	static inline void blkg_stat_reset(struct blkg_stat *stat)
	272	{
	273	stat->cnt = 0;
	274	}
	275
	276	/**
	277	* blkg_rwstat_add - add a value to a blkg_rwstat
	278	* @rwstat: target blkg_rwstat
	279	* @rw: mask of REQ_{WRITE\|SYNC}
	280	* @val: value to add
	281	*
	282	* Add @val to @rwstat. The counters are chosen according to @rw. The
	283	* caller is responsible for synchronizing calls to this function.
	284	*/
	285	static inline void blkg_rwstat_add(struct blkg_rwstat *rwstat,
	286	int rw, uint64_t val)
	287	{
	288	u64_stats_update_begin(&rwstat->syncp);
	289
	290	if (rw & REQ_WRITE)
	291	rwstat->cnt[BLKG_RWSTAT_WRITE] += val;
	292	else
	293	rwstat->cnt[BLKG_RWSTAT_READ] += val;
	294	if (rw & REQ_SYNC)
	295	rwstat->cnt[BLKG_RWSTAT_SYNC] += val;
	296	else
	297	rwstat->cnt[BLKG_RWSTAT_ASYNC] += val;
	298
	299	u64_stats_update_end(&rwstat->syncp);
	300	}
	301
	302	/**
	303	* blkg_rwstat_read - read the current values of a blkg_rwstat
	304	* @rwstat: blkg_rwstat to read
	305	*
	306	* Read the current snapshot of @rwstat and return it as the return value.
	307	* This function can be called without synchronization and takes care of
	308	* u64 atomicity.
	309	*/
	310	static inline struct blkg_rwstat blkg_rwstat_read(struct blkg_rwstat *rwstat)
	311	{
	312	unsigned int start;
	313	struct blkg_rwstat tmp;
	314
	315	do {
	316	start = u64_stats_fetch_begin(&rwstat->syncp);
	317	tmp = *rwstat;
	318	} while (u64_stats_fetch_retry(&rwstat->syncp, start));
	319
	320	return tmp;
	321	}
	322
	323	/**
	324	* blkg_rwstat_sum - read the total count of a blkg_rwstat
	325	* @rwstat: blkg_rwstat to read
	326	*
	327	* Return the total count of @rwstat regardless of the IO direction. This
	328	* function can be called without synchronization and takes care of u64
	329	* atomicity.
	330	*/
	331	static inline uint64_t blkg_rwstat_sum(struct blkg_rwstat *rwstat)
	332	{
	333	struct blkg_rwstat tmp = blkg_rwstat_read(rwstat);
	334
	335	return tmp.cnt[BLKG_RWSTAT_READ] + tmp.cnt[BLKG_RWSTAT_WRITE];
	336	}
	337
	338	/**
	339	* blkg_rwstat_reset - reset a blkg_rwstat
	340	* @rwstat: blkg_rwstat to reset
	341	*/
	342	static inline void blkg_rwstat_reset(struct blkg_rwstat *rwstat)
	343	{
	344	memset(rwstat->cnt, 0, sizeof(rwstat->cnt));
	345	}
	346
	347	#else /* CONFIG_BLK_CGROUP */
	348
	349	struct cgroup;
	350
	351	struct blkg_policy_data {
	352	};
	353
	354	struct blkcg_gq {
	355	};
	356
	357	struct blkcg_policy {
	358	};
	359
	360	static inline struct blkcg cgroup_to_blkcg(struct cgroup cgroup) { return NULL; }
	361	static inline struct blkcg bio_blkcg(struct bio bio) { return NULL; }
	362	static inline struct blkcg_gq blkg_lookup(struct blkcg blkcg, void *key) { return NULL; }
	363	static inline int blkcg_init_queue(struct request_queue *q) { return 0; }
	364	static inline void blkcg_drain_queue(struct request_queue *q) { }
	365	static inline void blkcg_exit_queue(struct request_queue *q) { }
	366	static inline int blkcg_policy_register(struct blkcg_policy *pol) { return 0; }
	367	static inline void blkcg_policy_unregister(struct blkcg_policy *pol) { }
	368	static inline int blkcg_activate_policy(struct request_queue *q,
	369	const struct blkcg_policy *pol) { return 0; }
	370	static inline void blkcg_deactivate_policy(struct request_queue *q,
	371	const struct blkcg_policy *pol) { }
	372
	373	static inline struct blkg_policy_data blkg_to_pd(struct blkcg_gq blkg,
	374	struct blkcg_policy *pol) { return NULL; }
	375	static inline struct blkcg_gq pd_to_blkg(struct blkg_policy_data pd) { return NULL; }
	376	static inline char blkg_path(struct blkcg_gq blkg) { return NULL; }
	377	static inline void blkg_get(struct blkcg_gq *blkg) { }
	378	static inline void blkg_put(struct blkcg_gq *blkg) { }
	379
	380	#endif /* CONFIG_BLK_CGROUP */
	381	#endif /* _BLK_CGROUP_H */