[net-next-2.6.git] / block / blk-cgroup.c

/*
 * 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/ioprio.h>
#include <linux/seq_file.h>
#include <linux/kdev_t.h>
#include <linux/module.h>
#include <linux/err.h>
#include "blk-cgroup.h"

static DEFINE_SPINLOCK(blkio_list_lock);
static LIST_HEAD(blkio_list);

struct blkio_cgroup blkio_root_cgroup = { .weight = 2*BLKIO_WEIGHT_DEFAULT };
EXPORT_SYMBOL_GPL(blkio_root_cgroup);

struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup)
{
	return container_of(cgroup_subsys_state(cgroup, blkio_subsys_id),
			    struct blkio_cgroup, css);
}
EXPORT_SYMBOL_GPL(cgroup_to_blkio_cgroup);

void blkiocg_update_blkio_group_stats(struct blkio_group *blkg,
			unsigned long time, unsigned long sectors)
{
	blkg->time += time;
	blkg->sectors += sectors;
}
EXPORT_SYMBOL_GPL(blkiocg_update_blkio_group_stats);

void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,
			struct blkio_group *blkg, void *key, dev_t dev)
{
	unsigned long flags;

	spin_lock_irqsave(&blkcg->lock, flags);
	rcu_assign_pointer(blkg->key, key);
	blkg->blkcg_id = css_id(&blkcg->css);
	hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
	spin_unlock_irqrestore(&blkcg->lock, flags);
#ifdef CONFIG_DEBUG_BLK_CGROUP
	/* Need to take css reference ? */
	cgroup_path(blkcg->css.cgroup, blkg->path, sizeof(blkg->path));
#endif
	blkg->dev = dev;
}
EXPORT_SYMBOL_GPL(blkiocg_add_blkio_group);

static void __blkiocg_del_blkio_group(struct blkio_group *blkg)
{
	hlist_del_init_rcu(&blkg->blkcg_node);
	blkg->blkcg_id = 0;
}

/*
 * returns 0 if blkio_group was still on cgroup list. Otherwise returns 1
 * indicating that blk_group was unhashed by the time we got to it.
 */
int blkiocg_del_blkio_group(struct blkio_group *blkg)
{
	struct blkio_cgroup *blkcg;
	unsigned long flags;
	struct cgroup_subsys_state *css;
	int ret = 1;

	rcu_read_lock();
	css = css_lookup(&blkio_subsys, blkg->blkcg_id);
	if (!css)
		goto out;

	blkcg = container_of(css, struct blkio_cgroup, css);
	spin_lock_irqsave(&blkcg->lock, flags);
	if (!hlist_unhashed(&blkg->blkcg_node)) {
		__blkiocg_del_blkio_group(blkg);
		ret = 0;
	}
	spin_unlock_irqrestore(&blkcg->lock, flags);
out:
	rcu_read_unlock();
	return ret;
}
EXPORT_SYMBOL_GPL(blkiocg_del_blkio_group);

/* called under rcu_read_lock(). */
struct blkio_group *blkiocg_lookup_group(struct blkio_cgroup *blkcg, void *key)
{
	struct blkio_group *blkg;
	struct hlist_node *n;
	void *__key;

	hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) {
		__key = blkg->key;
		if (__key == key)
			return blkg;
	}

	return NULL;
}
EXPORT_SYMBOL_GPL(blkiocg_lookup_group);

#define SHOW_FUNCTION(__VAR)						\
static u64 blkiocg_##__VAR##_read(struct cgroup *cgroup,		\
				       struct cftype *cftype)		\
{									\
	struct blkio_cgroup *blkcg;					\
									\
	blkcg = cgroup_to_blkio_cgroup(cgroup);				\
	return (u64)blkcg->__VAR;					\
}

SHOW_FUNCTION(weight);
#undef SHOW_FUNCTION

static int
blkiocg_weight_write(struct cgroup *cgroup, struct cftype *cftype, u64 val)
{
	struct blkio_cgroup *blkcg;
	struct blkio_group *blkg;
	struct hlist_node *n;
	struct blkio_policy_type *blkiop;

	if (val < BLKIO_WEIGHT_MIN || val > BLKIO_WEIGHT_MAX)
		return -EINVAL;

	blkcg = cgroup_to_blkio_cgroup(cgroup);
	spin_lock(&blkio_list_lock);
	spin_lock_irq(&blkcg->lock);
	blkcg->weight = (unsigned int)val;
	hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
		list_for_each_entry(blkiop, &blkio_list, list)
			blkiop->ops.blkio_update_group_weight_fn(blkg,
					blkcg->weight);
	}
	spin_unlock_irq(&blkcg->lock);
	spin_unlock(&blkio_list_lock);
	return 0;
}

#define SHOW_FUNCTION_PER_GROUP(__VAR)					\
static int blkiocg_##__VAR##_read(struct cgroup *cgroup,		\
			struct cftype *cftype, struct seq_file *m)	\
{									\
	struct blkio_cgroup *blkcg;					\
	struct blkio_group *blkg;					\
	struct hlist_node *n;						\
									\
	if (!cgroup_lock_live_group(cgroup))				\
		return -ENODEV;						\
									\
	blkcg = cgroup_to_blkio_cgroup(cgroup);				\
	rcu_read_lock();						\
	hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) {\
		if (blkg->dev)						\
			seq_printf(m, "%u:%u %lu\n", MAJOR(blkg->dev),	\
				 MINOR(blkg->dev), blkg->__VAR);	\
	}								\
	rcu_read_unlock();						\
	cgroup_unlock();						\
	return 0;							\
}

SHOW_FUNCTION_PER_GROUP(time);
SHOW_FUNCTION_PER_GROUP(sectors);
#ifdef CONFIG_DEBUG_BLK_CGROUP
SHOW_FUNCTION_PER_GROUP(dequeue);
#endif
#undef SHOW_FUNCTION_PER_GROUP

#ifdef CONFIG_DEBUG_BLK_CGROUP
void blkiocg_update_blkio_group_dequeue_stats(struct blkio_group *blkg,
			unsigned long dequeue)
{
	blkg->dequeue += dequeue;
}
EXPORT_SYMBOL_GPL(blkiocg_update_blkio_group_dequeue_stats);
#endif

struct cftype blkio_files[] = {
	{
		.name = "weight",
		.read_u64 = blkiocg_weight_read,
		.write_u64 = blkiocg_weight_write,
	},
	{
		.name = "time",
		.read_seq_string = blkiocg_time_read,
	},
	{
		.name = "sectors",
		.read_seq_string = blkiocg_sectors_read,
	},
#ifdef CONFIG_DEBUG_BLK_CGROUP
       {
		.name = "dequeue",
		.read_seq_string = blkiocg_dequeue_read,
       },
#endif
};

static int blkiocg_populate(struct cgroup_subsys *subsys, struct cgroup *cgroup)
{
	return cgroup_add_files(cgroup, subsys, blkio_files,
				ARRAY_SIZE(blkio_files));
}

static void blkiocg_destroy(struct cgroup_subsys *subsys, struct cgroup *cgroup)
{
	struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
	unsigned long flags;
	struct blkio_group *blkg;
	void *key;
	struct blkio_policy_type *blkiop;

	rcu_read_lock();
remove_entry:
	spin_lock_irqsave(&blkcg->lock, flags);

	if (hlist_empty(&blkcg->blkg_list)) {
		spin_unlock_irqrestore(&blkcg->lock, flags);
		goto done;
	}

	blkg = hlist_entry(blkcg->blkg_list.first, struct blkio_group,
				blkcg_node);
	key = rcu_dereference(blkg->key);
	__blkiocg_del_blkio_group(blkg);

	spin_unlock_irqrestore(&blkcg->lock, flags);

	/*
	 * This blkio_group is being unlinked as associated cgroup is going
	 * away. Let all the IO controlling policies know about this event.
	 *
	 * Currently this is static call to one io controlling policy. Once
	 * we have more policies in place, we need some dynamic registration
	 * of callback function.
	 */
	spin_lock(&blkio_list_lock);
	list_for_each_entry(blkiop, &blkio_list, list)
		blkiop->ops.blkio_unlink_group_fn(key, blkg);
	spin_unlock(&blkio_list_lock);
	goto remove_entry;
done:
	free_css_id(&blkio_subsys, &blkcg->css);
	rcu_read_unlock();
	kfree(blkcg);
}

static struct cgroup_subsys_state *
blkiocg_create(struct cgroup_subsys *subsys, struct cgroup *cgroup)
{
	struct blkio_cgroup *blkcg, *parent_blkcg;

	if (!cgroup->parent) {
		blkcg = &blkio_root_cgroup;
		goto done;
	}

	/* Currently we do not support hierarchy deeper than two level (0,1) */
	parent_blkcg = cgroup_to_blkio_cgroup(cgroup->parent);
	if (css_depth(&parent_blkcg->css) > 0)
		return ERR_PTR(-EINVAL);

	blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
	if (!blkcg)
		return ERR_PTR(-ENOMEM);

	blkcg->weight = BLKIO_WEIGHT_DEFAULT;
done:
	spin_lock_init(&blkcg->lock);
	INIT_HLIST_HEAD(&blkcg->blkg_list);

	return &blkcg->css;
}

/*
 * We cannot support shared io contexts, as we have no mean to support
 * two tasks with the same ioc in two different groups without major rework
 * of the main cic data structures.  For now we allow a task to change
 * its cgroup only if it's the only owner of its ioc.
 */
static int blkiocg_can_attach(struct cgroup_subsys *subsys,
				struct cgroup *cgroup, struct task_struct *tsk,
				bool threadgroup)
{
	struct io_context *ioc;
	int ret = 0;

	/* task_lock() is needed to avoid races with exit_io_context() */
	task_lock(tsk);
	ioc = tsk->io_context;
	if (ioc && atomic_read(&ioc->nr_tasks) > 1)
		ret = -EINVAL;
	task_unlock(tsk);

	return ret;
}

static void blkiocg_attach(struct cgroup_subsys *subsys, struct cgroup *cgroup,
				struct cgroup *prev, struct task_struct *tsk,
				bool threadgroup)
{
	struct io_context *ioc;

	task_lock(tsk);
	ioc = tsk->io_context;
	if (ioc)
		ioc->cgroup_changed = 1;
	task_unlock(tsk);
}

struct cgroup_subsys blkio_subsys = {
	.name = "blkio",
	.create = blkiocg_create,
	.can_attach = blkiocg_can_attach,
	.attach = blkiocg_attach,
	.destroy = blkiocg_destroy,
	.populate = blkiocg_populate,
	.subsys_id = blkio_subsys_id,
	.use_id = 1,
};

void blkio_policy_register(struct blkio_policy_type *blkiop)
{
	spin_lock(&blkio_list_lock);
	list_add_tail(&blkiop->list, &blkio_list);
	spin_unlock(&blkio_list_lock);
}
EXPORT_SYMBOL_GPL(blkio_policy_register);

void blkio_policy_unregister(struct blkio_policy_type *blkiop)
{
	spin_lock(&blkio_list_lock);
	list_del_init(&blkiop->list);
	spin_unlock(&blkio_list_lock);
}
EXPORT_SYMBOL_GPL(blkio_policy_unregister);
Commit	Line	Data
31e4c28d VG	1	/*
	2	* Common Block IO controller cgroup interface
	3	*
	4	* Based on ideas and code from CFQ, CFS and BFQ:
	5	* Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
	6	*
	7	* Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
	8	* Paolo Valente <paolo.valente@unimore.it>
	9	*
	10	* Copyright (C) 2009 Vivek Goyal <vgoyal@redhat.com>
	11	* Nauman Rafique <nauman@google.com>
	12	*/
	13	#include <linux/ioprio.h>
22084190 VG	14	#include <linux/seq_file.h>
22084190 VG	15	#include <linux/kdev_t.h>
9d6a986c	16	#include <linux/module.h>
accee785	17	#include <linux/err.h>
31e4c28d	18	#include "blk-cgroup.h"
3e252066 VG	19
	20	static DEFINE_SPINLOCK(blkio_list_lock);
	21	static LIST_HEAD(blkio_list);
b1c35769	22
31e4c28d	23	struct blkio_cgroup blkio_root_cgroup = { .weight = 2*BLKIO_WEIGHT_DEFAULT };
9d6a986c VG	24	EXPORT_SYMBOL_GPL(blkio_root_cgroup);
9d6a986c VG	25
31e4c28d VG	26	struct blkio_cgroup cgroup_to_blkio_cgroup(struct cgroup cgroup)
	27	{
	28	return container_of(cgroup_subsys_state(cgroup, blkio_subsys_id),
	29	struct blkio_cgroup, css);
	30	}
9d6a986c	31	EXPORT_SYMBOL_GPL(cgroup_to_blkio_cgroup);
31e4c28d	32
22084190 VG	33	void blkiocg_update_blkio_group_stats(struct blkio_group *blkg,
	34	unsigned long time, unsigned long sectors)
	35	{
	36	blkg->time += time;
	37	blkg->sectors += sectors;
	38	}
9d6a986c	39	EXPORT_SYMBOL_GPL(blkiocg_update_blkio_group_stats);
22084190	40
31e4c28d	41	void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,
22084190	42	struct blkio_group blkg, void key, dev_t dev)
31e4c28d VG	43	{
	44	unsigned long flags;
	45
	46	spin_lock_irqsave(&blkcg->lock, flags);
	47	rcu_assign_pointer(blkg->key, key);
b1c35769	48	blkg->blkcg_id = css_id(&blkcg->css);
31e4c28d VG	49	hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
31e4c28d VG	50	spin_unlock_irqrestore(&blkcg->lock, flags);
2868ef7b VG	51	#ifdef CONFIG_DEBUG_BLK_CGROUP
	52	/* Need to take css reference ? */
	53	cgroup_path(blkcg->css.cgroup, blkg->path, sizeof(blkg->path));
	54	#endif
22084190	55	blkg->dev = dev;
31e4c28d	56	}
9d6a986c	57	EXPORT_SYMBOL_GPL(blkiocg_add_blkio_group);
31e4c28d	58
b1c35769 VG	59	static void __blkiocg_del_blkio_group(struct blkio_group *blkg)
	60	{
	61	hlist_del_init_rcu(&blkg->blkcg_node);
	62	blkg->blkcg_id = 0;
	63	}
	64
	65	/*
	66	* returns 0 if blkio_group was still on cgroup list. Otherwise returns 1
	67	* indicating that blk_group was unhashed by the time we got to it.
	68	*/
31e4c28d VG	69	int blkiocg_del_blkio_group(struct blkio_group *blkg)
31e4c28d VG	70	{
b1c35769 VG	71	struct blkio_cgroup *blkcg;
	72	unsigned long flags;
	73	struct cgroup_subsys_state *css;
	74	int ret = 1;
	75
	76	rcu_read_lock();
	77	css = css_lookup(&blkio_subsys, blkg->blkcg_id);
	78	if (!css)
	79	goto out;
	80
	81	blkcg = container_of(css, struct blkio_cgroup, css);
	82	spin_lock_irqsave(&blkcg->lock, flags);
	83	if (!hlist_unhashed(&blkg->blkcg_node)) {
	84	__blkiocg_del_blkio_group(blkg);
	85	ret = 0;
	86	}
	87	spin_unlock_irqrestore(&blkcg->lock, flags);
	88	out:
	89	rcu_read_unlock();
	90	return ret;
31e4c28d	91	}
9d6a986c	92	EXPORT_SYMBOL_GPL(blkiocg_del_blkio_group);
31e4c28d VG	93
	94	/* called under rcu_read_lock(). */
	95	struct blkio_group blkiocg_lookup_group(struct blkio_cgroup blkcg, void *key)
	96	{
	97	struct blkio_group *blkg;
	98	struct hlist_node *n;
	99	void *__key;
	100
	101	hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) {
	102	__key = blkg->key;
	103	if (__key == key)
	104	return blkg;
	105	}
	106
	107	return NULL;
	108	}
9d6a986c	109	EXPORT_SYMBOL_GPL(blkiocg_lookup_group);
31e4c28d VG	110
	111	#define SHOW_FUNCTION(__VAR) \
	112	static u64 blkiocg_##__VAR##_read(struct cgroup *cgroup, \
	113	struct cftype *cftype) \
	114	{ \
	115	struct blkio_cgroup *blkcg; \
	116	\
	117	blkcg = cgroup_to_blkio_cgroup(cgroup); \
	118	return (u64)blkcg->__VAR; \
	119	}
	120
	121	SHOW_FUNCTION(weight);
	122	#undef SHOW_FUNCTION
	123
	124	static int
	125	blkiocg_weight_write(struct cgroup cgroup, struct cftype cftype, u64 val)
	126	{
	127	struct blkio_cgroup *blkcg;
f8d461d6 VG	128	struct blkio_group *blkg;
f8d461d6 VG	129	struct hlist_node *n;
3e252066	130	struct blkio_policy_type *blkiop;
31e4c28d VG	131
	132	if (val < BLKIO_WEIGHT_MIN \|\| val > BLKIO_WEIGHT_MAX)
	133	return -EINVAL;
	134
	135	blkcg = cgroup_to_blkio_cgroup(cgroup);
bcf4dd43	136	spin_lock(&blkio_list_lock);
f8d461d6	137	spin_lock_irq(&blkcg->lock);
31e4c28d	138	blkcg->weight = (unsigned int)val;
3e252066	139	hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
3e252066 VG	140	list_for_each_entry(blkiop, &blkio_list, list)
	141	blkiop->ops.blkio_update_group_weight_fn(blkg,
	142	blkcg->weight);
3e252066	143	}
f8d461d6	144	spin_unlock_irq(&blkcg->lock);
bcf4dd43	145	spin_unlock(&blkio_list_lock);
31e4c28d VG	146	return 0;
	147	}
	148
22084190 VG	149	#define SHOW_FUNCTION_PER_GROUP(__VAR) \
	150	static int blkiocg_##__VAR##_read(struct cgroup *cgroup, \
	151	struct cftype cftype, struct seq_file m) \
	152	{ \
	153	struct blkio_cgroup *blkcg; \
	154	struct blkio_group *blkg; \
	155	struct hlist_node *n; \
	156	\
	157	if (!cgroup_lock_live_group(cgroup)) \
	158	return -ENODEV; \
	159	\
	160	blkcg = cgroup_to_blkio_cgroup(cgroup); \
	161	rcu_read_lock(); \
	162	hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) {\
	163	if (blkg->dev) \
	164	seq_printf(m, "%u:%u %lu\n", MAJOR(blkg->dev), \
	165	MINOR(blkg->dev), blkg->__VAR); \
	166	} \
	167	rcu_read_unlock(); \
	168	cgroup_unlock(); \
	169	return 0; \
	170	}
	171
	172	SHOW_FUNCTION_PER_GROUP(time);
	173	SHOW_FUNCTION_PER_GROUP(sectors);
	174	#ifdef CONFIG_DEBUG_BLK_CGROUP
	175	SHOW_FUNCTION_PER_GROUP(dequeue);
	176	#endif
	177	#undef SHOW_FUNCTION_PER_GROUP
	178
	179	#ifdef CONFIG_DEBUG_BLK_CGROUP
	180	void blkiocg_update_blkio_group_dequeue_stats(struct blkio_group *blkg,
	181	unsigned long dequeue)
	182	{
	183	blkg->dequeue += dequeue;
	184	}
9d6a986c	185	EXPORT_SYMBOL_GPL(blkiocg_update_blkio_group_dequeue_stats);
22084190 VG	186	#endif
22084190 VG	187
31e4c28d VG	188	struct cftype blkio_files[] = {
	189	{
	190	.name = "weight",
	191	.read_u64 = blkiocg_weight_read,
	192	.write_u64 = blkiocg_weight_write,
	193	},
22084190 VG	194	{
	195	.name = "time",
	196	.read_seq_string = blkiocg_time_read,
	197	},
	198	{
	199	.name = "sectors",
	200	.read_seq_string = blkiocg_sectors_read,
	201	},
	202	#ifdef CONFIG_DEBUG_BLK_CGROUP
	203	{
	204	.name = "dequeue",
	205	.read_seq_string = blkiocg_dequeue_read,
	206	},
	207	#endif
31e4c28d VG	208	};
	209
	210	static int blkiocg_populate(struct cgroup_subsys subsys, struct cgroup cgroup)
	211	{
	212	return cgroup_add_files(cgroup, subsys, blkio_files,
	213	ARRAY_SIZE(blkio_files));
	214	}
	215
	216	static void blkiocg_destroy(struct cgroup_subsys subsys, struct cgroup cgroup)
	217	{
	218	struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
b1c35769 VG	219	unsigned long flags;
	220	struct blkio_group *blkg;
	221	void *key;
3e252066	222	struct blkio_policy_type *blkiop;
b1c35769 VG	223
	224	rcu_read_lock();
	225	remove_entry:
	226	spin_lock_irqsave(&blkcg->lock, flags);
	227
	228	if (hlist_empty(&blkcg->blkg_list)) {
	229	spin_unlock_irqrestore(&blkcg->lock, flags);
	230	goto done;
	231	}
	232
	233	blkg = hlist_entry(blkcg->blkg_list.first, struct blkio_group,
	234	blkcg_node);
	235	key = rcu_dereference(blkg->key);
	236	__blkiocg_del_blkio_group(blkg);
31e4c28d	237
b1c35769 VG	238	spin_unlock_irqrestore(&blkcg->lock, flags);
	239
	240	/*
	241	* This blkio_group is being unlinked as associated cgroup is going
	242	* away. Let all the IO controlling policies know about this event.
	243	*
	244	* Currently this is static call to one io controlling policy. Once
	245	* we have more policies in place, we need some dynamic registration
	246	* of callback function.
	247	*/
3e252066 VG	248	spin_lock(&blkio_list_lock);
	249	list_for_each_entry(blkiop, &blkio_list, list)
	250	blkiop->ops.blkio_unlink_group_fn(key, blkg);
	251	spin_unlock(&blkio_list_lock);
b1c35769 VG	252	goto remove_entry;
b1c35769 VG	253	done:
31e4c28d	254	free_css_id(&blkio_subsys, &blkcg->css);
b1c35769	255	rcu_read_unlock();
31e4c28d VG	256	kfree(blkcg);
	257	}
	258
	259	static struct cgroup_subsys_state *
	260	blkiocg_create(struct cgroup_subsys subsys, struct cgroup cgroup)
	261	{
	262	struct blkio_cgroup blkcg, parent_blkcg;
	263
	264	if (!cgroup->parent) {
	265	blkcg = &blkio_root_cgroup;
	266	goto done;
	267	}
	268
	269	/* Currently we do not support hierarchy deeper than two level (0,1) */
	270	parent_blkcg = cgroup_to_blkio_cgroup(cgroup->parent);
	271	if (css_depth(&parent_blkcg->css) > 0)
	272	return ERR_PTR(-EINVAL);
	273
	274	blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
	275	if (!blkcg)
	276	return ERR_PTR(-ENOMEM);
	277
	278	blkcg->weight = BLKIO_WEIGHT_DEFAULT;
	279	done:
	280	spin_lock_init(&blkcg->lock);
	281	INIT_HLIST_HEAD(&blkcg->blkg_list);
	282
	283	return &blkcg->css;
	284	}
	285
	286	/*
	287	* We cannot support shared io contexts, as we have no mean to support
	288	* two tasks with the same ioc in two different groups without major rework
	289	* of the main cic data structures. For now we allow a task to change
	290	* its cgroup only if it's the only owner of its ioc.
	291	*/
	292	static int blkiocg_can_attach(struct cgroup_subsys *subsys,
	293	struct cgroup cgroup, struct task_struct tsk,
	294	bool threadgroup)
	295	{
	296	struct io_context *ioc;
	297	int ret = 0;
	298
	299	/* task_lock() is needed to avoid races with exit_io_context() */
	300	task_lock(tsk);
	301	ioc = tsk->io_context;
	302	if (ioc && atomic_read(&ioc->nr_tasks) > 1)
	303	ret = -EINVAL;
	304	task_unlock(tsk);
	305
	306	return ret;
	307	}
	308
	309	static void blkiocg_attach(struct cgroup_subsys subsys, struct cgroup cgroup,
	310	struct cgroup prev, struct task_struct tsk,
	311	bool threadgroup)
	312	{
	313	struct io_context *ioc;
	314
	315	task_lock(tsk);
	316	ioc = tsk->io_context;
	317	if (ioc)
	318	ioc->cgroup_changed = 1;
	319	task_unlock(tsk);
320	}
321
322	struct cgroup_subsys blkio_subsys = {
323	.name = "blkio",
324	.create = blkiocg_create,
325	.can_attach = blkiocg_can_attach,
326	.attach = blkiocg_attach,
327	.destroy = blkiocg_destroy,
328	.populate = blkiocg_populate,
329	.subsys_id = blkio_subsys_id,
330	.use_id = 1,
331	};
3e252066 VG	332
	333	void blkio_policy_register(struct blkio_policy_type *blkiop)
	334	{
	335	spin_lock(&blkio_list_lock);
	336	list_add_tail(&blkiop->list, &blkio_list);
	337	spin_unlock(&blkio_list_lock);
	338	}
	339	EXPORT_SYMBOL_GPL(blkio_policy_register);
	340
	341	void blkio_policy_unregister(struct blkio_policy_type *blkiop)
	342	{
	343	spin_lock(&blkio_list_lock);
	344	list_del_init(&blkiop->list);
	345	spin_unlock(&blkio_list_lock);
	346	}
	347	EXPORT_SYMBOL_GPL(blkio_policy_unregister);