// SPDX-License-Identifier: GPL-2.0

  /*
   * Functions related to sysfs handling
   */
  #include <linux/kernel.h>

  #include <linux/slab.h>

  #include <linux/module.h>
  #include <linux/bio.h>
  #include <linux/blkdev.h>

  #include <linux/backing-dev.h>

  #include <linux/blktrace_api.h>

  #include <linux/blk-mq.h>

  #include <linux/blk-cgroup.h>

  #include <linux/debugfs.h>

  
  #include "blk.h"

  #include "blk-mq.h"

  #include "blk-mq-debugfs.h"

  #include "blk-wbt.h"

  
  struct queue_sysfs_entry {
  	struct attribute attr;
  	ssize_t (*show)(struct request_queue *, char *);
  	ssize_t (*store)(struct request_queue *, const char *, size_t);
  };
  
  static ssize_t

  queue_var_show(unsigned long var, char *page)

  {

  	return sprintf(page, "%lu
  ", var);

  }
  
  static ssize_t
  queue_var_store(unsigned long *var, const char *page, size_t count)
  {

  	int err;
  	unsigned long v;

  	err = kstrtoul(page, 10, &v);

  	if (err || v > UINT_MAX)
  		return -EINVAL;
  
  	*var = v;

  	return count;
  }

  static ssize_t queue_var_store64(s64 *var, const char *page)

  {
  	int err;

  	s64 v;

  	err = kstrtos64(page, 10, &v);

  	if (err < 0)
  		return err;
  
  	*var = v;
  	return 0;
  }

  static ssize_t queue_requests_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(q->nr_requests, (page));
  }
  
  static ssize_t
  queue_requests_store(struct request_queue *q, const char *page, size_t count)
  {

  	unsigned long nr;

  	int ret, err;

  	if (!queue_is_mq(q))

  		return -EINVAL;
  
  	ret = queue_var_store(&nr, page, count);

  	if (ret < 0)
  		return ret;

  	if (nr < BLKDEV_MIN_RQ)
  		nr = BLKDEV_MIN_RQ;

  	err = blk_mq_update_nr_requests(q, nr);

  	if (err)
  		return err;

  	return ret;
  }
  
  static ssize_t queue_ra_show(struct request_queue *q, char *page)
  {

  	unsigned long ra_kb = q->backing_dev_info->ra_pages <<

  					(PAGE_SHIFT - 10);

  
  	return queue_var_show(ra_kb, (page));
  }
  
  static ssize_t
  queue_ra_store(struct request_queue *q, const char *page, size_t count)
  {
  	unsigned long ra_kb;
  	ssize_t ret = queue_var_store(&ra_kb, page, count);

  	if (ret < 0)
  		return ret;

  	q->backing_dev_info->ra_pages = ra_kb >> (PAGE_SHIFT - 10);

  
  	return ret;
  }
  
  static ssize_t queue_max_sectors_show(struct request_queue *q, char *page)
  {

  	int max_sectors_kb = queue_max_sectors(q) >> 1;

  
  	return queue_var_show(max_sectors_kb, (page));
  }

  static ssize_t queue_max_segments_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(queue_max_segments(q), (page));
  }

  static ssize_t queue_max_discard_segments_show(struct request_queue *q,
  		char *page)
  {
  	return queue_var_show(queue_max_discard_segments(q), (page));
  }

  static ssize_t queue_max_integrity_segments_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(q->limits.max_integrity_segments, (page));
  }

  static ssize_t queue_max_segment_size_show(struct request_queue *q, char *page)
  {

  	return queue_var_show(queue_max_segment_size(q), (page));

  }

  static ssize_t queue_logical_block_size_show(struct request_queue *q, char *page)

  {

  	return queue_var_show(queue_logical_block_size(q), page);

  }

  static ssize_t queue_physical_block_size_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(queue_physical_block_size(q), page);
  }

  static ssize_t queue_chunk_sectors_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(q->limits.chunk_sectors, page);
  }

  static ssize_t queue_io_min_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(queue_io_min(q), page);
  }
  
  static ssize_t queue_io_opt_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(queue_io_opt(q), page);

  }

  static ssize_t queue_discard_granularity_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(q->limits.discard_granularity, page);
  }

  static ssize_t queue_discard_max_hw_show(struct request_queue *q, char *page)
  {

  	return sprintf(page, "%llu
  ",
  		(unsigned long long)q->limits.max_hw_discard_sectors << 9);

  }

  static ssize_t queue_discard_max_show(struct request_queue *q, char *page)
  {

  	return sprintf(page, "%llu
  ",
  		       (unsigned long long)q->limits.max_discard_sectors << 9);

  }

  static ssize_t queue_discard_max_store(struct request_queue *q,
  				       const char *page, size_t count)
  {
  	unsigned long max_discard;
  	ssize_t ret = queue_var_store(&max_discard, page, count);
  
  	if (ret < 0)
  		return ret;
  
  	if (max_discard & (q->limits.discard_granularity - 1))
  		return -EINVAL;
  
  	max_discard >>= 9;
  	if (max_discard > UINT_MAX)
  		return -EINVAL;
  
  	if (max_discard > q->limits.max_hw_discard_sectors)
  		max_discard = q->limits.max_hw_discard_sectors;
  
  	q->limits.max_discard_sectors = max_discard;
  	return ret;
  }

  static ssize_t queue_discard_zeroes_data_show(struct request_queue *q, char *page)
  {

  	return queue_var_show(0, page);

  }

  static ssize_t queue_write_same_max_show(struct request_queue *q, char *page)
  {
  	return sprintf(page, "%llu
  ",
  		(unsigned long long)q->limits.max_write_same_sectors << 9);
  }

  static ssize_t queue_write_zeroes_max_show(struct request_queue *q, char *page)
  {
  	return sprintf(page, "%llu
  ",
  		(unsigned long long)q->limits.max_write_zeroes_sectors << 9);
  }

  static ssize_t queue_zone_append_max_show(struct request_queue *q, char *page)
  {
  	unsigned long long max_sectors = q->limits.max_zone_append_sectors;
  
  	return sprintf(page, "%llu
  ", max_sectors << SECTOR_SHIFT);
  }

  static ssize_t
  queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
  {
  	unsigned long max_sectors_kb,

  		max_hw_sectors_kb = queue_max_hw_sectors(q) >> 1,

  			page_kb = 1 << (PAGE_SHIFT - 10);

  	ssize_t ret = queue_var_store(&max_sectors_kb, page, count);

  	if (ret < 0)
  		return ret;

  	max_hw_sectors_kb = min_not_zero(max_hw_sectors_kb, (unsigned long)
  					 q->limits.max_dev_sectors >> 1);

  	if (max_sectors_kb > max_hw_sectors_kb || max_sectors_kb < page_kb)
  		return -EINVAL;

  	spin_lock_irq(&q->queue_lock);

  	q->limits.max_sectors = max_sectors_kb << 1;

  	q->backing_dev_info->io_pages = max_sectors_kb >> (PAGE_SHIFT - 10);

  	spin_unlock_irq(&q->queue_lock);

  
  	return ret;
  }
  
  static ssize_t queue_max_hw_sectors_show(struct request_queue *q, char *page)
  {

  	int max_hw_sectors_kb = queue_max_hw_sectors(q) >> 1;

  
  	return queue_var_show(max_hw_sectors_kb, (page));
  }

  #define QUEUE_SYSFS_BIT_FNS(name, flag, neg)				\
  static ssize_t								\

  queue_##name##_show(struct request_queue *q, char *page)		\

  {									\
  	int bit;							\
  	bit = test_bit(QUEUE_FLAG_##flag, &q->queue_flags);		\
  	return queue_var_show(neg ? !bit : bit, page);			\
  }									\
  static ssize_t								\

  queue_##name##_store(struct request_queue *q, const char *page, size_t count) \

  {									\
  	unsigned long val;						\
  	ssize_t ret;							\
  	ret = queue_var_store(&val, page, count);			\

  	if (ret < 0)							\
  		 return ret;						\

  	if (neg)							\
  		val = !val;						\
  									\

  	if (val)							\

  		blk_queue_flag_set(QUEUE_FLAG_##flag, q);		\

  	else								\

  		blk_queue_flag_clear(QUEUE_FLAG_##flag, q);		\

  	return ret;							\

  }

  QUEUE_SYSFS_BIT_FNS(nonrot, NONROT, 1);
  QUEUE_SYSFS_BIT_FNS(random, ADD_RANDOM, 0);
  QUEUE_SYSFS_BIT_FNS(iostats, IO_STAT, 0);

  QUEUE_SYSFS_BIT_FNS(stable_writes, STABLE_WRITES, 0);

  #undef QUEUE_SYSFS_BIT_FNS

  static ssize_t queue_zoned_show(struct request_queue *q, char *page)
  {
  	switch (blk_queue_zoned_model(q)) {
  	case BLK_ZONED_HA:
  		return sprintf(page, "host-aware
  ");
  	case BLK_ZONED_HM:
  		return sprintf(page, "host-managed
  ");
  	default:
  		return sprintf(page, "none
  ");
  	}
  }

  static ssize_t queue_nr_zones_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(blk_queue_nr_zones(q), page);
  }

  static ssize_t queue_max_open_zones_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(queue_max_open_zones(q), page);
  }

  static ssize_t queue_max_active_zones_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(queue_max_active_zones(q), page);
  }

  static ssize_t queue_nomerges_show(struct request_queue *q, char *page)
  {

  	return queue_var_show((blk_queue_nomerges(q) << 1) |
  			       blk_queue_noxmerges(q), page);

  }
  
  static ssize_t queue_nomerges_store(struct request_queue *q, const char *page,
  				    size_t count)
  {
  	unsigned long nm;
  	ssize_t ret = queue_var_store(&nm, page, count);

  	if (ret < 0)
  		return ret;

  	blk_queue_flag_clear(QUEUE_FLAG_NOMERGES, q);
  	blk_queue_flag_clear(QUEUE_FLAG_NOXMERGES, q);

  	if (nm == 2)

  		blk_queue_flag_set(QUEUE_FLAG_NOMERGES, q);

  	else if (nm)

  		blk_queue_flag_set(QUEUE_FLAG_NOXMERGES, q);

  	return ret;
  }

  static ssize_t queue_rq_affinity_show(struct request_queue *q, char *page)
  {

  	bool set = test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags);

  	bool force = test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags);

  	return queue_var_show(set << force, page);

  }
  
  static ssize_t
  queue_rq_affinity_store(struct request_queue *q, const char *page, size_t count)
  {
  	ssize_t ret = -EINVAL;

  #ifdef CONFIG_SMP

  	unsigned long val;
  
  	ret = queue_var_store(&val, page, count);

  	if (ret < 0)
  		return ret;

  	if (val == 2) {

  		blk_queue_flag_set(QUEUE_FLAG_SAME_COMP, q);
  		blk_queue_flag_set(QUEUE_FLAG_SAME_FORCE, q);

  	} else if (val == 1) {

  		blk_queue_flag_set(QUEUE_FLAG_SAME_COMP, q);
  		blk_queue_flag_clear(QUEUE_FLAG_SAME_FORCE, q);

  	} else if (val == 0) {

  		blk_queue_flag_clear(QUEUE_FLAG_SAME_COMP, q);
  		blk_queue_flag_clear(QUEUE_FLAG_SAME_FORCE, q);

  	}

  #endif
  	return ret;
  }

  static ssize_t queue_poll_delay_show(struct request_queue *q, char *page)
  {

  	int val;

  	if (q->poll_nsec == BLK_MQ_POLL_CLASSIC)
  		val = BLK_MQ_POLL_CLASSIC;

  	else
  		val = q->poll_nsec / 1000;
  
  	return sprintf(page, "%d
  ", val);

  }
  
  static ssize_t queue_poll_delay_store(struct request_queue *q, const char *page,
  				size_t count)
  {

  	int err, val;

  
  	if (!q->mq_ops || !q->mq_ops->poll)
  		return -EINVAL;

  	err = kstrtoint(page, 10, &val);
  	if (err < 0)
  		return err;

  	if (val == BLK_MQ_POLL_CLASSIC)
  		q->poll_nsec = BLK_MQ_POLL_CLASSIC;
  	else if (val >= 0)

  		q->poll_nsec = val * 1000;

  	else
  		return -EINVAL;

  
  	return count;

  }

  static ssize_t queue_poll_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(test_bit(QUEUE_FLAG_POLL, &q->queue_flags), page);
  }
  
  static ssize_t queue_poll_store(struct request_queue *q, const char *page,
  				size_t count)
  {
  	unsigned long poll_on;
  	ssize_t ret;

  	if (!q->tag_set || q->tag_set->nr_maps <= HCTX_TYPE_POLL ||
  	    !q->tag_set->map[HCTX_TYPE_POLL].nr_queues)

  		return -EINVAL;
  
  	ret = queue_var_store(&poll_on, page, count);
  	if (ret < 0)
  		return ret;

  	if (poll_on)

  		blk_queue_flag_set(QUEUE_FLAG_POLL, q);

  	else

  		blk_queue_flag_clear(QUEUE_FLAG_POLL, q);

  
  	return ret;
  }

  static ssize_t queue_io_timeout_show(struct request_queue *q, char *page)
  {
  	return sprintf(page, "%u
  ", jiffies_to_msecs(q->rq_timeout));
  }
  
  static ssize_t queue_io_timeout_store(struct request_queue *q, const char *page,
  				  size_t count)
  {
  	unsigned int val;
  	int err;
  
  	err = kstrtou32(page, 10, &val);
  	if (err || val == 0)
  		return -EINVAL;
  
  	blk_queue_rq_timeout(q, msecs_to_jiffies(val));
  
  	return count;
  }

  static ssize_t queue_wb_lat_show(struct request_queue *q, char *page)
  {

  	if (!wbt_rq_qos(q))

  		return -EINVAL;

  	return sprintf(page, "%llu
  ", div_u64(wbt_get_min_lat(q), 1000));

  }
  
  static ssize_t queue_wb_lat_store(struct request_queue *q, const char *page,
  				  size_t count)
  {

  	struct rq_qos *rqos;

  	ssize_t ret;

  	s64 val;

  	ret = queue_var_store64(&val, page);
  	if (ret < 0)
  		return ret;

  	if (val < -1)
  		return -EINVAL;

  	rqos = wbt_rq_qos(q);
  	if (!rqos) {

  		ret = wbt_init(q);
  		if (ret)
  			return ret;

  	}

  	if (val == -1)

  		val = wbt_default_latency_nsec(q);

  	else if (val >= 0)

  		val *= 1000ULL;

  	if (wbt_get_min_lat(q) == val)
  		return count;

  	/*
  	 * Ensure that the queue is idled, in case the latency update
  	 * ends up either enabling or disabling wbt completely. We can't
  	 * have IO inflight if that happens.
  	 */

  	blk_mq_freeze_queue(q);
  	blk_mq_quiesce_queue(q);

  	wbt_set_min_lat(q, val);

  	blk_mq_unquiesce_queue(q);
  	blk_mq_unfreeze_queue(q);

  	return count;
  }

  static ssize_t queue_wc_show(struct request_queue *q, char *page)
  {
  	if (test_bit(QUEUE_FLAG_WC, &q->queue_flags))
  		return sprintf(page, "write back
  ");
  
  	return sprintf(page, "write through
  ");
  }
  
  static ssize_t queue_wc_store(struct request_queue *q, const char *page,
  			      size_t count)
  {
  	int set = -1;
  
  	if (!strncmp(page, "write back", 10))
  		set = 1;
  	else if (!strncmp(page, "write through", 13) ||
  		 !strncmp(page, "none", 4))
  		set = 0;
  
  	if (set == -1)
  		return -EINVAL;

  	if (set)

  		blk_queue_flag_set(QUEUE_FLAG_WC, q);

  	else

  		blk_queue_flag_clear(QUEUE_FLAG_WC, q);

  
  	return count;
  }

  static ssize_t queue_fua_show(struct request_queue *q, char *page)
  {
  	return sprintf(page, "%u
  ", test_bit(QUEUE_FLAG_FUA, &q->queue_flags));
  }

  static ssize_t queue_dax_show(struct request_queue *q, char *page)
  {
  	return queue_var_show(blk_queue_dax(q), page);
  }

  #define QUEUE_RO_ENTRY(_prefix, _name)			\
  static struct queue_sysfs_entry _prefix##_entry = {	\
  	.attr	= { .name = _name, .mode = 0444 },	\
  	.show	= _prefix##_show,			\
  };
  
  #define QUEUE_RW_ENTRY(_prefix, _name)			\
  static struct queue_sysfs_entry _prefix##_entry = {	\
  	.attr	= { .name = _name, .mode = 0644 },	\
  	.show	= _prefix##_show,			\
  	.store	= _prefix##_store,			\
  };
  
  QUEUE_RW_ENTRY(queue_requests, "nr_requests");
  QUEUE_RW_ENTRY(queue_ra, "read_ahead_kb");
  QUEUE_RW_ENTRY(queue_max_sectors, "max_sectors_kb");
  QUEUE_RO_ENTRY(queue_max_hw_sectors, "max_hw_sectors_kb");
  QUEUE_RO_ENTRY(queue_max_segments, "max_segments");
  QUEUE_RO_ENTRY(queue_max_integrity_segments, "max_integrity_segments");
  QUEUE_RO_ENTRY(queue_max_segment_size, "max_segment_size");
  QUEUE_RW_ENTRY(elv_iosched, "scheduler");
  
  QUEUE_RO_ENTRY(queue_logical_block_size, "logical_block_size");
  QUEUE_RO_ENTRY(queue_physical_block_size, "physical_block_size");
  QUEUE_RO_ENTRY(queue_chunk_sectors, "chunk_sectors");
  QUEUE_RO_ENTRY(queue_io_min, "minimum_io_size");
  QUEUE_RO_ENTRY(queue_io_opt, "optimal_io_size");
  
  QUEUE_RO_ENTRY(queue_max_discard_segments, "max_discard_segments");
  QUEUE_RO_ENTRY(queue_discard_granularity, "discard_granularity");
  QUEUE_RO_ENTRY(queue_discard_max_hw, "discard_max_hw_bytes");
  QUEUE_RW_ENTRY(queue_discard_max, "discard_max_bytes");
  QUEUE_RO_ENTRY(queue_discard_zeroes_data, "discard_zeroes_data");
  
  QUEUE_RO_ENTRY(queue_write_same_max, "write_same_max_bytes");
  QUEUE_RO_ENTRY(queue_write_zeroes_max, "write_zeroes_max_bytes");
  QUEUE_RO_ENTRY(queue_zone_append_max, "zone_append_max_bytes");
  
  QUEUE_RO_ENTRY(queue_zoned, "zoned");
  QUEUE_RO_ENTRY(queue_nr_zones, "nr_zones");
  QUEUE_RO_ENTRY(queue_max_open_zones, "max_open_zones");
  QUEUE_RO_ENTRY(queue_max_active_zones, "max_active_zones");
  
  QUEUE_RW_ENTRY(queue_nomerges, "nomerges");
  QUEUE_RW_ENTRY(queue_rq_affinity, "rq_affinity");
  QUEUE_RW_ENTRY(queue_poll, "io_poll");
  QUEUE_RW_ENTRY(queue_poll_delay, "io_poll_delay");
  QUEUE_RW_ENTRY(queue_wc, "write_cache");
  QUEUE_RO_ENTRY(queue_fua, "fua");
  QUEUE_RO_ENTRY(queue_dax, "dax");
  QUEUE_RW_ENTRY(queue_io_timeout, "io_timeout");
  QUEUE_RW_ENTRY(queue_wb_lat, "wbt_lat_usec");

  #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
  QUEUE_RW_ENTRY(blk_throtl_sample_time, "throttle_sample_time");
  #endif

  /* legacy alias for logical_block_size: */

  static struct queue_sysfs_entry queue_hw_sector_size_entry = {

  	.attr = {.name = "hw_sector_size", .mode = 0444 },

  	.show = queue_logical_block_size_show,
  };

  QUEUE_RW_ENTRY(queue_nonrot, "rotational");
  QUEUE_RW_ENTRY(queue_iostats, "iostats");
  QUEUE_RW_ENTRY(queue_random, "add_random");

  QUEUE_RW_ENTRY(queue_stable_writes, "stable_writes");

  static struct attribute *queue_attrs[] = {

  	&queue_requests_entry.attr,
  	&queue_ra_entry.attr,
  	&queue_max_hw_sectors_entry.attr,
  	&queue_max_sectors_entry.attr,

  	&queue_max_segments_entry.attr,

  	&queue_max_discard_segments_entry.attr,

  	&queue_max_integrity_segments_entry.attr,

  	&queue_max_segment_size_entry.attr,

  	&elv_iosched_entry.attr,

  	&queue_hw_sector_size_entry.attr,

  	&queue_logical_block_size_entry.attr,

  	&queue_physical_block_size_entry.attr,

  	&queue_chunk_sectors_entry.attr,

  	&queue_io_min_entry.attr,
  	&queue_io_opt_entry.attr,

  	&queue_discard_granularity_entry.attr,
  	&queue_discard_max_entry.attr,

  	&queue_discard_max_hw_entry.attr,

  	&queue_discard_zeroes_data_entry.attr,

  	&queue_write_same_max_entry.attr,

  	&queue_write_zeroes_max_entry.attr,

  	&queue_zone_append_max_entry.attr,

  	&queue_nonrot_entry.attr,

  	&queue_zoned_entry.attr,

  	&queue_nr_zones_entry.attr,

  	&queue_max_open_zones_entry.attr,

  	&queue_max_active_zones_entry.attr,

  	&queue_nomerges_entry.attr,

  	&queue_rq_affinity_entry.attr,

  	&queue_iostats_entry.attr,

  	&queue_stable_writes_entry.attr,

  	&queue_random_entry.attr,

  	&queue_poll_entry.attr,

  	&queue_wc_entry.attr,

  	&queue_fua_entry.attr,

  	&queue_dax_entry.attr,

  	&queue_wb_lat_entry.attr,

  	&queue_poll_delay_entry.attr,

  	&queue_io_timeout_entry.attr,

  #ifdef CONFIG_BLK_DEV_THROTTLING_LOW

  	&blk_throtl_sample_time_entry.attr,

  #endif

  	NULL,
  };

  static umode_t queue_attr_visible(struct kobject *kobj, struct attribute *attr,
  				int n)
  {
  	struct request_queue *q =
  		container_of(kobj, struct request_queue, kobj);
  
  	if (attr == &queue_io_timeout_entry.attr &&
  		(!q->mq_ops || !q->mq_ops->timeout))
  			return 0;

  	if ((attr == &queue_max_open_zones_entry.attr ||
  	     attr == &queue_max_active_zones_entry.attr) &&

  	    !blk_queue_is_zoned(q))
  		return 0;

  	return attr->mode;
  }
  
  static struct attribute_group queue_attr_group = {
  	.attrs = queue_attrs,
  	.is_visible = queue_attr_visible,
  };

  #define to_queue(atr) container_of((atr), struct queue_sysfs_entry, attr)
  
  static ssize_t
  queue_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
  {
  	struct queue_sysfs_entry *entry = to_queue(attr);
  	struct request_queue *q =
  		container_of(kobj, struct request_queue, kobj);
  	ssize_t res;
  
  	if (!entry->show)
  		return -EIO;
  	mutex_lock(&q->sysfs_lock);

  	res = entry->show(q, page);
  	mutex_unlock(&q->sysfs_lock);
  	return res;
  }
  
  static ssize_t
  queue_attr_store(struct kobject *kobj, struct attribute *attr,
  		    const char *page, size_t length)
  {
  	struct queue_sysfs_entry *entry = to_queue(attr);

  	struct request_queue *q;

  	ssize_t res;
  
  	if (!entry->store)
  		return -EIO;

  
  	q = container_of(kobj, struct request_queue, kobj);

  	mutex_lock(&q->sysfs_lock);

  	res = entry->store(q, page, length);
  	mutex_unlock(&q->sysfs_lock);
  	return res;
  }

  static void blk_free_queue_rcu(struct rcu_head *rcu_head)
  {
  	struct request_queue *q = container_of(rcu_head, struct request_queue,
  					       rcu_head);
  	kmem_cache_free(blk_requestq_cachep, q);
  }

  /* Unconfigure the I/O scheduler and dissociate from the cgroup controller. */
  static void blk_exit_queue(struct request_queue *q)
  {
  	/*
  	 * Since the I/O scheduler exit code may access cgroup information,
  	 * perform I/O scheduler exit before disassociating from the block
  	 * cgroup controller.
  	 */
  	if (q->elevator) {
  		ioc_clear_queue(q);

  		__elevator_exit(q, q->elevator);

  	}
  
  	/*
  	 * Remove all references to @q from the block cgroup controller before
  	 * restoring @q->queue_lock to avoid that restoring this pointer causes
  	 * e.g. blkcg_print_blkgs() to crash.
  	 */
  	blkcg_exit_queue(q);
  
  	/*
  	 * Since the cgroup code may dereference the @q->backing_dev_info
  	 * pointer, only decrease its reference count after having removed the
  	 * association with the block cgroup controller.
  	 */
  	bdi_put(q->backing_dev_info);
  }

  /**

   * blk_release_queue - releases all allocated resources of the request_queue
   * @kobj: pointer to a kobject, whose container is a request_queue
   *
   * This function releases all allocated resources of the request queue.
   *
   * The struct request_queue refcount is incremented with blk_get_queue() and
   * decremented with blk_put_queue(). Once the refcount reaches 0 this function
   * is called.
   *
   * For drivers that have a request_queue on a gendisk and added with
   * __device_add_disk() the refcount to request_queue will reach 0 with
   * the last put_disk() called by the driver. For drivers which don't use
   * __device_add_disk() this happens with blk_cleanup_queue().

   *

   * Drivers exist which depend on the release of the request_queue to be
   * synchronous, it should not be deferred.
   *
   * Context: can sleep

   */

  static void blk_release_queue(struct kobject *kobj)

  {

  	struct request_queue *q =
  		container_of(kobj, struct request_queue, kobj);
  
  	might_sleep();

  	if (test_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags))
  		blk_stat_remove_callback(q, q->poll_cb);
  	blk_stat_free_callback(q->poll_cb);

  	blk_free_queue_stats(q->stats);

  	if (queue_is_mq(q)) {
  		struct blk_mq_hw_ctx *hctx;
  		int i;

  		cancel_delayed_work_sync(&q->requeue_work);

  		queue_for_each_hw_ctx(q, hctx, i)
  			cancel_delayed_work_sync(&hctx->run_work);
  	}

  	blk_exit_queue(q);

  	blk_queue_free_zone_bitmaps(q);

  	if (queue_is_mq(q))

  		blk_mq_release(q);

  	blk_trace_shutdown(q);

  	mutex_lock(&q->debugfs_mutex);
  	debugfs_remove_recursive(q->debugfs_dir);
  	mutex_unlock(&q->debugfs_mutex);

  	if (queue_is_mq(q))

  		blk_mq_debugfs_unregister(q);

  	bioset_exit(&q->bio_split);

  	ida_simple_remove(&blk_queue_ida, q->id);

  	call_rcu(&q->rcu_head, blk_free_queue_rcu);

  }

  static const struct sysfs_ops queue_sysfs_ops = {

  	.show	= queue_attr_show,
  	.store	= queue_attr_store,
  };
  
  struct kobj_type blk_queue_ktype = {
  	.sysfs_ops	= &queue_sysfs_ops,

  	.release	= blk_release_queue,
  };

  /**
   * blk_register_queue - register a block layer queue with sysfs
   * @disk: Disk of which the request queue should be registered with sysfs.
   */

  int blk_register_queue(struct gendisk *disk)
  {
  	int ret;

  	struct device *dev = disk_to_dev(disk);

  	struct request_queue *q = disk->queue;

  	if (WARN_ON(!q))

  		return -ENXIO;

  	WARN_ONCE(blk_queue_registered(q),

  		  "%s is registering an already registered queue
  ",
  		  kobject_name(&dev->kobj));

  	/*

  	 * SCSI probing may synchronously create and destroy a lot of
  	 * request_queues for non-existent devices.  Shutting down a fully
  	 * functional queue takes measureable wallclock time as RCU grace
  	 * periods are involved.  To avoid excessive latency in these
  	 * cases, a request_queue starts out in a degraded mode which is
  	 * faster to shut down and is made fully functional here as
  	 * request_queues for non-existent devices never get registered.

  	 */

  	if (!blk_queue_init_done(q)) {

  		blk_queue_flag_set(QUEUE_FLAG_INIT_DONE, q);

  		percpu_ref_switch_to_percpu(&q->q_usage_counter);

  	}

  	blk_queue_update_readahead(q);

  	ret = blk_trace_init_sysfs(dev);
  	if (ret)
  		return ret;

  	mutex_lock(&q->sysfs_dir_lock);

  	ret = kobject_add(&q->kobj, kobject_get(&dev->kobj), "%s", "queue");

  	if (ret < 0) {
  		blk_trace_remove_sysfs(dev);

  		goto unlock;

  	}

  	ret = sysfs_create_group(&q->kobj, &queue_attr_group);
  	if (ret) {
  		blk_trace_remove_sysfs(dev);
  		kobject_del(&q->kobj);
  		kobject_put(&dev->kobj);
  		goto unlock;
  	}

  	mutex_lock(&q->debugfs_mutex);
  	q->debugfs_dir = debugfs_create_dir(kobject_name(q->kobj.parent),
  					    blk_debugfs_root);
  	mutex_unlock(&q->debugfs_mutex);

  	if (queue_is_mq(q)) {

  		__blk_mq_register_dev(dev, q);

  		blk_mq_debugfs_register(q);
  	}

  	mutex_lock(&q->sysfs_lock);

  	if (q->elevator) {

  		ret = elv_register_queue(q, false);

  		if (ret) {

  			mutex_unlock(&q->sysfs_lock);

  			mutex_unlock(&q->sysfs_dir_lock);

  			kobject_del(&q->kobj);
  			blk_trace_remove_sysfs(dev);
  			kobject_put(&dev->kobj);

  			return ret;

  		}

  	}

  	blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q);
  	wbt_enable_default(q);
  	blk_throtl_register_queue(q);
  
  	/* Now everything is ready and send out KOBJ_ADD uevent */
  	kobject_uevent(&q->kobj, KOBJ_ADD);

  	if (q->elevator)

  		kobject_uevent(&q->elevator->kobj, KOBJ_ADD);
  	mutex_unlock(&q->sysfs_lock);

  	ret = 0;
  unlock:

  	mutex_unlock(&q->sysfs_dir_lock);

  	return ret;

  }

  EXPORT_SYMBOL_GPL(blk_register_queue);

  /**
   * blk_unregister_queue - counterpart of blk_register_queue()
   * @disk: Disk of which the request queue should be unregistered from sysfs.
   *
   * Note: the caller is responsible for guaranteeing that this function is called
   * after blk_register_queue() has finished.
   */

  void blk_unregister_queue(struct gendisk *disk)
  {
  	struct request_queue *q = disk->queue;

  	if (WARN_ON(!q))
  		return;

  	/* Return early if disk->queue was never registered. */

  	if (!blk_queue_registered(q))

  		return;

  	/*

  	 * Since sysfs_remove_dir() prevents adding new directory entries
  	 * before removal of existing entries starts, protect against
  	 * concurrent elv_iosched_store() calls.

  	 */

  	mutex_lock(&q->sysfs_lock);

  	blk_queue_flag_clear(QUEUE_FLAG_REGISTERED, q);

  	mutex_unlock(&q->sysfs_lock);

  	mutex_lock(&q->sysfs_dir_lock);

  	/*
  	 * Remove the sysfs attributes before unregistering the queue data
  	 * structures that can be modified through sysfs.
  	 */

  	if (queue_is_mq(q))

  		blk_mq_unregister_dev(disk_to_dev(disk), q);

  	kobject_uevent(&q->kobj, KOBJ_REMOVE);
  	kobject_del(&q->kobj);
  	blk_trace_remove_sysfs(disk_to_dev(disk));

  	mutex_lock(&q->sysfs_lock);

  	if (q->elevator)

  		elv_unregister_queue(q);

  	mutex_unlock(&q->sysfs_lock);

  	mutex_unlock(&q->sysfs_dir_lock);

  
  	kobject_put(&disk_to_dev(disk)->kobj);

  }