drivers/block/null_blk.c

/*
 * Add configfs and memory store: Kyungchan Koh <kkc6196@fb.com> and
 * Shaohua Li <shli@fb.com>
 */
#include <linux/module.h>

#include <linux/moduleparam.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/blk-mq.h>
#include <linux/hrtimer.h>
#include <linux/lightnvm.h>
#include <linux/configfs.h>

#define SECTOR_SHIFT		9
#define PAGE_SECTORS_SHIFT	(PAGE_SHIFT - SECTOR_SHIFT)
#define PAGE_SECTORS		(1 << PAGE_SECTORS_SHIFT)
#define SECTOR_SIZE		(1 << SECTOR_SHIFT)
#define SECTOR_MASK		(PAGE_SECTORS - 1)

#define FREE_BATCH		16

struct nullb_cmd {
	struct list_head list;
	struct llist_node ll_list;
	struct call_single_data csd;
	struct request *rq;
	struct bio *bio;
	unsigned int tag;
	struct nullb_queue *nq;
	struct hrtimer timer;
	blk_status_t error;
};

struct nullb_queue {
	unsigned long *tag_map;
	wait_queue_head_t wait;
	unsigned int queue_depth;
	struct nullb_device *dev;

	struct nullb_cmd *cmds;
};

/*
 * Status flags for nullb_device.
 *
 * CONFIGURED:	Device has been configured and turned on. Cannot reconfigure.
 * UP:		Device is currently on and visible in userspace.
 */
enum nullb_device_flags {
	NULLB_DEV_FL_CONFIGURED	= 0,
	NULLB_DEV_FL_UP		= 1,
};

/*
 * nullb_page is a page in memory for nullb devices.
 *
 * @page:	The page holding the data.
 * @bitmap:	The bitmap represents which sector in the page has data.
 *		Each bit represents one block size. For example, sector 8
 *		will use the 7th bit
 */
struct nullb_page {
	struct page *page;
	unsigned long bitmap;
};

struct nullb_device {
	struct nullb *nullb;
	struct config_item item;
	struct radix_tree_root data; /* data stored in the disk */
	unsigned long flags; /* device flags */

	unsigned long size; /* device size in MB */
	unsigned long completion_nsec; /* time in ns to complete a request */
	unsigned int submit_queues; /* number of submission queues */
	unsigned int home_node; /* home node for the device */
	unsigned int queue_mode; /* block interface */
	unsigned int blocksize; /* block size */
	unsigned int irqmode; /* IRQ completion handler */
	unsigned int hw_queue_depth; /* queue depth */
	unsigned int index; /* index of the disk, only valid with a disk */
	bool use_lightnvm; /* register as a LightNVM device */
	bool blocking; /* blocking blk-mq device */
	bool use_per_node_hctx; /* use per-node allocation for hardware context */
	bool power; /* power on/off the device */
	bool memory_backed; /* if data is stored in memory */
};

struct nullb {
	struct nullb_device *dev;
	struct list_head list;
	unsigned int index;
	struct request_queue *q;
	struct gendisk *disk;
	struct nvm_dev *ndev;
	struct blk_mq_tag_set *tag_set;
	struct blk_mq_tag_set __tag_set;
	struct hrtimer timer;
	unsigned int queue_depth;
	spinlock_t lock;

	struct nullb_queue *queues;
	unsigned int nr_queues;
	char disk_name[DISK_NAME_LEN];
};

static LIST_HEAD(nullb_list);
static struct mutex lock;
static int null_major;
static DEFINE_IDA(nullb_indexes);
static struct kmem_cache *ppa_cache;
static struct blk_mq_tag_set tag_set;

enum {
	NULL_IRQ_NONE		= 0,
	NULL_IRQ_SOFTIRQ	= 1,
	NULL_IRQ_TIMER		= 2,
};

enum {
	NULL_Q_BIO		= 0,
	NULL_Q_RQ		= 1,
	NULL_Q_MQ		= 2,
};

static int g_submit_queues = 1;
module_param_named(submit_queues, g_submit_queues, int, S_IRUGO);
MODULE_PARM_DESC(submit_queues, "Number of submission queues");

static int g_home_node = NUMA_NO_NODE;
module_param_named(home_node, g_home_node, int, S_IRUGO);
MODULE_PARM_DESC(home_node, "Home node for the device");

static int g_queue_mode = NULL_Q_MQ;

static int null_param_store_val(const char *str, int *val, int min, int max)
{
	int ret, new_val;

	ret = kstrtoint(str, 10, &new_val);
	if (ret)
		return -EINVAL;

	if (new_val < min || new_val > max)
		return -EINVAL;

	*val = new_val;
	return 0;
}

static int null_set_queue_mode(const char *str, const struct kernel_param *kp)
{
	return null_param_store_val(str, &g_queue_mode, NULL_Q_BIO, NULL_Q_MQ);
}

static const struct kernel_param_ops null_queue_mode_param_ops = {
	.set	= null_set_queue_mode,
	.get	= param_get_int,
};

device_param_cb(queue_mode, &null_queue_mode_param_ops, &g_queue_mode, S_IRUGO);
MODULE_PARM_DESC(queue_mode, "Block interface to use (0=bio,1=rq,2=multiqueue)");

static int g_gb = 250;
module_param_named(gb, g_gb, int, S_IRUGO);
MODULE_PARM_DESC(gb, "Size in GB");

static int g_bs = 512;
module_param_named(bs, g_bs, int, S_IRUGO);
MODULE_PARM_DESC(bs, "Block size (in bytes)");

static int nr_devices = 1;
module_param(nr_devices, int, S_IRUGO);
MODULE_PARM_DESC(nr_devices, "Number of devices to register");

static bool g_use_lightnvm;
module_param_named(use_lightnvm, g_use_lightnvm, bool, S_IRUGO);
MODULE_PARM_DESC(use_lightnvm, "Register as a LightNVM device");

static bool g_blocking;
module_param_named(blocking, g_blocking, bool, S_IRUGO);
MODULE_PARM_DESC(blocking, "Register as a blocking blk-mq driver device");

static bool shared_tags;
module_param(shared_tags, bool, S_IRUGO);
MODULE_PARM_DESC(shared_tags, "Share tag set between devices for blk-mq");

static int g_irqmode = NULL_IRQ_SOFTIRQ;

static int null_set_irqmode(const char *str, const struct kernel_param *kp)
{
	return null_param_store_val(str, &g_irqmode, NULL_IRQ_NONE,
					NULL_IRQ_TIMER);
}

static const struct kernel_param_ops null_irqmode_param_ops = {
	.set	= null_set_irqmode,
	.get	= param_get_int,
};

device_param_cb(irqmode, &null_irqmode_param_ops, &g_irqmode, S_IRUGO);
MODULE_PARM_DESC(irqmode, "IRQ completion handler. 0-none, 1-softirq, 2-timer");

static unsigned long g_completion_nsec = 10000;
module_param_named(completion_nsec, g_completion_nsec, ulong, S_IRUGO);
MODULE_PARM_DESC(completion_nsec, "Time in ns to complete a request in hardware. Default: 10,000ns");

static int g_hw_queue_depth = 64;
module_param_named(hw_queue_depth, g_hw_queue_depth, int, S_IRUGO);
MODULE_PARM_DESC(hw_queue_depth, "Queue depth for each hardware queue. Default: 64");

static bool g_use_per_node_hctx;
module_param_named(use_per_node_hctx, g_use_per_node_hctx, bool, S_IRUGO);
MODULE_PARM_DESC(use_per_node_hctx, "Use per-node allocation for hardware context queues. Default: false");

static struct nullb_device *null_alloc_dev(void);
static void null_free_dev(struct nullb_device *dev);
static void null_del_dev(struct nullb *nullb);
static int null_add_dev(struct nullb_device *dev);
static void null_free_device_storage(struct nullb_device *dev);

static inline struct nullb_device *to_nullb_device(struct config_item *item)
{
	return item ? container_of(item, struct nullb_device, item) : NULL;
}

static inline ssize_t nullb_device_uint_attr_show(unsigned int val, char *page)
{
	return snprintf(page, PAGE_SIZE, "%u\n", val);
}

static inline ssize_t nullb_device_ulong_attr_show(unsigned long val,
	char *page)
{
	return snprintf(page, PAGE_SIZE, "%lu\n", val);
}

static inline ssize_t nullb_device_bool_attr_show(bool val, char *page)
{
	return snprintf(page, PAGE_SIZE, "%u\n", val);
}

static ssize_t nullb_device_uint_attr_store(unsigned int *val,
	const char *page, size_t count)
{
	unsigned int tmp;
	int result;

	result = kstrtouint(page, 0, &tmp);
	if (result)
		return result;

	*val = tmp;
	return count;
}

static ssize_t nullb_device_ulong_attr_store(unsigned long *val,
	const char *page, size_t count)
{
	int result;
	unsigned long tmp;

	result = kstrtoul(page, 0, &tmp);
	if (result)
		return result;

	*val = tmp;
	return count;
}

static ssize_t nullb_device_bool_attr_store(bool *val, const char *page,
	size_t count)
{
	bool tmp;
	int result;

	result = kstrtobool(page,  &tmp);
	if (result)
		return result;

	*val = tmp;
	return count;
}

/* The following macro should only be used with TYPE = {uint, ulong, bool}. */
#define NULLB_DEVICE_ATTR(NAME, TYPE)						\
static ssize_t									\
nullb_device_##NAME##_show(struct config_item *item, char *page)		\
{										\
	return nullb_device_##TYPE##_attr_show(					\
				to_nullb_device(item)->NAME, page);		\
}										\
static ssize_t									\
nullb_device_##NAME##_store(struct config_item *item, const char *page,		\
			    size_t count)					\
{										\
	if (test_bit(NULLB_DEV_FL_CONFIGURED, &to_nullb_device(item)->flags))	\
		return -EBUSY;							\
	return nullb_device_##TYPE##_attr_store(				\
			&to_nullb_device(item)->NAME, page, count);		\
}										\
CONFIGFS_ATTR(nullb_device_, NAME);

NULLB_DEVICE_ATTR(size, ulong);
NULLB_DEVICE_ATTR(completion_nsec, ulong);
NULLB_DEVICE_ATTR(submit_queues, uint);
NULLB_DEVICE_ATTR(home_node, uint);
NULLB_DEVICE_ATTR(queue_mode, uint);
NULLB_DEVICE_ATTR(blocksize, uint);
NULLB_DEVICE_ATTR(irqmode, uint);
NULLB_DEVICE_ATTR(hw_queue_depth, uint);
NULLB_DEVICE_ATTR(index, uint);
NULLB_DEVICE_ATTR(use_lightnvm, bool);
NULLB_DEVICE_ATTR(blocking, bool);
NULLB_DEVICE_ATTR(use_per_node_hctx, bool);
NULLB_DEVICE_ATTR(memory_backed, bool);

static ssize_t nullb_device_power_show(struct config_item *item, char *page)
{
	return nullb_device_bool_attr_show(to_nullb_device(item)->power, page);
}

static ssize_t nullb_device_power_store(struct config_item *item,
				     const char *page, size_t count)
{
	struct nullb_device *dev = to_nullb_device(item);
	bool newp = false;
	ssize_t ret;

	ret = nullb_device_bool_attr_store(&newp, page, count);
	if (ret < 0)
		return ret;

	if (!dev->power && newp) {
		if (test_and_set_bit(NULLB_DEV_FL_UP, &dev->flags))
			return count;
		if (null_add_dev(dev)) {
			clear_bit(NULLB_DEV_FL_UP, &dev->flags);
			return -ENOMEM;
		}

		set_bit(NULLB_DEV_FL_CONFIGURED, &dev->flags);
		dev->power = newp;
	} else if (to_nullb_device(item)->power && !newp) {
		mutex_lock(&lock);
		dev->power = newp;
		null_del_dev(dev->nullb);
		mutex_unlock(&lock);
		clear_bit(NULLB_DEV_FL_UP, &dev->flags);
	}

	return count;
}

CONFIGFS_ATTR(nullb_device_, power);

static struct configfs_attribute *nullb_device_attrs[] = {
	&nullb_device_attr_size,
	&nullb_device_attr_completion_nsec,
	&nullb_device_attr_submit_queues,
	&nullb_device_attr_home_node,
	&nullb_device_attr_queue_mode,
	&nullb_device_attr_blocksize,
	&nullb_device_attr_irqmode,
	&nullb_device_attr_hw_queue_depth,
	&nullb_device_attr_index,
	&nullb_device_attr_use_lightnvm,
	&nullb_device_attr_blocking,
	&nullb_device_attr_use_per_node_hctx,
	&nullb_device_attr_power,
	&nullb_device_attr_memory_backed,
	NULL,
};

static void nullb_device_release(struct config_item *item)
{
	struct nullb_device *dev = to_nullb_device(item);

	null_free_device_storage(dev);
	null_free_dev(dev);
}

static struct configfs_item_operations nullb_device_ops = {
	.release	= nullb_device_release,
};

static struct config_item_type nullb_device_type = {
	.ct_item_ops	= &nullb_device_ops,
	.ct_attrs	= nullb_device_attrs,
	.ct_owner	= THIS_MODULE,
};

static struct
config_item *nullb_group_make_item(struct config_group *group, const char *name)
{
	struct nullb_device *dev;

	dev = null_alloc_dev();
	if (!dev)
		return ERR_PTR(-ENOMEM);

	config_item_init_type_name(&dev->item, name, &nullb_device_type);

	return &dev->item;
}

static void
nullb_group_drop_item(struct config_group *group, struct config_item *item)
{
	struct nullb_device *dev = to_nullb_device(item);

	if (test_and_clear_bit(NULLB_DEV_FL_UP, &dev->flags)) {
		mutex_lock(&lock);
		dev->power = false;
		null_del_dev(dev->nullb);
		mutex_unlock(&lock);
	}

	config_item_put(item);
}

static ssize_t memb_group_features_show(struct config_item *item, char *page)
{
	return snprintf(page, PAGE_SIZE, "memory_backed\n");
}

CONFIGFS_ATTR_RO(memb_group_, features);

static struct configfs_attribute *nullb_group_attrs[] = {
	&memb_group_attr_features,
	NULL,
};

static struct configfs_group_operations nullb_group_ops = {
	.make_item	= nullb_group_make_item,
	.drop_item	= nullb_group_drop_item,
};

static struct config_item_type nullb_group_type = {
	.ct_group_ops	= &nullb_group_ops,
	.ct_attrs	= nullb_group_attrs,
	.ct_owner	= THIS_MODULE,
};

static struct configfs_subsystem nullb_subsys = {
	.su_group = {
		.cg_item = {
			.ci_namebuf = "nullb",
			.ci_type = &nullb_group_type,
		},
	},
};

static struct nullb_device *null_alloc_dev(void)
{
	struct nullb_device *dev;

	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (!dev)
		return NULL;
	INIT_RADIX_TREE(&dev->data, GFP_ATOMIC);
	dev->size = g_gb * 1024;
	dev->completion_nsec = g_completion_nsec;
	dev->submit_queues = g_submit_queues;
	dev->home_node = g_home_node;
	dev->queue_mode = g_queue_mode;
	dev->blocksize = g_bs;
	dev->irqmode = g_irqmode;
	dev->hw_queue_depth = g_hw_queue_depth;
	dev->use_lightnvm = g_use_lightnvm;
	dev->blocking = g_blocking;
	dev->use_per_node_hctx = g_use_per_node_hctx;
	return dev;
}

static void null_free_dev(struct nullb_device *dev)
{
	kfree(dev);
}

static void put_tag(struct nullb_queue *nq, unsigned int tag)
{
	clear_bit_unlock(tag, nq->tag_map);

	if (waitqueue_active(&nq->wait))
		wake_up(&nq->wait);
}

static unsigned int get_tag(struct nullb_queue *nq)
{
	unsigned int tag;

	do {
		tag = find_first_zero_bit(nq->tag_map, nq->queue_depth);
		if (tag >= nq->queue_depth)
			return -1U;
	} while (test_and_set_bit_lock(tag, nq->tag_map));

	return tag;
}

static void free_cmd(struct nullb_cmd *cmd)
{
	put_tag(cmd->nq, cmd->tag);
}

static enum hrtimer_restart null_cmd_timer_expired(struct hrtimer *timer);

static struct nullb_cmd *__alloc_cmd(struct nullb_queue *nq)
{
	struct nullb_cmd *cmd;
	unsigned int tag;

	tag = get_tag(nq);
	if (tag != -1U) {
		cmd = &nq->cmds[tag];
		cmd->tag = tag;
		cmd->nq = nq;
		if (nq->dev->irqmode == NULL_IRQ_TIMER) {
			hrtimer_init(&cmd->timer, CLOCK_MONOTONIC,
				     HRTIMER_MODE_REL);
			cmd->timer.function = null_cmd_timer_expired;
		}
		return cmd;
	}

	return NULL;
}

static struct nullb_cmd *alloc_cmd(struct nullb_queue *nq, int can_wait)
{
	struct nullb_cmd *cmd;
	DEFINE_WAIT(wait);

	cmd = __alloc_cmd(nq);
	if (cmd || !can_wait)
		return cmd;

	do {
		prepare_to_wait(&nq->wait, &wait, TASK_UNINTERRUPTIBLE);
		cmd = __alloc_cmd(nq);
		if (cmd)
			break;

		io_schedule();
	} while (1);

	finish_wait(&nq->wait, &wait);
	return cmd;
}

static void end_cmd(struct nullb_cmd *cmd)
{
	struct request_queue *q = NULL;
	int queue_mode = cmd->nq->dev->queue_mode;

	if (cmd->rq)
		q = cmd->rq->q;

	switch (queue_mode)  {
	case NULL_Q_MQ:
		blk_mq_end_request(cmd->rq, cmd->error);
		return;
	case NULL_Q_RQ:
		INIT_LIST_HEAD(&cmd->rq->queuelist);
		blk_end_request_all(cmd->rq, cmd->error);
		break;
	case NULL_Q_BIO:
		cmd->bio->bi_status = cmd->error;
		bio_endio(cmd->bio);
		break;
	}

	free_cmd(cmd);

	/* Restart queue if needed, as we are freeing a tag */
	if (queue_mode == NULL_Q_RQ && blk_queue_stopped(q)) {
		unsigned long flags;

		spin_lock_irqsave(q->queue_lock, flags);
		blk_start_queue_async(q);
		spin_unlock_irqrestore(q->queue_lock, flags);
	}
}

static enum hrtimer_restart null_cmd_timer_expired(struct hrtimer *timer)
{
	end_cmd(container_of(timer, struct nullb_cmd, timer));

	return HRTIMER_NORESTART;
}

static void null_cmd_end_timer(struct nullb_cmd *cmd)
{
	ktime_t kt = cmd->nq->dev->completion_nsec;

	hrtimer_start(&cmd->timer, kt, HRTIMER_MODE_REL);
}

static void null_softirq_done_fn(struct request *rq)
{
	struct nullb *nullb = rq->q->queuedata;

	if (nullb->dev->queue_mode == NULL_Q_MQ)
		end_cmd(blk_mq_rq_to_pdu(rq));
	else
		end_cmd(rq->special);
}

static struct nullb_page *null_alloc_page(gfp_t gfp_flags)
{
	struct nullb_page *t_page;

	t_page = kmalloc(sizeof(struct nullb_page), gfp_flags);
	if (!t_page)
		goto out;

	t_page->page = alloc_pages(gfp_flags, 0);
	if (!t_page->page)
		goto out_freepage;

	t_page->bitmap = 0;
	return t_page;
out_freepage:
	kfree(t_page);
out:
	return NULL;
}

static void null_free_page(struct nullb_page *t_page)
{
	__free_page(t_page->page);
	kfree(t_page);
}

static void null_free_sector(struct nullb *nullb, sector_t sector)
{
	unsigned int sector_bit;
	u64 idx;
	struct nullb_page *t_page, *ret;
	struct radix_tree_root *root;

	root = &nullb->dev->data;
	idx = sector >> PAGE_SECTORS_SHIFT;
	sector_bit = (sector & SECTOR_MASK);

	t_page = radix_tree_lookup(root, idx);
	if (t_page) {
		__clear_bit(sector_bit, &t_page->bitmap);

		if (!t_page->bitmap) {
			ret = radix_tree_delete_item(root, idx, t_page);
			WARN_ON(ret != t_page);
			null_free_page(ret);
		}
	}
}

static struct nullb_page *null_radix_tree_insert(struct nullb *nullb, u64 idx,
	struct nullb_page *t_page)
{
	struct radix_tree_root *root;

	root = &nullb->dev->data;

	if (radix_tree_insert(root, idx, t_page)) {
		null_free_page(t_page);
		t_page = radix_tree_lookup(root, idx);
		WARN_ON(!t_page || t_page->page->index != idx);
	}

	return t_page;
}

static void null_free_device_storage(struct nullb_device *dev)
{
	unsigned long pos = 0;
	int nr_pages;
	struct nullb_page *ret, *t_pages[FREE_BATCH];
	struct radix_tree_root *root;

	root = &dev->data;

	do {
		int i;

		nr_pages = radix_tree_gang_lookup(root,
				(void **)t_pages, pos, FREE_BATCH);

		for (i = 0; i < nr_pages; i++) {
			pos = t_pages[i]->page->index;
			ret = radix_tree_delete_item(root, pos, t_pages[i]);
			WARN_ON(ret != t_pages[i]);
			null_free_page(ret);
		}

		pos++;
	} while (nr_pages == FREE_BATCH);
}

static struct nullb_page *null_lookup_page(struct nullb *nullb,
	sector_t sector, bool for_write)
{
	unsigned int sector_bit;
	u64 idx;
	struct nullb_page *t_page;

	idx = sector >> PAGE_SECTORS_SHIFT;
	sector_bit = (sector & SECTOR_MASK);

	t_page = radix_tree_lookup(&nullb->dev->data, idx);
	WARN_ON(t_page && t_page->page->index != idx);

	if (t_page && (for_write || test_bit(sector_bit, &t_page->bitmap)))
		return t_page;

	return NULL;
}

static struct nullb_page *null_insert_page(struct nullb *nullb,
	sector_t sector)
{
	u64 idx;
	struct nullb_page *t_page;

	t_page = null_lookup_page(nullb, sector, true);
	if (t_page)
		return t_page;

	spin_unlock_irq(&nullb->lock);

	t_page = null_alloc_page(GFP_NOIO);
	if (!t_page)
		goto out_lock;

	if (radix_tree_preload(GFP_NOIO))
		goto out_freepage;

	spin_lock_irq(&nullb->lock);
	idx = sector >> PAGE_SECTORS_SHIFT;
	t_page->page->index = idx;
	t_page = null_radix_tree_insert(nullb, idx, t_page);
	radix_tree_preload_end();

	return t_page;
out_freepage:
	null_free_page(t_page);
out_lock:
	spin_lock_irq(&nullb->lock);
	return null_lookup_page(nullb, sector, true);
}

static int copy_to_nullb(struct nullb *nullb, struct page *source,
	unsigned int off, sector_t sector, size_t n)
{
	size_t temp, count = 0;
	unsigned int offset;
	struct nullb_page *t_page;
	void *dst, *src;

	while (count < n) {
		temp = min_t(size_t, nullb->dev->blocksize, n - count);

		offset = (sector & SECTOR_MASK) << SECTOR_SHIFT;
		t_page = null_insert_page(nullb, sector);
		if (!t_page)
			return -ENOSPC;

		src = kmap_atomic(source);
		dst = kmap_atomic(t_page->page);
		memcpy(dst + offset, src + off + count, temp);
		kunmap_atomic(dst);
		kunmap_atomic(src);

		__set_bit(sector & SECTOR_MASK, &t_page->bitmap);

		count += temp;
		sector += temp >> SECTOR_SHIFT;
	}
	return 0;
}

static int copy_from_nullb(struct nullb *nullb, struct page *dest,
	unsigned int off, sector_t sector, size_t n)
{
	size_t temp, count = 0;
	unsigned int offset;
	struct nullb_page *t_page;
	void *dst, *src;

	while (count < n) {
		temp = min_t(size_t, nullb->dev->blocksize, n - count);

		offset = (sector & SECTOR_MASK) << SECTOR_SHIFT;
		t_page = null_lookup_page(nullb, sector, false);

		dst = kmap_atomic(dest);
		if (!t_page) {
			memset(dst + off + count, 0, temp);
			goto next;
		}
		src = kmap_atomic(t_page->page);
		memcpy(dst + off + count, src + offset, temp);
		kunmap_atomic(src);
next:
		kunmap_atomic(dst);

		count += temp;
		sector += temp >> SECTOR_SHIFT;
	}
	return 0;
}

static int null_transfer(struct nullb *nullb, struct page *page,
	unsigned int len, unsigned int off, bool is_write, sector_t sector)
{
	int err = 0;

	if (!is_write) {
		err = copy_from_nullb(nullb, page, off, sector, len);
		flush_dcache_page(page);
	} else {
		flush_dcache_page(page);
		err = copy_to_nullb(nullb, page, off, sector, len);
	}

	return err;
}

static int null_handle_rq(struct nullb_cmd *cmd)
{
	struct request *rq = cmd->rq;
	struct nullb *nullb = cmd->nq->dev->nullb;
	int err;
	unsigned int len;
	sector_t sector;
	struct req_iterator iter;
	struct bio_vec bvec;

	sector = blk_rq_pos(rq);

	spin_lock_irq(&nullb->lock);
	rq_for_each_segment(bvec, rq, iter) {
		len = bvec.bv_len;
		err = null_transfer(nullb, bvec.bv_page, len, bvec.bv_offset,
				     op_is_write(req_op(rq)), sector);
		if (err) {
			spin_unlock_irq(&nullb->lock);
			return err;
		}
		sector += len >> SECTOR_SHIFT;
	}
	spin_unlock_irq(&nullb->lock);

	return 0;
}

static int null_handle_bio(struct nullb_cmd *cmd)
{
	struct bio *bio = cmd->bio;
	struct nullb *nullb = cmd->nq->dev->nullb;
	int err;
	unsigned int len;
	sector_t sector;
	struct bio_vec bvec;
	struct bvec_iter iter;

	sector = bio->bi_iter.bi_sector;

	spin_lock_irq(&nullb->lock);
	bio_for_each_segment(bvec, bio, iter) {
		len = bvec.bv_len;
		err = null_transfer(nullb, bvec.bv_page, len, bvec.bv_offset,
				     op_is_write(bio_op(bio)), sector);
		if (err) {
			spin_unlock_irq(&nullb->lock);
			return err;
		}
		sector += len >> SECTOR_SHIFT;
	}
	spin_unlock_irq(&nullb->lock);
	return 0;
}

static blk_status_t null_handle_cmd(struct nullb_cmd *cmd)
{
	struct nullb_device *dev = cmd->nq->dev;
	int err = 0;

	if (dev->memory_backed) {
		if (dev->queue_mode == NULL_Q_BIO)
			err = null_handle_bio(cmd);
		else
			err = null_handle_rq(cmd);
	}
	cmd->error = errno_to_blk_status(err);
	/* Complete IO by inline, softirq or timer */
	switch (dev->irqmode) {
	case NULL_IRQ_SOFTIRQ:
		switch (dev->queue_mode)  {
		case NULL_Q_MQ:
			blk_mq_complete_request(cmd->rq);
			break;
		case NULL_Q_RQ:
			blk_complete_request(cmd->rq);
			break;
		case NULL_Q_BIO:
			/*
			 * XXX: no proper submitting cpu information available.
			 */
			end_cmd(cmd);
			break;
		}
		break;
	case NULL_IRQ_NONE:
		end_cmd(cmd);
		break;
	case NULL_IRQ_TIMER:
		null_cmd_end_timer(cmd);
		break;
	}
	return BLK_STS_OK;
}

static struct nullb_queue *nullb_to_queue(struct nullb *nullb)
{
	int index = 0;

	if (nullb->nr_queues != 1)
		index = raw_smp_processor_id() / ((nr_cpu_ids + nullb->nr_queues - 1) / nullb->nr_queues);

	return &nullb->queues[index];
}

static blk_qc_t null_queue_bio(struct request_queue *q, struct bio *bio)
{
	struct nullb *nullb = q->queuedata;
	struct nullb_queue *nq = nullb_to_queue(nullb);
	struct nullb_cmd *cmd;

	cmd = alloc_cmd(nq, 1);
	cmd->bio = bio;

	null_handle_cmd(cmd);
	return BLK_QC_T_NONE;
}

static int null_rq_prep_fn(struct request_queue *q, struct request *req)
{
	struct nullb *nullb = q->queuedata;
	struct nullb_queue *nq = nullb_to_queue(nullb);
	struct nullb_cmd *cmd;

	cmd = alloc_cmd(nq, 0);
	if (cmd) {
		cmd->rq = req;
		req->special = cmd;
		return BLKPREP_OK;
	}
	blk_stop_queue(q);

	return BLKPREP_DEFER;
}

static void null_request_fn(struct request_queue *q)
{
	struct request *rq;

	while ((rq = blk_fetch_request(q)) != NULL) {
		struct nullb_cmd *cmd = rq->special;

		spin_unlock_irq(q->queue_lock);
		null_handle_cmd(cmd);
		spin_lock_irq(q->queue_lock);
	}
}

static blk_status_t null_queue_rq(struct blk_mq_hw_ctx *hctx,
			 const struct blk_mq_queue_data *bd)
{
	struct nullb_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
	struct nullb_queue *nq = hctx->driver_data;

	might_sleep_if(hctx->flags & BLK_MQ_F_BLOCKING);

	if (nq->dev->irqmode == NULL_IRQ_TIMER) {
		hrtimer_init(&cmd->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
		cmd->timer.function = null_cmd_timer_expired;
	}
	cmd->rq = bd->rq;
	cmd->nq = nq;

	blk_mq_start_request(bd->rq);

	return null_handle_cmd(cmd);
}

static const struct blk_mq_ops null_mq_ops = {
	.queue_rq       = null_queue_rq,
	.complete	= null_softirq_done_fn,
};

static void cleanup_queue(struct nullb_queue *nq)
{
	kfree(nq->tag_map);
	kfree(nq->cmds);
}

static void cleanup_queues(struct nullb *nullb)
{
	int i;

	for (i = 0; i < nullb->nr_queues; i++)
		cleanup_queue(&nullb->queues[i]);

	kfree(nullb->queues);
}

#ifdef CONFIG_NVM

static void null_lnvm_end_io(struct request *rq, blk_status_t status)
{
	struct nvm_rq *rqd = rq->end_io_data;

	/* XXX: lighnvm core seems to expect NVM_RSP_* values here.. */
	rqd->error = status ? -EIO : 0;
	nvm_end_io(rqd);

	blk_put_request(rq);
}

static int null_lnvm_submit_io(struct nvm_dev *dev, struct nvm_rq *rqd)
{
	struct request_queue *q = dev->q;
	struct request *rq;
	struct bio *bio = rqd->bio;

	rq = blk_mq_alloc_request(q,
		op_is_write(bio_op(bio)) ? REQ_OP_DRV_OUT : REQ_OP_DRV_IN, 0);
	if (IS_ERR(rq))
		return -ENOMEM;

	blk_init_request_from_bio(rq, bio);

	rq->end_io_data = rqd;

	blk_execute_rq_nowait(q, NULL, rq, 0, null_lnvm_end_io);

	return 0;
}

static int null_lnvm_id(struct nvm_dev *dev, struct nvm_id *id)
{
	struct nullb *nullb = dev->q->queuedata;
	sector_t size = (sector_t)nullb->dev->size * 1024 * 1024ULL;
	sector_t blksize;
	struct nvm_id_group *grp;

	id->ver_id = 0x1;
	id->vmnt = 0;
	id->cap = 0x2;
	id->dom = 0x1;

	id->ppaf.blk_offset = 0;
	id->ppaf.blk_len = 16;
	id->ppaf.pg_offset = 16;
	id->ppaf.pg_len = 16;
	id->ppaf.sect_offset = 32;
	id->ppaf.sect_len = 8;
	id->ppaf.pln_offset = 40;
	id->ppaf.pln_len = 8;
	id->ppaf.lun_offset = 48;
	id->ppaf.lun_len = 8;
	id->ppaf.ch_offset = 56;
	id->ppaf.ch_len = 8;

	sector_div(size, nullb->dev->blocksize); /* convert size to pages */
	size >>= 8; /* concert size to pgs pr blk */
	grp = &id->grp;
	grp->mtype = 0;
	grp->fmtype = 0;
	grp->num_ch = 1;
	grp->num_pg = 256;
	blksize = size;
	size >>= 16;
	grp->num_lun = size + 1;
	sector_div(blksize, grp->num_lun);
	grp->num_blk = blksize;
	grp->num_pln = 1;

	grp->fpg_sz = nullb->dev->blocksize;
	grp->csecs = nullb->dev->blocksize;
	grp->trdt = 25000;
	grp->trdm = 25000;
	grp->tprt = 500000;
	grp->tprm = 500000;
	grp->tbet = 1500000;
	grp->tbem = 1500000;
	grp->mpos = 0x010101; /* single plane rwe */
	grp->cpar = nullb->dev->hw_queue_depth;

	return 0;
}

static void *null_lnvm_create_dma_pool(struct nvm_dev *dev, char *name)
{
	mempool_t *virtmem_pool;

	virtmem_pool = mempool_create_slab_pool(64, ppa_cache);
	if (!virtmem_pool) {
		pr_err("null_blk: Unable to create virtual memory pool\n");
		return NULL;
	}

	return virtmem_pool;
}

static void null_lnvm_destroy_dma_pool(void *pool)
{
	mempool_destroy(pool);
}

static void *null_lnvm_dev_dma_alloc(struct nvm_dev *dev, void *pool,
				gfp_t mem_flags, dma_addr_t *dma_handler)
{
	return mempool_alloc(pool, mem_flags);
}

static void null_lnvm_dev_dma_free(void *pool, void *entry,
							dma_addr_t dma_handler)
{
	mempool_free(entry, pool);
}

static struct nvm_dev_ops null_lnvm_dev_ops = {
	.identity		= null_lnvm_id,
	.submit_io		= null_lnvm_submit_io,

	.create_dma_pool	= null_lnvm_create_dma_pool,
	.destroy_dma_pool	= null_lnvm_destroy_dma_pool,
	.dev_dma_alloc		= null_lnvm_dev_dma_alloc,
	.dev_dma_free		= null_lnvm_dev_dma_free,

	/* Simulate nvme protocol restriction */
	.max_phys_sect		= 64,
};

static int null_nvm_register(struct nullb *nullb)
{
	struct nvm_dev *dev;
	int rv;

	dev = nvm_alloc_dev(0);
	if (!dev)
		return -ENOMEM;

	dev->q = nullb->q;
	memcpy(dev->name, nullb->disk_name, DISK_NAME_LEN);
	dev->ops = &null_lnvm_dev_ops;

	rv = nvm_register(dev);
	if (rv) {
		kfree(dev);
		return rv;
	}
	nullb->ndev = dev;
	return 0;
}

static void null_nvm_unregister(struct nullb *nullb)
{
	nvm_unregister(nullb->ndev);
}
#else
static int null_nvm_register(struct nullb *nullb)
{
	pr_err("null_blk: CONFIG_NVM needs to be enabled for LightNVM\n");
	return -EINVAL;
}
static void null_nvm_unregister(struct nullb *nullb) {}
#endif /* CONFIG_NVM */

static void null_del_dev(struct nullb *nullb)
{
	struct nullb_device *dev = nullb->dev;

	ida_simple_remove(&nullb_indexes, nullb->index);

	list_del_init(&nullb->list);

	if (dev->use_lightnvm)
		null_nvm_unregister(nullb);
	else
		del_gendisk(nullb->disk);
	blk_cleanup_queue(nullb->q);
	if (dev->queue_mode == NULL_Q_MQ &&
	    nullb->tag_set == &nullb->__tag_set)
		blk_mq_free_tag_set(nullb->tag_set);
	if (!dev->use_lightnvm)
		put_disk(nullb->disk);
	cleanup_queues(nullb);
	kfree(nullb);
	dev->nullb = NULL;
}

static int null_open(struct block_device *bdev, fmode_t mode)
{
	return 0;
}

static void null_release(struct gendisk *disk, fmode_t mode)
{
}

static const struct block_device_operations null_fops = {
	.owner =	THIS_MODULE,
	.open =		null_open,
	.release =	null_release,
};

static void null_init_queue(struct nullb *nullb, struct nullb_queue *nq)
{
	BUG_ON(!nullb);
	BUG_ON(!nq);

	init_waitqueue_head(&nq->wait);
	nq->queue_depth = nullb->queue_depth;
	nq->dev = nullb->dev;
}

static void null_init_queues(struct nullb *nullb)
{
	struct request_queue *q = nullb->q;
	struct blk_mq_hw_ctx *hctx;
	struct nullb_queue *nq;
	int i;

	queue_for_each_hw_ctx(q, hctx, i) {
		if (!hctx->nr_ctx || !hctx->tags)
			continue;
		nq = &nullb->queues[i];
		hctx->driver_data = nq;
		null_init_queue(nullb, nq);
		nullb->nr_queues++;
	}
}

static int setup_commands(struct nullb_queue *nq)
{
	struct nullb_cmd *cmd;
	int i, tag_size;

	nq->cmds = kzalloc(nq->queue_depth * sizeof(*cmd), GFP_KERNEL);
	if (!nq->cmds)
		return -ENOMEM;

	tag_size = ALIGN(nq->queue_depth, BITS_PER_LONG) / BITS_PER_LONG;
	nq->tag_map = kzalloc(tag_size * sizeof(unsigned long), GFP_KERNEL);
	if (!nq->tag_map) {
		kfree(nq->cmds);
		return -ENOMEM;
	}

	for (i = 0; i < nq->queue_depth; i++) {
		cmd = &nq->cmds[i];
		INIT_LIST_HEAD(&cmd->list);
		cmd->ll_list.next = NULL;
		cmd->tag = -1U;
	}

	return 0;
}

static int setup_queues(struct nullb *nullb)
{
	nullb->queues = kzalloc(nullb->dev->submit_queues *
		sizeof(struct nullb_queue), GFP_KERNEL);
	if (!nullb->queues)
		return -ENOMEM;

	nullb->nr_queues = 0;
	nullb->queue_depth = nullb->dev->hw_queue_depth;

	return 0;
}

static int init_driver_queues(struct nullb *nullb)
{
	struct nullb_queue *nq;
	int i, ret = 0;

	for (i = 0; i < nullb->dev->submit_queues; i++) {
		nq = &nullb->queues[i];

		null_init_queue(nullb, nq);

		ret = setup_commands(nq);
		if (ret)
			return ret;
		nullb->nr_queues++;
	}
	return 0;
}

static int null_gendisk_register(struct nullb *nullb)
{
	struct gendisk *disk;
	sector_t size;

	disk = nullb->disk = alloc_disk_node(1, nullb->dev->home_node);
	if (!disk)
		return -ENOMEM;
	size = (sector_t)nullb->dev->size * 1024 * 1024ULL;
	set_capacity(disk, size >> 9);

	disk->flags |= GENHD_FL_EXT_DEVT | GENHD_FL_SUPPRESS_PARTITION_INFO;
	disk->major		= null_major;
	disk->first_minor	= nullb->index;
	disk->fops		= &null_fops;
	disk->private_data	= nullb;
	disk->queue		= nullb->q;
	strncpy(disk->disk_name, nullb->disk_name, DISK_NAME_LEN);

	add_disk(disk);
	return 0;
}

static int null_init_tag_set(struct nullb *nullb, struct blk_mq_tag_set *set)
{
	set->ops = &null_mq_ops;
	set->nr_hw_queues = nullb ? nullb->dev->submit_queues :
						g_submit_queues;
	set->queue_depth = nullb ? nullb->dev->hw_queue_depth :
						g_hw_queue_depth;
	set->numa_node = nullb ? nullb->dev->home_node : g_home_node;
	set->cmd_size	= sizeof(struct nullb_cmd);
	set->flags = BLK_MQ_F_SHOULD_MERGE;
	set->driver_data = NULL;

	if (nullb->dev->blocking)
		set->flags |= BLK_MQ_F_BLOCKING;

	return blk_mq_alloc_tag_set(set);
}

static void null_validate_conf(struct nullb_device *dev)
{
	dev->blocksize = round_down(dev->blocksize, 512);
	dev->blocksize = clamp_t(unsigned int, dev->blocksize, 512, 4096);
	if (dev->use_lightnvm && dev->blocksize != 4096)
		dev->blocksize = 4096;

	if (dev->use_lightnvm && dev->queue_mode != NULL_Q_MQ)
		dev->queue_mode = NULL_Q_MQ;

	if (dev->queue_mode == NULL_Q_MQ && dev->use_per_node_hctx) {
		if (dev->submit_queues != nr_online_nodes)
			dev->submit_queues = nr_online_nodes;
	} else if (dev->submit_queues > nr_cpu_ids)
		dev->submit_queues = nr_cpu_ids;
	else if (dev->submit_queues == 0)
		dev->submit_queues = 1;

	dev->queue_mode = min_t(unsigned int, dev->queue_mode, NULL_Q_MQ);
	dev->irqmode = min_t(unsigned int, dev->irqmode, NULL_IRQ_TIMER);

	/* Do memory allocation, so set blocking */
	if (dev->memory_backed)
		dev->blocking = true;
}

static int null_add_dev(struct nullb_device *dev)
{
	struct nullb *nullb;
	int rv;

	null_validate_conf(dev);

	nullb = kzalloc_node(sizeof(*nullb), GFP_KERNEL, dev->home_node);
	if (!nullb) {
		rv = -ENOMEM;
		goto out;
	}
	nullb->dev = dev;
	dev->nullb = nullb;

	spin_lock_init(&nullb->lock);

	rv = setup_queues(nullb);
	if (rv)
		goto out_free_nullb;

	if (dev->queue_mode == NULL_Q_MQ) {
		if (shared_tags) {
			nullb->tag_set = &tag_set;
			rv = 0;
		} else {
			nullb->tag_set = &nullb->__tag_set;
			rv = null_init_tag_set(nullb, nullb->tag_set);
		}

		if (rv)
			goto out_cleanup_queues;

		nullb->q = blk_mq_init_queue(nullb->tag_set);
		if (IS_ERR(nullb->q)) {
			rv = -ENOMEM;
			goto out_cleanup_tags;
		}
		null_init_queues(nullb);
	} else if (dev->queue_mode == NULL_Q_BIO) {
		nullb->q = blk_alloc_queue_node(GFP_KERNEL, dev->home_node);
		if (!nullb->q) {
			rv = -ENOMEM;
			goto out_cleanup_queues;
		}
		blk_queue_make_request(nullb->q, null_queue_bio);
		rv = init_driver_queues(nullb);
		if (rv)
			goto out_cleanup_blk_queue;
	} else {
		nullb->q = blk_init_queue_node(null_request_fn, &nullb->lock,
						dev->home_node);
		if (!nullb->q) {
			rv = -ENOMEM;
			goto out_cleanup_queues;
		}
		blk_queue_prep_rq(nullb->q, null_rq_prep_fn);
		blk_queue_softirq_done(nullb->q, null_softirq_done_fn);
		rv = init_driver_queues(nullb);
		if (rv)
			goto out_cleanup_blk_queue;
	}

	nullb->q->queuedata = nullb;
	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, nullb->q);
	queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, nullb->q);

	mutex_lock(&lock);
	nullb->index = ida_simple_get(&nullb_indexes, 0, 0, GFP_KERNEL);
	dev->index = nullb->index;
	mutex_unlock(&lock);

	blk_queue_logical_block_size(nullb->q, dev->blocksize);
	blk_queue_physical_block_size(nullb->q, dev->blocksize);

	sprintf(nullb->disk_name, "nullb%d", nullb->index);

	if (dev->use_lightnvm)
		rv = null_nvm_register(nullb);
	else
		rv = null_gendisk_register(nullb);

	if (rv)
		goto out_cleanup_blk_queue;

	mutex_lock(&lock);
	list_add_tail(&nullb->list, &nullb_list);
	mutex_unlock(&lock);

	return 0;
out_cleanup_blk_queue:
	blk_cleanup_queue(nullb->q);
out_cleanup_tags:
	if (dev->queue_mode == NULL_Q_MQ && nullb->tag_set == &nullb->__tag_set)
		blk_mq_free_tag_set(nullb->tag_set);
out_cleanup_queues:
	cleanup_queues(nullb);
out_free_nullb:
	kfree(nullb);
out:
	null_free_dev(dev);
	return rv;
}

static int __init null_init(void)
{
	int ret = 0;
	unsigned int i;
	struct nullb *nullb;
	struct nullb_device *dev;

	if (g_bs > PAGE_SIZE) {
		pr_warn("null_blk: invalid block size\n");
		pr_warn("null_blk: defaults block size to %lu\n", PAGE_SIZE);
		g_bs = PAGE_SIZE;
	}

	if (g_use_lightnvm && g_bs != 4096) {
		pr_warn("null_blk: LightNVM only supports 4k block size\n");
		pr_warn("null_blk: defaults block size to 4k\n");
		g_bs = 4096;
	}

	if (g_use_lightnvm && g_queue_mode != NULL_Q_MQ) {
		pr_warn("null_blk: LightNVM only supported for blk-mq\n");
		pr_warn("null_blk: defaults queue mode to blk-mq\n");
		g_queue_mode = NULL_Q_MQ;
	}

	if (g_queue_mode == NULL_Q_MQ && g_use_per_node_hctx) {
		if (g_submit_queues != nr_online_nodes) {
			pr_warn("null_blk: submit_queues param is set to %u.\n",
							nr_online_nodes);
			g_submit_queues = nr_online_nodes;
		}
	} else if (g_submit_queues > nr_cpu_ids)
		g_submit_queues = nr_cpu_ids;
	else if (g_submit_queues <= 0)
		g_submit_queues = 1;

	if (g_queue_mode == NULL_Q_MQ && shared_tags) {
		ret = null_init_tag_set(NULL, &tag_set);
		if (ret)
			return ret;
	}

	config_group_init(&nullb_subsys.su_group);
	mutex_init(&nullb_subsys.su_mutex);

	ret = configfs_register_subsystem(&nullb_subsys);
	if (ret)
		goto err_tagset;

	mutex_init(&lock);

	null_major = register_blkdev(0, "nullb");
	if (null_major < 0) {
		ret = null_major;
		goto err_conf;
	}

	if (g_use_lightnvm) {
		ppa_cache = kmem_cache_create("ppa_cache", 64 * sizeof(u64),
								0, 0, NULL);
		if (!ppa_cache) {
			pr_err("null_blk: unable to create ppa cache\n");
			ret = -ENOMEM;
			goto err_ppa;
		}
	}

	for (i = 0; i < nr_devices; i++) {
		dev = null_alloc_dev();
		if (!dev)
			goto err_dev;
		ret = null_add_dev(dev);
		if (ret) {
			null_free_dev(dev);
			goto err_dev;
		}
	}

	pr_info("null: module loaded\n");
	return 0;

err_dev:
	while (!list_empty(&nullb_list)) {
		nullb = list_entry(nullb_list.next, struct nullb, list);
		dev = nullb->dev;
		null_del_dev(nullb);
		null_free_dev(dev);
	}
	kmem_cache_destroy(ppa_cache);
err_ppa:
	unregister_blkdev(null_major, "nullb");
err_conf:
	configfs_unregister_subsystem(&nullb_subsys);
err_tagset:
	if (g_queue_mode == NULL_Q_MQ && shared_tags)
		blk_mq_free_tag_set(&tag_set);
	return ret;
}

static void __exit null_exit(void)
{
	struct nullb *nullb;

	configfs_unregister_subsystem(&nullb_subsys);

	unregister_blkdev(null_major, "nullb");

	mutex_lock(&lock);
	while (!list_empty(&nullb_list)) {
		struct nullb_device *dev;

		nullb = list_entry(nullb_list.next, struct nullb, list);
		dev = nullb->dev;
		null_del_dev(nullb);
		null_free_dev(dev);
	}
	mutex_unlock(&lock);

	if (g_queue_mode == NULL_Q_MQ && shared_tags)
		blk_mq_free_tag_set(&tag_set);

	kmem_cache_destroy(ppa_cache);
}

module_init(null_init);
module_exit(null_exit);

MODULE_AUTHOR("Jens Axboe <jaxboe@fusionio.com>");
MODULE_LICENSE("GPL");