drivers/block/null_blk.c - kernel/msm-4.9 - Gitiles

 #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>

 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;
 };

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

 	struct nullb_cmd *cmds;
 };

 struct nullb {
 	struct list_head list;
 	unsigned int index;
 	struct request_queue *q;
 	struct gendisk *disk;
 	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 int nullb_indexes;
 static struct kmem_cache *ppa_cache;

 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 submit_queues;
 module_param(submit_queues, int, S_IRUGO);
 MODULE_PARM_DESC(submit_queues, "Number of submission queues");

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

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

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

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

 static int nr_devices = 2;
 module_param(nr_devices, int, S_IRUGO);
 MODULE_PARM_DESC(nr_devices, "Number of devices to register");

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

 static int irqmode = NULL_IRQ_SOFTIRQ;

 static int null_set_irqmode(const char *str, const struct kernel_param *kp)
 {
 	return null_param_store_val(str, &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, &irqmode, S_IRUGO);
 MODULE_PARM_DESC(irqmode, "IRQ completion handler. 0-none, 1-softirq, 2-timer");

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

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

 static bool use_per_node_hctx = false;
 module_param(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 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 (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;

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

 	switch (queue_mode)  {
 	case NULL_Q_MQ:
 		blk_mq_end_request(cmd->rq, 0);
 		return;
 	case NULL_Q_RQ:
 		INIT_LIST_HEAD(&cmd->rq->queuelist);
 		blk_end_request_all(cmd->rq, 0);
 		break;
 	case NULL_Q_BIO:
 		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 = ktime_set(0, completion_nsec);

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

 static void null_softirq_done_fn(struct request *rq)
 {
 	if (queue_mode == NULL_Q_MQ)
 		end_cmd(blk_mq_rq_to_pdu(rq));
 	else
 		end_cmd(rq->special);
 }

 static inline void null_handle_cmd(struct nullb_cmd *cmd)
 {
 	/* Complete IO by inline, softirq or timer */
 	switch (irqmode) {
 	case NULL_IRQ_SOFTIRQ:
 		switch (queue_mode)  {
 		case NULL_Q_MQ:
 			blk_mq_complete_request(cmd->rq, cmd->rq->errors);
 			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;
 	}
 }

 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 int 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);

 	if (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 = hctx->driver_data;

 	blk_mq_start_request(bd->rq);

 	null_handle_cmd(cmd);
 	return BLK_MQ_RQ_QUEUE_OK;
 }

 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;
 }

 static int null_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
 			  unsigned int index)
 {
 	struct nullb *nullb = data;
 	struct nullb_queue *nq = &nullb->queues[index];

 	hctx->driver_data = nq;
 	null_init_queue(nullb, nq);
 	nullb->nr_queues++;

 	return 0;
 }

 static struct blk_mq_ops null_mq_ops = {
 	.queue_rq       = null_queue_rq,
 	.map_queue      = blk_mq_map_queue,
 	.init_hctx	= null_init_hctx,
 	.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);
 }

 static void null_del_dev(struct nullb *nullb)
 {
 	list_del_init(&nullb->list);

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

 #ifdef CONFIG_NVM

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

 	nvm_end_io(rqd, error);

 	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, bio_rw(bio), 0);
 	if (IS_ERR(rq))
 		return -ENOMEM;

 	rq->cmd_type = REQ_TYPE_DRV_PRIV;
 	rq->__sector = bio->bi_iter.bi_sector;
 	rq->ioprio = bio_prio(bio);

 	if (bio_has_data(bio))
 		rq->nr_phys_segments = bio_phys_segments(q, bio);

 	rq->__data_len = bio->bi_iter.bi_size;
 	rq->bio = rq->biotail = 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)
 {
 	sector_t size = gb * 1024 * 1024 * 1024ULL;
 	sector_t blksize;
 	struct nvm_id_group *grp;

 	id->ver_id = 0x1;
 	id->vmnt = 0;
 	id->cgrps = 1;
 	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, bs); /* convert size to pages */
 	size >>= 8; /* concert size to pgs pr blk */
 	grp = &id->groups[0];
 	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 = bs;
 	grp->csecs = bs;
 	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 = 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,
 };
 #else
 static struct nvm_dev_ops null_lnvm_dev_ops;
 #endif /* CONFIG_NVM */

 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 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(submit_queues * sizeof(struct nullb_queue),
 								GFP_KERNEL);
 	if (!nullb->queues)
 		return -ENOMEM;

 	nullb->nr_queues = 0;
 	nullb->queue_depth = 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 < 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_add_dev(void)
 {
 	struct gendisk *disk;
 	struct nullb *nullb;
 	sector_t size;
 	int rv;

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

 	spin_lock_init(&nullb->lock);

 	if (queue_mode == NULL_Q_MQ && use_per_node_hctx)
 		submit_queues = nr_online_nodes;

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

 	if (queue_mode == NULL_Q_MQ) {
 		nullb->tag_set.ops = &null_mq_ops;
 		nullb->tag_set.nr_hw_queues = submit_queues;
 		nullb->tag_set.queue_depth = hw_queue_depth;
 		nullb->tag_set.numa_node = home_node;
 		nullb->tag_set.cmd_size	= sizeof(struct nullb_cmd);
 		nullb->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
 		nullb->tag_set.driver_data = nullb;

 		rv = blk_mq_alloc_tag_set(&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;
 		}
 	} else if (queue_mode == NULL_Q_BIO) {
 		nullb->q = blk_alloc_queue_node(GFP_KERNEL, 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, 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 = nullb_indexes++;
 	mutex_unlock(&lock);

 	blk_queue_logical_block_size(nullb->q, bs);
 	blk_queue_physical_block_size(nullb->q, bs);

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

 	if (use_lightnvm) {
 		rv = nvm_register(nullb->q, nullb->disk_name,
 							&null_lnvm_dev_ops);
 		if (rv)
 			goto out_cleanup_blk_queue;
 		goto done;
 	}

 	disk = nullb->disk = alloc_disk_node(1, home_node);
 	if (!disk) {
 		rv = -ENOMEM;
 		goto out_cleanup_lightnvm;
 	}
 	size = gb * 1024 * 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);

 	mutex_lock(&lock);
 	list_add_tail(&nullb->list, &nullb_list);
 	mutex_unlock(&lock);
 done:
 	return 0;

 out_cleanup_lightnvm:
 	if (use_lightnvm)
 		nvm_unregister(nullb->disk_name);
 out_cleanup_blk_queue:
 	blk_cleanup_queue(nullb->q);
 out_cleanup_tags:
 	if (queue_mode == NULL_Q_MQ)
 		blk_mq_free_tag_set(&nullb->tag_set);
 out_cleanup_queues:
 	cleanup_queues(nullb);
 out_free_nullb:
 	kfree(nullb);
 out:
 	return rv;
 }

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

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

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

 	if (use_lightnvm && 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");
 		queue_mode = NULL_Q_MQ;
 	}

 	if (queue_mode == NULL_Q_MQ && use_per_node_hctx) {
 		if (submit_queues < nr_online_nodes) {
 			pr_warn("null_blk: submit_queues param is set to %u.",
 							nr_online_nodes);
 			submit_queues = nr_online_nodes;
 		}
 	} else if (submit_queues > nr_cpu_ids)
 		submit_queues = nr_cpu_ids;
 	else if (!submit_queues)
 		submit_queues = 1;

 	mutex_init(&lock);

 	null_major = register_blkdev(0, "nullb");
 	if (null_major < 0)
 		return null_major;

 	if (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++) {
 		ret = null_add_dev();
 		if (ret)
 			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);
 		null_del_dev(nullb);
 	}
 	kmem_cache_destroy(ppa_cache);
 err_ppa:
 	unregister_blkdev(null_major, "nullb");
 	return ret;
 }

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

 	unregister_blkdev(null_major, "nullb");

 	mutex_lock(&lock);
 	while (!list_empty(&nullb_list)) {
 		nullb = list_entry(nullb_list.next, struct nullb, list);
 		null_del_dev(nullb);
 	}
 	mutex_unlock(&lock);

 	kmem_cache_destroy(ppa_cache);
 }

 module_init(null_init);
 module_exit(null_exit);

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

	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;
	};

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

	struct nullb_cmd *cmds;
	};

	struct nullb {
	struct list_head list;
	unsigned int index;
	struct request_queue *q;
	struct gendisk *disk;
	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 int nullb_indexes;
	static struct kmem_cache *ppa_cache;

	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 submit_queues;
	module_param(submit_queues, int, S_IRUGO);
	MODULE_PARM_DESC(submit_queues, "Number of submission queues");

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

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

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

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

	static int nr_devices = 2;
	module_param(nr_devices, int, S_IRUGO);
	MODULE_PARM_DESC(nr_devices, "Number of devices to register");

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

	static int irqmode = NULL_IRQ_SOFTIRQ;

	static int null_set_irqmode(const char str, const struct kernel_param kp)
	{
	return null_param_store_val(str, &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, &irqmode, S_IRUGO);
	MODULE_PARM_DESC(irqmode, "IRQ completion handler. 0-none, 1-softirq, 2-timer");

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

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

	static bool use_per_node_hctx = false;
	module_param(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 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 (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;

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

	switch (queue_mode) {
	case NULL_Q_MQ:
	blk_mq_end_request(cmd->rq, 0);
	return;
	case NULL_Q_RQ:
	INIT_LIST_HEAD(&cmd->rq->queuelist);
	blk_end_request_all(cmd->rq, 0);
	break;
	case NULL_Q_BIO:
	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 = ktime_set(0, completion_nsec);

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

	static void null_softirq_done_fn(struct request *rq)
	{
	if (queue_mode == NULL_Q_MQ)
	end_cmd(blk_mq_rq_to_pdu(rq));
	else
	end_cmd(rq->special);
	}

	static inline void null_handle_cmd(struct nullb_cmd *cmd)
	{
	/* Complete IO by inline, softirq or timer */
	switch (irqmode) {
	case NULL_IRQ_SOFTIRQ:
	switch (queue_mode) {
	case NULL_Q_MQ:
	blk_mq_complete_request(cmd->rq, cmd->rq->errors);
	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;
	}
	}

	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 int 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);

	if (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 = hctx->driver_data;

	blk_mq_start_request(bd->rq);

	null_handle_cmd(cmd);
	return BLK_MQ_RQ_QUEUE_OK;
	}

	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;
	}

	static int null_init_hctx(struct blk_mq_hw_ctx hctx, void data,
	unsigned int index)
	{
	struct nullb *nullb = data;
	struct nullb_queue *nq = &nullb->queues[index];

	hctx->driver_data = nq;
	null_init_queue(nullb, nq);
	nullb->nr_queues++;

	return 0;
	}

	static struct blk_mq_ops null_mq_ops = {
	.queue_rq = null_queue_rq,
	.map_queue = blk_mq_map_queue,
	.init_hctx = null_init_hctx,
	.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);
	}

	static void null_del_dev(struct nullb *nullb)
	{
	list_del_init(&nullb->list);

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

	#ifdef CONFIG_NVM

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

	nvm_end_io(rqd, error);

	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, bio_rw(bio), 0);
	if (IS_ERR(rq))
	return -ENOMEM;

	rq->cmd_type = REQ_TYPE_DRV_PRIV;
	rq->__sector = bio->bi_iter.bi_sector;
	rq->ioprio = bio_prio(bio);

	if (bio_has_data(bio))
	rq->nr_phys_segments = bio_phys_segments(q, bio);

	rq->__data_len = bio->bi_iter.bi_size;
	rq->bio = rq->biotail = 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)
	{
	sector_t size = gb * 1024 * 1024 * 1024ULL;
	sector_t blksize;
	struct nvm_id_group *grp;

	id->ver_id = 0x1;
	id->vmnt = 0;
	id->cgrps = 1;
	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, bs); /* convert size to pages */
	size >>= 8; /* concert size to pgs pr blk */
	grp = &id->groups[0];
	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 = bs;
	grp->csecs = bs;
	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 = 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,
	};
	#else
	static struct nvm_dev_ops null_lnvm_dev_ops;
	#endif /* CONFIG_NVM */

	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 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(submit_queues * sizeof(struct nullb_queue),
	GFP_KERNEL);
	if (!nullb->queues)
	return -ENOMEM;

	nullb->nr_queues = 0;
	nullb->queue_depth = 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 < 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_add_dev(void)
	{
	struct gendisk *disk;
	struct nullb *nullb;
	sector_t size;
	int rv;

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

	spin_lock_init(&nullb->lock);

	if (queue_mode == NULL_Q_MQ && use_per_node_hctx)
	submit_queues = nr_online_nodes;

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

	if (queue_mode == NULL_Q_MQ) {
	nullb->tag_set.ops = &null_mq_ops;
	nullb->tag_set.nr_hw_queues = submit_queues;
	nullb->tag_set.queue_depth = hw_queue_depth;
	nullb->tag_set.numa_node = home_node;
	nullb->tag_set.cmd_size = sizeof(struct nullb_cmd);
	nullb->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
	nullb->tag_set.driver_data = nullb;

	rv = blk_mq_alloc_tag_set(&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;
	}
	} else if (queue_mode == NULL_Q_BIO) {
	nullb->q = blk_alloc_queue_node(GFP_KERNEL, 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, 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 = nullb_indexes++;
	mutex_unlock(&lock);

	blk_queue_logical_block_size(nullb->q, bs);
	blk_queue_physical_block_size(nullb->q, bs);

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

	if (use_lightnvm) {
	rv = nvm_register(nullb->q, nullb->disk_name,
	&null_lnvm_dev_ops);
	if (rv)
	goto out_cleanup_blk_queue;
	goto done;
	}

	disk = nullb->disk = alloc_disk_node(1, home_node);
	if (!disk) {
	rv = -ENOMEM;
	goto out_cleanup_lightnvm;
	}
	size = gb * 1024 * 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);

	mutex_lock(&lock);
	list_add_tail(&nullb->list, &nullb_list);
	mutex_unlock(&lock);
	done:
	return 0;

	out_cleanup_lightnvm:
	if (use_lightnvm)
	nvm_unregister(nullb->disk_name);
	out_cleanup_blk_queue:
	blk_cleanup_queue(nullb->q);
	out_cleanup_tags:
	if (queue_mode == NULL_Q_MQ)
	blk_mq_free_tag_set(&nullb->tag_set);
	out_cleanup_queues:
	cleanup_queues(nullb);
	out_free_nullb:
	kfree(nullb);
	out:
	return rv;
	}

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

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

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

	if (use_lightnvm && 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");
	queue_mode = NULL_Q_MQ;
	}

	if (queue_mode == NULL_Q_MQ && use_per_node_hctx) {
	if (submit_queues < nr_online_nodes) {
	pr_warn("null_blk: submit_queues param is set to %u.",
	nr_online_nodes);
	submit_queues = nr_online_nodes;
	}
	} else if (submit_queues > nr_cpu_ids)
	submit_queues = nr_cpu_ids;
	else if (!submit_queues)
	submit_queues = 1;

	mutex_init(&lock);

	null_major = register_blkdev(0, "nullb");
	if (null_major < 0)
	return null_major;

	if (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++) {
	ret = null_add_dev();
	if (ret)
	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);
	null_del_dev(nullb);
	}
	kmem_cache_destroy(ppa_cache);
	err_ppa:
	unregister_blkdev(null_major, "nullb");
	return ret;
	}

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

	unregister_blkdev(null_major, "nullb");

	mutex_lock(&lock);
	while (!list_empty(&nullb_list)) {
	nullb = list_entry(nullb_list.next, struct nullb, list);
	null_del_dev(nullb);
	}
	mutex_unlock(&lock);

	kmem_cache_destroy(ppa_cache);
	}

	module_init(null_init);
	module_exit(null_exit);

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