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>

 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 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 hrtimer timer;
 	unsigned int queue_depth;
 	spinlock_t lock;

 	struct nullb_queue *queues;
 	unsigned int nr_queues;
 };

 static LIST_HEAD(nullb_list);
 static struct mutex lock;
 static int null_major;
 static int nullb_indexes;

 struct completion_queue {
 	struct llist_head list;
 	struct hrtimer timer;
 };

 /*
  * These are per-cpu for now, they will need to be configured by the
  * complete_queues parameter and appropriately mapped.
  */
 static DEFINE_PER_CPU(struct completion_queue, completion_queues);

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

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

 static int submit_queues = 1;
 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;
 module_param(queue_mode, int, S_IRUGO);
 MODULE_PARM_DESC(use_mq, "Use blk-mq interface (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 int irqmode = NULL_IRQ_SOFTIRQ;
 module_param(irqmode, int, S_IRUGO);
 MODULE_PARM_DESC(irqmode, "IRQ completion handler. 0-none, 1-softirq, 2-timer");

 static int completion_nsec = 10000;
 module_param(completion_nsec, int, 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 = true;
 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: true");

 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 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;
 		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)
 {
 	if (cmd->rq) {
 		if (queue_mode == NULL_Q_MQ)
 			blk_mq_end_io(cmd->rq, 0);
 		else {
 			INIT_LIST_HEAD(&cmd->rq->queuelist);
 			blk_end_request_all(cmd->rq, 0);
 		}
 	} else if (cmd->bio)
 		bio_endio(cmd->bio, 0);

 	if (queue_mode != NULL_Q_MQ)
 		free_cmd(cmd);
 }

 static enum hrtimer_restart null_cmd_timer_expired(struct hrtimer *timer)
 {
 	struct completion_queue *cq;
 	struct llist_node *entry;
 	struct nullb_cmd *cmd;

 	cq = &per_cpu(completion_queues, smp_processor_id());

 	while ((entry = llist_del_all(&cq->list)) != NULL) {
 		do {
 			cmd = container_of(entry, struct nullb_cmd, ll_list);
 			end_cmd(cmd);
 			entry = entry->next;
 		} while (entry);
 	}

 	return HRTIMER_NORESTART;
 }

 static void null_cmd_end_timer(struct nullb_cmd *cmd)
 {
 	struct completion_queue *cq = &per_cpu(completion_queues, get_cpu());

 	cmd->ll_list.next = NULL;
 	if (llist_add(&cmd->ll_list, &cq->list)) {
 		ktime_t kt = ktime_set(0, completion_nsec);

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

 	put_cpu();
 }

 static void null_softirq_done_fn(struct request *rq)
 {
 	blk_end_request_all(rq, 0);
 }

 #if defined(CONFIG_SMP) && defined(CONFIG_USE_GENERIC_SMP_HELPERS)

 static void null_ipi_cmd_end_io(void *data)
 {
 	struct completion_queue *cq;
 	struct llist_node *entry, *next;
 	struct nullb_cmd *cmd;

 	cq = &per_cpu(completion_queues, smp_processor_id());

 	entry = llist_del_all(&cq->list);

 	while (entry) {
 		next = entry->next;
 		cmd = llist_entry(entry, struct nullb_cmd, ll_list);
 		end_cmd(cmd);
 		entry = next;
 	}
 }

 static void null_cmd_end_ipi(struct nullb_cmd *cmd)
 {
 	struct call_single_data *data = &cmd->csd;
 	int cpu = get_cpu();
 	struct completion_queue *cq = &per_cpu(completion_queues, cpu);

 	cmd->ll_list.next = NULL;

 	if (llist_add(&cmd->ll_list, &cq->list)) {
 		data->func = null_ipi_cmd_end_io;
 		data->flags = 0;
 		__smp_call_function_single(cpu, data, 0);
 	}

 	put_cpu();
 }

 #endif /* CONFIG_SMP && CONFIG_USE_GENERIC_SMP_HELPERS */

 static inline void null_handle_cmd(struct nullb_cmd *cmd)
 {
 	/* Complete IO by inline, softirq or timer */
 	switch (irqmode) {
 	case NULL_IRQ_NONE:
 		end_cmd(cmd);
 		break;
 	case NULL_IRQ_SOFTIRQ:
 #if defined(CONFIG_SMP) && defined(CONFIG_USE_GENERIC_SMP_HELPERS)
 		null_cmd_end_ipi(cmd);
 #else
 		end_cmd(cmd);
 #endif
 		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 void 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);
 }

 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;
 	}

 	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, struct request *rq)
 {
 	struct nullb_cmd *cmd = rq->special;

 	cmd->rq = rq;
 	cmd->nq = hctx->driver_data;

 	null_handle_cmd(cmd);
 	return BLK_MQ_RQ_QUEUE_OK;
 }

 static struct blk_mq_hw_ctx *null_alloc_hctx(struct blk_mq_reg *reg, unsigned int hctx_index)
 {
 	return kzalloc_node(sizeof(struct blk_mq_hw_ctx), GFP_KERNEL,
 				hctx_index);
 }

 static void null_free_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_index)
 {
 	kfree(hctx);
 }

 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];

 	init_waitqueue_head(&nq->wait);
 	nq->queue_depth = nullb->queue_depth;
 	nullb->nr_queues++;
 	hctx->driver_data = nq;

 	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,
 };

 static struct blk_mq_reg null_mq_reg = {
 	.ops		= &null_mq_ops,
 	.queue_depth	= 64,
 	.cmd_size	= sizeof(struct nullb_cmd),
 	.flags		= BLK_MQ_F_SHOULD_MERGE,
 };

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

 	del_gendisk(nullb->disk);
 	if (queue_mode == NULL_Q_MQ)
 		blk_mq_free_queue(nullb->q);
 	else
 		blk_cleanup_queue(nullb->q);
 	put_disk(nullb->disk);
 	kfree(nullb);
 }

 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 1;

 	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 1;
 	}

 	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 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 int setup_queues(struct nullb *nullb)
 {
 	struct nullb_queue *nq;
 	int i;

 	nullb->queues = kzalloc(submit_queues * sizeof(*nq), GFP_KERNEL);
 	if (!nullb->queues)
 		return 1;

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

 	if (queue_mode == NULL_Q_MQ)
 		return 0;

 	for (i = 0; i < submit_queues; i++) {
 		nq = &nullb->queues[i];
 		init_waitqueue_head(&nq->wait);
 		nq->queue_depth = hw_queue_depth;
 		if (setup_commands(nq))
 			break;
 		nullb->nr_queues++;
 	}

 	if (i == submit_queues)
 		return 0;

 	cleanup_queues(nullb);
 	return 1;
 }

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

 	nullb = kzalloc_node(sizeof(*nullb), GFP_KERNEL, home_node);
 	if (!nullb)
 		return -ENOMEM;

 	spin_lock_init(&nullb->lock);

 	if (setup_queues(nullb))
 		goto err;

 	if (queue_mode == NULL_Q_MQ) {
 		null_mq_reg.numa_node = home_node;
 		null_mq_reg.queue_depth = hw_queue_depth;

 		if (use_per_node_hctx) {
 			null_mq_reg.ops->alloc_hctx = null_alloc_hctx;
 			null_mq_reg.ops->free_hctx = null_free_hctx;

 			null_mq_reg.nr_hw_queues = nr_online_nodes;
 		} else {
 			null_mq_reg.ops->alloc_hctx = blk_mq_alloc_single_hw_queue;
 			null_mq_reg.ops->free_hctx = blk_mq_free_single_hw_queue;

 			null_mq_reg.nr_hw_queues = submit_queues;
 		}

 		nullb->q = blk_mq_init_queue(&null_mq_reg, nullb);
 	} else if (queue_mode == NULL_Q_BIO) {
 		nullb->q = blk_alloc_queue_node(GFP_KERNEL, home_node);
 		blk_queue_make_request(nullb->q, null_queue_bio);
 	} else {
 		nullb->q = blk_init_queue_node(null_request_fn, &nullb->lock, home_node);
 		blk_queue_prep_rq(nullb->q, null_rq_prep_fn);
 		if (nullb->q)
 			blk_queue_softirq_done(nullb->q, null_softirq_done_fn);
 	}

 	if (!nullb->q)
 		goto queue_fail;

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

 	disk = nullb->disk = alloc_disk_node(1, home_node);
 	if (!disk) {
 queue_fail:
 		if (queue_mode == NULL_Q_MQ)
 			blk_mq_free_queue(nullb->q);
 		else
 			blk_cleanup_queue(nullb->q);
 		cleanup_queues(nullb);
 err:
 		kfree(nullb);
 		return -ENOMEM;
 	}

 	mutex_lock(&lock);
 	list_add_tail(&nullb->list, &nullb_list);
 	nullb->index = nullb_indexes++;
 	mutex_unlock(&lock);

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

 	size = gb * 1024 * 1024 * 1024ULL;
 	sector_div(size, bs);
 	set_capacity(disk, size);

 	disk->flags |= GENHD_FL_EXT_DEVT;
 	disk->major		= null_major;
 	disk->first_minor	= nullb->index;
 	disk->fops		= &null_fops;
 	disk->private_data	= nullb;
 	disk->queue		= nullb->q;
 	sprintf(disk->disk_name, "nullb%d", nullb->index);
 	add_disk(disk);
 	return 0;
 }

 static int __init null_init(void)
 {
 	unsigned int i;

 #if !defined(CONFIG_SMP) || !defined(CONFIG_USE_GENERIC_SMP_HELPERS)
 	if (irqmode == NULL_IRQ_SOFTIRQ) {
 		pr_warn("null_blk: softirq completions not available.\n");
 		pr_warn("null_blk: using direct completions.\n");
 		irqmode = NULL_IRQ_NONE;
 	}
 #endif

 	if (submit_queues > nr_cpu_ids)
 		submit_queues = nr_cpu_ids;
 	else if (!submit_queues)
 		submit_queues = 1;

 	mutex_init(&lock);

 	/* Initialize a separate list for each CPU for issuing softirqs */
 	for_each_possible_cpu(i) {
 		struct completion_queue *cq = &per_cpu(completion_queues, i);

 		init_llist_head(&cq->list);

 		if (irqmode != NULL_IRQ_TIMER)
 			continue;

 		hrtimer_init(&cq->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 		cq->timer.function = null_cmd_timer_expired;
 	}

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

 	for (i = 0; i < nr_devices; i++) {
 		if (null_add_dev()) {
 			unregister_blkdev(null_major, "nullb");
 			return -EINVAL;
 		}
 	}

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

 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);
 }

 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>

	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 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 hrtimer timer;
	unsigned int queue_depth;
	spinlock_t lock;

	struct nullb_queue *queues;
	unsigned int nr_queues;
	};

	static LIST_HEAD(nullb_list);
	static struct mutex lock;
	static int null_major;
	static int nullb_indexes;

	struct completion_queue {
	struct llist_head list;
	struct hrtimer timer;
	};

	/*
	* These are per-cpu for now, they will need to be configured by the
	* complete_queues parameter and appropriately mapped.
	*/
	static DEFINE_PER_CPU(struct completion_queue, completion_queues);

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

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

	static int submit_queues = 1;
	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;
	module_param(queue_mode, int, S_IRUGO);
	MODULE_PARM_DESC(use_mq, "Use blk-mq interface (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 int irqmode = NULL_IRQ_SOFTIRQ;
	module_param(irqmode, int, S_IRUGO);
	MODULE_PARM_DESC(irqmode, "IRQ completion handler. 0-none, 1-softirq, 2-timer");

	static int completion_nsec = 10000;
	module_param(completion_nsec, int, 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 = true;
	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: true");

	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 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;
	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)
	{
	if (cmd->rq) {
	if (queue_mode == NULL_Q_MQ)
	blk_mq_end_io(cmd->rq, 0);
	else {
	INIT_LIST_HEAD(&cmd->rq->queuelist);
	blk_end_request_all(cmd->rq, 0);
	}
	} else if (cmd->bio)
	bio_endio(cmd->bio, 0);

	if (queue_mode != NULL_Q_MQ)
	free_cmd(cmd);
	}

	static enum hrtimer_restart null_cmd_timer_expired(struct hrtimer *timer)
	{
	struct completion_queue *cq;
	struct llist_node *entry;
	struct nullb_cmd *cmd;

	cq = &per_cpu(completion_queues, smp_processor_id());

	while ((entry = llist_del_all(&cq->list)) != NULL) {
	do {
	cmd = container_of(entry, struct nullb_cmd, ll_list);
	end_cmd(cmd);
	entry = entry->next;
	} while (entry);
	}

	return HRTIMER_NORESTART;
	}

	static void null_cmd_end_timer(struct nullb_cmd *cmd)
	{
	struct completion_queue *cq = &per_cpu(completion_queues, get_cpu());

	cmd->ll_list.next = NULL;
	if (llist_add(&cmd->ll_list, &cq->list)) {
	ktime_t kt = ktime_set(0, completion_nsec);

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

	put_cpu();
	}

	static void null_softirq_done_fn(struct request *rq)
	{
	blk_end_request_all(rq, 0);
	}

	#if defined(CONFIG_SMP) && defined(CONFIG_USE_GENERIC_SMP_HELPERS)

	static void null_ipi_cmd_end_io(void *data)
	{
	struct completion_queue *cq;
	struct llist_node entry, next;
	struct nullb_cmd *cmd;

	cq = &per_cpu(completion_queues, smp_processor_id());

	entry = llist_del_all(&cq->list);

	while (entry) {
	next = entry->next;
	cmd = llist_entry(entry, struct nullb_cmd, ll_list);
	end_cmd(cmd);
	entry = next;
	}
	}

	static void null_cmd_end_ipi(struct nullb_cmd *cmd)
	{
	struct call_single_data *data = &cmd->csd;
	int cpu = get_cpu();
	struct completion_queue *cq = &per_cpu(completion_queues, cpu);

	cmd->ll_list.next = NULL;

	if (llist_add(&cmd->ll_list, &cq->list)) {
	data->func = null_ipi_cmd_end_io;
	data->flags = 0;
	__smp_call_function_single(cpu, data, 0);
	}

	put_cpu();
	}

	#endif /* CONFIG_SMP && CONFIG_USE_GENERIC_SMP_HELPERS */

	static inline void null_handle_cmd(struct nullb_cmd *cmd)
	{
	/* Complete IO by inline, softirq or timer */
	switch (irqmode) {
	case NULL_IRQ_NONE:
	end_cmd(cmd);
	break;
	case NULL_IRQ_SOFTIRQ:
	#if defined(CONFIG_SMP) && defined(CONFIG_USE_GENERIC_SMP_HELPERS)
	null_cmd_end_ipi(cmd);
	#else
	end_cmd(cmd);
	#endif
	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 void 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);
	}

	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;
	}

	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, struct request rq)
	{
	struct nullb_cmd *cmd = rq->special;

	cmd->rq = rq;
	cmd->nq = hctx->driver_data;

	null_handle_cmd(cmd);
	return BLK_MQ_RQ_QUEUE_OK;
	}

	static struct blk_mq_hw_ctx null_alloc_hctx(struct blk_mq_reg reg, unsigned int hctx_index)
	{
	return kzalloc_node(sizeof(struct blk_mq_hw_ctx), GFP_KERNEL,
	hctx_index);
	}

	static void null_free_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_index)
	{
	kfree(hctx);
	}

	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];

	init_waitqueue_head(&nq->wait);
	nq->queue_depth = nullb->queue_depth;
	nullb->nr_queues++;
	hctx->driver_data = nq;

	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,
	};

	static struct blk_mq_reg null_mq_reg = {
	.ops = &null_mq_ops,
	.queue_depth = 64,
	.cmd_size = sizeof(struct nullb_cmd),
	.flags = BLK_MQ_F_SHOULD_MERGE,
	};

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

	del_gendisk(nullb->disk);
	if (queue_mode == NULL_Q_MQ)
	blk_mq_free_queue(nullb->q);
	else
	blk_cleanup_queue(nullb->q);
	put_disk(nullb->disk);
	kfree(nullb);
	}

	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 1;

	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 1;
	}

	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 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 int setup_queues(struct nullb *nullb)
	{
	struct nullb_queue *nq;
	int i;

	nullb->queues = kzalloc(submit_queues * sizeof(*nq), GFP_KERNEL);
	if (!nullb->queues)
	return 1;

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

	if (queue_mode == NULL_Q_MQ)
	return 0;

	for (i = 0; i < submit_queues; i++) {
	nq = &nullb->queues[i];
	init_waitqueue_head(&nq->wait);
	nq->queue_depth = hw_queue_depth;
	if (setup_commands(nq))
	break;
	nullb->nr_queues++;
	}

	if (i == submit_queues)
	return 0;

	cleanup_queues(nullb);
	return 1;
	}

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

	nullb = kzalloc_node(sizeof(*nullb), GFP_KERNEL, home_node);
	if (!nullb)
	return -ENOMEM;

	spin_lock_init(&nullb->lock);

	if (setup_queues(nullb))
	goto err;

	if (queue_mode == NULL_Q_MQ) {
	null_mq_reg.numa_node = home_node;
	null_mq_reg.queue_depth = hw_queue_depth;

	if (use_per_node_hctx) {
	null_mq_reg.ops->alloc_hctx = null_alloc_hctx;
	null_mq_reg.ops->free_hctx = null_free_hctx;

	null_mq_reg.nr_hw_queues = nr_online_nodes;
	} else {
	null_mq_reg.ops->alloc_hctx = blk_mq_alloc_single_hw_queue;
	null_mq_reg.ops->free_hctx = blk_mq_free_single_hw_queue;

	null_mq_reg.nr_hw_queues = submit_queues;
	}

	nullb->q = blk_mq_init_queue(&null_mq_reg, nullb);
	} else if (queue_mode == NULL_Q_BIO) {
	nullb->q = blk_alloc_queue_node(GFP_KERNEL, home_node);
	blk_queue_make_request(nullb->q, null_queue_bio);
	} else {
	nullb->q = blk_init_queue_node(null_request_fn, &nullb->lock, home_node);
	blk_queue_prep_rq(nullb->q, null_rq_prep_fn);
	if (nullb->q)
	blk_queue_softirq_done(nullb->q, null_softirq_done_fn);
	}

	if (!nullb->q)
	goto queue_fail;

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

	disk = nullb->disk = alloc_disk_node(1, home_node);
	if (!disk) {
	queue_fail:
	if (queue_mode == NULL_Q_MQ)
	blk_mq_free_queue(nullb->q);
	else
	blk_cleanup_queue(nullb->q);
	cleanup_queues(nullb);
	err:
	kfree(nullb);
	return -ENOMEM;
	}

	mutex_lock(&lock);
	list_add_tail(&nullb->list, &nullb_list);
	nullb->index = nullb_indexes++;
	mutex_unlock(&lock);

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

	size = gb * 1024 * 1024 * 1024ULL;
	sector_div(size, bs);
	set_capacity(disk, size);

	disk->flags \|= GENHD_FL_EXT_DEVT;
	disk->major = null_major;
	disk->first_minor = nullb->index;
	disk->fops = &null_fops;
	disk->private_data = nullb;
	disk->queue = nullb->q;
	sprintf(disk->disk_name, "nullb%d", nullb->index);
	add_disk(disk);
	return 0;
	}

	static int __init null_init(void)
	{
	unsigned int i;

	#if !defined(CONFIG_SMP) \|\| !defined(CONFIG_USE_GENERIC_SMP_HELPERS)
	if (irqmode == NULL_IRQ_SOFTIRQ) {
	pr_warn("null_blk: softirq completions not available.\n");
	pr_warn("null_blk: using direct completions.\n");
	irqmode = NULL_IRQ_NONE;
	}
	#endif

	if (submit_queues > nr_cpu_ids)
	submit_queues = nr_cpu_ids;
	else if (!submit_queues)
	submit_queues = 1;

	mutex_init(&lock);

	/* Initialize a separate list for each CPU for issuing softirqs */
	for_each_possible_cpu(i) {
	struct completion_queue *cq = &per_cpu(completion_queues, i);

	init_llist_head(&cq->list);

	if (irqmode != NULL_IRQ_TIMER)
	continue;

	hrtimer_init(&cq->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
	cq->timer.function = null_cmd_timer_expired;
	}

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

	for (i = 0; i < nr_devices; i++) {
	if (null_add_dev()) {
	unregister_blkdev(null_major, "nullb");
	return -EINVAL;
	}
	}

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

	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);
	}

	module_init(null_init);
	module_exit(null_exit);

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