blob: d946e1eeac8ef0dafbf3510f3aaa57925ea5f07c [file] [log] [blame]
#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 nvm_dev *ndev;
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 bool blocking;
module_param(blocking, bool, S_IRUGO);
MODULE_PARM_DESC(blocking, "Register as a blocking blk-mq driver 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 = 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);
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);
might_sleep_if(hctx->flags & BLK_MQ_F_BLOCKING);
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 const struct blk_mq_ops null_mq_ops = {
.queue_rq = null_queue_rq,
.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);
}
#ifdef CONFIG_NVM
static void null_lnvm_end_io(struct request *rq, int error)
{
struct nvm_rq *rqd = rq->end_io_data;
rqd->error = error;
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)
{
sector_t size = gb * 1024 * 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, bs); /* 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 = 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,
};
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)
{
list_del_init(&nullb->list);
if (use_lightnvm)
null_nvm_unregister(nullb);
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);
}
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_gendisk_register(struct nullb *nullb)
{
struct gendisk *disk;
sector_t size;
disk = nullb->disk = alloc_disk_node(1, home_node);
if (!disk)
return -ENOMEM;
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);
return 0;
}
static int null_add_dev(void)
{
struct nullb *nullb;
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;
if (blocking)
nullb->tag_set.flags |= BLK_MQ_F_BLOCKING;
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 = 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 (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");