/*
 * bio-integrity.c - bio data integrity extensions
 *
 * Copyright (C) 2007, 2008, 2009 Oracle Corporation
 * Written by: Martin K. Petersen <martin.petersen@oracle.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version
 * 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; see the file COPYING.  If not, write to
 * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139,
 * USA.
 *
 */

#include <linux/blkdev.h>
#include <linux/mempool.h>
#include <linux/export.h>
#include <linux/bio.h>
#include <linux/workqueue.h>
#include <linux/slab.h>

struct integrity_slab {
        struct kmem_cache *slab;
        unsigned short nr_vecs;
        char name[8];
};

#define IS(x) { .nr_vecs = x, .name = "bip-"__stringify(x) }
struct integrity_slab bip_slab[BIOVEC_NR_POOLS] __read_mostly = {
        IS(1), IS(4), IS(16), IS(64), IS(128), IS(BIO_MAX_PAGES),
};
#undef IS

static struct workqueue_struct *kintegrityd_wq;

static inline unsigned int vecs_to_idx(unsigned int nr)
{
        switch (nr) {
        case 1:
                return 0;
        case 2 ... 4:
                return 1;
        case 5 ... 16:
                return 2;
        case 17 ... 64:
                return 3;
        case 65 ... 128:
                return 4;
        case 129 ... BIO_MAX_PAGES:
                return 5;
        default:
                BUG();
        }
}

static inline int use_bip_pool(unsigned int idx)
{
        if (idx == BIOVEC_MAX_IDX)
                return 1;

        return 0;
}

/**
 * bio_integrity_alloc - Allocate integrity payload and attach it to bio
 * @bio:        bio to attach integrity metadata to
 * @gfp_mask:   Memory allocation mask
 * @nr_vecs:    Number of integrity metadata scatter-gather elements
 *
 * Description: This function prepares a bio for attaching integrity
 * metadata.  nr_vecs specifies the maximum number of pages containing
 * integrity metadata that can be attached.
 */
struct bio_integrity_payload *bio_integrity_alloc(struct bio *bio,
                                                  gfp_t gfp_mask,
                                                  unsigned int nr_vecs)
{
        struct bio_integrity_payload *bip;
        unsigned int idx = vecs_to_idx(nr_vecs);
        struct bio_set *bs = bio->bi_pool;

        if (!bs)
                bs = fs_bio_set;

        BUG_ON(bio == NULL);
        bip = NULL;

        /* Lower order allocations come straight from slab */
        if (!use_bip_pool(idx))
                bip = kmem_cache_alloc(bip_slab[idx].slab, gfp_mask);

        /* Use mempool if lower order alloc failed or max vecs were requested */
        if (bip == NULL) {
                idx = BIOVEC_MAX_IDX;  /* so we free the payload properly later */
                bip = mempool_alloc(bs->bio_integrity_pool, gfp_mask);

                if (unlikely(bip == NULL)) {
                        printk(KERN_ERR "%s: could not alloc bip\n", __func__);
                        return NULL;
                }
        }

        memset(bip, 0, sizeof(*bip));

        bip->bip_slab = idx;
        bip->bip_bio = bio;
        bio->bi_integrity = bip;

        return bip;
}
EXPORT_SYMBOL(bio_integrity_alloc);

/**
 * bio_integrity_free - Free bio integrity payload
 * @bio:        bio containing bip to be freed
 *
 * Description: Used to free the integrity portion of a bio. Usually
 * called from bio_free().
 */
void bio_integrity_free(struct bio *bio)
{
        struct bio_integrity_payload *bip = bio->bi_integrity;
        struct bio_set *bs = bio->bi_pool;

        if (!bs)
                bs = fs_bio_set;

        BUG_ON(bip == NULL);

        /* A cloned bio doesn't own the integrity metadata */
        if (!bio_flagged(bio, BIO_CLONED) && !bio_flagged(bio, BIO_FS_INTEGRITY)
            && bip->bip_buf != NULL)
                kfree(bip->bip_buf);

        if (use_bip_pool(bip->bip_slab))
                mempool_free(bip, bs->bio_integrity_pool);
        else
                kmem_cache_free(bip_slab[bip->bip_slab].slab, bip);

        bio->bi_integrity = NULL;
}
EXPORT_SYMBOL(bio_integrity_free);

/**
 * bio_integrity_add_page - Attach integrity metadata
 * @bio:        bio to update
 * @page:       page containing integrity metadata
 * @len:        number of bytes of integrity metadata in page
 * @offset:     start offset within page
 *
 * Description: Attach a page containing integrity metadata to bio.
 */
int bio_integrity_add_page(struct bio *bio, struct page *page,
                           unsigned int len, unsigned int offset)
{
        struct bio_integrity_payload *bip = bio->bi_integrity;
        struct bio_vec *iv;

        if (bip->bip_vcnt >= bvec_nr_vecs(bip->bip_slab)) {
                printk(KERN_ERR "%s: bip_vec full\n", __func__);
                return 0;
        }

        iv = bip_vec_idx(bip, bip->bip_vcnt);
        BUG_ON(iv == NULL);

        iv->bv_page = page;
        iv->bv_len = len;
        iv->bv_offset = offset;
        bip->bip_vcnt++;

        return len;
}
EXPORT_SYMBOL(bio_integrity_add_page);

static int bdev_integrity_enabled(struct block_device *bdev, int rw)
{
        struct blk_integrity *bi = bdev_get_integrity(bdev);

        if (bi == NULL)
                return 0;

        if (rw == READ && bi->verify_fn != NULL &&
            (bi->flags & INTEGRITY_FLAG_READ))
                return 1;

        if (rw == WRITE && bi->generate_fn != NULL &&
            (bi->flags & INTEGRITY_FLAG_WRITE))
                return 1;

        return 0;
}

/**
 * bio_integrity_enabled - Check whether integrity can be passed
 * @bio:        bio to check
 *
 * Description: Determines whether bio_integrity_prep() can be called
 * on this bio or not.  bio data direction and target device must be
 * set prior to calling.  The functions honors the write_generate and
 * read_verify flags in sysfs.
 */
int bio_integrity_enabled(struct bio *bio)
{
        /* Already protected? */
        if (bio_integrity(bio))
                return 0;

        return bdev_integrity_enabled(bio->bi_bdev, bio_data_dir(bio));
}
EXPORT_SYMBOL(bio_integrity_enabled);

/**
 * bio_integrity_hw_sectors - Convert 512b sectors to hardware ditto
 * @bi:         blk_integrity profile for device
 * @sectors:    Number of 512 sectors to convert
 *
 * Description: The block layer calculates everything in 512 byte
 * sectors but integrity metadata is done in terms of the hardware
 * sector size of the storage device.  Convert the block layer sectors
 * to physical sectors.
 */
static inline unsigned int bio_integrity_hw_sectors(struct blk_integrity *bi,
                                                    unsigned int sectors)
{
        /* At this point there are only 512b or 4096b DIF/EPP devices */
        if (bi->sector_size == 4096)
                return sectors >>= 3;

        return sectors;
}

/**
 * bio_integrity_tag_size - Retrieve integrity tag space
 * @bio:        bio to inspect
 *
 * Description: Returns the maximum number of tag bytes that can be
 * attached to this bio. Filesystems can use this to determine how
 * much metadata to attach to an I/O.
 */
unsigned int bio_integrity_tag_size(struct bio *bio)
{
        struct blk_integrity *bi = bdev_get_integrity(bio->bi_bdev);

        BUG_ON(bio->bi_size == 0);

        return bi->tag_size * (bio->bi_size / bi->sector_size);
}
EXPORT_SYMBOL(bio_integrity_tag_size);

int bio_integrity_tag(struct bio *bio, void *tag_buf, unsigned int len, int set)
{
        struct bio_integrity_payload *bip = bio->bi_integrity;
        struct blk_integrity *bi = bdev_get_integrity(bio->bi_bdev);
        unsigned int nr_sectors;

        BUG_ON(bip->bip_buf == NULL);

        if (bi->tag_size == 0)
                return -1;

        nr_sectors = bio_integrity_hw_sectors(bi,
                                        DIV_ROUND_UP(len, bi->tag_size));

        if (nr_sectors * bi->tuple_size > bip->bip_size) {
                printk(KERN_ERR "%s: tag too big for bio: %u > %u\n",
                       __func__, nr_sectors * bi->tuple_size, bip->bip_size);
                return -1;
        }

        if (set)
                bi->set_tag_fn(bip->bip_buf, tag_buf, nr_sectors);
        else
                bi->get_tag_fn(bip->bip_buf, tag_buf, nr_sectors);

        return 0;
}

/**
 * bio_integrity_set_tag - Attach a tag buffer to a bio
 * @bio:        bio to attach buffer to
 * @tag_buf:    Pointer to a buffer containing tag data
 * @len:        Length of the included buffer
 *
 * Description: Use this function to tag a bio by leveraging the extra
 * space provided by devices formatted with integrity protection.  The
 * size of the integrity buffer must be <= to the size reported by
 * bio_integrity_tag_size().
 */
int bio_integrity_set_tag(struct bio *bio, void *tag_buf, unsigned int len)
{
        BUG_ON(bio_data_dir(bio) != WRITE);

        return bio_integrity_tag(bio, tag_buf, len, 1);
}
EXPORT_SYMBOL(bio_integrity_set_tag);

/**
 * bio_integrity_get_tag - Retrieve a tag buffer from a bio
 * @bio:        bio to retrieve buffer from
 * @tag_buf:    Pointer to a buffer for the tag data
 * @len:        Length of the target buffer
 *
 * Description: Use this function to retrieve the tag buffer from a
 * completed I/O. The size of the integrity buffer must be <= to the
 * size reported by bio_integrity_tag_size().
 */
int bio_integrity_get_tag(struct bio *bio, void *tag_buf, unsigned int len)
{
        BUG_ON(bio_data_dir(bio) != READ);

        return bio_integrity_tag(bio, tag_buf, len, 0);
}
EXPORT_SYMBOL(bio_integrity_get_tag);

/**
 * bio_integrity_generate - Generate integrity metadata for a bio
 * @bio:        bio to generate integrity metadata for
 *
 * Description: Generates integrity metadata for a bio by calling the
 * block device's generation callback function.  The bio must have a
 * bip attached with enough room to accommodate the generated
 * integrity metadata.
 */
static void bio_integrity_generate(struct bio *bio)
{
        struct blk_integrity *bi = bdev_get_integrity(bio->bi_bdev);
        struct blk_integrity_exchg bix;
        struct bio_vec *bv;
        sector_t sector = bio->bi_sector;
        unsigned int i, sectors, total;
        void *prot_buf = bio->bi_integrity->bip_buf;

        total = 0;
        bix.disk_name = bio->bi_bdev->bd_disk->disk_name;
        bix.sector_size = bi->sector_size;

        bio_for_each_segment(bv, bio, i) {
                void *kaddr = kmap_atomic(bv->bv_page);
                bix.data_buf = kaddr + bv->bv_offset;
                bix.data_size = bv->bv_len;
                bix.prot_buf = prot_buf;
                bix.sector = sector;

                bi->generate_fn(&bix);

                sectors = bv->bv_len / bi->sector_size;
                sector += sectors;
                prot_buf += sectors * bi->tuple_size;
                total += sectors * bi->tuple_size;
                BUG_ON(total > bio->bi_integrity->bip_size);

                kunmap_atomic(kaddr);
        }
}

static inline unsigned short blk_integrity_tuple_size(struct blk_integrity *bi)
{
        if (bi)
                return bi->tuple_size;

        return 0;
}

/**
 * bio_integrity_prep - Prepare bio for integrity I/O
 * @bio:        bio to prepare
 *
 * Description: Allocates a buffer for integrity metadata, maps the
 * pages and attaches them to a bio.  The bio must have data
 * direction, target device and start sector set priot to calling.  In
 * the WRITE case, integrity metadata will be generated using the
 * block device's integrity function.  In the READ case, the buffer
 * will be prepared for DMA and a suitable end_io handler set up.
 */
int bio_integrity_prep(struct bio *bio)
{
        struct bio_integrity_payload *bip;
        struct blk_integrity *bi;
        struct request_queue *q;
        void *buf;
        unsigned long start, end;
        unsigned int len, nr_pages;
        unsigned int bytes, offset, i;
        unsigned int sectors;

        bi = bdev_get_integrity(bio->bi_bdev);
        q = bdev_get_queue(bio->bi_bdev);
        BUG_ON(bi == NULL);
        BUG_ON(bio_integrity(bio));

        sectors = bio_integrity_hw_sectors(bi, bio_sectors(bio));

        /* Allocate kernel buffer for protection data */
        len = sectors * blk_integrity_tuple_size(bi);
        buf = kmalloc(len, GFP_NOIO | q->bounce_gfp);
        if (unlikely(buf == NULL)) {
                printk(KERN_ERR "could not allocate integrity buffer\n");
                return -ENOMEM;
        }

        end = (((unsigned long) buf) + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
        start = ((unsigned long) buf) >> PAGE_SHIFT;
        nr_pages = end - start;

        /* Allocate bio integrity payload and integrity vectors */
        bip = bio_integrity_alloc(bio, GFP_NOIO, nr_pages);
        if (unlikely(bip == NULL)) {
                printk(KERN_ERR "could not allocate data integrity bioset\n");
                kfree(buf);
                return -EIO;
        }

        bip->bip_buf = buf;
        bip->bip_size = len;
        bip->bip_sector = bio->bi_sector;

        /* Map it */
        offset = offset_in_page(buf);
        for (i = 0 ; i < nr_pages ; i++) {
                int ret;
                bytes = PAGE_SIZE - offset;

                if (len <= 0)
                        break;

                if (bytes > len)
                        bytes = len;

                ret = bio_integrity_add_page(bio, virt_to_page(buf),
                                             bytes, offset);

                if (ret == 0)
                        return 0;

                if (ret < bytes)
                        break;

                buf += bytes;
                len -= bytes;
                offset = 0;
        }

        /* Install custom I/O completion handler if read verify is enabled */
        if (bio_data_dir(bio) == READ) {
                bip->bip_end_io = bio->bi_end_io;
                bio->bi_end_io = bio_integrity_endio;
        }

        /* Auto-generate integrity metadata if this is a write */
        if (bio_data_dir(bio) == WRITE)
                bio_integrity_generate(bio);

        return 0;
}
EXPORT_SYMBOL(bio_integrity_prep);

/**
 * bio_integrity_verify - Verify integrity metadata for a bio
 * @bio:        bio to verify
 *
 * Description: This function is called to verify the integrity of a
 * bio.  The data in the bio io_vec is compared to the integrity
 * metadata returned by the HBA.
 */
static int bio_integrity_verify(struct bio *bio)
{
        struct blk_integrity *bi = bdev_get_integrity(bio->bi_bdev);
        struct blk_integrity_exchg bix;
        struct bio_vec *bv;
        sector_t sector = bio->bi_integrity->bip_sector;
        unsigned int i, sectors, total, ret;
        void *prot_buf = bio->bi_integrity->bip_buf;

        ret = total = 0;
        bix.disk_name = bio->bi_bdev->bd_disk->disk_name;
        bix.sector_size = bi->sector_size;

        bio_for_each_segment(bv, bio, i) {
                void *kaddr = kmap_atomic(bv->bv_page);
                bix.data_buf = kaddr + bv->bv_offset;
                bix.data_size = bv->bv_len;
                bix.prot_buf = prot_buf;
                bix.sector = sector;

                ret = bi->verify_fn(&bix);

                if (ret) {
                        kunmap_atomic(kaddr);
                        return ret;
                }

                sectors = bv->bv_len / bi->sector_size;
                sector += sectors;
                prot_buf += sectors * bi->tuple_size;
                total += sectors * bi->tuple_size;
                BUG_ON(total > bio->bi_integrity->bip_size);

                kunmap_atomic(kaddr);
        }

        return ret;
}

/**
 * bio_integrity_verify_fn - Integrity I/O completion worker
 * @work:       Work struct stored in bio to be verified
 *
 * Description: This workqueue function is called to complete a READ
 * request.  The function verifies the transferred integrity metadata
 * and then calls the original bio end_io function.
 */
static void bio_integrity_verify_fn(struct work_struct *work)
{
        struct bio_integrity_payload *bip =
                container_of(work, struct bio_integrity_payload, bip_work);
        struct bio *bio = bip->bip_bio;
        int error;

        error = bio_integrity_verify(bio);

        /* Restore original bio completion handler */
        bio->bi_end_io = bip->bip_end_io;
        bio_endio(bio, error);
}

/**
 * bio_integrity_endio - Integrity I/O completion function
 * @bio:        Protected bio
 * @error:      Pointer to errno
 *
 * Description: Completion for integrity I/O
 *
 * Normally I/O completion is done in interrupt context.  However,
 * verifying I/O integrity is a time-consuming task which must be run
 * in process context.  This function postpones completion
 * accordingly.
 */
void bio_integrity_endio(struct bio *bio, int error)
{
        struct bio_integrity_payload *bip = bio->bi_integrity;

        BUG_ON(bip->bip_bio != bio);

        /* In case of an I/O error there is no point in verifying the
         * integrity metadata.  Restore original bio end_io handler
         * and run it.
         */
        if (error) {
                bio->bi_end_io = bip->bip_end_io;
                bio_endio(bio, error);

                return;
        }

        INIT_WORK(&bip->bip_work, bio_integrity_verify_fn);
        queue_work(kintegrityd_wq, &bip->bip_work);
}
EXPORT_SYMBOL(bio_integrity_endio);

/**
 * bio_integrity_mark_head - Advance bip_vec skip bytes
 * @bip:        Integrity vector to advance
 * @skip:       Number of bytes to advance it
 */
void bio_integrity_mark_head(struct bio_integrity_payload *bip,
                             unsigned int skip)
{
        struct bio_vec *iv;
        unsigned int i;

        bip_for_each_vec(iv, bip, i) {
                if (skip == 0) {
                        bip->bip_idx = i;
                        return;
                } else if (skip >= iv->bv_len) {
                        skip -= iv->bv_len;
                } else { /* skip < iv->bv_len) */
                        iv->bv_offset += skip;
                        iv->bv_len -= skip;
                        bip->bip_idx = i;
                        return;
                }
        }
}

/**
 * bio_integrity_mark_tail - Truncate bip_vec to be len bytes long
 * @bip:        Integrity vector to truncate
 * @len:        New length of integrity vector
 */
void bio_integrity_mark_tail(struct bio_integrity_payload *bip,
                             unsigned int len)
{
        struct bio_vec *iv;
        unsigned int i;

        bip_for_each_vec(iv, bip, i) {
                if (len == 0) {
                        bip->bip_vcnt = i;
                        return;
                } else if (len >= iv->bv_len) {
                        len -= iv->bv_len;
                } else { /* len < iv->bv_len) */
                        iv->bv_len = len;
                        len = 0;
                }
        }
}

/**
 * bio_integrity_advance - Advance integrity vector
 * @bio:        bio whose integrity vector to update
 * @bytes_done: number of data bytes that have been completed
 *
 * Description: This function calculates how many integrity bytes the
 * number of completed data bytes correspond to and advances the
 * integrity vector accordingly.
 */
void bio_integrity_advance(struct bio *bio, unsigned int bytes_done)
{
        struct bio_integrity_payload *bip = bio->bi_integrity;
        struct blk_integrity *bi = bdev_get_integrity(bio->bi_bdev);
        unsigned int nr_sectors;

        BUG_ON(bip == NULL);
        BUG_ON(bi == NULL);

        nr_sectors = bio_integrity_hw_sectors(bi, bytes_done >> 9);
        bio_integrity_mark_head(bip, nr_sectors * bi->tuple_size);
}
EXPORT_SYMBOL(bio_integrity_advance);

/**
 * bio_integrity_trim - Trim integrity vector
 * @bio:        bio whose integrity vector to update
 * @offset:     offset to first data sector
 * @sectors:    number of data sectors
 *
 * Description: Used to trim the integrity vector in a cloned bio.
 * The ivec will be advanced corresponding to 'offset' data sectors
 * and the length will be truncated corresponding to 'len' data
 * sectors.
 */
void bio_integrity_trim(struct bio *bio, unsigned int offset,
                        unsigned int sectors)
{
        struct bio_integrity_payload *bip = bio->bi_integrity;
        struct blk_integrity *bi = bdev_get_integrity(bio->bi_bdev);
        unsigned int nr_sectors;

        BUG_ON(bip == NULL);
        BUG_ON(bi == NULL);
        BUG_ON(!bio_flagged(bio, BIO_CLONED));

        nr_sectors = bio_integrity_hw_sectors(bi, sectors);
        bip->bip_sector = bip->bip_sector + offset;
        bio_integrity_mark_head(bip, offset * bi->tuple_size);
        bio_integrity_mark_tail(bip, sectors * bi->tuple_size);
}
EXPORT_SYMBOL(bio_integrity_trim);

/**
 * bio_integrity_split - Split integrity metadata
 * @bio:        Protected bio
 * @bp:         Resulting bio_pair
 * @sectors:    Offset
 *
 * Description: Splits an integrity page into a bio_pair.
 */
void bio_integrity_split(struct bio *bio, struct bio_pair *bp, int sectors)
{
        struct blk_integrity *bi;
        struct bio_integrity_payload *bip = bio->bi_integrity;
        unsigned int nr_sectors;

        if (bio_integrity(bio) == 0)
                return;

        bi = bdev_get_integrity(bio->bi_bdev);
        BUG_ON(bi == NULL);
        BUG_ON(bip->bip_vcnt != 1);

        nr_sectors = bio_integrity_hw_sectors(bi, sectors);

        bp->bio1.bi_integrity = &bp->bip1;
        bp->bio2.bi_integrity = &bp->bip2;

        bp->iv1 = bip->bip_vec[0];
        bp->iv2 = bip->bip_vec[0];

        bp->bip1.bip_vec[0] = bp->iv1;
        bp->bip2.bip_vec[0] = bp->iv2;

        bp->iv1.bv_len = sectors * bi->tuple_size;
        bp->iv2.bv_offset += sectors * bi->tuple_size;
        bp->iv2.bv_len -= sectors * bi->tuple_size;

        bp->bip1.bip_sector = bio->bi_integrity->bip_sector;
        bp->bip2.bip_sector = bio->bi_integrity->bip_sector + nr_sectors;

        bp->bip1.bip_vcnt = bp->bip2.bip_vcnt = 1;
        bp->bip1.bip_idx = bp->bip2.bip_idx = 0;
}
EXPORT_SYMBOL(bio_integrity_split);

/**
 * bio_integrity_clone - Callback for cloning bios with integrity metadata
 * @bio:        New bio
 * @bio_src:    Original bio
 * @gfp_mask:   Memory allocation mask
 *
 * Description: Called to allocate a bip when cloning a bio
 */
int bio_integrity_clone(struct bio *bio, struct bio *bio_src,
                        gfp_t gfp_mask)
{
        struct bio_integrity_payload *bip_src = bio_src->bi_integrity;
        struct bio_integrity_payload *bip;

        BUG_ON(bip_src == NULL);

        bip = bio_integrity_alloc(bio, gfp_mask, bip_src->bip_vcnt);

        if (bip == NULL)
                return -EIO;

        memcpy(bip->bip_vec, bip_src->bip_vec,
               bip_src->bip_vcnt * sizeof(struct bio_vec));

        bip->bip_sector = bip_src->bip_sector;
        bip->bip_vcnt = bip_src->bip_vcnt;
        bip->bip_idx = bip_src->bip_idx;

        return 0;
}
EXPORT_SYMBOL(bio_integrity_clone);

int bioset_integrity_create(struct bio_set *bs, int pool_size)
{
        unsigned int max_slab = vecs_to_idx(BIO_MAX_PAGES);

        if (bs->bio_integrity_pool)
                return 0;

        bs->bio_integrity_pool =
                mempool_create_slab_pool(pool_size, bip_slab[max_slab].slab);

        if (!bs->bio_integrity_pool)
                return -1;

        return 0;
}
EXPORT_SYMBOL(bioset_integrity_create);

void bioset_integrity_free(struct bio_set *bs)
{
        if (bs->bio_integrity_pool)
                mempool_destroy(bs->bio_integrity_pool);
}
EXPORT_SYMBOL(bioset_integrity_free);

void __init bio_integrity_init(void)
{
        unsigned int i;

        /*
         * kintegrityd won't block much but may burn a lot of CPU cycles.
         * Make it highpri CPU intensive wq with max concurrency of 1.
         */
        kintegrityd_wq = alloc_workqueue("kintegrityd", WQ_MEM_RECLAIM |
                                         WQ_HIGHPRI | WQ_CPU_INTENSIVE, 1);
        if (!kintegrityd_wq)
                panic("Failed to create kintegrityd\n");

        for (i = 0 ; i < BIOVEC_NR_POOLS ; i++) {
                unsigned int size;

                size = sizeof(struct bio_integrity_payload)
                        + bip_slab[i].nr_vecs * sizeof(struct bio_vec);

                bip_slab[i].slab =
                        kmem_cache_create(bip_slab[i].name, size, 0,
                                          SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
        }
}