// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2018 Red Hat. All rights reserved.
 *
 * This file is released under the GPL.
 */

#include <linux/device-mapper.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/vmalloc.h>
#include <linux/kthread.h>
#include <linux/dm-io.h>
#include <linux/dm-kcopyd.h>
#include <linux/dax.h>
#include <linux/pfn_t.h>
#include <linux/libnvdimm.h>

#define DM_MSG_PREFIX "writecache"

#define HIGH_WATERMARK                  50
#define LOW_WATERMARK                   45
#define MAX_WRITEBACK_JOBS              0
#define ENDIO_LATENCY                   16
#define WRITEBACK_LATENCY               64
#define AUTOCOMMIT_BLOCKS_SSD           65536
#define AUTOCOMMIT_BLOCKS_PMEM          64
#define AUTOCOMMIT_MSEC                 1000

#define BITMAP_GRANULARITY      65536
#if BITMAP_GRANULARITY < PAGE_SIZE
#undef BITMAP_GRANULARITY
#define BITMAP_GRANULARITY      PAGE_SIZE
#endif

#if IS_ENABLED(CONFIG_ARCH_HAS_PMEM_API) && IS_ENABLED(CONFIG_DAX_DRIVER)
#define DM_WRITECACHE_HAS_PMEM
#endif

#ifdef DM_WRITECACHE_HAS_PMEM
#define pmem_assign(dest, src)                                  \
do {                                                            \
        typeof(dest) uniq = (src);                              \
        memcpy_flushcache(&(dest), &uniq, sizeof(dest));        \
} while (0)
#else
#define pmem_assign(dest, src)  ((dest) = (src))
#endif

#if defined(__HAVE_ARCH_MEMCPY_MCSAFE) && defined(DM_WRITECACHE_HAS_PMEM)
#define DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
#endif

#define MEMORY_SUPERBLOCK_MAGIC         0x23489321
#define MEMORY_SUPERBLOCK_VERSION       1

struct wc_memory_entry {
        __le64 original_sector;
        __le64 seq_count;
};

struct wc_memory_superblock {
        union {
                struct {
                        __le32 magic;
                        __le32 version;
                        __le32 block_size;
                        __le32 pad;
                        __le64 n_blocks;
                        __le64 seq_count;
                };
                __le64 padding[8];
        };
        struct wc_memory_entry entries[0];
};

struct wc_entry {
        struct rb_node rb_node;
        struct list_head lru;
        unsigned short wc_list_contiguous;
        bool write_in_progress
#if BITS_PER_LONG == 64
                :1
#endif
        ;
        unsigned long index
#if BITS_PER_LONG == 64
                :47
#endif
        ;
#ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
        uint64_t original_sector;
        uint64_t seq_count;
#endif
};

#ifdef DM_WRITECACHE_HAS_PMEM
#define WC_MODE_PMEM(wc)                        ((wc)->pmem_mode)
#define WC_MODE_FUA(wc)                         ((wc)->writeback_fua)
#else
#define WC_MODE_PMEM(wc)                        false
#define WC_MODE_FUA(wc)                         false
#endif
#define WC_MODE_SORT_FREELIST(wc)               (!WC_MODE_PMEM(wc))

struct dm_writecache {
        struct mutex lock;
        struct list_head lru;
        union {
                struct list_head freelist;
                struct {
                        struct rb_root freetree;
                        struct wc_entry *current_free;
                };
        };
        struct rb_root tree;

        size_t freelist_size;
        size_t writeback_size;
        size_t freelist_high_watermark;
        size_t freelist_low_watermark;

        unsigned uncommitted_blocks;
        unsigned autocommit_blocks;
        unsigned max_writeback_jobs;

        int error;

        unsigned long autocommit_jiffies;
        struct timer_list autocommit_timer;
        struct wait_queue_head freelist_wait;

        atomic_t bio_in_progress[2];
        struct wait_queue_head bio_in_progress_wait[2];

        struct dm_target *ti;
        struct dm_dev *dev;
        struct dm_dev *ssd_dev;
        sector_t start_sector;
        void *memory_map;
        uint64_t memory_map_size;
        size_t metadata_sectors;
        size_t n_blocks;
        uint64_t seq_count;
        void *block_start;
        struct wc_entry *entries;
        unsigned block_size;
        unsigned char block_size_bits;

        bool pmem_mode:1;
        bool writeback_fua:1;

        bool overwrote_committed:1;
        bool memory_vmapped:1;

        bool high_wm_percent_set:1;
        bool low_wm_percent_set:1;
        bool max_writeback_jobs_set:1;
        bool autocommit_blocks_set:1;
        bool autocommit_time_set:1;
        bool writeback_fua_set:1;
        bool flush_on_suspend:1;

        unsigned writeback_all;
        struct workqueue_struct *writeback_wq;
        struct work_struct writeback_work;
        struct work_struct flush_work;

        struct dm_io_client *dm_io;

        raw_spinlock_t endio_list_lock;
        struct list_head endio_list;
        struct task_struct *endio_thread;

        struct task_struct *flush_thread;
        struct bio_list flush_list;

        struct dm_kcopyd_client *dm_kcopyd;
        unsigned long *dirty_bitmap;
        unsigned dirty_bitmap_size;

        struct bio_set bio_set;
        mempool_t copy_pool;
};

#define WB_LIST_INLINE          16

struct writeback_struct {
        struct list_head endio_entry;
        struct dm_writecache *wc;
        struct wc_entry **wc_list;
        unsigned wc_list_n;
        struct page *page;
        struct wc_entry *wc_list_inline[WB_LIST_INLINE];
        struct bio bio;
};

struct copy_struct {
        struct list_head endio_entry;
        struct dm_writecache *wc;
        struct wc_entry *e;
        unsigned n_entries;
        int error;
};

DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(dm_writecache_throttle,
                                            "A percentage of time allocated for data copying");

static void wc_lock(struct dm_writecache *wc)
{
        mutex_lock(&wc->lock);
}

static void wc_unlock(struct dm_writecache *wc)
{
        mutex_unlock(&wc->lock);
}

#ifdef DM_WRITECACHE_HAS_PMEM
static int persistent_memory_claim(struct dm_writecache *wc)
{
        int r;
        loff_t s;
        long p, da;
        pfn_t pfn;
        int id;
        struct page **pages;

        wc->memory_vmapped = false;

        if (!wc->ssd_dev->dax_dev) {
                r = -EOPNOTSUPP;
                goto err1;
        }
        s = wc->memory_map_size;
        p = s >> PAGE_SHIFT;
        if (!p) {
                r = -EINVAL;
                goto err1;
        }
        if (p != s >> PAGE_SHIFT) {
                r = -EOVERFLOW;
                goto err1;
        }

        id = dax_read_lock();

        da = dax_direct_access(wc->ssd_dev->dax_dev, 0, p, &wc->memory_map, &pfn);
        if (da < 0) {
                wc->memory_map = NULL;
                r = da;
                goto err2;
        }
        if (!pfn_t_has_page(pfn)) {
                wc->memory_map = NULL;
                r = -EOPNOTSUPP;
                goto err2;
        }
        if (da != p) {
                long i;
                wc->memory_map = NULL;
                pages = kvmalloc_array(p, sizeof(struct page *), GFP_KERNEL);
                if (!pages) {
                        r = -ENOMEM;
                        goto err2;
                }
                i = 0;
                do {
                        long daa;
                        daa = dax_direct_access(wc->ssd_dev->dax_dev, i, p - i,
                                                NULL, &pfn);
                        if (daa <= 0) {
                                r = daa ? daa : -EINVAL;
                                goto err3;
                        }
                        if (!pfn_t_has_page(pfn)) {
                                r = -EOPNOTSUPP;
                                goto err3;
                        }
                        while (daa-- && i < p) {
                                pages[i++] = pfn_t_to_page(pfn);
                                pfn.val++;
                        }
                } while (i < p);
                wc->memory_map = vmap(pages, p, VM_MAP, PAGE_KERNEL);
                if (!wc->memory_map) {
                        r = -ENOMEM;
                        goto err3;
                }
                kvfree(pages);
                wc->memory_vmapped = true;
        }

        dax_read_unlock(id);

        wc->memory_map += (size_t)wc->start_sector << SECTOR_SHIFT;
        wc->memory_map_size -= (size_t)wc->start_sector << SECTOR_SHIFT;

        return 0;
err3:
        kvfree(pages);
err2:
        dax_read_unlock(id);
err1:
        return r;
}
#else
static int persistent_memory_claim(struct dm_writecache *wc)
{
        BUG();
}
#endif

static void persistent_memory_release(struct dm_writecache *wc)
{
        if (wc->memory_vmapped)
                vunmap(wc->memory_map - ((size_t)wc->start_sector << SECTOR_SHIFT));
}

static struct page *persistent_memory_page(void *addr)
{
        if (is_vmalloc_addr(addr))
                return vmalloc_to_page(addr);
        else
                return virt_to_page(addr);
}

static unsigned persistent_memory_page_offset(void *addr)
{
        return (unsigned long)addr & (PAGE_SIZE - 1);
}

static void persistent_memory_flush_cache(void *ptr, size_t size)
{
        if (is_vmalloc_addr(ptr))
                flush_kernel_vmap_range(ptr, size);
}

static void persistent_memory_invalidate_cache(void *ptr, size_t size)
{
        if (is_vmalloc_addr(ptr))
                invalidate_kernel_vmap_range(ptr, size);
}

static struct wc_memory_superblock *sb(struct dm_writecache *wc)
{
        return wc->memory_map;
}

static struct wc_memory_entry *memory_entry(struct dm_writecache *wc, struct wc_entry *e)
{
        return &sb(wc)->entries[e->index];
}

static void *memory_data(struct dm_writecache *wc, struct wc_entry *e)
{
        return (char *)wc->block_start + (e->index << wc->block_size_bits);
}

static sector_t cache_sector(struct dm_writecache *wc, struct wc_entry *e)
{
        return wc->start_sector + wc->metadata_sectors +
                ((sector_t)e->index << (wc->block_size_bits - SECTOR_SHIFT));
}

static uint64_t read_original_sector(struct dm_writecache *wc, struct wc_entry *e)
{
#ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
        return e->original_sector;
#else
        return le64_to_cpu(memory_entry(wc, e)->original_sector);
#endif
}

static uint64_t read_seq_count(struct dm_writecache *wc, struct wc_entry *e)
{
#ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
        return e->seq_count;
#else
        return le64_to_cpu(memory_entry(wc, e)->seq_count);
#endif
}

static void clear_seq_count(struct dm_writecache *wc, struct wc_entry *e)
{
#ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
        e->seq_count = -1;
#endif
        pmem_assign(memory_entry(wc, e)->seq_count, cpu_to_le64(-1));
}

static void write_original_sector_seq_count(struct dm_writecache *wc, struct wc_entry *e,
                                            uint64_t original_sector, uint64_t seq_count)
{
        struct wc_memory_entry me;
#ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
        e->original_sector = original_sector;
        e->seq_count = seq_count;
#endif
        me.original_sector = cpu_to_le64(original_sector);
        me.seq_count = cpu_to_le64(seq_count);
        pmem_assign(*memory_entry(wc, e), me);
}

#define writecache_error(wc, err, msg, arg...)                          \
do {                                                                    \
        if (!cmpxchg(&(wc)->error, 0, err))                             \
                DMERR(msg, ##arg);                                      \
        wake_up(&(wc)->freelist_wait);                                  \
} while (0)

#define writecache_has_error(wc)        (unlikely(READ_ONCE((wc)->error)))

static void writecache_flush_all_metadata(struct dm_writecache *wc)
{
        if (!WC_MODE_PMEM(wc))
                memset(wc->dirty_bitmap, -1, wc->dirty_bitmap_size);
}

static void writecache_flush_region(struct dm_writecache *wc, void *ptr, size_t size)
{
        if (!WC_MODE_PMEM(wc))
                __set_bit(((char *)ptr - (char *)wc->memory_map) / BITMAP_GRANULARITY,
                          wc->dirty_bitmap);
}

static void writecache_disk_flush(struct dm_writecache *wc, struct dm_dev *dev);

struct io_notify {
        struct dm_writecache *wc;
        struct completion c;
        atomic_t count;
};

static void writecache_notify_io(unsigned long error, void *context)
{
        struct io_notify *endio = context;

        if (unlikely(error != 0))
                writecache_error(endio->wc, -EIO, "error writing metadata");
        BUG_ON(atomic_read(&endio->count) <= 0);
        if (atomic_dec_and_test(&endio->count))
                complete(&endio->c);
}

static void ssd_commit_flushed(struct dm_writecache *wc)
{
        struct dm_io_region region;
        struct dm_io_request req;
        struct io_notify endio = {
                wc,
                COMPLETION_INITIALIZER_ONSTACK(endio.c),
                ATOMIC_INIT(1),
        };
        unsigned bitmap_bits = wc->dirty_bitmap_size * 8;
        unsigned i = 0;

        while (1) {
                unsigned j;
                i = find_next_bit(wc->dirty_bitmap, bitmap_bits, i);
                if (unlikely(i == bitmap_bits))
                        break;
                j = find_next_zero_bit(wc->dirty_bitmap, bitmap_bits, i);

                region.bdev = wc->ssd_dev->bdev;
                region.sector = (sector_t)i * (BITMAP_GRANULARITY >> SECTOR_SHIFT);
                region.count = (sector_t)(j - i) * (BITMAP_GRANULARITY >> SECTOR_SHIFT);

                if (unlikely(region.sector >= wc->metadata_sectors))
                        break;
                if (unlikely(region.sector + region.count > wc->metadata_sectors))
                        region.count = wc->metadata_sectors - region.sector;

                region.sector += wc->start_sector;
                atomic_inc(&endio.count);
                req.bi_op = REQ_OP_WRITE;
                req.bi_op_flags = REQ_SYNC;
                req.mem.type = DM_IO_VMA;
                req.mem.ptr.vma = (char *)wc->memory_map + (size_t)i * BITMAP_GRANULARITY;
                req.client = wc->dm_io;
                req.notify.fn = writecache_notify_io;
                req.notify.context = &endio;

                /* writing via async dm-io (implied by notify.fn above) won't return an error */
                (void) dm_io(&req, 1, &region, NULL);
                i = j;
        }

        writecache_notify_io(0, &endio);
        wait_for_completion_io(&endio.c);

        writecache_disk_flush(wc, wc->ssd_dev);

        memset(wc->dirty_bitmap, 0, wc->dirty_bitmap_size);
}

static void writecache_commit_flushed(struct dm_writecache *wc)
{
        if (WC_MODE_PMEM(wc))
                wmb();
        else
                ssd_commit_flushed(wc);
}

static void writecache_disk_flush(struct dm_writecache *wc, struct dm_dev *dev)
{
        int r;
        struct dm_io_region region;
        struct dm_io_request req;

        region.bdev = dev->bdev;
        region.sector = 0;
        region.count = 0;
        req.bi_op = REQ_OP_WRITE;
        req.bi_op_flags = REQ_PREFLUSH;
        req.mem.type = DM_IO_KMEM;
        req.mem.ptr.addr = NULL;
        req.client = wc->dm_io;
        req.notify.fn = NULL;

        r = dm_io(&req, 1, &region, NULL);
        if (unlikely(r))
                writecache_error(wc, r, "error flushing metadata: %d", r);
}

static void writecache_wait_for_ios(struct dm_writecache *wc, int direction)
{
        wait_event(wc->bio_in_progress_wait[direction],
                   !atomic_read(&wc->bio_in_progress[direction]));
}

#define WFE_RETURN_FOLLOWING    1
#define WFE_LOWEST_SEQ          2

static struct wc_entry *writecache_find_entry(struct dm_writecache *wc,
                                              uint64_t block, int flags)
{
        struct wc_entry *e;
        struct rb_node *node = wc->tree.rb_node;

        if (unlikely(!node))
                return NULL;

        while (1) {
                e = container_of(node, struct wc_entry, rb_node);
                if (read_original_sector(wc, e) == block)
                        break;

                node = (read_original_sector(wc, e) >= block ?
                        e->rb_node.rb_left : e->rb_node.rb_right);
                if (unlikely(!node)) {
                        if (!(flags & WFE_RETURN_FOLLOWING))
                                return NULL;
                        if (read_original_sector(wc, e) >= block) {
                                return e;
                        } else {
                                node = rb_next(&e->rb_node);
                                if (unlikely(!node))
                                        return NULL;
                                e = container_of(node, struct wc_entry, rb_node);
                                return e;
                        }
                }
        }

        while (1) {
                struct wc_entry *e2;
                if (flags & WFE_LOWEST_SEQ)
                        node = rb_prev(&e->rb_node);
                else
                        node = rb_next(&e->rb_node);
                if (unlikely(!node))
                        return e;
                e2 = container_of(node, struct wc_entry, rb_node);
                if (read_original_sector(wc, e2) != block)
                        return e;
                e = e2;
        }
}

static void writecache_insert_entry(struct dm_writecache *wc, struct wc_entry *ins)
{
        struct wc_entry *e;
        struct rb_node **node = &wc->tree.rb_node, *parent = NULL;

        while (*node) {
                e = container_of(*node, struct wc_entry, rb_node);
                parent = &e->rb_node;
                if (read_original_sector(wc, e) > read_original_sector(wc, ins))
                        node = &parent->rb_left;
                else
                        node = &parent->rb_right;
        }
        rb_link_node(&ins->rb_node, parent, node);
        rb_insert_color(&ins->rb_node, &wc->tree);
        list_add(&ins->lru, &wc->lru);
}

static void writecache_unlink(struct dm_writecache *wc, struct wc_entry *e)
{
        list_del(&e->lru);
        rb_erase(&e->rb_node, &wc->tree);
}

static void writecache_add_to_freelist(struct dm_writecache *wc, struct wc_entry *e)
{
        if (WC_MODE_SORT_FREELIST(wc)) {
                struct rb_node **node = &wc->freetree.rb_node, *parent = NULL;
                if (unlikely(!*node))
                        wc->current_free = e;
                while (*node) {
                        parent = *node;
                        if (&e->rb_node < *node)
                                node = &parent->rb_left;
                        else
                                node = &parent->rb_right;
                }
                rb_link_node(&e->rb_node, parent, node);
                rb_insert_color(&e->rb_node, &wc->freetree);
        } else {
                list_add_tail(&e->lru, &wc->freelist);
        }
        wc->freelist_size++;
}

static struct wc_entry *writecache_pop_from_freelist(struct dm_writecache *wc)
{
        struct wc_entry *e;

        if (WC_MODE_SORT_FREELIST(wc)) {
                struct rb_node *next;
                if (unlikely(!wc->current_free))
                        return NULL;
                e = wc->current_free;
                next = rb_next(&e->rb_node);
                rb_erase(&e->rb_node, &wc->freetree);
                if (unlikely(!next))
                        next = rb_first(&wc->freetree);
                wc->current_free = next ? container_of(next, struct wc_entry, rb_node) : NULL;
        } else {
                if (unlikely(list_empty(&wc->freelist)))
                        return NULL;
                e = container_of(wc->freelist.next, struct wc_entry, lru);
                list_del(&e->lru);
        }
        wc->freelist_size--;
        if (unlikely(wc->freelist_size + wc->writeback_size <= wc->freelist_high_watermark))
                queue_work(wc->writeback_wq, &wc->writeback_work);

        return e;
}

static void writecache_free_entry(struct dm_writecache *wc, struct wc_entry *e)
{
        writecache_unlink(wc, e);
        writecache_add_to_freelist(wc, e);
        clear_seq_count(wc, e);
        writecache_flush_region(wc, memory_entry(wc, e), sizeof(struct wc_memory_entry));
        if (unlikely(waitqueue_active(&wc->freelist_wait)))
                wake_up(&wc->freelist_wait);
}

static void writecache_wait_on_freelist(struct dm_writecache *wc)
{
        DEFINE_WAIT(wait);

        prepare_to_wait(&wc->freelist_wait, &wait, TASK_UNINTERRUPTIBLE);
        wc_unlock(wc);
        io_schedule();
        finish_wait(&wc->freelist_wait, &wait);
        wc_lock(wc);
}

static void writecache_poison_lists(struct dm_writecache *wc)
{
        /*
         * Catch incorrect access to these values while the device is suspended.
         */
        memset(&wc->tree, -1, sizeof wc->tree);
        wc->lru.next = LIST_POISON1;
        wc->lru.prev = LIST_POISON2;
        wc->freelist.next = LIST_POISON1;
        wc->freelist.prev = LIST_POISON2;
}

static void writecache_flush_entry(struct dm_writecache *wc, struct wc_entry *e)
{
        writecache_flush_region(wc, memory_entry(wc, e), sizeof(struct wc_memory_entry));
        if (WC_MODE_PMEM(wc))
                writecache_flush_region(wc, memory_data(wc, e), wc->block_size);
}

static bool writecache_entry_is_committed(struct dm_writecache *wc, struct wc_entry *e)
{
        return read_seq_count(wc, e) < wc->seq_count;
}

static void writecache_flush(struct dm_writecache *wc)
{
        struct wc_entry *e, *e2;
        bool need_flush_after_free;

        wc->uncommitted_blocks = 0;
        del_timer(&wc->autocommit_timer);

        if (list_empty(&wc->lru))
                return;

        e = container_of(wc->lru.next, struct wc_entry, lru);
        if (writecache_entry_is_committed(wc, e)) {
                if (wc->overwrote_committed) {
                        writecache_wait_for_ios(wc, WRITE);
                        writecache_disk_flush(wc, wc->ssd_dev);
                        wc->overwrote_committed = false;
                }
                return;
        }
        while (1) {
                writecache_flush_entry(wc, e);
                if (unlikely(e->lru.next == &wc->lru))
                        break;
                e2 = container_of(e->lru.next, struct wc_entry, lru);
                if (writecache_entry_is_committed(wc, e2))
                        break;
                e = e2;
                cond_resched();
        }
        writecache_commit_flushed(wc);

        writecache_wait_for_ios(wc, WRITE);

        wc->seq_count++;
        pmem_assign(sb(wc)->seq_count, cpu_to_le64(wc->seq_count));
        writecache_flush_region(wc, &sb(wc)->seq_count, sizeof sb(wc)->seq_count);
        writecache_commit_flushed(wc);

        wc->overwrote_committed = false;

        need_flush_after_free = false;
        while (1) {
                /* Free another committed entry with lower seq-count */
                struct rb_node *rb_node = rb_prev(&e->rb_node);

                if (rb_node) {
                        e2 = container_of(rb_node, struct wc_entry, rb_node);
                        if (read_original_sector(wc, e2) == read_original_sector(wc, e) &&
                            likely(!e2->write_in_progress)) {
                                writecache_free_entry(wc, e2);
                                need_flush_after_free = true;
                        }
                }
                if (unlikely(e->lru.prev == &wc->lru))
                        break;
                e = container_of(e->lru.prev, struct wc_entry, lru);
                cond_resched();
        }

        if (need_flush_after_free)
                writecache_commit_flushed(wc);
}

static void writecache_flush_work(struct work_struct *work)
{
        struct dm_writecache *wc = container_of(work, struct dm_writecache, flush_work);

        wc_lock(wc);
        writecache_flush(wc);
        wc_unlock(wc);
}

static void writecache_autocommit_timer(struct timer_list *t)
{
        struct dm_writecache *wc = from_timer(wc, t, autocommit_timer);
        if (!writecache_has_error(wc))
                queue_work(wc->writeback_wq, &wc->flush_work);
}

static void writecache_schedule_autocommit(struct dm_writecache *wc)
{
        if (!timer_pending(&wc->autocommit_timer))
                mod_timer(&wc->autocommit_timer, jiffies + wc->autocommit_jiffies);
}

static void writecache_discard(struct dm_writecache *wc, sector_t start, sector_t end)
{
        struct wc_entry *e;
        bool discarded_something = false;

        e = writecache_find_entry(wc, start, WFE_RETURN_FOLLOWING | WFE_LOWEST_SEQ);
        if (unlikely(!e))
                return;

        while (read_original_sector(wc, e) < end) {
                struct rb_node *node = rb_next(&e->rb_node);

                if (likely(!e->write_in_progress)) {
                        if (!discarded_something) {
                                writecache_wait_for_ios(wc, READ);
                                writecache_wait_for_ios(wc, WRITE);
                                discarded_something = true;
                        }
                        writecache_free_entry(wc, e);
                }

                if (unlikely(!node))
                        break;

                e = container_of(node, struct wc_entry, rb_node);
        }

        if (discarded_something)
                writecache_commit_flushed(wc);
}

static bool writecache_wait_for_writeback(struct dm_writecache *wc)
{
        if (wc->writeback_size) {
                writecache_wait_on_freelist(wc);
                return true;
        }
        return false;
}

static void writecache_suspend(struct dm_target *ti)
{
        struct dm_writecache *wc = ti->private;
        bool flush_on_suspend;

        del_timer_sync(&wc->autocommit_timer);

        wc_lock(wc);
        writecache_flush(wc);
        flush_on_suspend = wc->flush_on_suspend;
        if (flush_on_suspend) {
                wc->flush_on_suspend = false;
                wc->writeback_all++;
                queue_work(wc->writeback_wq, &wc->writeback_work);
        }
        wc_unlock(wc);

        flush_workqueue(wc->writeback_wq);

        wc_lock(wc);
        if (flush_on_suspend)
                wc->writeback_all--;
        while (writecache_wait_for_writeback(wc));

        if (WC_MODE_PMEM(wc))
                persistent_memory_flush_cache(wc->memory_map, wc->memory_map_size);

        writecache_poison_lists(wc);

        wc_unlock(wc);
}

static int writecache_alloc_entries(struct dm_writecache *wc)
{
        size_t b;

        if (wc->entries)
                return 0;
        wc->entries = vmalloc(array_size(sizeof(struct wc_entry), wc->n_blocks));
        if (!wc->entries)
                return -ENOMEM;
        for (b = 0; b < wc->n_blocks; b++) {
                struct wc_entry *e = &wc->entries[b];
                e->index = b;
                e->write_in_progress = false;
        }

        return 0;
}

static void writecache_resume(struct dm_target *ti)
{
        struct dm_writecache *wc = ti->private;
        size_t b;
        bool need_flush = false;
        __le64 sb_seq_count;
        int r;

        wc_lock(wc);

        if (WC_MODE_PMEM(wc))
                persistent_memory_invalidate_cache(wc->memory_map, wc->memory_map_size);

        wc->tree = RB_ROOT;
        INIT_LIST_HEAD(&wc->lru);
        if (WC_MODE_SORT_FREELIST(wc)) {
                wc->freetree = RB_ROOT;
                wc->current_free = NULL;
        } else {
                INIT_LIST_HEAD(&wc->freelist);
        }
        wc->freelist_size = 0;

        r = memcpy_mcsafe(&sb_seq_count, &sb(wc)->seq_count, sizeof(uint64_t));
        if (r) {
                writecache_error(wc, r, "hardware memory error when reading superblock: %d", r);
                sb_seq_count = cpu_to_le64(0);
        }
        wc->seq_count = le64_to_cpu(sb_seq_count);

#ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
        for (b = 0; b < wc->n_blocks; b++) {
                struct wc_entry *e = &wc->entries[b];
                struct wc_memory_entry wme;
                if (writecache_has_error(wc)) {
                        e->original_sector = -1;
                        e->seq_count = -1;
                        continue;
                }
                r = memcpy_mcsafe(&wme, memory_entry(wc, e), sizeof(struct wc_memory_entry));
                if (r) {
                        writecache_error(wc, r, "hardware memory error when reading metadata entry %lu: %d",
                                         (unsigned long)b, r);
                        e->original_sector = -1;
                        e->seq_count = -1;
                } else {
                        e->original_sector = le64_to_cpu(wme.original_sector);
                        e->seq_count = le64_to_cpu(wme.seq_count);
                }
        }
#endif
        for (b = 0; b < wc->n_blocks; b++) {
                struct wc_entry *e = &wc->entries[b];
                if (!writecache_entry_is_committed(wc, e)) {
                        if (read_seq_count(wc, e) != -1) {
erase_this:
                                clear_seq_count(wc, e);
                                need_flush = true;
                        }
                        writecache_add_to_freelist(wc, e);
                } else {
                        struct wc_entry *old;

                        old = writecache_find_entry(wc, read_original_sector(wc, e), 0);
                        if (!old) {
                                writecache_insert_entry(wc, e);
                        } else {
                                if (read_seq_count(wc, old) == read_seq_count(wc, e)) {
                                        writecache_error(wc, -EINVAL,
                                                 "two identical entries, position %llu, sector %llu, sequence %llu",
                                                 (unsigned long long)b, (unsigned long long)read_original_sector(wc, e),
                                                 (unsigned long long)read_seq_count(wc, e));
                                }
                                if (read_seq_count(wc, old) > read_seq_count(wc, e)) {
                                        goto erase_this;
                                } else {
                                        writecache_free_entry(wc, old);
                                        writecache_insert_entry(wc, e);
                                        need_flush = true;
                                }
                        }
                }
                cond_resched();
        }

        if (need_flush) {
                writecache_flush_all_metadata(wc);
                writecache_commit_flushed(wc);
        }

        wc_unlock(wc);
}

static int process_flush_mesg(unsigned argc, char **argv, struct dm_writecache *wc)
{
        if (argc != 1)
                return -EINVAL;

        wc_lock(wc);
        if (dm_suspended(wc->ti)) {
                wc_unlock(wc);
                return -EBUSY;
        }
        if (writecache_has_error(wc)) {
                wc_unlock(wc);
                return -EIO;
        }

        writecache_flush(wc);
        wc->writeback_all++;
        queue_work(wc->writeback_wq, &wc->writeback_work);
        wc_unlock(wc);

        flush_workqueue(wc->writeback_wq);

        wc_lock(wc);
        wc->writeback_all--;
        if (writecache_has_error(wc)) {
                wc_unlock(wc);
                return -EIO;
        }
        wc_unlock(wc);

        return 0;
}

static int process_flush_on_suspend_mesg(unsigned argc, char **argv, struct dm_writecache *wc)

{
        if (argc != 1)
                return -EINVAL;

        wc_lock(wc);
        wc->flush_on_suspend = true;
        wc_unlock(wc);

        return 0;
}

static int writecache_message(struct dm_target *ti, unsigned argc, char **argv,
                              char *result, unsigned maxlen)
{
        int r = -EINVAL;
        struct dm_writecache *wc = ti->private;

        if (!strcasecmp(argv[0], "flush"))
                r = process_flush_mesg(argc, argv, wc);
        else if (!strcasecmp(argv[0], "flush_on_suspend"))
                r = process_flush_on_suspend_mesg(argc, argv, wc);
        else
                DMERR("unrecognised message received: %s", argv[0]);

        return r;
}

static void bio_copy_block(struct dm_writecache *wc, struct bio *bio, void *data)
{
        void *buf;
        unsigned long flags;
        unsigned size;
        int rw = bio_data_dir(bio);
        unsigned remaining_size = wc->block_size;

        do {
                struct bio_vec bv = bio_iter_iovec(bio, bio->bi_iter);
                buf = bvec_kmap_irq(&bv, &flags);
                size = bv.bv_len;
                if (unlikely(size > remaining_size))
                        size = remaining_size;

                if (rw == READ) {
                        int r;
                        r = memcpy_mcsafe(buf, data, size);
                        flush_dcache_page(bio_page(bio));
                        if (unlikely(r)) {
                                writecache_error(wc, r, "hardware memory error when reading data: %d", r);
                                bio->bi_status = BLK_STS_IOERR;
                        }
                } else {
                        flush_dcache_page(bio_page(bio));
                        memcpy_flushcache(data, buf, size);
                }

                bvec_kunmap_irq(buf, &flags);

                data = (char *)data + size;
                remaining_size -= size;
                bio_advance(bio, size);
        } while (unlikely(remaining_size));
}

static int writecache_flush_thread(void *data)
{
        struct dm_writecache *wc = data;

        while (1) {
                struct bio *bio;

                wc_lock(wc);
                bio = bio_list_pop(&wc->flush_list);
                if (!bio) {
                        set_current_state(TASK_INTERRUPTIBLE);
                        wc_unlock(wc);

                        if (unlikely(kthread_should_stop())) {
                                set_current_state(TASK_RUNNING);
                                break;
                        }

                        schedule();
                        continue;
                }

                if (bio_op(bio) == REQ_OP_DISCARD) {
                        writecache_discard(wc, bio->bi_iter.bi_sector,
                                           bio_end_sector(bio));
                        wc_unlock(wc);
                        bio_set_dev(bio, wc->dev->bdev);
                        generic_make_request(bio);
                } else {
                        writecache_flush(wc);
                        wc_unlock(wc);
                        if (writecache_has_error(wc))
                                bio->bi_status = BLK_STS_IOERR;
                        bio_endio(bio);
                }
        }

        return 0;
}

static void writecache_offload_bio(struct dm_writecache *wc, struct bio *bio)
{
        if (bio_list_empty(&wc->flush_list))
                wake_up_process(wc->flush_thread);
        bio_list_add(&wc->flush_list, bio);
}

static int writecache_map(struct dm_target *ti, struct bio *bio)
{
        struct wc_entry *e;
        struct dm_writecache *wc = ti->private;

        bio->bi_private = NULL;

        wc_lock(wc);

        if (unlikely(bio->bi_opf & REQ_PREFLUSH)) {
                if (writecache_has_error(wc))
                        goto unlock_error;
                if (WC_MODE_PMEM(wc)) {
                        writecache_flush(wc);
                        if (writecache_has_error(wc))
                                goto unlock_error;
                        goto unlock_submit;
                } else {
                        writecache_offload_bio(wc, bio);
                        goto unlock_return;
                }
        }

        bio->bi_iter.bi_sector = dm_target_offset(ti, bio->bi_iter.bi_sector);

        if (unlikely((((unsigned)bio->bi_iter.bi_sector | bio_sectors(bio)) &
                                (wc->block_size / 512 - 1)) != 0)) {
                DMERR("I/O is not aligned, sector %llu, size %u, block size %u",
                      (unsigned long long)bio->bi_iter.bi_sector,
                      bio->bi_iter.bi_size, wc->block_size);
                goto unlock_error;
        }

        if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
                if (writecache_has_error(wc))
                        goto unlock_error;
                if (WC_MODE_PMEM(wc)) {
                        writecache_discard(wc, bio->bi_iter.bi_sector, bio_end_sector(bio));
                        goto unlock_remap_origin;
                } else {
                        writecache_offload_bio(wc, bio);
                        goto unlock_return;
                }
        }

        if (bio_data_dir(bio) == READ) {
read_next_block:
                e = writecache_find_entry(wc, bio->bi_iter.bi_sector, WFE_RETURN_FOLLOWING);
                if (e && read_original_sector(wc, e) == bio->bi_iter.bi_sector) {
                        if (WC_MODE_PMEM(wc)) {
                                bio_copy_block(wc, bio, memory_data(wc, e));
                                if (bio->bi_iter.bi_size)
                                        goto read_next_block;
                                goto unlock_submit;
                        } else {
                                dm_accept_partial_bio(bio, wc->block_size >> SECTOR_SHIFT);
                                bio_set_dev(bio, wc->ssd_dev->bdev);
                                bio->bi_iter.bi_sector = cache_sector(wc, e);
                                if (!writecache_entry_is_committed(wc, e))
                                        writecache_wait_for_ios(wc, WRITE);
                                goto unlock_remap;
                        }
                } else {
                        if (e) {
                                sector_t next_boundary =
                                        read_original_sector(wc, e) - bio->bi_iter.bi_sector;
                                if (next_boundary < bio->bi_iter.bi_size >> SECTOR_SHIFT) {
                                        dm_accept_partial_bio(bio, next_boundary);
                                }
                        }
                        goto unlock_remap_origin;
                }
        } else {
                do {
                        if (writecache_has_error(wc))
                                goto unlock_error;
                        e = writecache_find_entry(wc, bio->bi_iter.bi_sector, 0);
                        if (e) {
                                if (!writecache_entry_is_committed(wc, e))
                                        goto bio_copy;
                                if (!WC_MODE_PMEM(wc) && !e->write_in_progress) {
                                        wc->overwrote_committed = true;
                                        goto bio_copy;
                                }
                        }
                        e = writecache_pop_from_freelist(wc);
                        if (unlikely(!e)) {
                                writecache_wait_on_freelist(wc);
                                continue;
                        }
                        write_original_sector_seq_count(wc, e, bio->bi_iter.bi_sector, wc->seq_count);
                        writecache_insert_entry(wc, e);
                        wc->uncommitted_blocks++;
bio_copy:
                        if (WC_MODE_PMEM(wc)) {
                                bio_copy_block(wc, bio, memory_data(wc, e));
                        } else {
                                dm_accept_partial_bio(bio, wc->block_size >> SECTOR_SHIFT);
                                bio_set_dev(bio, wc->ssd_dev->bdev);
                                bio->bi_iter.bi_sector = cache_sector(wc, e);
                                if (unlikely(wc->uncommitted_blocks >= wc->autocommit_blocks)) {
                                        wc->uncommitted_blocks = 0;
                                        queue_work(wc->writeback_wq, &wc->flush_work);
                                } else {
                                        writecache_schedule_autocommit(wc);
                                }
                                goto unlock_remap;
                        }
                } while (bio->bi_iter.bi_size);

                if (unlikely(wc->uncommitted_blocks >= wc->autocommit_blocks))
                        writecache_flush(wc);
                else
                        writecache_schedule_autocommit(wc);
                goto unlock_submit;
        }

unlock_remap_origin:
        bio_set_dev(bio, wc->dev->bdev);
        wc_unlock(wc);
        return DM_MAPIO_REMAPPED;

unlock_remap:
        /* make sure that writecache_end_io decrements bio_in_progress: */
        bio->bi_private = (void *)1;
        atomic_inc(&wc->bio_in_progress[bio_data_dir(bio)]);
        wc_unlock(wc);
        return DM_MAPIO_REMAPPED;

unlock_submit:
        wc_unlock(wc);
        bio_endio(bio);
        return DM_MAPIO_SUBMITTED;

unlock_return:
        wc_unlock(wc);
        return DM_MAPIO_SUBMITTED;

unlock_error:
        wc_unlock(wc);
        bio_io_error(bio);
        return DM_MAPIO_SUBMITTED;
}

static int writecache_end_io(struct dm_target *ti, struct bio *bio, blk_status_t *status)
{
        struct dm_writecache *wc = ti->private;

        if (bio->bi_private != NULL) {
                int dir = bio_data_dir(bio);
                if (atomic_dec_and_test(&wc->bio_in_progress[dir]))
                        if (unlikely(waitqueue_active(&wc->bio_in_progress_wait[dir])))
                                wake_up(&wc->bio_in_progress_wait[dir]);
        }
        return 0;
}

static int writecache_iterate_devices(struct dm_target *ti,
                                      iterate_devices_callout_fn fn, void *data)
{
        struct dm_writecache *wc = ti->private;

        return fn(ti, wc->dev, 0, ti->len, data);
}

static void writecache_io_hints(struct dm_target *ti, struct queue_limits *limits)
{
        struct dm_writecache *wc = ti->private;

        if (limits->logical_block_size < wc->block_size)
                limits->logical_block_size = wc->block_size;

        if (limits->physical_block_size < wc->block_size)
                limits->physical_block_size = wc->block_size;

        if (limits->io_min < wc->block_size)
                limits->io_min = wc->block_size;
}


static void writecache_writeback_endio(struct bio *bio)
{
        struct writeback_struct *wb = container_of(bio, struct writeback_struct, bio);
        struct dm_writecache *wc = wb->wc;
        unsigned long flags;

        raw_spin_lock_irqsave(&wc->endio_list_lock, flags);
        if (unlikely(list_empty(&wc->endio_list)))
                wake_up_process(wc->endio_thread);
        list_add_tail(&wb->endio_entry, &wc->endio_list);
        raw_spin_unlock_irqrestore(&wc->endio_list_lock, flags);
}

static void writecache_copy_endio(int read_err, unsigned long write_err, void *ptr)
{
        struct copy_struct *c = ptr;
        struct dm_writecache *wc = c->wc;

        c->error = likely(!(read_err | write_err)) ? 0 : -EIO;

        raw_spin_lock_irq(&wc->endio_list_lock);
        if (unlikely(list_empty(&wc->endio_list)))
                wake_up_process(wc->endio_thread);
        list_add_tail(&c->endio_entry, &wc->endio_list);
        raw_spin_unlock_irq(&wc->endio_list_lock);
}

static void __writecache_endio_pmem(struct dm_writecache *wc, struct list_head *list)
{
        unsigned i;
        struct writeback_struct *wb;
        struct wc_entry *e;
        unsigned long n_walked = 0;

        do {
                wb = list_entry(list->next, struct writeback_struct, endio_entry);
                list_del(&wb->endio_entry);

                if (unlikely(wb->bio.bi_status != BLK_STS_OK))
                        writecache_error(wc, blk_status_to_errno(wb->bio.bi_status),
                                        "write error %d", wb->bio.bi_status);
                i = 0;
                do {
                        e = wb->wc_list[i];
                        BUG_ON(!e->write_in_progress);
                        e->write_in_progress = false;
                        INIT_LIST_HEAD(&e->lru);
                        if (!writecache_has_error(wc))
                                writecache_free_entry(wc, e);
                        BUG_ON(!wc->writeback_size);
                        wc->writeback_size--;
                        n_walked++;
                        if (unlikely(n_walked >= ENDIO_LATENCY)) {
                                writecache_commit_flushed(wc);
                                wc_unlock(wc);
                                wc_lock(wc);
                                n_walked = 0;
                        }
                } while (++i < wb->wc_list_n);

                if (wb->wc_list != wb->wc_list_inline)
                        kfree(wb->wc_list);
                bio_put(&wb->bio);
        } while (!list_empty(list));
}

static void __writecache_endio_ssd(struct dm_writecache *wc, struct list_head *list)
{
        struct copy_struct *c;
        struct wc_entry *e;

        do {
                c = list_entry(list->next, struct copy_struct, endio_entry);
                list_del(&c->endio_entry);

                if (unlikely(c->error))
                        writecache_error(wc, c->error, "copy error");

                e = c->e;
                do {
                        BUG_ON(!e->write_in_progress);
                        e->write_in_progress = false;
                        INIT_LIST_HEAD(&e->lru);
                        if (!writecache_has_error(wc))
                                writecache_free_entry(wc, e);

                        BUG_ON(!wc->writeback_size);
                        wc->writeback_size--;
                        e++;
                } while (--c->n_entries);
                mempool_free(c, &wc->copy_pool);
        } while (!list_empty(list));
}

static int writecache_endio_thread(void *data)
{
        struct dm_writecache *wc = data;

        while (1) {
                struct list_head list;

                raw_spin_lock_irq(&wc->endio_list_lock);
                if (!list_empty(&wc->endio_list))
                        goto pop_from_list;
                set_current_state(TASK_INTERRUPTIBLE);
                raw_spin_unlock_irq(&wc->endio_list_lock);

                if (unlikely(kthread_should_stop())) {
                        set_current_state(TASK_RUNNING);
                        break;
                }

                schedule();

                continue;

pop_from_list:
                list = wc->endio_list;
                list.next->prev = list.prev->next = &list;
                INIT_LIST_HEAD(&wc->endio_list);
                raw_spin_unlock_irq(&wc->endio_list_lock);

                if (!WC_MODE_FUA(wc))
                        writecache_disk_flush(wc, wc->dev);

                wc_lock(wc);

                if (WC_MODE_PMEM(wc)) {
                        __writecache_endio_pmem(wc, &list);
                } else {
                        __writecache_endio_ssd(wc, &list);
                        writecache_wait_for_ios(wc, READ);
                }

                writecache_commit_flushed(wc);

                wc_unlock(wc);
        }

        return 0;
}

static bool wc_add_block(struct writeback_struct *wb, struct wc_entry *e, gfp_t gfp)
{
        struct dm_writecache *wc = wb->wc;
        unsigned block_size = wc->block_size;
        void *address = memory_data(wc, e);

        persistent_memory_flush_cache(address, block_size);
        return bio_add_page(&wb->bio, persistent_memory_page(address),
                            block_size, persistent_memory_page_offset(address)) != 0;
}

struct writeback_list {
        struct list_head list;
        size_t size;
};

static void __writeback_throttle(struct dm_writecache *wc, struct writeback_list *wbl)
{
        if (unlikely(wc->max_writeback_jobs)) {
                if (READ_ONCE(wc->writeback_size) - wbl->size >= wc->max_writeback_jobs) {
                        wc_lock(wc);
                        while (wc->writeback_size - wbl->size >= wc->max_writeback_jobs)
                                writecache_wait_on_freelist(wc);
                        wc_unlock(wc);
                }
        }
        cond_resched();
}

static void __writecache_writeback_pmem(struct dm_writecache *wc, struct writeback_list *wbl)
{
        struct wc_entry *e, *f;
        struct bio *bio;
        struct writeback_struct *wb;
        unsigned max_pages;

        while (wbl->size) {
                wbl->size--;
                e = container_of(wbl->list.prev, struct wc_entry, lru);
                list_del(&e->lru);

                max_pages = e->wc_list_contiguous;

                bio = bio_alloc_bioset(GFP_NOIO, max_pages, &wc->bio_set);
                wb = container_of(bio, struct writeback_struct, bio);
                wb->wc = wc;
                bio->bi_end_io = writecache_writeback_endio;
                bio_set_dev(bio, wc->dev->bdev);
                bio->bi_iter.bi_sector = read_original_sector(wc, e);
                if (max_pages <= WB_LIST_INLINE ||
                    unlikely(!(wb->wc_list = kmalloc_array(max_pages, sizeof(struct wc_entry *),
                                                           GFP_NOIO | __GFP_NORETRY |
                                                           __GFP_NOMEMALLOC | __GFP_NOWARN)))) {
                        wb->wc_list = wb->wc_list_inline;
                        max_pages = WB_LIST_INLINE;
                }

                BUG_ON(!wc_add_block(wb, e, GFP_NOIO));

                wb->wc_list[0] = e;
                wb->wc_list_n = 1;

                while (wbl->size && wb->wc_list_n < max_pages) {
                        f = container_of(wbl->list.prev, struct wc_entry, lru);
                        if (read_original_sector(wc, f) !=
                            read_original_sector(wc, e) + (wc->block_size >> SECTOR_SHIFT))
                                break;
                        if (!wc_add_block(wb, f, GFP_NOWAIT | __GFP_NOWARN))
                                break;
                        wbl->size--;
                        list_del(&f->lru);
                        wb->wc_list[wb->wc_list_n++] = f;
                        e = f;
                }
                bio_set_op_attrs(bio, REQ_OP_WRITE, WC_MODE_FUA(wc) * REQ_FUA);
                if (writecache_has_error(wc)) {
                        bio->bi_status = BLK_STS_IOERR;
                        bio_endio(bio);
                } else {
                        submit_bio(bio);
                }

                __writeback_throttle(wc, wbl);
        }
}

static void __writecache_writeback_ssd(struct dm_writecache *wc, struct writeback_list *wbl)
{
        struct wc_entry *e, *f;
        struct dm_io_region from, to;
        struct copy_struct *c;

        while (wbl->size) {
                unsigned n_sectors;

                wbl->size--;
                e = container_of(wbl->list.prev, struct wc_entry, lru);
                list_del(&e->lru);

                n_sectors = e->wc_list_contiguous << (wc->block_size_bits - SECTOR_SHIFT);

                from.bdev = wc->ssd_dev->bdev;
                from.sector = cache_sector(wc, e);
                from.count = n_sectors;
                to.bdev = wc->dev->bdev;
                to.sector = read_original_sector(wc, e);
                to.count = n_sectors;

                c = mempool_alloc(&wc->copy_pool, GFP_NOIO);
                c->wc = wc;
                c->e = e;
                c->n_entries = e->wc_list_contiguous;

                while ((n_sectors -= wc->block_size >> SECTOR_SHIFT)) {
                        wbl->size--;
                        f = container_of(wbl->list.prev, struct wc_entry, lru);
                        BUG_ON(f != e + 1);
                        list_del(&f->lru);
                        e = f;
                }

                dm_kcopyd_copy(wc->dm_kcopyd, &from, 1, &to, 0, writecache_copy_endio, c);

                __writeback_throttle(wc, wbl);
        }
}

static void writecache_writeback(struct work_struct *work)
{
        struct dm_writecache *wc = container_of(work, struct dm_writecache, writeback_work);
        struct blk_plug plug;
        struct wc_entry *e, *f, *g;
        struct rb_node *node, *next_node;
        struct list_head skipped;
        struct writeback_list wbl;
        unsigned long n_walked;

        wc_lock(wc);
restart:
        if (writecache_has_error(wc)) {
                wc_unlock(wc);
                return;
        }

        if (unlikely(wc->writeback_all)) {
                if (writecache_wait_for_writeback(wc))
                        goto restart;
        }

        if (wc->overwrote_committed) {
                writecache_wait_for_ios(wc, WRITE);
        }

        n_walked = 0;
        INIT_LIST_HEAD(&skipped);
        INIT_LIST_HEAD(&wbl.list);
        wbl.size = 0;
        while (!list_empty(&wc->lru) &&
               (wc->writeback_all ||
                wc->freelist_size + wc->writeback_size <= wc->freelist_low_watermark)) {

                n_walked++;
                if (unlikely(n_walked > WRITEBACK_LATENCY) &&
                    likely(!wc->writeback_all) && likely(!dm_suspended(wc->ti))) {
                        queue_work(wc->writeback_wq, &wc->writeback_work);
                        break;
                }

                e = container_of(wc->lru.prev, struct wc_entry, lru);
                BUG_ON(e->write_in_progress);
                if (unlikely(!writecache_entry_is_committed(wc, e))) {
                        writecache_flush(wc);
                }
                node = rb_prev(&e->rb_node);
                if (node) {
                        f = container_of(node, struct wc_entry, rb_node);
                        if (unlikely(read_original_sector(wc, f) ==
                                     read_original_sector(wc, e))) {
                                BUG_ON(!f->write_in_progress);
                                list_del(&e->lru);
                                list_add(&e->lru, &skipped);
                                cond_resched();
                                continue;
                        }
                }
                wc->writeback_size++;
                list_del(&e->lru);
                list_add(&e->lru, &wbl.list);
                wbl.size++;
                e->write_in_progress = true;
                e->wc_list_contiguous = 1;

                f = e;

                while (1) {
                        next_node = rb_next(&f->rb_node);
                        if (unlikely(!next_node))
                                break;
                        g = container_of(next_node, struct wc_entry, rb_node);
                        if (read_original_sector(wc, g) ==
                            read_original_sector(wc, f)) {
                                f = g;
                                continue;
                        }
                        if (read_original_sector(wc, g) !=
                            read_original_sector(wc, f) + (wc->block_size >> SECTOR_SHIFT))
                                break;
                        if (unlikely(g->write_in_progress))
                                break;
                        if (unlikely(!writecache_entry_is_committed(wc, g)))
                                break;

                        if (!WC_MODE_PMEM(wc)) {
                                if (g != f + 1)
                                        break;
                        }

                        n_walked++;
                        //if (unlikely(n_walked > WRITEBACK_LATENCY) && likely(!wc->writeback_all))
                        //      break;

                        wc->writeback_size++;
                        list_del(&g->lru);
                        list_add(&g->lru, &wbl.list);
                        wbl.size++;
                        g->write_in_progress = true;
                        g->wc_list_contiguous = BIO_MAX_PAGES;
                        f = g;
                        e->wc_list_contiguous++;
                        if (unlikely(e->wc_list_contiguous == BIO_MAX_PAGES))
                                break;
                }
                cond_resched();
        }

        if (!list_empty(&skipped)) {
                list_splice_tail(&skipped, &wc->lru);
                /*
                 * If we didn't do any progress, we must wait until some
                 * writeback finishes to avoid burning CPU in a loop
                 */
                if (unlikely(!wbl.size))
                        writecache_wait_for_writeback(wc);
        }

        wc_unlock(wc);

        blk_start_plug(&plug);

        if (WC_MODE_PMEM(wc))
                __writecache_writeback_pmem(wc, &wbl);
        else
                __writecache_writeback_ssd(wc, &wbl);

        blk_finish_plug(&plug);

        if (unlikely(wc->writeback_all)) {
                wc_lock(wc);
                while (writecache_wait_for_writeback(wc));
                wc_unlock(wc);
        }
}

static int calculate_memory_size(uint64_t device_size, unsigned block_size,
                                 size_t *n_blocks_p, size_t *n_metadata_blocks_p)
{
        uint64_t n_blocks, offset;
        struct wc_entry e;

        n_blocks = device_size;
        do_div(n_blocks, block_size + sizeof(struct wc_memory_entry));

        while (1) {
                if (!n_blocks)
                        return -ENOSPC;
                /* Verify the following entries[n_blocks] won't overflow */
                if (n_blocks >= ((size_t)-sizeof(struct wc_memory_superblock) /
                                 sizeof(struct wc_memory_entry)))
                        return -EFBIG;
                offset = offsetof(struct wc_memory_superblock, entries[n_blocks]);
                offset = (offset + block_size - 1) & ~(uint64_t)(block_size - 1);
                if (offset + n_blocks * block_size <= device_size)
                        break;
                n_blocks--;
        }

        /* check if the bit field overflows */
        e.index = n_blocks;
        if (e.index != n_blocks)
                return -EFBIG;

        if (n_blocks_p)
                *n_blocks_p = n_blocks;
        if (n_metadata_blocks_p)
                *n_metadata_blocks_p = offset >> __ffs(block_size);
        return 0;
}

static int init_memory(struct dm_writecache *wc)
{
        size_t b;
        int r;

        r = calculate_memory_size(wc->memory_map_size, wc->block_size, &wc->n_blocks, NULL);
        if (r)
                return r;

        r = writecache_alloc_entries(wc);
        if (r)
                return r;

        for (b = 0; b < ARRAY_SIZE(sb(wc)->padding); b++)
                pmem_assign(sb(wc)->padding[b], cpu_to_le64(0));
        pmem_assign(sb(wc)->version, cpu_to_le32(MEMORY_SUPERBLOCK_VERSION));
        pmem_assign(sb(wc)->block_size, cpu_to_le32(wc->block_size));
        pmem_assign(sb(wc)->n_blocks, cpu_to_le64(wc->n_blocks));
        pmem_assign(sb(wc)->seq_count, cpu_to_le64(0));

        for (b = 0; b < wc->n_blocks; b++)
                write_original_sector_seq_count(wc, &wc->entries[b], -1, -1);

        writecache_flush_all_metadata(wc);
        writecache_commit_flushed(wc);
        pmem_assign(sb(wc)->magic, cpu_to_le32(MEMORY_SUPERBLOCK_MAGIC));
        writecache_flush_region(wc, &sb(wc)->magic, sizeof sb(wc)->magic);
        writecache_commit_flushed(wc);

        return 0;
}

static void writecache_dtr(struct dm_target *ti)
{
        struct dm_writecache *wc = ti->private;

        if (!wc)
                return;

        if (wc->endio_thread)
                kthread_stop(wc->endio_thread);

        if (wc->flush_thread)
                kthread_stop(wc->flush_thread);

        bioset_exit(&wc->bio_set);

        mempool_exit(&wc->copy_pool);

        if (wc->writeback_wq)
                destroy_workqueue(wc->writeback_wq);

        if (wc->dev)
                dm_put_device(ti, wc->dev);

        if (wc->ssd_dev)
                dm_put_device(ti, wc->ssd_dev);

        if (wc->entries)
                vfree(wc->entries);

        if (wc->memory_map) {
                if (WC_MODE_PMEM(wc))
                        persistent_memory_release(wc);
                else
                        vfree(wc->memory_map);
        }

        if (wc->dm_kcopyd)
                dm_kcopyd_client_destroy(wc->dm_kcopyd);

        if (wc->dm_io)
                dm_io_client_destroy(wc->dm_io);

        if (wc->dirty_bitmap)
                vfree(wc->dirty_bitmap);

        kfree(wc);
}

static int writecache_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
        struct dm_writecache *wc;
        struct dm_arg_set as;
        const char *string;
        unsigned opt_params;
        size_t offset, data_size;
        int i, r;
        char dummy;
        int high_wm_percent = HIGH_WATERMARK;
        int low_wm_percent = LOW_WATERMARK;
        uint64_t x;
        struct wc_memory_superblock s;

        static struct dm_arg _args[] = {
                {0, 10, "Invalid number of feature args"},
        };

        as.argc = argc;
        as.argv = argv;

        wc = kzalloc(sizeof(struct dm_writecache), GFP_KERNEL);
        if (!wc) {
                ti->error = "Cannot allocate writecache structure";
                r = -ENOMEM;
                goto bad;
        }
        ti->private = wc;
        wc->ti = ti;

        mutex_init(&wc->lock);
        writecache_poison_lists(wc);
        init_waitqueue_head(&wc->freelist_wait);
        timer_setup(&wc->autocommit_timer, writecache_autocommit_timer, 0);

        for (i = 0; i < 2; i++) {
                atomic_set(&wc->bio_in_progress[i], 0);
                init_waitqueue_head(&wc->bio_in_progress_wait[i]);
        }

        wc->dm_io = dm_io_client_create();
        if (IS_ERR(wc->dm_io)) {
                r = PTR_ERR(wc->dm_io);
                ti->error = "Unable to allocate dm-io client";
                wc->dm_io = NULL;
                goto bad;
        }

        wc->writeback_wq = alloc_workqueue("writecache-writeback", WQ_MEM_RECLAIM, 1);
        if (!wc->writeback_wq) {
                r = -ENOMEM;
                ti->error = "Could not allocate writeback workqueue";
                goto bad;
        }
        INIT_WORK(&wc->writeback_work, writecache_writeback);
        INIT_WORK(&wc->flush_work, writecache_flush_work);

        raw_spin_lock_init(&wc->endio_list_lock);
        INIT_LIST_HEAD(&wc->endio_list);
        wc->endio_thread = kthread_create(writecache_endio_thread, wc, "writecache_endio");
        if (IS_ERR(wc->endio_thread)) {
                r = PTR_ERR(wc->endio_thread);
                wc->endio_thread = NULL;
                ti->error = "Couldn't spawn endio thread";
                goto bad;
        }
        wake_up_process(wc->endio_thread);

        /*
         * Parse the mode (pmem or ssd)
         */
        string = dm_shift_arg(&as);
        if (!string)
                goto bad_arguments;

        if (!strcasecmp(string, "s")) {
                wc->pmem_mode = false;
        } else if (!strcasecmp(string, "p")) {
#ifdef DM_WRITECACHE_HAS_PMEM
                wc->pmem_mode = true;
                wc->writeback_fua = true;
#else
                /*
                 * If the architecture doesn't support persistent memory or
                 * the kernel doesn't support any DAX drivers, this driver can
                 * only be used in SSD-only mode.
                 */
                r = -EOPNOTSUPP;
                ti->error = "Persistent memory or DAX not supported on this system";
                goto bad;
#endif
        } else {
                goto bad_arguments;
        }

        if (WC_MODE_PMEM(wc)) {
                r = bioset_init(&wc->bio_set, BIO_POOL_SIZE,
                                offsetof(struct writeback_struct, bio),
                                BIOSET_NEED_BVECS);
                if (r) {
                        ti->error = "Could not allocate bio set";
                        goto bad;
                }
        } else {
                r = mempool_init_kmalloc_pool(&wc->copy_pool, 1, sizeof(struct copy_struct));
                if (r) {
                        ti->error = "Could not allocate mempool";
                        goto bad;
                }
        }

        /*
         * Parse the origin data device
         */
        string = dm_shift_arg(&as);
        if (!string)
                goto bad_arguments;
        r = dm_get_device(ti, string, dm_table_get_mode(ti->table), &wc->dev);
        if (r) {
                ti->error = "Origin data device lookup failed";
                goto bad;
        }

        /*
         * Parse cache data device (be it pmem or ssd)
         */
        string = dm_shift_arg(&as);
        if (!string)
                goto bad_arguments;

        r = dm_get_device(ti, string, dm_table_get_mode(ti->table), &wc->ssd_dev);
        if (r) {
                ti->error = "Cache data device lookup failed";
                goto bad;
        }
        wc->memory_map_size = i_size_read(wc->ssd_dev->bdev->bd_inode);

        /*
         * Parse the cache block size
         */
        string = dm_shift_arg(&as);
        if (!string)
                goto bad_arguments;
        if (sscanf(string, "%u%c", &wc->block_size, &dummy) != 1 ||
            wc->block_size < 512 || wc->block_size > PAGE_SIZE ||
            (wc->block_size & (wc->block_size - 1))) {
                r = -EINVAL;
                ti->error = "Invalid block size";
                goto bad;
        }
        wc->block_size_bits = __ffs(wc->block_size);

        wc->max_writeback_jobs = MAX_WRITEBACK_JOBS;
        wc->autocommit_blocks = !WC_MODE_PMEM(wc) ? AUTOCOMMIT_BLOCKS_SSD : AUTOCOMMIT_BLOCKS_PMEM;
        wc->autocommit_jiffies = msecs_to_jiffies(AUTOCOMMIT_MSEC);

        /*
         * Parse optional arguments
         */
        r = dm_read_arg_group(_args, &as, &opt_params, &ti->error);
        if (r)
                goto bad;

        while (opt_params) {
                string = dm_shift_arg(&as), opt_params--;
                if (!strcasecmp(string, "start_sector") && opt_params >= 1) {
                        unsigned long long start_sector;
                        string = dm_shift_arg(&as), opt_params--;
                        if (sscanf(string, "%llu%c", &start_sector, &dummy) != 1)
                                goto invalid_optional;
                        wc->start_sector = start_sector;
                        if (wc->start_sector != start_sector ||
                            wc->start_sector >= wc->memory_map_size >> SECTOR_SHIFT)
                                goto invalid_optional;
                } else if (!strcasecmp(string, "high_watermark") && opt_params >= 1) {
                        string = dm_shift_arg(&as), opt_params--;
                        if (sscanf(string, "%d%c", &high_wm_percent, &dummy) != 1)
                                goto invalid_optional;
                        if (high_wm_percent < 0 || high_wm_percent > 100)
                                goto invalid_optional;
                        wc->high_wm_percent_set = true;
                } else if (!strcasecmp(string, "low_watermark") && opt_params >= 1) {
                        string = dm_shift_arg(&as), opt_params--;
                        if (sscanf(string, "%d%c", &low_wm_percent, &dummy) != 1)
                                goto invalid_optional;
                        if (low_wm_percent < 0 || low_wm_percent > 100)
                                goto invalid_optional;
                        wc->low_wm_percent_set = true;
                } else if (!strcasecmp(string, "writeback_jobs") && opt_params >= 1) {
                        string = dm_shift_arg(&as), opt_params--;

                        if (sscanf(string, "%u%c", &wc->max_writeback_jobs, &dummy) != 1)
                                goto invalid_optional;
                        wc->max_writeback_jobs_set = true;
                } else if (!strcasecmp(string, "autocommit_blocks") && opt_params >= 1) {
                        string = dm_shift_arg(&as), opt_params--;
                        if (sscanf(string, "%u%c", &wc->autocommit_blocks, &dummy) != 1)
                                goto invalid_optional;
                        wc->autocommit_blocks_set = true;
                } else if (!strcasecmp(string, "autocommit_time") && opt_params >= 1) {
                        unsigned autocommit_msecs;
                        string = dm_shift_arg(&as), opt_params--;
                        if (sscanf(string, "%u%c", &autocommit_msecs, &dummy) != 1)
                                goto invalid_optional;
                        if (autocommit_msecs > 3600000)
                                goto invalid_optional;
                        wc->autocommit_jiffies = msecs_to_jiffies(autocommit_msecs);
                        wc->autocommit_time_set = true;
                } else if (!strcasecmp(string, "fua")) {
                        if (WC_MODE_PMEM(wc)) {
                                wc->writeback_fua = true;
                                wc->writeback_fua_set = true;
                        } else goto invalid_optional;
                } else if (!strcasecmp(string, "nofua")) {
                        if (WC_MODE_PMEM(wc)) {
                                wc->writeback_fua = false;
                                wc->writeback_fua_set = true;
                        } else goto invalid_optional;
                } else {
invalid_optional:
                        r = -EINVAL;
                        ti->error = "Invalid optional argument";
                        goto bad;
                }
        }

        if (high_wm_percent < low_wm_percent) {
                r = -EINVAL;
                ti->error = "High watermark must be greater than or equal to low watermark";
                goto bad;
        }

        if (WC_MODE_PMEM(wc)) {
                r = persistent_memory_claim(wc);
                if (r) {
                        ti->error = "Unable to map persistent memory for cache";
                        goto bad;
                }
        } else {
                struct dm_io_region region;
                struct dm_io_request req;
                size_t n_blocks, n_metadata_blocks;
                uint64_t n_bitmap_bits;

                wc->memory_map_size -= (uint64_t)wc->start_sector << SECTOR_SHIFT;

                bio_list_init(&wc->flush_list);
                wc->flush_thread = kthread_create(writecache_flush_thread, wc, "dm_writecache_flush");
                if (IS_ERR(wc->flush_thread)) {
                        r = PTR_ERR(wc->flush_thread);
                        wc->flush_thread = NULL;
                        ti->error = "Couldn't spawn flush thread";
                        goto bad;
                }
                wake_up_process(wc->flush_thread);

                r = calculate_memory_size(wc->memory_map_size, wc->block_size,
                                          &n_blocks, &n_metadata_blocks);
                if (r) {
                        ti->error = "Invalid device size";
                        goto bad;
                }

                n_bitmap_bits = (((uint64_t)n_metadata_blocks << wc->block_size_bits) +
                                 BITMAP_GRANULARITY - 1) / BITMAP_GRANULARITY;
                /* this is limitation of test_bit functions */
                if (n_bitmap_bits > 1U << 31) {
                        r = -EFBIG;
                        ti->error = "Invalid device size";
                        goto bad;
                }

                wc->memory_map = vmalloc(n_metadata_blocks << wc->block_size_bits);
                if (!wc->memory_map) {
                        r = -ENOMEM;
                        ti->error = "Unable to allocate memory for metadata";
                        goto bad;
                }

                wc->dm_kcopyd = dm_kcopyd_client_create(&dm_kcopyd_throttle);
                if (IS_ERR(wc->dm_kcopyd)) {
                        r = PTR_ERR(wc->dm_kcopyd);
                        ti->error = "Unable to allocate dm-kcopyd client";
                        wc->dm_kcopyd = NULL;
                        goto bad;
                }

                wc->metadata_sectors = n_metadata_blocks << (wc->block_size_bits - SECTOR_SHIFT);
                wc->dirty_bitmap_size = (n_bitmap_bits + BITS_PER_LONG - 1) /
                        BITS_PER_LONG * sizeof(unsigned long);
                wc->dirty_bitmap = vzalloc(wc->dirty_bitmap_size);
                if (!wc->dirty_bitmap) {
                        r = -ENOMEM;
                        ti->error = "Unable to allocate dirty bitmap";
                        goto bad;
                }

                region.bdev = wc->ssd_dev->bdev;
                region.sector = wc->start_sector;
                region.count = wc->metadata_sectors;
                req.bi_op = REQ_OP_READ;
                req.bi_op_flags = REQ_SYNC;
                req.mem.type = DM_IO_VMA;
                req.mem.ptr.vma = (char *)wc->memory_map;
                req.client = wc->dm_io;
                req.notify.fn = NULL;

                r = dm_io(&req, 1, &region, NULL);
                if (r) {
                        ti->error = "Unable to read metadata";
                        goto bad;
                }
        }

        r = memcpy_mcsafe(&s, sb(wc), sizeof(struct wc_memory_superblock));
        if (r) {
                ti->error = "Hardware memory error when reading superblock";
                goto bad;
        }
        if (!le32_to_cpu(s.magic) && !le32_to_cpu(s.version)) {
                r = init_memory(wc);
                if (r) {
                        ti->error = "Unable to initialize device";
                        goto bad;
                }
                r = memcpy_mcsafe(&s, sb(wc), sizeof(struct wc_memory_superblock));
                if (r) {
                        ti->error = "Hardware memory error when reading superblock";
                        goto bad;
                }
        }

        if (le32_to_cpu(s.magic) != MEMORY_SUPERBLOCK_MAGIC) {
                ti->error = "Invalid magic in the superblock";
                r = -EINVAL;
                goto bad;
        }

        if (le32_to_cpu(s.version) != MEMORY_SUPERBLOCK_VERSION) {
                ti->error = "Invalid version in the superblock";
                r = -EINVAL;
                goto bad;
        }

        if (le32_to_cpu(s.block_size) != wc->block_size) {
                ti->error = "Block size does not match superblock";
                r = -EINVAL;
                goto bad;
        }

        wc->n_blocks = le64_to_cpu(s.n_blocks);

        offset = wc->n_blocks * sizeof(struct wc_memory_entry);
        if (offset / sizeof(struct wc_memory_entry) != le64_to_cpu(sb(wc)->n_blocks)) {
overflow:
                ti->error = "Overflow in size calculation";
                r = -EINVAL;
                goto bad;
        }
        offset += sizeof(struct wc_memory_superblock);
        if (offset < sizeof(struct wc_memory_superblock))
                goto overflow;
        offset = (offset + wc->block_size - 1) & ~(size_t)(wc->block_size - 1);
        data_size = wc->n_blocks * (size_t)wc->block_size;
        if (!offset || (data_size / wc->block_size != wc->n_blocks) ||
            (offset + data_size < offset))
                goto overflow;
        if (offset + data_size > wc->memory_map_size) {
                ti->error = "Memory area is too small";
                r = -EINVAL;
                goto bad;
        }

        wc->metadata_sectors = offset >> SECTOR_SHIFT;
        wc->block_start = (char *)sb(wc) + offset;

        x = (uint64_t)wc->n_blocks * (100 - high_wm_percent);
        x += 50;
        do_div(x, 100);
        wc->freelist_high_watermark = x;
        x = (uint64_t)wc->n_blocks * (100 - low_wm_percent);
        x += 50;
        do_div(x, 100);
        wc->freelist_low_watermark = x;

        r = writecache_alloc_entries(wc);
        if (r) {
                ti->error = "Cannot allocate memory";
                goto bad;
        }

        ti->num_flush_bios = 1;
        ti->flush_supported = true;
        ti->num_discard_bios = 1;

        if (WC_MODE_PMEM(wc))
                persistent_memory_flush_cache(wc->memory_map, wc->memory_map_size);

        return 0;

bad_arguments:
        r = -EINVAL;
        ti->error = "Bad arguments";
bad:
        writecache_dtr(ti);
        return r;
}

static void writecache_status(struct dm_target *ti, status_type_t type,
                              unsigned status_flags, char *result, unsigned maxlen)
{
        struct dm_writecache *wc = ti->private;
        unsigned extra_args;
        unsigned sz = 0;
        uint64_t x;

        switch (type) {
        case STATUSTYPE_INFO:
                DMEMIT("%ld %llu %llu %llu", writecache_has_error(wc),
                       (unsigned long long)wc->n_blocks, (unsigned long long)wc->freelist_size,
                       (unsigned long long)wc->writeback_size);
                break;
        case STATUSTYPE_TABLE:
                DMEMIT("%c %s %s %u ", WC_MODE_PMEM(wc) ? 'p' : 's',
                                wc->dev->name, wc->ssd_dev->name, wc->block_size);
                extra_args = 0;
                if (wc->start_sector)
                        extra_args += 2;
                if (wc->high_wm_percent_set)
                        extra_args += 2;
                if (wc->low_wm_percent_set)
                        extra_args += 2;
                if (wc->max_writeback_jobs_set)
                        extra_args += 2;
                if (wc->autocommit_blocks_set)
                        extra_args += 2;
                if (wc->autocommit_time_set)
                        extra_args += 2;
                if (wc->writeback_fua_set)
                        extra_args++;

                DMEMIT("%u", extra_args);
                if (wc->start_sector)
                        DMEMIT(" start_sector %llu", (unsigned long long)wc->start_sector);
                if (wc->high_wm_percent_set) {
                        x = (uint64_t)wc->freelist_high_watermark * 100;
                        x += wc->n_blocks / 2;
                        do_div(x, (size_t)wc->n_blocks);
                        DMEMIT(" high_watermark %u", 100 - (unsigned)x);
                }
                if (wc->low_wm_percent_set) {
                        x = (uint64_t)wc->freelist_low_watermark * 100;
                        x += wc->n_blocks / 2;
                        do_div(x, (size_t)wc->n_blocks);
                        DMEMIT(" low_watermark %u", 100 - (unsigned)x);
                }
                if (wc->max_writeback_jobs_set)
                        DMEMIT(" writeback_jobs %u", wc->max_writeback_jobs);
                if (wc->autocommit_blocks_set)
                        DMEMIT(" autocommit_blocks %u", wc->autocommit_blocks);
                if (wc->autocommit_time_set)
                        DMEMIT(" autocommit_time %u", jiffies_to_msecs(wc->autocommit_jiffies));
                if (wc->writeback_fua_set)
                        DMEMIT(" %sfua", wc->writeback_fua ? "" : "no");
                break;
        }
}

static struct target_type writecache_target = {
        .name                   = "writecache",
        .version                = {1, 1, 1},
        .module                 = THIS_MODULE,
        .ctr                    = writecache_ctr,
        .dtr                    = writecache_dtr,
        .status                 = writecache_status,
        .postsuspend            = writecache_suspend,
        .resume                 = writecache_resume,
        .message                = writecache_message,
        .map                    = writecache_map,
        .end_io                 = writecache_end_io,
        .iterate_devices        = writecache_iterate_devices,
        .io_hints               = writecache_io_hints,
};

static int __init dm_writecache_init(void)
{
        int r;

        r = dm_register_target(&writecache_target);
        if (r < 0) {
                DMERR("register failed %d", r);
                return r;
        }

        return 0;
}

static void __exit dm_writecache_exit(void)
{
        dm_unregister_target(&writecache_target);
}

module_init(dm_writecache_init);
module_exit(dm_writecache_exit);

MODULE_DESCRIPTION(DM_NAME " writecache target");
MODULE_AUTHOR("Mikulas Patocka <dm-devel@redhat.com>");
MODULE_LICENSE("GPL");