/*
 * Copyright (C) 2015 Shaohua Li <shli@fb.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope 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.
 *
 */
#include <linux/kernel.h>
#include <linux/wait.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include <linux/raid/md_p.h>
#include <linux/crc32c.h>
#include <linux/random.h>
#include "md.h"
#include "raid5.h"

/*
 * metadata/data stored in disk with 4k size unit (a block) regardless
 * underneath hardware sector size. only works with PAGE_SIZE == 4096
 */
#define BLOCK_SECTORS (8)

/*
 * reclaim runs every 1/4 disk size or 10G reclaimable space. This can prevent
 * recovery scans a very long log
 */
#define RECLAIM_MAX_FREE_SPACE (10 * 1024 * 1024 * 2) /* sector */
#define RECLAIM_MAX_FREE_SPACE_SHIFT (2)

/*
 * We only need 2 bios per I/O unit to make progress, but ensure we
 * have a few more available to not get too tight.
 */
#define R5L_POOL_SIZE   4

struct r5l_log {
        struct md_rdev *rdev;

        u32 uuid_checksum;

        sector_t device_size;           /* log device size, round to
                                         * BLOCK_SECTORS */
        sector_t max_free_space;        /* reclaim run if free space is at
                                         * this size */

        sector_t last_checkpoint;       /* log tail. where recovery scan
                                         * starts from */
        u64 last_cp_seq;                /* log tail sequence */

        sector_t log_start;             /* log head. where new data appends */
        u64 seq;                        /* log head sequence */

        sector_t next_checkpoint;
        u64 next_cp_seq;

        struct mutex io_mutex;
        struct r5l_io_unit *current_io; /* current io_unit accepting new data */

        spinlock_t io_list_lock;
        struct list_head running_ios;   /* io_units which are still running,
                                         * and have not yet been completely
                                         * written to the log */
        struct list_head io_end_ios;    /* io_units which have been completely
                                         * written to the log but not yet written
                                         * to the RAID */
        struct list_head flushing_ios;  /* io_units which are waiting for log
                                         * cache flush */
        struct list_head finished_ios;  /* io_units which settle down in log disk */
        struct bio flush_bio;

        struct list_head no_mem_stripes;   /* pending stripes, -ENOMEM */

        struct kmem_cache *io_kc;
        mempool_t *io_pool;
        struct bio_set *bs;
        mempool_t *meta_pool;

        struct md_thread *reclaim_thread;
        unsigned long reclaim_target;   /* number of space that need to be
                                         * reclaimed.  if it's 0, reclaim spaces
                                         * used by io_units which are in
                                         * IO_UNIT_STRIPE_END state (eg, reclaim
                                         * dones't wait for specific io_unit
                                         * switching to IO_UNIT_STRIPE_END
                                         * state) */
        wait_queue_head_t iounit_wait;

        struct list_head no_space_stripes; /* pending stripes, log has no space */
        spinlock_t no_space_stripes_lock;

        bool need_cache_flush;
        bool in_teardown;
};

/*
 * an IO range starts from a meta data block and end at the next meta data
 * block. The io unit's the meta data block tracks data/parity followed it. io
 * unit is written to log disk with normal write, as we always flush log disk
 * first and then start move data to raid disks, there is no requirement to
 * write io unit with FLUSH/FUA
 */
struct r5l_io_unit {
        struct r5l_log *log;

        struct page *meta_page; /* store meta block */
        int meta_offset;        /* current offset in meta_page */

        struct bio *current_bio;/* current_bio accepting new data */

        atomic_t pending_stripe;/* how many stripes not flushed to raid */
        u64 seq;                /* seq number of the metablock */
        sector_t log_start;     /* where the io_unit starts */
        sector_t log_end;       /* where the io_unit ends */
        struct list_head log_sibling; /* log->running_ios */
        struct list_head stripe_list; /* stripes added to the io_unit */

        int state;
        bool need_split_bio;
};

/* r5l_io_unit state */
enum r5l_io_unit_state {
        IO_UNIT_RUNNING = 0,    /* accepting new IO */
        IO_UNIT_IO_START = 1,   /* io_unit bio start writing to log,
                                 * don't accepting new bio */
        IO_UNIT_IO_END = 2,     /* io_unit bio finish writing to log */
        IO_UNIT_STRIPE_END = 3, /* stripes data finished writing to raid */
};

static sector_t r5l_ring_add(struct r5l_log *log, sector_t start, sector_t inc)
{
        start += inc;
        if (start >= log->device_size)
                start = start - log->device_size;
        return start;
}

static sector_t r5l_ring_distance(struct r5l_log *log, sector_t start,
                                  sector_t end)
{
        if (end >= start)
                return end - start;
        else
                return end + log->device_size - start;
}

static bool r5l_has_free_space(struct r5l_log *log, sector_t size)
{
        sector_t used_size;

        used_size = r5l_ring_distance(log, log->last_checkpoint,
                                        log->log_start);

        return log->device_size > used_size + size;
}

static void __r5l_set_io_unit_state(struct r5l_io_unit *io,
                                    enum r5l_io_unit_state state)
{
        if (WARN_ON(io->state >= state))
                return;
        io->state = state;
}

static void r5l_io_run_stripes(struct r5l_io_unit *io)
{
        struct stripe_head *sh, *next;

        list_for_each_entry_safe(sh, next, &io->stripe_list, log_list) {
                list_del_init(&sh->log_list);
                set_bit(STRIPE_HANDLE, &sh->state);
                raid5_release_stripe(sh);
        }
}

static void r5l_log_run_stripes(struct r5l_log *log)
{
        struct r5l_io_unit *io, *next;

        assert_spin_locked(&log->io_list_lock);

        list_for_each_entry_safe(io, next, &log->running_ios, log_sibling) {
                /* don't change list order */
                if (io->state < IO_UNIT_IO_END)
                        break;

                list_move_tail(&io->log_sibling, &log->finished_ios);
                r5l_io_run_stripes(io);
        }
}

static void r5l_move_to_end_ios(struct r5l_log *log)
{
        struct r5l_io_unit *io, *next;

        assert_spin_locked(&log->io_list_lock);

        list_for_each_entry_safe(io, next, &log->running_ios, log_sibling) {
                /* don't change list order */
                if (io->state < IO_UNIT_IO_END)
                        break;
                list_move_tail(&io->log_sibling, &log->io_end_ios);
        }
}

static void r5l_log_endio(struct bio *bio)
{
        struct r5l_io_unit *io = bio->bi_private;
        struct r5l_log *log = io->log;
        unsigned long flags;

        if (bio->bi_error)
                md_error(log->rdev->mddev, log->rdev);

        bio_put(bio);
        mempool_free(io->meta_page, log->meta_pool);

        spin_lock_irqsave(&log->io_list_lock, flags);
        __r5l_set_io_unit_state(io, IO_UNIT_IO_END);
        if (log->need_cache_flush)
                r5l_move_to_end_ios(log);
        else
                r5l_log_run_stripes(log);
        spin_unlock_irqrestore(&log->io_list_lock, flags);

        if (log->need_cache_flush)
                md_wakeup_thread(log->rdev->mddev->thread);
}

static void r5l_submit_current_io(struct r5l_log *log)
{
        struct r5l_io_unit *io = log->current_io;
        struct r5l_meta_block *block;
        unsigned long flags;
        u32 crc;

        if (!io)
                return;

        block = page_address(io->meta_page);
        block->meta_size = cpu_to_le32(io->meta_offset);
        crc = crc32c_le(log->uuid_checksum, block, PAGE_SIZE);
        block->checksum = cpu_to_le32(crc);

        log->current_io = NULL;
        spin_lock_irqsave(&log->io_list_lock, flags);
        __r5l_set_io_unit_state(io, IO_UNIT_IO_START);
        spin_unlock_irqrestore(&log->io_list_lock, flags);

        submit_bio(WRITE, io->current_bio);
}

static struct bio *r5l_bio_alloc(struct r5l_log *log)
{
        struct bio *bio = bio_alloc_bioset(GFP_NOIO, BIO_MAX_PAGES, log->bs);

        bio->bi_rw = WRITE;
        bio->bi_bdev = log->rdev->bdev;
        bio->bi_iter.bi_sector = log->rdev->data_offset + log->log_start;

        return bio;
}

static void r5_reserve_log_entry(struct r5l_log *log, struct r5l_io_unit *io)
{
        log->log_start = r5l_ring_add(log, log->log_start, BLOCK_SECTORS);

        /*
         * If we filled up the log device start from the beginning again,
         * which will require a new bio.
         *
         * Note: for this to work properly the log size needs to me a multiple
         * of BLOCK_SECTORS.
         */
        if (log->log_start == 0)
                io->need_split_bio = true;

        io->log_end = log->log_start;
}

static struct r5l_io_unit *r5l_new_meta(struct r5l_log *log)
{
        struct r5l_io_unit *io;
        struct r5l_meta_block *block;

        io = mempool_alloc(log->io_pool, GFP_ATOMIC);
        if (!io)
                return NULL;
        memset(io, 0, sizeof(*io));

        io->log = log;
        INIT_LIST_HEAD(&io->log_sibling);
        INIT_LIST_HEAD(&io->stripe_list);
        io->state = IO_UNIT_RUNNING;

        io->meta_page = mempool_alloc(log->meta_pool, GFP_NOIO);
        block = page_address(io->meta_page);
        clear_page(block);
        block->magic = cpu_to_le32(R5LOG_MAGIC);
        block->version = R5LOG_VERSION;
        block->seq = cpu_to_le64(log->seq);
        block->position = cpu_to_le64(log->log_start);

        io->log_start = log->log_start;
        io->meta_offset = sizeof(struct r5l_meta_block);
        io->seq = log->seq++;

        io->current_bio = r5l_bio_alloc(log);
        io->current_bio->bi_end_io = r5l_log_endio;
        io->current_bio->bi_private = io;
        bio_add_page(io->current_bio, io->meta_page, PAGE_SIZE, 0);

        r5_reserve_log_entry(log, io);

        spin_lock_irq(&log->io_list_lock);
        list_add_tail(&io->log_sibling, &log->running_ios);
        spin_unlock_irq(&log->io_list_lock);

        return io;
}

static int r5l_get_meta(struct r5l_log *log, unsigned int payload_size)
{
        if (log->current_io &&
            log->current_io->meta_offset + payload_size > PAGE_SIZE)
                r5l_submit_current_io(log);

        if (!log->current_io) {
                log->current_io = r5l_new_meta(log);
                if (!log->current_io)
                        return -ENOMEM;
        }

        return 0;
}

static void r5l_append_payload_meta(struct r5l_log *log, u16 type,
                                    sector_t location,
                                    u32 checksum1, u32 checksum2,
                                    bool checksum2_valid)
{
        struct r5l_io_unit *io = log->current_io;
        struct r5l_payload_data_parity *payload;

        payload = page_address(io->meta_page) + io->meta_offset;
        payload->header.type = cpu_to_le16(type);
        payload->header.flags = cpu_to_le16(0);
        payload->size = cpu_to_le32((1 + !!checksum2_valid) <<
                                    (PAGE_SHIFT - 9));
        payload->location = cpu_to_le64(location);
        payload->checksum[0] = cpu_to_le32(checksum1);
        if (checksum2_valid)
                payload->checksum[1] = cpu_to_le32(checksum2);

        io->meta_offset += sizeof(struct r5l_payload_data_parity) +
                sizeof(__le32) * (1 + !!checksum2_valid);
}

static void r5l_append_payload_page(struct r5l_log *log, struct page *page)
{
        struct r5l_io_unit *io = log->current_io;

        if (io->need_split_bio) {
                struct bio *prev = io->current_bio;

                io->current_bio = r5l_bio_alloc(log);
                bio_chain(io->current_bio, prev);

                submit_bio(WRITE, prev);
        }

        if (!bio_add_page(io->current_bio, page, PAGE_SIZE, 0))
                BUG();

        r5_reserve_log_entry(log, io);
}

static int r5l_log_stripe(struct r5l_log *log, struct stripe_head *sh,
                           int data_pages, int parity_pages)
{
        int i;
        int meta_size;
        int ret;
        struct r5l_io_unit *io;

        meta_size =
                ((sizeof(struct r5l_payload_data_parity) + sizeof(__le32))
                 * data_pages) +
                sizeof(struct r5l_payload_data_parity) +
                sizeof(__le32) * parity_pages;

        ret = r5l_get_meta(log, meta_size);
        if (ret)
                return ret;

        io = log->current_io;

        for (i = 0; i < sh->disks; i++) {
                if (!test_bit(R5_Wantwrite, &sh->dev[i].flags))
                        continue;
                if (i == sh->pd_idx || i == sh->qd_idx)
                        continue;
                r5l_append_payload_meta(log, R5LOG_PAYLOAD_DATA,
                                        raid5_compute_blocknr(sh, i, 0),
                                        sh->dev[i].log_checksum, 0, false);
                r5l_append_payload_page(log, sh->dev[i].page);
        }

        if (sh->qd_idx >= 0) {
                r5l_append_payload_meta(log, R5LOG_PAYLOAD_PARITY,
                                        sh->sector, sh->dev[sh->pd_idx].log_checksum,
                                        sh->dev[sh->qd_idx].log_checksum, true);
                r5l_append_payload_page(log, sh->dev[sh->pd_idx].page);
                r5l_append_payload_page(log, sh->dev[sh->qd_idx].page);
        } else {
                r5l_append_payload_meta(log, R5LOG_PAYLOAD_PARITY,
                                        sh->sector, sh->dev[sh->pd_idx].log_checksum,
                                        0, false);
                r5l_append_payload_page(log, sh->dev[sh->pd_idx].page);
        }

        list_add_tail(&sh->log_list, &io->stripe_list);
        atomic_inc(&io->pending_stripe);
        sh->log_io = io;

        return 0;
}

static void r5l_wake_reclaim(struct r5l_log *log, sector_t space);
/*
 * running in raid5d, where reclaim could wait for raid5d too (when it flushes
 * data from log to raid disks), so we shouldn't wait for reclaim here
 */
int r5l_write_stripe(struct r5l_log *log, struct stripe_head *sh)
{
        int write_disks = 0;
        int data_pages, parity_pages;
        int meta_size;
        int reserve;
        int i;
        int ret = 0;

        if (!log)
                return -EAGAIN;
        /* Don't support stripe batch */
        if (sh->log_io || !test_bit(R5_Wantwrite, &sh->dev[sh->pd_idx].flags) ||
            test_bit(STRIPE_SYNCING, &sh->state)) {
                /* the stripe is written to log, we start writing it to raid */
                clear_bit(STRIPE_LOG_TRAPPED, &sh->state);
                return -EAGAIN;
        }

        for (i = 0; i < sh->disks; i++) {
                void *addr;

                if (!test_bit(R5_Wantwrite, &sh->dev[i].flags))
                        continue;
                write_disks++;
                /* checksum is already calculated in last run */
                if (test_bit(STRIPE_LOG_TRAPPED, &sh->state))
                        continue;
                addr = kmap_atomic(sh->dev[i].page);
                sh->dev[i].log_checksum = crc32c_le(log->uuid_checksum,
                                                    addr, PAGE_SIZE);
                kunmap_atomic(addr);
        }
        parity_pages = 1 + !!(sh->qd_idx >= 0);
        data_pages = write_disks - parity_pages;

        meta_size =
                ((sizeof(struct r5l_payload_data_parity) + sizeof(__le32))
                 * data_pages) +
                sizeof(struct r5l_payload_data_parity) +
                sizeof(__le32) * parity_pages;
        /* Doesn't work with very big raid array */
        if (meta_size + sizeof(struct r5l_meta_block) > PAGE_SIZE)
                return -EINVAL;

        set_bit(STRIPE_LOG_TRAPPED, &sh->state);
        /*
         * The stripe must enter state machine again to finish the write, so
         * don't delay.
         */
        clear_bit(STRIPE_DELAYED, &sh->state);
        atomic_inc(&sh->count);

        mutex_lock(&log->io_mutex);
        /* meta + data */
        reserve = (1 + write_disks) << (PAGE_SHIFT - 9);
        if (!r5l_has_free_space(log, reserve)) {
                spin_lock(&log->no_space_stripes_lock);
                list_add_tail(&sh->log_list, &log->no_space_stripes);
                spin_unlock(&log->no_space_stripes_lock);

                r5l_wake_reclaim(log, reserve);
        } else {
                ret = r5l_log_stripe(log, sh, data_pages, parity_pages);
                if (ret) {
                        spin_lock_irq(&log->io_list_lock);
                        list_add_tail(&sh->log_list, &log->no_mem_stripes);
                        spin_unlock_irq(&log->io_list_lock);
                }
        }

        mutex_unlock(&log->io_mutex);
        return 0;
}

void r5l_write_stripe_run(struct r5l_log *log)
{
        if (!log)
                return;
        mutex_lock(&log->io_mutex);
        r5l_submit_current_io(log);
        mutex_unlock(&log->io_mutex);
}

int r5l_handle_flush_request(struct r5l_log *log, struct bio *bio)
{
        if (!log)
                return -ENODEV;
        /*
         * we flush log disk cache first, then write stripe data to raid disks.
         * So if bio is finished, the log disk cache is flushed already. The
         * recovery guarantees we can recovery the bio from log disk, so we
         * don't need to flush again
         */
        if (bio->bi_iter.bi_size == 0) {
                bio_endio(bio);
                return 0;
        }
        bio->bi_rw &= ~REQ_FLUSH;
        return -EAGAIN;
}

/* This will run after log space is reclaimed */
static void r5l_run_no_space_stripes(struct r5l_log *log)
{
        struct stripe_head *sh;

        spin_lock(&log->no_space_stripes_lock);
        while (!list_empty(&log->no_space_stripes)) {
                sh = list_first_entry(&log->no_space_stripes,
                                      struct stripe_head, log_list);
                list_del_init(&sh->log_list);
                set_bit(STRIPE_HANDLE, &sh->state);
                raid5_release_stripe(sh);
        }
        spin_unlock(&log->no_space_stripes_lock);
}

static sector_t r5l_reclaimable_space(struct r5l_log *log)
{
        return r5l_ring_distance(log, log->last_checkpoint,
                                 log->next_checkpoint);
}

static void r5l_run_no_mem_stripe(struct r5l_log *log)
{
        struct stripe_head *sh;

        assert_spin_locked(&log->io_list_lock);

        if (!list_empty(&log->no_mem_stripes)) {
                sh = list_first_entry(&log->no_mem_stripes,
                                      struct stripe_head, log_list);
                list_del_init(&sh->log_list);
                set_bit(STRIPE_HANDLE, &sh->state);
                raid5_release_stripe(sh);
        }
}

static bool r5l_complete_finished_ios(struct r5l_log *log)
{
        struct r5l_io_unit *io, *next;
        bool found = false;

        assert_spin_locked(&log->io_list_lock);

        list_for_each_entry_safe(io, next, &log->finished_ios, log_sibling) {
                /* don't change list order */
                if (io->state < IO_UNIT_STRIPE_END)
                        break;

                log->next_checkpoint = io->log_start;
                log->next_cp_seq = io->seq;

                list_del(&io->log_sibling);
                mempool_free(io, log->io_pool);
                r5l_run_no_mem_stripe(log);

                found = true;
        }

        return found;
}

static void __r5l_stripe_write_finished(struct r5l_io_unit *io)
{
        struct r5l_log *log = io->log;
        unsigned long flags;

        spin_lock_irqsave(&log->io_list_lock, flags);
        __r5l_set_io_unit_state(io, IO_UNIT_STRIPE_END);

        if (!r5l_complete_finished_ios(log)) {
                spin_unlock_irqrestore(&log->io_list_lock, flags);
                return;
        }

        if (r5l_reclaimable_space(log) > log->max_free_space)
                r5l_wake_reclaim(log, 0);

        spin_unlock_irqrestore(&log->io_list_lock, flags);
        wake_up(&log->iounit_wait);
}

void r5l_stripe_write_finished(struct stripe_head *sh)
{
        struct r5l_io_unit *io;

        io = sh->log_io;
        sh->log_io = NULL;

        if (io && atomic_dec_and_test(&io->pending_stripe))
                __r5l_stripe_write_finished(io);
}

static void r5l_log_flush_endio(struct bio *bio)
{
        struct r5l_log *log = container_of(bio, struct r5l_log,
                flush_bio);
        unsigned long flags;
        struct r5l_io_unit *io;

        if (bio->bi_error)
                md_error(log->rdev->mddev, log->rdev);

        spin_lock_irqsave(&log->io_list_lock, flags);
        list_for_each_entry(io, &log->flushing_ios, log_sibling)
                r5l_io_run_stripes(io);
        list_splice_tail_init(&log->flushing_ios, &log->finished_ios);
        spin_unlock_irqrestore(&log->io_list_lock, flags);
}

/*
 * Starting dispatch IO to raid.
 * io_unit(meta) consists of a log. There is one situation we want to avoid. A
 * broken meta in the middle of a log causes recovery can't find meta at the
 * head of log. If operations require meta at the head persistent in log, we
 * must make sure meta before it persistent in log too. A case is:
 *
 * stripe data/parity is in log, we start write stripe to raid disks. stripe
 * data/parity must be persistent in log before we do the write to raid disks.
 *
 * The solution is we restrictly maintain io_unit list order. In this case, we
 * only write stripes of an io_unit to raid disks till the io_unit is the first
 * one whose data/parity is in log.
 */
void r5l_flush_stripe_to_raid(struct r5l_log *log)
{
        bool do_flush;

        if (!log || !log->need_cache_flush)
                return;

        spin_lock_irq(&log->io_list_lock);
        /* flush bio is running */
        if (!list_empty(&log->flushing_ios)) {
                spin_unlock_irq(&log->io_list_lock);
                return;
        }
        list_splice_tail_init(&log->io_end_ios, &log->flushing_ios);
        do_flush = !list_empty(&log->flushing_ios);
        spin_unlock_irq(&log->io_list_lock);

        if (!do_flush)
                return;
        bio_reset(&log->flush_bio);
        log->flush_bio.bi_bdev = log->rdev->bdev;
        log->flush_bio.bi_end_io = r5l_log_flush_endio;
        submit_bio(WRITE_FLUSH, &log->flush_bio);
}

static void r5l_write_super(struct r5l_log *log, sector_t cp);
static void r5l_write_super_and_discard_space(struct r5l_log *log,
        sector_t end)
{
        struct block_device *bdev = log->rdev->bdev;
        struct mddev *mddev;

        r5l_write_super(log, end);

        if (!blk_queue_discard(bdev_get_queue(bdev)))
                return;

        mddev = log->rdev->mddev;
        /*
         * This is to avoid a deadlock. r5l_quiesce holds reconfig_mutex and
         * wait for this thread to finish. This thread waits for
         * MD_CHANGE_PENDING clear, which is supposed to be done in
         * md_check_recovery(). md_check_recovery() tries to get
         * reconfig_mutex. Since r5l_quiesce already holds the mutex,
         * md_check_recovery() fails, so the PENDING never get cleared. The
         * in_teardown check workaround this issue.
         */
        if (!log->in_teardown) {
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                set_bit(MD_CHANGE_PENDING, &mddev->flags);
                md_wakeup_thread(mddev->thread);
                wait_event(mddev->sb_wait,
                        !test_bit(MD_CHANGE_PENDING, &mddev->flags) ||
                        log->in_teardown);
                /*
                 * r5l_quiesce could run after in_teardown check and hold
                 * mutex first. Superblock might get updated twice.
                 */
                if (log->in_teardown)
                        md_update_sb(mddev, 1);
        } else {
                WARN_ON(!mddev_is_locked(mddev));
                md_update_sb(mddev, 1);
        }

        /* discard IO error really doesn't matter, ignore it */
        if (log->last_checkpoint < end) {
                blkdev_issue_discard(bdev,
                                log->last_checkpoint + log->rdev->data_offset,
                                end - log->last_checkpoint, GFP_NOIO, 0);
        } else {
                blkdev_issue_discard(bdev,
                                log->last_checkpoint + log->rdev->data_offset,
                                log->device_size - log->last_checkpoint,
                                GFP_NOIO, 0);
                blkdev_issue_discard(bdev, log->rdev->data_offset, end,
                                GFP_NOIO, 0);
        }
}


static void r5l_do_reclaim(struct r5l_log *log)
{
        sector_t reclaim_target = xchg(&log->reclaim_target, 0);
        sector_t reclaimable;
        sector_t next_checkpoint;
        u64 next_cp_seq;

        spin_lock_irq(&log->io_list_lock);
        /*
         * move proper io_unit to reclaim list. We should not change the order.
         * reclaimable/unreclaimable io_unit can be mixed in the list, we
         * shouldn't reuse space of an unreclaimable io_unit
         */
        while (1) {
                reclaimable = r5l_reclaimable_space(log);
                if (reclaimable >= reclaim_target ||
                    (list_empty(&log->running_ios) &&
                     list_empty(&log->io_end_ios) &&
                     list_empty(&log->flushing_ios) &&
                     list_empty(&log->finished_ios)))
                        break;

                md_wakeup_thread(log->rdev->mddev->thread);
                wait_event_lock_irq(log->iounit_wait,
                                    r5l_reclaimable_space(log) > reclaimable,
                                    log->io_list_lock);
        }

        next_checkpoint = log->next_checkpoint;
        next_cp_seq = log->next_cp_seq;
        spin_unlock_irq(&log->io_list_lock);

        BUG_ON(reclaimable < 0);
        if (reclaimable == 0)
                return;

        /*
         * write_super will flush cache of each raid disk. We must write super
         * here, because the log area might be reused soon and we don't want to
         * confuse recovery
         */
        r5l_write_super_and_discard_space(log, next_checkpoint);

        mutex_lock(&log->io_mutex);
        log->last_checkpoint = next_checkpoint;
        log->last_cp_seq = next_cp_seq;
        mutex_unlock(&log->io_mutex);

        r5l_run_no_space_stripes(log);
}

static void r5l_reclaim_thread(struct md_thread *thread)
{
        struct mddev *mddev = thread->mddev;
        struct r5conf *conf = mddev->private;
        struct r5l_log *log = conf->log;

        if (!log)
                return;
        r5l_do_reclaim(log);
}

static void r5l_wake_reclaim(struct r5l_log *log, sector_t space)
{
        unsigned long target;
        unsigned long new = (unsigned long)space; /* overflow in theory */

        do {
                target = log->reclaim_target;
                if (new < target)
                        return;
        } while (cmpxchg(&log->reclaim_target, target, new) != target);
        md_wakeup_thread(log->reclaim_thread);
}

void r5l_quiesce(struct r5l_log *log, int state)
{
        struct mddev *mddev;
        if (!log || state == 2)
                return;
        if (state == 0) {
                log->in_teardown = 0;
                /*
                 * This is a special case for hotadd. In suspend, the array has
                 * no journal. In resume, journal is initialized as well as the
                 * reclaim thread.
                 */
                if (log->reclaim_thread)
                        return;
                log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
                                        log->rdev->mddev, "reclaim");
        } else if (state == 1) {
                /*
                 * at this point all stripes are finished, so io_unit is at
                 * least in STRIPE_END state
                 */
                log->in_teardown = 1;
                /* make sure r5l_write_super_and_discard_space exits */
                mddev = log->rdev->mddev;
                wake_up(&mddev->sb_wait);
                r5l_wake_reclaim(log, -1L);
                md_unregister_thread(&log->reclaim_thread);
                r5l_do_reclaim(log);
        }
}

bool r5l_log_disk_error(struct r5conf *conf)
{
        struct r5l_log *log;
        bool ret;
        /* don't allow write if journal disk is missing */
        rcu_read_lock();
        log = rcu_dereference(conf->log);

        if (!log)
                ret = test_bit(MD_HAS_JOURNAL, &conf->mddev->flags);
        else
                ret = test_bit(Faulty, &log->rdev->flags);
        rcu_read_unlock();
        return ret;
}

struct r5l_recovery_ctx {
        struct page *meta_page;         /* current meta */
        sector_t meta_total_blocks;     /* total size of current meta and data */
        sector_t pos;                   /* recovery position */
        u64 seq;                        /* recovery position seq */
};

static int r5l_read_meta_block(struct r5l_log *log,
                               struct r5l_recovery_ctx *ctx)
{
        struct page *page = ctx->meta_page;
        struct r5l_meta_block *mb;
        u32 crc, stored_crc;

        if (!sync_page_io(log->rdev, ctx->pos, PAGE_SIZE, page, READ, false))
                return -EIO;

        mb = page_address(page);
        stored_crc = le32_to_cpu(mb->checksum);
        mb->checksum = 0;

        if (le32_to_cpu(mb->magic) != R5LOG_MAGIC ||
            le64_to_cpu(mb->seq) != ctx->seq ||
            mb->version != R5LOG_VERSION ||
            le64_to_cpu(mb->position) != ctx->pos)
                return -EINVAL;

        crc = crc32c_le(log->uuid_checksum, mb, PAGE_SIZE);
        if (stored_crc != crc)
                return -EINVAL;

        if (le32_to_cpu(mb->meta_size) > PAGE_SIZE)
                return -EINVAL;

        ctx->meta_total_blocks = BLOCK_SECTORS;

        return 0;
}

static int r5l_recovery_flush_one_stripe(struct r5l_log *log,
                                         struct r5l_recovery_ctx *ctx,
                                         sector_t stripe_sect,
                                         int *offset, sector_t *log_offset)
{
        struct r5conf *conf = log->rdev->mddev->private;
        struct stripe_head *sh;
        struct r5l_payload_data_parity *payload;
        int disk_index;

        sh = raid5_get_active_stripe(conf, stripe_sect, 0, 0, 0);
        while (1) {
                payload = page_address(ctx->meta_page) + *offset;

                if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_DATA) {
                        raid5_compute_sector(conf,
                                             le64_to_cpu(payload->location), 0,
                                             &disk_index, sh);

                        sync_page_io(log->rdev, *log_offset, PAGE_SIZE,
                                     sh->dev[disk_index].page, READ, false);
                        sh->dev[disk_index].log_checksum =
                                le32_to_cpu(payload->checksum[0]);
                        set_bit(R5_Wantwrite, &sh->dev[disk_index].flags);
                        ctx->meta_total_blocks += BLOCK_SECTORS;
                } else {
                        disk_index = sh->pd_idx;
                        sync_page_io(log->rdev, *log_offset, PAGE_SIZE,
                                     sh->dev[disk_index].page, READ, false);
                        sh->dev[disk_index].log_checksum =
                                le32_to_cpu(payload->checksum[0]);
                        set_bit(R5_Wantwrite, &sh->dev[disk_index].flags);

                        if (sh->qd_idx >= 0) {
                                disk_index = sh->qd_idx;
                                sync_page_io(log->rdev,
                                             r5l_ring_add(log, *log_offset, BLOCK_SECTORS),
                                             PAGE_SIZE, sh->dev[disk_index].page,
                                             READ, false);
                                sh->dev[disk_index].log_checksum =
                                        le32_to_cpu(payload->checksum[1]);
                                set_bit(R5_Wantwrite,
                                        &sh->dev[disk_index].flags);
                        }
                        ctx->meta_total_blocks += BLOCK_SECTORS * conf->max_degraded;
                }

                *log_offset = r5l_ring_add(log, *log_offset,
                                           le32_to_cpu(payload->size));
                *offset += sizeof(struct r5l_payload_data_parity) +
                        sizeof(__le32) *
                        (le32_to_cpu(payload->size) >> (PAGE_SHIFT - 9));
                if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_PARITY)
                        break;
        }

        for (disk_index = 0; disk_index < sh->disks; disk_index++) {
                void *addr;
                u32 checksum;

                if (!test_bit(R5_Wantwrite, &sh->dev[disk_index].flags))
                        continue;
                addr = kmap_atomic(sh->dev[disk_index].page);
                checksum = crc32c_le(log->uuid_checksum, addr, PAGE_SIZE);
                kunmap_atomic(addr);
                if (checksum != sh->dev[disk_index].log_checksum)
                        goto error;
        }

        for (disk_index = 0; disk_index < sh->disks; disk_index++) {
                struct md_rdev *rdev, *rrdev;

                if (!test_and_clear_bit(R5_Wantwrite,
                                        &sh->dev[disk_index].flags))
                        continue;

                /* in case device is broken */
                rdev = rcu_dereference(conf->disks[disk_index].rdev);
                if (rdev)
                        sync_page_io(rdev, stripe_sect, PAGE_SIZE,
                                     sh->dev[disk_index].page, WRITE, false);
                rrdev = rcu_dereference(conf->disks[disk_index].replacement);
                if (rrdev)
                        sync_page_io(rrdev, stripe_sect, PAGE_SIZE,
                                     sh->dev[disk_index].page, WRITE, false);
        }
        raid5_release_stripe(sh);
        return 0;

error:
        for (disk_index = 0; disk_index < sh->disks; disk_index++)
                sh->dev[disk_index].flags = 0;

        raid5_release_stripe(sh);
        return -EINVAL;
}

static int r5l_recovery_flush_one_meta(struct r5l_log *log,
                                       struct r5l_recovery_ctx *ctx)
{
        struct r5conf *conf = log->rdev->mddev->private;
        struct r5l_payload_data_parity *payload;
        struct r5l_meta_block *mb;
        int offset;
        sector_t log_offset;
        sector_t stripe_sector;

        mb = page_address(ctx->meta_page);
        offset = sizeof(struct r5l_meta_block);
        log_offset = r5l_ring_add(log, ctx->pos, BLOCK_SECTORS);

        while (offset < le32_to_cpu(mb->meta_size)) {
                int dd;

                payload = (void *)mb + offset;
                stripe_sector = raid5_compute_sector(conf,
                                                     le64_to_cpu(payload->location), 0, &dd, NULL);
                if (r5l_recovery_flush_one_stripe(log, ctx, stripe_sector,
                                                  &offset, &log_offset))
                        return -EINVAL;
        }
        return 0;
}

/* copy data/parity from log to raid disks */
static void r5l_recovery_flush_log(struct r5l_log *log,
                                   struct r5l_recovery_ctx *ctx)
{
        while (1) {
                if (r5l_read_meta_block(log, ctx))
                        return;
                if (r5l_recovery_flush_one_meta(log, ctx))
                        return;
                ctx->seq++;
                ctx->pos = r5l_ring_add(log, ctx->pos, ctx->meta_total_blocks);
        }
}

static int r5l_log_write_empty_meta_block(struct r5l_log *log, sector_t pos,
                                          u64 seq)
{
        struct page *page;
        struct r5l_meta_block *mb;
        u32 crc;

        page = alloc_page(GFP_KERNEL | __GFP_ZERO);
        if (!page)
                return -ENOMEM;
        mb = page_address(page);
        mb->magic = cpu_to_le32(R5LOG_MAGIC);
        mb->version = R5LOG_VERSION;
        mb->meta_size = cpu_to_le32(sizeof(struct r5l_meta_block));
        mb->seq = cpu_to_le64(seq);
        mb->position = cpu_to_le64(pos);
        crc = crc32c_le(log->uuid_checksum, mb, PAGE_SIZE);
        mb->checksum = cpu_to_le32(crc);

        if (!sync_page_io(log->rdev, pos, PAGE_SIZE, page, WRITE_FUA, false)) {
                __free_page(page);
                return -EIO;
        }
        __free_page(page);
        return 0;
}

static int r5l_recovery_log(struct r5l_log *log)
{
        struct r5l_recovery_ctx ctx;

        ctx.pos = log->last_checkpoint;
        ctx.seq = log->last_cp_seq;
        ctx.meta_page = alloc_page(GFP_KERNEL);
        if (!ctx.meta_page)
                return -ENOMEM;

        r5l_recovery_flush_log(log, &ctx);
        __free_page(ctx.meta_page);

        /*
         * we did a recovery. Now ctx.pos points to an invalid meta block. New
         * log will start here. but we can't let superblock point to last valid
         * meta block. The log might looks like:
         * | meta 1| meta 2| meta 3|
         * meta 1 is valid, meta 2 is invalid. meta 3 could be valid. If
         * superblock points to meta 1, we write a new valid meta 2n.  if crash
         * happens again, new recovery will start from meta 1. Since meta 2n is
         * valid now, recovery will think meta 3 is valid, which is wrong.
         * The solution is we create a new meta in meta2 with its seq == meta
         * 1's seq + 10 and let superblock points to meta2. The same recovery will
         * not think meta 3 is a valid meta, because its seq doesn't match
         */
        if (ctx.seq > log->last_cp_seq + 1) {
                int ret;

                ret = r5l_log_write_empty_meta_block(log, ctx.pos, ctx.seq + 10);
                if (ret)
                        return ret;
                log->seq = ctx.seq + 11;
                log->log_start = r5l_ring_add(log, ctx.pos, BLOCK_SECTORS);
                r5l_write_super(log, ctx.pos);
        } else {
                log->log_start = ctx.pos;
                log->seq = ctx.seq;
        }
        return 0;
}

static void r5l_write_super(struct r5l_log *log, sector_t cp)
{
        struct mddev *mddev = log->rdev->mddev;

        log->rdev->journal_tail = cp;
        set_bit(MD_CHANGE_DEVS, &mddev->flags);
}

static int r5l_load_log(struct r5l_log *log)
{
        struct md_rdev *rdev = log->rdev;
        struct page *page;
        struct r5l_meta_block *mb;
        sector_t cp = log->rdev->journal_tail;
        u32 stored_crc, expected_crc;
        bool create_super = false;
        int ret;

        /* Make sure it's valid */
        if (cp >= rdev->sectors || round_down(cp, BLOCK_SECTORS) != cp)
                cp = 0;
        page = alloc_page(GFP_KERNEL);
        if (!page)
                return -ENOMEM;

        if (!sync_page_io(rdev, cp, PAGE_SIZE, page, READ, false)) {
                ret = -EIO;
                goto ioerr;
        }
        mb = page_address(page);

        if (le32_to_cpu(mb->magic) != R5LOG_MAGIC ||
            mb->version != R5LOG_VERSION) {
                create_super = true;
                goto create;
        }
        stored_crc = le32_to_cpu(mb->checksum);
        mb->checksum = 0;
        expected_crc = crc32c_le(log->uuid_checksum, mb, PAGE_SIZE);
        if (stored_crc != expected_crc) {
                create_super = true;
                goto create;
        }
        if (le64_to_cpu(mb->position) != cp) {
                create_super = true;
                goto create;
        }
create:
        if (create_super) {
                log->last_cp_seq = prandom_u32();
                cp = 0;
                /*
                 * Make sure super points to correct address. Log might have
                 * data very soon. If super hasn't correct log tail address,
                 * recovery can't find the log
                 */
                r5l_write_super(log, cp);
        } else
                log->last_cp_seq = le64_to_cpu(mb->seq);

        log->device_size = round_down(rdev->sectors, BLOCK_SECTORS);
        log->max_free_space = log->device_size >> RECLAIM_MAX_FREE_SPACE_SHIFT;
        if (log->max_free_space > RECLAIM_MAX_FREE_SPACE)
                log->max_free_space = RECLAIM_MAX_FREE_SPACE;
        log->last_checkpoint = cp;

        __free_page(page);

        return r5l_recovery_log(log);
ioerr:
        __free_page(page);
        return ret;
}

int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
{
        struct r5l_log *log;

        if (PAGE_SIZE != 4096)
                return -EINVAL;
        log = kzalloc(sizeof(*log), GFP_KERNEL);
        if (!log)
                return -ENOMEM;
        log->rdev = rdev;

        log->need_cache_flush = (rdev->bdev->bd_disk->queue->flush_flags != 0);

        log->uuid_checksum = crc32c_le(~0, rdev->mddev->uuid,
                                       sizeof(rdev->mddev->uuid));

        mutex_init(&log->io_mutex);

        spin_lock_init(&log->io_list_lock);
        INIT_LIST_HEAD(&log->running_ios);
        INIT_LIST_HEAD(&log->io_end_ios);
        INIT_LIST_HEAD(&log->flushing_ios);
        INIT_LIST_HEAD(&log->finished_ios);
        bio_init(&log->flush_bio);

        log->io_kc = KMEM_CACHE(r5l_io_unit, 0);
        if (!log->io_kc)
                goto io_kc;

        log->io_pool = mempool_create_slab_pool(R5L_POOL_SIZE, log->io_kc);
        if (!log->io_pool)
                goto io_pool;

        log->bs = bioset_create(R5L_POOL_SIZE, 0);
        if (!log->bs)
                goto io_bs;

        log->meta_pool = mempool_create_page_pool(R5L_POOL_SIZE, 0);
        if (!log->meta_pool)
                goto out_mempool;

        log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
                                                 log->rdev->mddev, "reclaim");
        if (!log->reclaim_thread)
                goto reclaim_thread;
        init_waitqueue_head(&log->iounit_wait);

        INIT_LIST_HEAD(&log->no_mem_stripes);

        INIT_LIST_HEAD(&log->no_space_stripes);
        spin_lock_init(&log->no_space_stripes_lock);

        if (r5l_load_log(log))
                goto error;

        rcu_assign_pointer(conf->log, log);
        set_bit(MD_HAS_JOURNAL, &conf->mddev->flags);
        return 0;

error:
        md_unregister_thread(&log->reclaim_thread);
reclaim_thread:
        mempool_destroy(log->meta_pool);
out_mempool:
        bioset_free(log->bs);
io_bs:
        mempool_destroy(log->io_pool);
io_pool:
        kmem_cache_destroy(log->io_kc);
io_kc:
        kfree(log);
        return -EINVAL;
}

void r5l_exit_log(struct r5l_log *log)
{
        md_unregister_thread(&log->reclaim_thread);
        mempool_destroy(log->meta_pool);
        bioset_free(log->bs);
        mempool_destroy(log->io_pool);
        kmem_cache_destroy(log->io_kc);
        kfree(log);
}