// SPDX-License-Identifier: GPL-2.0+
/*
 * cpfile.c - NILFS checkpoint file.
 *
 * Copyright (C) 2006-2008 Nippon Telegraph and Telephone Corporation.
 *
 * Written by Koji Sato.
 */

#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/buffer_head.h>
#include <linux/errno.h>
#include "mdt.h"
#include "cpfile.h"


static inline unsigned long
nilfs_cpfile_checkpoints_per_block(const struct inode *cpfile)
{
        return NILFS_MDT(cpfile)->mi_entries_per_block;
}

/* block number from the beginning of the file */
static unsigned long
nilfs_cpfile_get_blkoff(const struct inode *cpfile, __u64 cno)
{
        __u64 tcno = cno + NILFS_MDT(cpfile)->mi_first_entry_offset - 1;

        do_div(tcno, nilfs_cpfile_checkpoints_per_block(cpfile));
        return (unsigned long)tcno;
}

/* offset in block */
static unsigned long
nilfs_cpfile_get_offset(const struct inode *cpfile, __u64 cno)
{
        __u64 tcno = cno + NILFS_MDT(cpfile)->mi_first_entry_offset - 1;

        return do_div(tcno, nilfs_cpfile_checkpoints_per_block(cpfile));
}

static __u64 nilfs_cpfile_first_checkpoint_in_block(const struct inode *cpfile,
                                                    unsigned long blkoff)
{
        return (__u64)nilfs_cpfile_checkpoints_per_block(cpfile) * blkoff
                + 1 - NILFS_MDT(cpfile)->mi_first_entry_offset;
}

static unsigned long
nilfs_cpfile_checkpoints_in_block(const struct inode *cpfile,
                                  __u64 curr,
                                  __u64 max)
{
        return min_t(__u64,
                     nilfs_cpfile_checkpoints_per_block(cpfile) -
                     nilfs_cpfile_get_offset(cpfile, curr),
                     max - curr);
}

static inline int nilfs_cpfile_is_in_first(const struct inode *cpfile,
                                           __u64 cno)
{
        return nilfs_cpfile_get_blkoff(cpfile, cno) == 0;
}

static unsigned int
nilfs_cpfile_block_add_valid_checkpoints(const struct inode *cpfile,
                                         struct buffer_head *bh,
                                         void *kaddr,
                                         unsigned int n)
{
        struct nilfs_checkpoint *cp = kaddr + bh_offset(bh);
        unsigned int count;

        count = le32_to_cpu(cp->cp_checkpoints_count) + n;
        cp->cp_checkpoints_count = cpu_to_le32(count);
        return count;
}

static unsigned int
nilfs_cpfile_block_sub_valid_checkpoints(const struct inode *cpfile,
                                         struct buffer_head *bh,
                                         void *kaddr,
                                         unsigned int n)
{
        struct nilfs_checkpoint *cp = kaddr + bh_offset(bh);
        unsigned int count;

        WARN_ON(le32_to_cpu(cp->cp_checkpoints_count) < n);
        count = le32_to_cpu(cp->cp_checkpoints_count) - n;
        cp->cp_checkpoints_count = cpu_to_le32(count);
        return count;
}

static inline struct nilfs_cpfile_header *
nilfs_cpfile_block_get_header(const struct inode *cpfile,
                              struct buffer_head *bh,
                              void *kaddr)
{
        return kaddr + bh_offset(bh);
}

static struct nilfs_checkpoint *
nilfs_cpfile_block_get_checkpoint(const struct inode *cpfile, __u64 cno,
                                  struct buffer_head *bh,
                                  void *kaddr)
{
        return kaddr + bh_offset(bh) + nilfs_cpfile_get_offset(cpfile, cno) *
                NILFS_MDT(cpfile)->mi_entry_size;
}

static void nilfs_cpfile_block_init(struct inode *cpfile,
                                    struct buffer_head *bh,
                                    void *kaddr)
{
        struct nilfs_checkpoint *cp = kaddr + bh_offset(bh);
        size_t cpsz = NILFS_MDT(cpfile)->mi_entry_size;
        int n = nilfs_cpfile_checkpoints_per_block(cpfile);

        while (n-- > 0) {
                nilfs_checkpoint_set_invalid(cp);
                cp = (void *)cp + cpsz;
        }
}

static inline int nilfs_cpfile_get_header_block(struct inode *cpfile,
                                                struct buffer_head **bhp)
{
        return nilfs_mdt_get_block(cpfile, 0, 0, NULL, bhp);
}

static inline int nilfs_cpfile_get_checkpoint_block(struct inode *cpfile,
                                                    __u64 cno,
                                                    int create,
                                                    struct buffer_head **bhp)
{
        return nilfs_mdt_get_block(cpfile,
                                   nilfs_cpfile_get_blkoff(cpfile, cno),
                                   create, nilfs_cpfile_block_init, bhp);
}

/**
 * nilfs_cpfile_find_checkpoint_block - find and get a buffer on cpfile
 * @cpfile: inode of cpfile
 * @start_cno: start checkpoint number (inclusive)
 * @end_cno: end checkpoint number (inclusive)
 * @cnop: place to store the next checkpoint number
 * @bhp: place to store a pointer to buffer_head struct
 *
 * Return Value: On success, it returns 0. On error, the following negative
 * error code is returned.
 *
 * %-ENOMEM - Insufficient memory available.
 *
 * %-EIO - I/O error
 *
 * %-ENOENT - no block exists in the range.
 */
static int nilfs_cpfile_find_checkpoint_block(struct inode *cpfile,
                                              __u64 start_cno, __u64 end_cno,
                                              __u64 *cnop,
                                              struct buffer_head **bhp)
{
        unsigned long start, end, blkoff;
        int ret;

        if (unlikely(start_cno > end_cno))
                return -ENOENT;

        start = nilfs_cpfile_get_blkoff(cpfile, start_cno);
        end = nilfs_cpfile_get_blkoff(cpfile, end_cno);

        ret = nilfs_mdt_find_block(cpfile, start, end, &blkoff, bhp);
        if (!ret)
                *cnop = (blkoff == start) ? start_cno :
                        nilfs_cpfile_first_checkpoint_in_block(cpfile, blkoff);
        return ret;
}

static inline int nilfs_cpfile_delete_checkpoint_block(struct inode *cpfile,
                                                       __u64 cno)
{
        return nilfs_mdt_delete_block(cpfile,
                                      nilfs_cpfile_get_blkoff(cpfile, cno));
}

/**
 * nilfs_cpfile_get_checkpoint - get a checkpoint
 * @cpfile: inode of checkpoint file
 * @cno: checkpoint number
 * @create: create flag
 * @cpp: pointer to a checkpoint
 * @bhp: pointer to a buffer head
 *
 * Description: nilfs_cpfile_get_checkpoint() acquires the checkpoint
 * specified by @cno. A new checkpoint will be created if @cno is the current
 * checkpoint number and @create is nonzero.
 *
 * Return Value: On success, 0 is returned, and the checkpoint and the
 * buffer head of the buffer on which the checkpoint is located are stored in
 * the place pointed by @cpp and @bhp, respectively. On error, one of the
 * following negative error codes is returned.
 *
 * %-EIO - I/O error.
 *
 * %-ENOMEM - Insufficient amount of memory available.
 *
 * %-ENOENT - No such checkpoint.
 *
 * %-EINVAL - invalid checkpoint.
 */
int nilfs_cpfile_get_checkpoint(struct inode *cpfile,
                                __u64 cno,
                                int create,
                                struct nilfs_checkpoint **cpp,
                                struct buffer_head **bhp)
{
        struct buffer_head *header_bh, *cp_bh;
        struct nilfs_cpfile_header *header;
        struct nilfs_checkpoint *cp;
        void *kaddr;
        int ret;

        if (unlikely(cno < 1 || cno > nilfs_mdt_cno(cpfile) ||
                     (cno < nilfs_mdt_cno(cpfile) && create)))
                return -EINVAL;

        down_write(&NILFS_MDT(cpfile)->mi_sem);

        ret = nilfs_cpfile_get_header_block(cpfile, &header_bh);
        if (ret < 0)
                goto out_sem;
        ret = nilfs_cpfile_get_checkpoint_block(cpfile, cno, create, &cp_bh);
        if (ret < 0)
                goto out_header;
        kaddr = kmap(cp_bh->b_page);
        cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, cp_bh, kaddr);
        if (nilfs_checkpoint_invalid(cp)) {
                if (!create) {
                        kunmap(cp_bh->b_page);
                        brelse(cp_bh);
                        ret = -ENOENT;
                        goto out_header;
                }
                /* a newly-created checkpoint */
                nilfs_checkpoint_clear_invalid(cp);
                if (!nilfs_cpfile_is_in_first(cpfile, cno))
                        nilfs_cpfile_block_add_valid_checkpoints(cpfile, cp_bh,
                                                                 kaddr, 1);
                mark_buffer_dirty(cp_bh);

                kaddr = kmap_atomic(header_bh->b_page);
                header = nilfs_cpfile_block_get_header(cpfile, header_bh,
                                                       kaddr);
                le64_add_cpu(&header->ch_ncheckpoints, 1);
                kunmap_atomic(kaddr);
                mark_buffer_dirty(header_bh);
                nilfs_mdt_mark_dirty(cpfile);
        }

        if (cpp != NULL)
                *cpp = cp;
        *bhp = cp_bh;

 out_header:
        brelse(header_bh);

 out_sem:
        up_write(&NILFS_MDT(cpfile)->mi_sem);
        return ret;
}

/**
 * nilfs_cpfile_put_checkpoint - put a checkpoint
 * @cpfile: inode of checkpoint file
 * @cno: checkpoint number
 * @bh: buffer head
 *
 * Description: nilfs_cpfile_put_checkpoint() releases the checkpoint
 * specified by @cno. @bh must be the buffer head which has been returned by
 * a previous call to nilfs_cpfile_get_checkpoint() with @cno.
 */
void nilfs_cpfile_put_checkpoint(struct inode *cpfile, __u64 cno,
                                 struct buffer_head *bh)
{
        kunmap(bh->b_page);
        brelse(bh);
}

/**
 * nilfs_cpfile_delete_checkpoints - delete checkpoints
 * @cpfile: inode of checkpoint file
 * @start: start checkpoint number
 * @end: end checkpoint number
 *
 * Description: nilfs_cpfile_delete_checkpoints() deletes the checkpoints in
 * the period from @start to @end, excluding @end itself. The checkpoints
 * which have been already deleted are ignored.
 *
 * Return Value: On success, 0 is returned. On error, one of the following
 * negative error codes is returned.
 *
 * %-EIO - I/O error.
 *
 * %-ENOMEM - Insufficient amount of memory available.
 *
 * %-EINVAL - invalid checkpoints.
 */
int nilfs_cpfile_delete_checkpoints(struct inode *cpfile,
                                    __u64 start,
                                    __u64 end)
{
        struct buffer_head *header_bh, *cp_bh;
        struct nilfs_cpfile_header *header;
        struct nilfs_checkpoint *cp;
        size_t cpsz = NILFS_MDT(cpfile)->mi_entry_size;
        __u64 cno;
        void *kaddr;
        unsigned long tnicps;
        int ret, ncps, nicps, nss, count, i;

        if (unlikely(start == 0 || start > end)) {
                nilfs_err(cpfile->i_sb,
                          "cannot delete checkpoints: invalid range [%llu, %llu)",
                          (unsigned long long)start, (unsigned long long)end);
                return -EINVAL;
        }

        down_write(&NILFS_MDT(cpfile)->mi_sem);

        ret = nilfs_cpfile_get_header_block(cpfile, &header_bh);
        if (ret < 0)
                goto out_sem;
        tnicps = 0;
        nss = 0;

        for (cno = start; cno < end; cno += ncps) {
                ncps = nilfs_cpfile_checkpoints_in_block(cpfile, cno, end);
                ret = nilfs_cpfile_get_checkpoint_block(cpfile, cno, 0, &cp_bh);
                if (ret < 0) {
                        if (ret != -ENOENT)
                                break;
                        /* skip hole */
                        ret = 0;
                        continue;
                }

                kaddr = kmap_atomic(cp_bh->b_page);
                cp = nilfs_cpfile_block_get_checkpoint(
                        cpfile, cno, cp_bh, kaddr);
                nicps = 0;
                for (i = 0; i < ncps; i++, cp = (void *)cp + cpsz) {
                        if (nilfs_checkpoint_snapshot(cp)) {
                                nss++;
                        } else if (!nilfs_checkpoint_invalid(cp)) {
                                nilfs_checkpoint_set_invalid(cp);
                                nicps++;
                        }
                }
                if (nicps > 0) {
                        tnicps += nicps;
                        mark_buffer_dirty(cp_bh);
                        nilfs_mdt_mark_dirty(cpfile);
                        if (!nilfs_cpfile_is_in_first(cpfile, cno)) {
                                count =
                                  nilfs_cpfile_block_sub_valid_checkpoints(
                                                cpfile, cp_bh, kaddr, nicps);
                                if (count == 0) {
                                        /* make hole */
                                        kunmap_atomic(kaddr);
                                        brelse(cp_bh);
                                        ret =
                                          nilfs_cpfile_delete_checkpoint_block(
                                                                   cpfile, cno);
                                        if (ret == 0)
                                                continue;
                                        nilfs_err(cpfile->i_sb,
                                                  "error %d deleting checkpoint block",
                                                  ret);
                                        break;
                                }
                        }
                }

                kunmap_atomic(kaddr);
                brelse(cp_bh);
        }

        if (tnicps > 0) {
                kaddr = kmap_atomic(header_bh->b_page);
                header = nilfs_cpfile_block_get_header(cpfile, header_bh,
                                                       kaddr);
                le64_add_cpu(&header->ch_ncheckpoints, -(u64)tnicps);
                mark_buffer_dirty(header_bh);
                nilfs_mdt_mark_dirty(cpfile);
                kunmap_atomic(kaddr);
        }

        brelse(header_bh);
        if (nss > 0)
                ret = -EBUSY;

 out_sem:
        up_write(&NILFS_MDT(cpfile)->mi_sem);
        return ret;
}

static void nilfs_cpfile_checkpoint_to_cpinfo(struct inode *cpfile,
                                              struct nilfs_checkpoint *cp,
                                              struct nilfs_cpinfo *ci)
{
        ci->ci_flags = le32_to_cpu(cp->cp_flags);
        ci->ci_cno = le64_to_cpu(cp->cp_cno);
        ci->ci_create = le64_to_cpu(cp->cp_create);
        ci->ci_nblk_inc = le64_to_cpu(cp->cp_nblk_inc);
        ci->ci_inodes_count = le64_to_cpu(cp->cp_inodes_count);
        ci->ci_blocks_count = le64_to_cpu(cp->cp_blocks_count);
        ci->ci_next = le64_to_cpu(cp->cp_snapshot_list.ssl_next);
}

static ssize_t nilfs_cpfile_do_get_cpinfo(struct inode *cpfile, __u64 *cnop,
                                          void *buf, unsigned int cisz,
                                          size_t nci)
{
        struct nilfs_checkpoint *cp;
        struct nilfs_cpinfo *ci = buf;
        struct buffer_head *bh;
        size_t cpsz = NILFS_MDT(cpfile)->mi_entry_size;
        __u64 cur_cno = nilfs_mdt_cno(cpfile), cno = *cnop;
        void *kaddr;
        int n, ret;
        int ncps, i;

        if (cno == 0)
                return -ENOENT; /* checkpoint number 0 is invalid */
        down_read(&NILFS_MDT(cpfile)->mi_sem);

        for (n = 0; n < nci; cno += ncps) {
                ret = nilfs_cpfile_find_checkpoint_block(
                        cpfile, cno, cur_cno - 1, &cno, &bh);
                if (ret < 0) {
                        if (likely(ret == -ENOENT))
                                break;
                        goto out;
                }
                ncps = nilfs_cpfile_checkpoints_in_block(cpfile, cno, cur_cno);

                kaddr = kmap_atomic(bh->b_page);
                cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, bh, kaddr);
                for (i = 0; i < ncps && n < nci; i++, cp = (void *)cp + cpsz) {
                        if (!nilfs_checkpoint_invalid(cp)) {
                                nilfs_cpfile_checkpoint_to_cpinfo(cpfile, cp,
                                                                  ci);
                                ci = (void *)ci + cisz;
                                n++;
                        }
                }
                kunmap_atomic(kaddr);
                brelse(bh);
        }

        ret = n;
        if (n > 0) {
                ci = (void *)ci - cisz;
                *cnop = ci->ci_cno + 1;
        }

 out:
        up_read(&NILFS_MDT(cpfile)->mi_sem);
        return ret;
}

static ssize_t nilfs_cpfile_do_get_ssinfo(struct inode *cpfile, __u64 *cnop,
                                          void *buf, unsigned int cisz,
                                          size_t nci)
{
        struct buffer_head *bh;
        struct nilfs_cpfile_header *header;
        struct nilfs_checkpoint *cp;
        struct nilfs_cpinfo *ci = buf;
        __u64 curr = *cnop, next;
        unsigned long curr_blkoff, next_blkoff;
        void *kaddr;
        int n = 0, ret;

        down_read(&NILFS_MDT(cpfile)->mi_sem);

        if (curr == 0) {
                ret = nilfs_cpfile_get_header_block(cpfile, &bh);
                if (ret < 0)
                        goto out;
                kaddr = kmap_atomic(bh->b_page);
                header = nilfs_cpfile_block_get_header(cpfile, bh, kaddr);
                curr = le64_to_cpu(header->ch_snapshot_list.ssl_next);
                kunmap_atomic(kaddr);
                brelse(bh);
                if (curr == 0) {
                        ret = 0;
                        goto out;
                }
        } else if (unlikely(curr == ~(__u64)0)) {
                ret = 0;
                goto out;
        }

        curr_blkoff = nilfs_cpfile_get_blkoff(cpfile, curr);
        ret = nilfs_cpfile_get_checkpoint_block(cpfile, curr, 0, &bh);
        if (unlikely(ret < 0)) {
                if (ret == -ENOENT)
                        ret = 0; /* No snapshots (started from a hole block) */
                goto out;
        }
        kaddr = kmap_atomic(bh->b_page);
        while (n < nci) {
                cp = nilfs_cpfile_block_get_checkpoint(cpfile, curr, bh, kaddr);
                curr = ~(__u64)0; /* Terminator */
                if (unlikely(nilfs_checkpoint_invalid(cp) ||
                             !nilfs_checkpoint_snapshot(cp)))
                        break;
                nilfs_cpfile_checkpoint_to_cpinfo(cpfile, cp, ci);
                ci = (void *)ci + cisz;
                n++;
                next = le64_to_cpu(cp->cp_snapshot_list.ssl_next);
                if (next == 0)
                        break; /* reach end of the snapshot list */

                next_blkoff = nilfs_cpfile_get_blkoff(cpfile, next);
                if (curr_blkoff != next_blkoff) {
                        kunmap_atomic(kaddr);
                        brelse(bh);
                        ret = nilfs_cpfile_get_checkpoint_block(cpfile, next,
                                                                0, &bh);
                        if (unlikely(ret < 0)) {
                                WARN_ON(ret == -ENOENT);
                                goto out;
                        }
                        kaddr = kmap_atomic(bh->b_page);
                }
                curr = next;
                curr_blkoff = next_blkoff;
        }
        kunmap_atomic(kaddr);
        brelse(bh);
        *cnop = curr;
        ret = n;

 out:
        up_read(&NILFS_MDT(cpfile)->mi_sem);
        return ret;
}

/**
 * nilfs_cpfile_get_cpinfo -
 * @cpfile:
 * @cno:
 * @ci:
 * @nci:
 */

ssize_t nilfs_cpfile_get_cpinfo(struct inode *cpfile, __u64 *cnop, int mode,
                                void *buf, unsigned int cisz, size_t nci)
{
        switch (mode) {
        case NILFS_CHECKPOINT:
                return nilfs_cpfile_do_get_cpinfo(cpfile, cnop, buf, cisz, nci);
        case NILFS_SNAPSHOT:
                return nilfs_cpfile_do_get_ssinfo(cpfile, cnop, buf, cisz, nci);
        default:
                return -EINVAL;
        }
}

/**
 * nilfs_cpfile_delete_checkpoint -
 * @cpfile:
 * @cno:
 */
int nilfs_cpfile_delete_checkpoint(struct inode *cpfile, __u64 cno)
{
        struct nilfs_cpinfo ci;
        __u64 tcno = cno;
        ssize_t nci;

        nci = nilfs_cpfile_do_get_cpinfo(cpfile, &tcno, &ci, sizeof(ci), 1);
        if (nci < 0)
                return nci;
        else if (nci == 0 || ci.ci_cno != cno)
                return -ENOENT;
        else if (nilfs_cpinfo_snapshot(&ci))
                return -EBUSY;

        return nilfs_cpfile_delete_checkpoints(cpfile, cno, cno + 1);
}

static struct nilfs_snapshot_list *
nilfs_cpfile_block_get_snapshot_list(const struct inode *cpfile,
                                     __u64 cno,
                                     struct buffer_head *bh,
                                     void *kaddr)
{
        struct nilfs_cpfile_header *header;
        struct nilfs_checkpoint *cp;
        struct nilfs_snapshot_list *list;

        if (cno != 0) {
                cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, bh, kaddr);
                list = &cp->cp_snapshot_list;
        } else {
                header = nilfs_cpfile_block_get_header(cpfile, bh, kaddr);
                list = &header->ch_snapshot_list;
        }
        return list;
}

static int nilfs_cpfile_set_snapshot(struct inode *cpfile, __u64 cno)
{
        struct buffer_head *header_bh, *curr_bh, *prev_bh, *cp_bh;
        struct nilfs_cpfile_header *header;
        struct nilfs_checkpoint *cp;
        struct nilfs_snapshot_list *list;
        __u64 curr, prev;
        unsigned long curr_blkoff, prev_blkoff;
        void *kaddr;
        int ret;

        if (cno == 0)
                return -ENOENT; /* checkpoint number 0 is invalid */
        down_write(&NILFS_MDT(cpfile)->mi_sem);

        ret = nilfs_cpfile_get_checkpoint_block(cpfile, cno, 0, &cp_bh);
        if (ret < 0)
                goto out_sem;
        kaddr = kmap_atomic(cp_bh->b_page);
        cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, cp_bh, kaddr);
        if (nilfs_checkpoint_invalid(cp)) {
                ret = -ENOENT;
                kunmap_atomic(kaddr);
                goto out_cp;
        }
        if (nilfs_checkpoint_snapshot(cp)) {
                ret = 0;
                kunmap_atomic(kaddr);
                goto out_cp;
        }
        kunmap_atomic(kaddr);

        ret = nilfs_cpfile_get_header_block(cpfile, &header_bh);
        if (ret < 0)
                goto out_cp;
        kaddr = kmap_atomic(header_bh->b_page);
        header = nilfs_cpfile_block_get_header(cpfile, header_bh, kaddr);
        list = &header->ch_snapshot_list;
        curr_bh = header_bh;
        get_bh(curr_bh);
        curr = 0;
        curr_blkoff = 0;
        prev = le64_to_cpu(list->ssl_prev);
        while (prev > cno) {
                prev_blkoff = nilfs_cpfile_get_blkoff(cpfile, prev);
                curr = prev;
                if (curr_blkoff != prev_blkoff) {
                        kunmap_atomic(kaddr);
                        brelse(curr_bh);
                        ret = nilfs_cpfile_get_checkpoint_block(cpfile, curr,
                                                                0, &curr_bh);
                        if (ret < 0)
                                goto out_header;
                        kaddr = kmap_atomic(curr_bh->b_page);
                }
                curr_blkoff = prev_blkoff;
                cp = nilfs_cpfile_block_get_checkpoint(
                        cpfile, curr, curr_bh, kaddr);
                list = &cp->cp_snapshot_list;
                prev = le64_to_cpu(list->ssl_prev);
        }
        kunmap_atomic(kaddr);

        if (prev != 0) {
                ret = nilfs_cpfile_get_checkpoint_block(cpfile, prev, 0,
                                                        &prev_bh);
                if (ret < 0)
                        goto out_curr;
        } else {
                prev_bh = header_bh;
                get_bh(prev_bh);
        }

        kaddr = kmap_atomic(curr_bh->b_page);
        list = nilfs_cpfile_block_get_snapshot_list(
                cpfile, curr, curr_bh, kaddr);
        list->ssl_prev = cpu_to_le64(cno);
        kunmap_atomic(kaddr);

        kaddr = kmap_atomic(cp_bh->b_page);
        cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, cp_bh, kaddr);
        cp->cp_snapshot_list.ssl_next = cpu_to_le64(curr);
        cp->cp_snapshot_list.ssl_prev = cpu_to_le64(prev);
        nilfs_checkpoint_set_snapshot(cp);
        kunmap_atomic(kaddr);

        kaddr = kmap_atomic(prev_bh->b_page);
        list = nilfs_cpfile_block_get_snapshot_list(
                cpfile, prev, prev_bh, kaddr);
        list->ssl_next = cpu_to_le64(cno);
        kunmap_atomic(kaddr);

        kaddr = kmap_atomic(header_bh->b_page);
        header = nilfs_cpfile_block_get_header(cpfile, header_bh, kaddr);
        le64_add_cpu(&header->ch_nsnapshots, 1);
        kunmap_atomic(kaddr);

        mark_buffer_dirty(prev_bh);
        mark_buffer_dirty(curr_bh);
        mark_buffer_dirty(cp_bh);
        mark_buffer_dirty(header_bh);
        nilfs_mdt_mark_dirty(cpfile);

        brelse(prev_bh);

 out_curr:
        brelse(curr_bh);

 out_header:
        brelse(header_bh);

 out_cp:
        brelse(cp_bh);

 out_sem:
        up_write(&NILFS_MDT(cpfile)->mi_sem);
        return ret;
}

static int nilfs_cpfile_clear_snapshot(struct inode *cpfile, __u64 cno)
{
        struct buffer_head *header_bh, *next_bh, *prev_bh, *cp_bh;
        struct nilfs_cpfile_header *header;
        struct nilfs_checkpoint *cp;
        struct nilfs_snapshot_list *list;
        __u64 next, prev;
        void *kaddr;
        int ret;

        if (cno == 0)
                return -ENOENT; /* checkpoint number 0 is invalid */
        down_write(&NILFS_MDT(cpfile)->mi_sem);

        ret = nilfs_cpfile_get_checkpoint_block(cpfile, cno, 0, &cp_bh);
        if (ret < 0)
                goto out_sem;
        kaddr = kmap_atomic(cp_bh->b_page);
        cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, cp_bh, kaddr);
        if (nilfs_checkpoint_invalid(cp)) {
                ret = -ENOENT;
                kunmap_atomic(kaddr);
                goto out_cp;
        }
        if (!nilfs_checkpoint_snapshot(cp)) {
                ret = 0;
                kunmap_atomic(kaddr);
                goto out_cp;
        }

        list = &cp->cp_snapshot_list;
        next = le64_to_cpu(list->ssl_next);
        prev = le64_to_cpu(list->ssl_prev);
        kunmap_atomic(kaddr);

        ret = nilfs_cpfile_get_header_block(cpfile, &header_bh);
        if (ret < 0)
                goto out_cp;
        if (next != 0) {
                ret = nilfs_cpfile_get_checkpoint_block(cpfile, next, 0,
                                                        &next_bh);
                if (ret < 0)
                        goto out_header;
        } else {
                next_bh = header_bh;
                get_bh(next_bh);
        }
        if (prev != 0) {
                ret = nilfs_cpfile_get_checkpoint_block(cpfile, prev, 0,
                                                        &prev_bh);
                if (ret < 0)
                        goto out_next;
        } else {
                prev_bh = header_bh;
                get_bh(prev_bh);
        }

        kaddr = kmap_atomic(next_bh->b_page);
        list = nilfs_cpfile_block_get_snapshot_list(
                cpfile, next, next_bh, kaddr);
        list->ssl_prev = cpu_to_le64(prev);
        kunmap_atomic(kaddr);

        kaddr = kmap_atomic(prev_bh->b_page);
        list = nilfs_cpfile_block_get_snapshot_list(
                cpfile, prev, prev_bh, kaddr);
        list->ssl_next = cpu_to_le64(next);
        kunmap_atomic(kaddr);

        kaddr = kmap_atomic(cp_bh->b_page);
        cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, cp_bh, kaddr);
        cp->cp_snapshot_list.ssl_next = cpu_to_le64(0);
        cp->cp_snapshot_list.ssl_prev = cpu_to_le64(0);
        nilfs_checkpoint_clear_snapshot(cp);
        kunmap_atomic(kaddr);

        kaddr = kmap_atomic(header_bh->b_page);
        header = nilfs_cpfile_block_get_header(cpfile, header_bh, kaddr);
        le64_add_cpu(&header->ch_nsnapshots, -1);
        kunmap_atomic(kaddr);

        mark_buffer_dirty(next_bh);
        mark_buffer_dirty(prev_bh);
        mark_buffer_dirty(cp_bh);
        mark_buffer_dirty(header_bh);
        nilfs_mdt_mark_dirty(cpfile);

        brelse(prev_bh);

 out_next:
        brelse(next_bh);

 out_header:
        brelse(header_bh);

 out_cp:
        brelse(cp_bh);

 out_sem:
        up_write(&NILFS_MDT(cpfile)->mi_sem);
        return ret;
}

/**
 * nilfs_cpfile_is_snapshot -
 * @cpfile: inode of checkpoint file
 * @cno: checkpoint number
 *
 * Description:
 *
 * Return Value: On success, 1 is returned if the checkpoint specified by
 * @cno is a snapshot, or 0 if not. On error, one of the following negative
 * error codes is returned.
 *
 * %-EIO - I/O error.
 *
 * %-ENOMEM - Insufficient amount of memory available.
 *
 * %-ENOENT - No such checkpoint.
 */
int nilfs_cpfile_is_snapshot(struct inode *cpfile, __u64 cno)
{
        struct buffer_head *bh;
        struct nilfs_checkpoint *cp;
        void *kaddr;
        int ret;

        /*
         * CP number is invalid if it's zero or larger than the
         * largest existing one.
         */
        if (cno == 0 || cno >= nilfs_mdt_cno(cpfile))
                return -ENOENT;
        down_read(&NILFS_MDT(cpfile)->mi_sem);

        ret = nilfs_cpfile_get_checkpoint_block(cpfile, cno, 0, &bh);
        if (ret < 0)
                goto out;
        kaddr = kmap_atomic(bh->b_page);
        cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, bh, kaddr);
        if (nilfs_checkpoint_invalid(cp))
                ret = -ENOENT;
        else
                ret = nilfs_checkpoint_snapshot(cp);
        kunmap_atomic(kaddr);
        brelse(bh);

 out:
        up_read(&NILFS_MDT(cpfile)->mi_sem);
        return ret;
}

/**
 * nilfs_cpfile_change_cpmode - change checkpoint mode
 * @cpfile: inode of checkpoint file
 * @cno: checkpoint number
 * @mode: mode of checkpoint
 *
 * Description: nilfs_change_cpmode() changes the mode of the checkpoint
 * specified by @cno. The mode @mode is NILFS_CHECKPOINT or NILFS_SNAPSHOT.
 *
 * Return Value: On success, 0 is returned. On error, one of the following
 * negative error codes is returned.
 *
 * %-EIO - I/O error.
 *
 * %-ENOMEM - Insufficient amount of memory available.
 *
 * %-ENOENT - No such checkpoint.
 */
int nilfs_cpfile_change_cpmode(struct inode *cpfile, __u64 cno, int mode)
{
        int ret;

        switch (mode) {
        case NILFS_CHECKPOINT:
                if (nilfs_checkpoint_is_mounted(cpfile->i_sb, cno))
                        /*
                         * Current implementation does not have to protect
                         * plain read-only mounts since they are exclusive
                         * with a read/write mount and are protected from the
                         * cleaner.
                         */
                        ret = -EBUSY;
                else
                        ret = nilfs_cpfile_clear_snapshot(cpfile, cno);
                return ret;
        case NILFS_SNAPSHOT:
                return nilfs_cpfile_set_snapshot(cpfile, cno);
        default:
                return -EINVAL;
        }
}

/**
 * nilfs_cpfile_get_stat - get checkpoint statistics
 * @cpfile: inode of checkpoint file
 * @cpstat: pointer to a structure of checkpoint statistics
 *
 * Description: nilfs_cpfile_get_stat() returns information about checkpoints.
 *
 * Return Value: On success, 0 is returned, and checkpoints information is
 * stored in the place pointed by @cpstat. On error, one of the following
 * negative error codes is returned.
 *
 * %-EIO - I/O error.
 *
 * %-ENOMEM - Insufficient amount of memory available.
 */
int nilfs_cpfile_get_stat(struct inode *cpfile, struct nilfs_cpstat *cpstat)
{
        struct buffer_head *bh;
        struct nilfs_cpfile_header *header;
        void *kaddr;
        int ret;

        down_read(&NILFS_MDT(cpfile)->mi_sem);

        ret = nilfs_cpfile_get_header_block(cpfile, &bh);
        if (ret < 0)
                goto out_sem;
        kaddr = kmap_atomic(bh->b_page);
        header = nilfs_cpfile_block_get_header(cpfile, bh, kaddr);
        cpstat->cs_cno = nilfs_mdt_cno(cpfile);
        cpstat->cs_ncps = le64_to_cpu(header->ch_ncheckpoints);
        cpstat->cs_nsss = le64_to_cpu(header->ch_nsnapshots);
        kunmap_atomic(kaddr);
        brelse(bh);

 out_sem:
        up_read(&NILFS_MDT(cpfile)->mi_sem);
        return ret;
}

/**
 * nilfs_cpfile_read - read or get cpfile inode
 * @sb: super block instance
 * @cpsize: size of a checkpoint entry
 * @raw_inode: on-disk cpfile inode
 * @inodep: buffer to store the inode
 */
int nilfs_cpfile_read(struct super_block *sb, size_t cpsize,
                      struct nilfs_inode *raw_inode, struct inode **inodep)
{
        struct inode *cpfile;
        int err;

        if (cpsize > sb->s_blocksize) {
                nilfs_err(sb, "too large checkpoint size: %zu bytes", cpsize);
                return -EINVAL;
        } else if (cpsize < NILFS_MIN_CHECKPOINT_SIZE) {
                nilfs_err(sb, "too small checkpoint size: %zu bytes", cpsize);
                return -EINVAL;
        }

        cpfile = nilfs_iget_locked(sb, NULL, NILFS_CPFILE_INO);
        if (unlikely(!cpfile))
                return -ENOMEM;
        if (!(cpfile->i_state & I_NEW))
                goto out;

        err = nilfs_mdt_init(cpfile, NILFS_MDT_GFP, 0);
        if (err)
                goto failed;

        nilfs_mdt_set_entry_size(cpfile, cpsize,
                                 sizeof(struct nilfs_cpfile_header));

        err = nilfs_read_inode_common(cpfile, raw_inode);
        if (err)
                goto failed;

        unlock_new_inode(cpfile);
 out:
        *inodep = cpfile;
        return 0;
 failed:
        iget_failed(cpfile);
        return err;
}