cpfile.c

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/*
 * cpfile.c - NILFS checkpoint file.
 *
 * Copyright (C) 2006-2008 Nippon Telegraph and Telephone Corporation.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * Written by Koji Sato <[email protected]>.
 */

#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/buffer_head.h>
#include <linux/errno.h>
#include <linux/nilfs2_fs.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 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);
}

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));
}

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;
}

void nilfs_cpfile_put_checkpoint(struct inode *cpfile, __u64 cno,
                 struct buffer_head *bh)
{
    kunmap(bh->b_page);
    brelse(bh);
}

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)) {
        printk(KERN_ERR "%s: invalid range of checkpoint numbers: "
               "[%llu, %llu)\n", __func__,
               (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;
                    printk(KERN_ERR
                           "%s: cannot delete block\n",
                           __func__);
                    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 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; cno < cur_cno && n < nci; cno += ncps) {
        ncps = nilfs_cpfile_checkpoints_in_block(cpfile, cno, cur_cno);
        ret = nilfs_cpfile_get_checkpoint_block(cpfile, cno, 0, &bh);
        if (ret < 0) {
            if (ret != -ENOENT)
                goto out;
            continue; /* skip hole */
        }

        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 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;
}

ssize_t nilfs_cpfile_get_cpinfo(struct inode *cpfile, __u64 *cnop, int mode,
                void *buf, unsigned 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;
    }
}

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;
}

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 exist 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;
}

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;
    }
}

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;
}

int nilfs_cpfile_read(struct super_block *sb, size_t cpsize,
              struct nilfs_inode *raw_inode, struct inode **inodep)
{
    struct inode *cpfile;
    int err;

    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;
}