nilfs2: checkpoint file

This adds a meta data file which holds checkpoint entries in its data
blocks.

Signed-off-by: Koji Sato <sato.koji@lab.ntt.co.jp>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 908 insertions, 0 deletions

diff --git a/fs/nilfs2/cpfile.c b/fs/nilfs2/cpfile.c
new file mode 100644
index 000000000000..991633aad1d8
--- /dev/null
+++ b/fs/nilfs2/cpfile.c
@@ -0,0 +1,908 @@
+/*
+ * 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 <koji@osrg.net>.
+ */
+
+#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;
+
+        BUG_ON(cno == 0); /* checkpoint number 0 is invalid */
+        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;
+
+        BUG_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));
+}
+
+/**
+ * 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.
+ */
+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;
+
+        BUG_ON(cno < 1 || cno > nilfs_mdt_cno(cpfile) ||
+               (cno < nilfs_mdt_cno(cpfile) && create));
+
+        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);
+                nilfs_mdt_mark_buffer_dirty(cp_bh);
+
+                kaddr = kmap_atomic(header_bh->b_page, KM_USER0);
+                header = nilfs_cpfile_block_get_header(cpfile, header_bh,
+                                                       kaddr);
+                le64_add_cpu(&header->ch_ncheckpoints, 1);
+                kunmap_atomic(kaddr, KM_USER0);
+                nilfs_mdt_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 numer
+ *
+ * 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, count, i;
+
+        if ((start == 0) || (start > end)) {
+                printk(KERN_CRIT "%s: start = %llu, end = %llu\n",
+                       __func__,
+                       (unsigned long long)start,
+                       (unsigned long long)end);
+                BUG();
+        }
+
+        /* cannot delete the latest checkpoint */
+        if (start == nilfs_mdt_cno(cpfile) - 1)
+                return -EPERM;
+
+        down_write(&NILFS_MDT(cpfile)->mi_sem);
+
+        ret = nilfs_cpfile_get_header_block(cpfile, &header_bh);
+        if (ret < 0)
+                goto out_sem;
+        tnicps = 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)
+                                goto out_sem;
+                        /* skip hole */
+                        ret = 0;
+                        continue;
+                }
+
+                kaddr = kmap_atomic(cp_bh->b_page, KM_USER0);
+                cp = nilfs_cpfile_block_get_checkpoint(
+                        cpfile, cno, cp_bh, kaddr);
+                nicps = 0;
+                for (i = 0; i < ncps; i++, cp = (void *)cp + cpsz) {
+                        BUG_ON(nilfs_checkpoint_snapshot(cp));
+                        if (!nilfs_checkpoint_invalid(cp)) {
+                                nilfs_checkpoint_set_invalid(cp);
+                                nicps++;
+                        }
+                }
+                if (nicps > 0) {
+                        tnicps += nicps;
+                        nilfs_mdt_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)) == 0) {
+                                /* make hole */
+                                kunmap_atomic(kaddr, KM_USER0);
+                                brelse(cp_bh);
+                                ret = nilfs_cpfile_delete_checkpoint_block(
+                                        cpfile, cno);
+                                if (ret == 0)
+                                        continue;
+                                printk(KERN_ERR "%s: cannot delete block\n",
+                                       __func__);
+                                goto out_sem;
+                        }
+                }
+
+                kunmap_atomic(kaddr, KM_USER0);
+                brelse(cp_bh);
+        }
+
+        if (tnicps > 0) {
+                kaddr = kmap_atomic(header_bh->b_page, KM_USER0);
+                header = nilfs_cpfile_block_get_header(cpfile, header_bh,
+                                                       kaddr);
+                le64_add_cpu(&header->ch_ncheckpoints, -tnicps);
+                nilfs_mdt_mark_buffer_dirty(header_bh);
+                nilfs_mdt_mark_dirty(cpfile);
+                kunmap_atomic(kaddr, KM_USER0);
+        }
+        brelse(header_bh);
+
+ 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 cno,
+                                          struct nilfs_cpinfo *ci, size_t nci)
+{
+        struct nilfs_checkpoint *cp;
+        struct buffer_head *bh;
+        size_t cpsz = NILFS_MDT(cpfile)->mi_entry_size;
+        __u64 cur_cno = nilfs_mdt_cno(cpfile);
+        void *kaddr;
+        int n, ret;
+        int ncps, i;
+
+        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, KM_USER0);
+                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[n++]);
+                }
+                kunmap_atomic(kaddr, KM_USER0);
+                brelse(bh);
+        }
+
+        ret = n;
+
+ out:
+        up_read(&NILFS_MDT(cpfile)->mi_sem);
+        return ret;
+}
+
+static ssize_t nilfs_cpfile_do_get_ssinfo(struct inode *cpfile, __u64 cno,
+                                          struct nilfs_cpinfo *ci, size_t nci)
+{
+        struct buffer_head *bh;
+        struct nilfs_cpfile_header *header;
+        struct nilfs_checkpoint *cp;
+        __u64 curr, next;
+        unsigned long curr_blkoff, next_blkoff;
+        void *kaddr;
+        int n, ret;
+
+        down_read(&NILFS_MDT(cpfile)->mi_sem);
+
+        if (cno == 0) {
+                ret = nilfs_cpfile_get_header_block(cpfile, &bh);
+                if (ret < 0)
+                        goto out;
+                kaddr = kmap_atomic(bh->b_page, KM_USER0);
+                header = nilfs_cpfile_block_get_header(cpfile, bh, kaddr);
+                curr = le64_to_cpu(header->ch_snapshot_list.ssl_next);
+                kunmap_atomic(kaddr, KM_USER0);
+                brelse(bh);
+                if (curr == 0) {
+                        ret = 0;
+                        goto out;
+                }
+        } else
+                curr = cno;
+        curr_blkoff = nilfs_cpfile_get_blkoff(cpfile, curr);
+        ret = nilfs_cpfile_get_checkpoint_block(cpfile, curr, 0, &bh);
+        if (ret < 0)
+                goto out;
+        kaddr = kmap_atomic(bh->b_page, KM_USER0);
+        for (n = 0; n < nci; n++) {
+                cp = nilfs_cpfile_block_get_checkpoint(
+                        cpfile, curr, bh, kaddr);
+                nilfs_cpfile_checkpoint_to_cpinfo(cpfile, cp, &ci[n]);
+                next = le64_to_cpu(cp->cp_snapshot_list.ssl_next);
+                if (next == 0) {
+                        curr = next;
+                        n++;
+                        break;
+                }
+                next_blkoff = nilfs_cpfile_get_blkoff(cpfile, next);
+                if (curr_blkoff != next_blkoff) {
+                        kunmap_atomic(kaddr, KM_USER0);
+                        brelse(bh);
+                        ret = nilfs_cpfile_get_checkpoint_block(cpfile, next,
+                                                                0, &bh);
+                        if (ret < 0)
+                                goto out;
+                        kaddr = kmap_atomic(bh->b_page, KM_USER0);
+                }
+                curr = next;
+                curr_blkoff = next_blkoff;
+        }
+        kunmap_atomic(kaddr, KM_USER0);
+        brelse(bh);
+        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 cno, int mode,
+                                struct nilfs_cpinfo *ci, size_t nci)
+{
+        switch (mode) {
+        case NILFS_CHECKPOINT:
+                return nilfs_cpfile_do_get_cpinfo(cpfile, cno, ci, nci);
+        case NILFS_SNAPSHOT:
+                return nilfs_cpfile_do_get_ssinfo(cpfile, cno, ci, nci);
+        default:
+                return -EINVAL;
+        }
+}
+
+/**
+ * nilfs_cpfile_delete_checkpoint -
+ * @cpfile:
+ * @cno:
+ */
+int nilfs_cpfile_delete_checkpoint(struct inode *cpfile, __u64 cno)
+{
+        struct nilfs_cpinfo ci;
+        ssize_t nci;
+        int ret;
+
+        /* checkpoint number 0 is invalid */
+        if (cno == 0)
+                return -ENOENT;
+        nci = nilfs_cpfile_do_get_cpinfo(cpfile, cno, &ci, 1);
+        if (nci < 0)
+                return nci;
+        else if (nci == 0 || ci.ci_cno != cno)
+                return -ENOENT;
+
+        /* cannot delete the latest checkpoint nor snapshots */
+        ret = nilfs_cpinfo_snapshot(&ci);
+        if (ret < 0)
+                return ret;
+        else if (ret > 0 || cno == nilfs_mdt_cno(cpfile) - 1)
+                return -EPERM;
+
+        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;
+
+        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, KM_USER0);
+        cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, cp_bh, kaddr);
+        if (nilfs_checkpoint_invalid(cp)) {
+                ret = -ENOENT;
+                kunmap_atomic(kaddr, KM_USER0);
+                goto out_cp;
+        }
+        if (nilfs_checkpoint_snapshot(cp)) {
+                ret = 0;
+                kunmap_atomic(kaddr, KM_USER0);
+                goto out_cp;
+        }
+        kunmap_atomic(kaddr, KM_USER0);
+
+        ret = nilfs_cpfile_get_header_block(cpfile, &header_bh);
+        if (ret < 0)
+                goto out_cp;
+        kaddr = kmap_atomic(header_bh->b_page, KM_USER0);
+        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, KM_USER0);
+                        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, KM_USER0);
+                }
+                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, KM_USER0);
+
+        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, KM_USER0);
+        list = nilfs_cpfile_block_get_snapshot_list(
+                cpfile, curr, curr_bh, kaddr);
+        list->ssl_prev = cpu_to_le64(cno);
+        kunmap_atomic(kaddr, KM_USER0);
+
+        kaddr = kmap_atomic(cp_bh->b_page, KM_USER0);
+        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, KM_USER0);
+
+        kaddr = kmap_atomic(prev_bh->b_page, KM_USER0);
+        list = nilfs_cpfile_block_get_snapshot_list(
+                cpfile, prev, prev_bh, kaddr);
+        list->ssl_next = cpu_to_le64(cno);
+        kunmap_atomic(kaddr, KM_USER0);
+
+        kaddr = kmap_atomic(header_bh->b_page, KM_USER0);
+        header = nilfs_cpfile_block_get_header(cpfile, header_bh, kaddr);
+        le64_add_cpu(&header->ch_nsnapshots, 1);
+        kunmap_atomic(kaddr, KM_USER0);
+
+        nilfs_mdt_mark_buffer_dirty(prev_bh);
+        nilfs_mdt_mark_buffer_dirty(curr_bh);
+        nilfs_mdt_mark_buffer_dirty(cp_bh);
+        nilfs_mdt_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;
+
+        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, KM_USER0);
+        cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, cp_bh, kaddr);
+        if (nilfs_checkpoint_invalid(cp)) {
+                ret = -ENOENT;
+                kunmap_atomic(kaddr, KM_USER0);
+                goto out_cp;
+        }
+        if (!nilfs_checkpoint_snapshot(cp)) {
+                ret = 0;
+                kunmap_atomic(kaddr, KM_USER0);
+                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, KM_USER0);
+
+        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, KM_USER0);
+        list = nilfs_cpfile_block_get_snapshot_list(
+                cpfile, next, next_bh, kaddr);
+        list->ssl_prev = cpu_to_le64(prev);
+        kunmap_atomic(kaddr, KM_USER0);
+
+        kaddr = kmap_atomic(prev_bh->b_page, KM_USER0);
+        list = nilfs_cpfile_block_get_snapshot_list(
+                cpfile, prev, prev_bh, kaddr);
+        list->ssl_next = cpu_to_le64(next);
+        kunmap_atomic(kaddr, KM_USER0);
+
+        kaddr = kmap_atomic(cp_bh->b_page, KM_USER0);
+        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, KM_USER0);
+
+        kaddr = kmap_atomic(header_bh->b_page, KM_USER0);
+        header = nilfs_cpfile_block_get_header(cpfile, header_bh, kaddr);
+        le64_add_cpu(&header->ch_nsnapshots, -1);
+        kunmap_atomic(kaddr, KM_USER0);
+
+        nilfs_mdt_mark_buffer_dirty(next_bh);
+        nilfs_mdt_mark_buffer_dirty(prev_bh);
+        nilfs_mdt_mark_buffer_dirty(cp_bh);
+        nilfs_mdt_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;
+
+        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, KM_USER0);
+        cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, bh, kaddr);
+        ret = nilfs_checkpoint_snapshot(cp);
+        kunmap_atomic(kaddr, KM_USER0);
+        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
+ * @status: 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)
+{
+        struct the_nilfs *nilfs;
+        int ret;
+
+        nilfs = NILFS_MDT(cpfile)->mi_nilfs;
+
+        switch (mode) {
+        case NILFS_CHECKPOINT:
+                /*
+                 * Check for protecting existing snapshot mounts:
+                 * bd_mount_sem is used to make this operation atomic and
+                 * exclusive with a new mount job.  Though it doesn't cover
+                 * umount, it's enough for the purpose.
+                 */
+                down(&nilfs->ns_bdev->bd_mount_sem);
+                if (nilfs_checkpoint_is_mounted(nilfs, cno, 1)) {
+                        /* 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);
+                up(&nilfs->ns_bdev->bd_mount_sem);
+                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
+ * @stat: 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 @stat. 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, KM_USER0);
+        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, KM_USER0);
+        brelse(bh);
+
+ out_sem:
+        up_read(&NILFS_MDT(cpfile)->mi_sem);
+        return ret;
+}