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;
+}