/*
   * 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 = 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));
  }
  
  /**
   * 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 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, nss, count, i;
  
  	if (unlikely(start == 0 || start > end)) {
  		printk(KERN_ERR "%s: invalid range of checkpoint numbers: "
  		       "[%llu, %llu)
  ", __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
  ",
  					       __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;
  }
  
  /**
   * nilfs_cpfile_get_cpinfo -
   * @cpfile:
   * @cno:
   * @ci:
   * @nci:
   */
  
  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;
  	}
  }
  
  /**
   * 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	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;
  }
  
  /**
   * 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)
  {
  	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
   * @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);
  	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;
  
  	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;
  }