fs/nilfs2/the_nilfs.c - fp2-dev/kernel/msm - Gitiles

 /*
  * the_nilfs.c - the_nilfs shared structure.
  *
  * Copyright (C) 2005-2008 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 Ryusuke Konishi <ryusuke@osrg.net>
  *
  */

 #include <linux/buffer_head.h>
 #include <linux/slab.h>
 #include <linux/blkdev.h>
 #include <linux/backing-dev.h>
 #include <linux/crc32.h>
 #include "nilfs.h"
 #include "segment.h"
 #include "alloc.h"
 #include "cpfile.h"
 #include "sufile.h"
 #include "dat.h"
 #include "segbuf.h"


 static LIST_HEAD(nilfs_objects);
 static DEFINE_SPINLOCK(nilfs_lock);

 void nilfs_set_last_segment(struct the_nilfs *nilfs,
 			    sector_t start_blocknr, u64 seq, __u64 cno)
 {
 	spin_lock(&nilfs->ns_last_segment_lock);
 	nilfs->ns_last_pseg = start_blocknr;
 	nilfs->ns_last_seq = seq;
 	nilfs->ns_last_cno = cno;
 	spin_unlock(&nilfs->ns_last_segment_lock);
 }

 /**
  * alloc_nilfs - allocate the_nilfs structure
  * @bdev: block device to which the_nilfs is related
  *
  * alloc_nilfs() allocates memory for the_nilfs and
  * initializes its reference count and locks.
  *
  * Return Value: On success, pointer to the_nilfs is returned.
  * On error, NULL is returned.
  */
 static struct the_nilfs *alloc_nilfs(struct block_device *bdev)
 {
 	struct the_nilfs *nilfs;

 	nilfs = kzalloc(sizeof(*nilfs), GFP_KERNEL);
 	if (!nilfs)
 		return NULL;

 	nilfs->ns_bdev = bdev;
 	atomic_set(&nilfs->ns_count, 1);
 	atomic_set(&nilfs->ns_writer_refcount, -1);
 	atomic_set(&nilfs->ns_ndirtyblks, 0);
 	init_rwsem(&nilfs->ns_sem);
 	init_rwsem(&nilfs->ns_super_sem);
 	mutex_init(&nilfs->ns_mount_mutex);
 	mutex_init(&nilfs->ns_writer_mutex);
 	INIT_LIST_HEAD(&nilfs->ns_list);
 	INIT_LIST_HEAD(&nilfs->ns_supers);
 	spin_lock_init(&nilfs->ns_last_segment_lock);
 	nilfs->ns_gc_inodes_h = NULL;
 	init_rwsem(&nilfs->ns_segctor_sem);

 	return nilfs;
 }

 /**
  * find_or_create_nilfs - find or create nilfs object
  * @bdev: block device to which the_nilfs is related
  *
  * find_nilfs() looks up an existent nilfs object created on the
  * device and gets the reference count of the object.  If no nilfs object
  * is found on the device, a new nilfs object is allocated.
  *
  * Return Value: On success, pointer to the nilfs object is returned.
  * On error, NULL is returned.
  */
 struct the_nilfs *find_or_create_nilfs(struct block_device *bdev)
 {
 	struct the_nilfs *nilfs, *new = NULL;

  retry:
 	spin_lock(&nilfs_lock);
 	list_for_each_entry(nilfs, &nilfs_objects, ns_list) {
 		if (nilfs->ns_bdev == bdev) {
 			get_nilfs(nilfs);
 			spin_unlock(&nilfs_lock);
 			if (new)
 				put_nilfs(new);
 			return nilfs; /* existing object */
 		}
 	}
 	if (new) {
 		list_add_tail(&new->ns_list, &nilfs_objects);
 		spin_unlock(&nilfs_lock);
 		return new; /* new object */
 	}
 	spin_unlock(&nilfs_lock);

 	new = alloc_nilfs(bdev);
 	if (new)
 		goto retry;
 	return NULL; /* insufficient memory */
 }

 /**
  * put_nilfs - release a reference to the_nilfs
  * @nilfs: the_nilfs structure to be released
  *
  * put_nilfs() decrements a reference counter of the_nilfs.
  * If the reference count reaches zero, the_nilfs is freed.
  */
 void put_nilfs(struct the_nilfs *nilfs)
 {
 	spin_lock(&nilfs_lock);
 	if (!atomic_dec_and_test(&nilfs->ns_count)) {
 		spin_unlock(&nilfs_lock);
 		return;
 	}
 	list_del_init(&nilfs->ns_list);
 	spin_unlock(&nilfs_lock);

 	/*
 	 * Increment of ns_count never occurs below because the caller
 	 * of get_nilfs() holds at least one reference to the_nilfs.
 	 * Thus its exclusion control is not required here.
 	 */

 	might_sleep();
 	if (nilfs_loaded(nilfs)) {
 		nilfs_mdt_clear(nilfs->ns_sufile);
 		nilfs_mdt_destroy(nilfs->ns_sufile);
 		nilfs_mdt_clear(nilfs->ns_cpfile);
 		nilfs_mdt_destroy(nilfs->ns_cpfile);
 		nilfs_mdt_clear(nilfs->ns_dat);
 		nilfs_mdt_destroy(nilfs->ns_dat);
 		/* XXX: how and when to clear nilfs->ns_gc_dat? */
 		nilfs_mdt_destroy(nilfs->ns_gc_dat);
 	}
 	if (nilfs_init(nilfs)) {
 		nilfs_destroy_gccache(nilfs);
 		brelse(nilfs->ns_sbh[0]);
 		brelse(nilfs->ns_sbh[1]);
 	}
 	kfree(nilfs);
 }

 static int nilfs_load_super_root(struct the_nilfs *nilfs,
 				 struct nilfs_sb_info *sbi, sector_t sr_block)
 {
 	static struct lock_class_key dat_lock_key;
 	struct buffer_head *bh_sr;
 	struct nilfs_super_root *raw_sr;
 	struct nilfs_super_block **sbp = nilfs->ns_sbp;
 	unsigned dat_entry_size, segment_usage_size, checkpoint_size;
 	unsigned inode_size;
 	int err;

 	err = nilfs_read_super_root_block(sbi->s_super, sr_block, &bh_sr, 1);
 	if (unlikely(err))
 		return err;

 	down_read(&nilfs->ns_sem);
 	dat_entry_size = le16_to_cpu(sbp[0]->s_dat_entry_size);
 	checkpoint_size = le16_to_cpu(sbp[0]->s_checkpoint_size);
 	segment_usage_size = le16_to_cpu(sbp[0]->s_segment_usage_size);
 	up_read(&nilfs->ns_sem);

 	inode_size = nilfs->ns_inode_size;

 	err = -ENOMEM;
 	nilfs->ns_dat = nilfs_mdt_new(
 		nilfs, NULL, NILFS_DAT_INO, NILFS_DAT_GFP);
 	if (unlikely(!nilfs->ns_dat))
 		goto failed;

 	nilfs->ns_gc_dat = nilfs_mdt_new(
 		nilfs, NULL, NILFS_DAT_INO, NILFS_DAT_GFP);
 	if (unlikely(!nilfs->ns_gc_dat))
 		goto failed_dat;

 	nilfs->ns_cpfile = nilfs_mdt_new(
 		nilfs, NULL, NILFS_CPFILE_INO, NILFS_CPFILE_GFP);
 	if (unlikely(!nilfs->ns_cpfile))
 		goto failed_gc_dat;

 	nilfs->ns_sufile = nilfs_mdt_new(
 		nilfs, NULL, NILFS_SUFILE_INO, NILFS_SUFILE_GFP);
 	if (unlikely(!nilfs->ns_sufile))
 		goto failed_cpfile;

 	err = nilfs_palloc_init_blockgroup(nilfs->ns_dat, dat_entry_size);
 	if (unlikely(err))
 		goto failed_sufile;

 	err = nilfs_palloc_init_blockgroup(nilfs->ns_gc_dat, dat_entry_size);
 	if (unlikely(err))
 		goto failed_sufile;

 	lockdep_set_class(&NILFS_MDT(nilfs->ns_dat)->mi_sem, &dat_lock_key);
 	lockdep_set_class(&NILFS_MDT(nilfs->ns_gc_dat)->mi_sem, &dat_lock_key);

 	nilfs_mdt_set_shadow(nilfs->ns_dat, nilfs->ns_gc_dat);
 	nilfs_mdt_set_entry_size(nilfs->ns_cpfile, checkpoint_size,
 				 sizeof(struct nilfs_cpfile_header));
 	nilfs_mdt_set_entry_size(nilfs->ns_sufile, segment_usage_size,
 				 sizeof(struct nilfs_sufile_header));

 	err = nilfs_mdt_read_inode_direct(
 		nilfs->ns_dat, bh_sr, NILFS_SR_DAT_OFFSET(inode_size));
 	if (unlikely(err))
 		goto failed_sufile;

 	err = nilfs_mdt_read_inode_direct(
 		nilfs->ns_cpfile, bh_sr, NILFS_SR_CPFILE_OFFSET(inode_size));
 	if (unlikely(err))
 		goto failed_sufile;

 	err = nilfs_mdt_read_inode_direct(
 		nilfs->ns_sufile, bh_sr, NILFS_SR_SUFILE_OFFSET(inode_size));
 	if (unlikely(err))
 		goto failed_sufile;

 	raw_sr = (struct nilfs_super_root *)bh_sr->b_data;
 	nilfs->ns_nongc_ctime = le64_to_cpu(raw_sr->sr_nongc_ctime);

  failed:
 	brelse(bh_sr);
 	return err;

  failed_sufile:
 	nilfs_mdt_destroy(nilfs->ns_sufile);

  failed_cpfile:
 	nilfs_mdt_destroy(nilfs->ns_cpfile);

  failed_gc_dat:
 	nilfs_mdt_destroy(nilfs->ns_gc_dat);

  failed_dat:
 	nilfs_mdt_destroy(nilfs->ns_dat);
 	goto failed;
 }

 static void nilfs_init_recovery_info(struct nilfs_recovery_info *ri)
 {
 	memset(ri, 0, sizeof(*ri));
 	INIT_LIST_HEAD(&ri->ri_used_segments);
 }

 static void nilfs_clear_recovery_info(struct nilfs_recovery_info *ri)
 {
 	nilfs_dispose_segment_list(&ri->ri_used_segments);
 }

 /**
  * load_nilfs - load and recover the nilfs
  * @nilfs: the_nilfs structure to be released
  * @sbi: nilfs_sb_info used to recover past segment
  *
  * load_nilfs() searches and load the latest super root,
  * attaches the last segment, and does recovery if needed.
  * The caller must call this exclusively for simultaneous mounts.
  */
 int load_nilfs(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi)
 {
 	struct nilfs_recovery_info ri;
 	unsigned int s_flags = sbi->s_super->s_flags;
 	int really_read_only = bdev_read_only(nilfs->ns_bdev);
 	unsigned valid_fs;
 	int err = 0;

 	nilfs_init_recovery_info(&ri);

 	down_write(&nilfs->ns_sem);
 	valid_fs = (nilfs->ns_mount_state & NILFS_VALID_FS);
 	up_write(&nilfs->ns_sem);

 	if (!valid_fs && (s_flags & MS_RDONLY)) {
 		printk(KERN_INFO "NILFS: INFO: recovery "
 		       "required for readonly filesystem.\n");
 		if (really_read_only) {
 			printk(KERN_ERR "NILFS: write access "
 			       "unavailable, cannot proceed.\n");
 			err = -EROFS;
 			goto failed;
 		}
 		printk(KERN_INFO "NILFS: write access will "
 		       "be enabled during recovery.\n");
 		sbi->s_super->s_flags &= ~MS_RDONLY;
 	}

 	err = nilfs_search_super_root(nilfs, sbi, &ri);
 	if (unlikely(err)) {
 		printk(KERN_ERR "NILFS: error searching super root.\n");
 		goto failed;
 	}

 	err = nilfs_load_super_root(nilfs, sbi, ri.ri_super_root);
 	if (unlikely(err)) {
 		printk(KERN_ERR "NILFS: error loading super root.\n");
 		goto failed;
 	}

 	if (!valid_fs) {
 		err = nilfs_recover_logical_segments(nilfs, sbi, &ri);
 		if (unlikely(err)) {
 			nilfs_mdt_destroy(nilfs->ns_cpfile);
 			nilfs_mdt_destroy(nilfs->ns_sufile);
 			nilfs_mdt_destroy(nilfs->ns_dat);
 			goto failed;
 		}
 		if (ri.ri_need_recovery == NILFS_RECOVERY_SR_UPDATED)
 			sbi->s_super->s_dirt = 1;
 	}

 	set_nilfs_loaded(nilfs);

  failed:
 	nilfs_clear_recovery_info(&ri);
 	sbi->s_super->s_flags = s_flags;
 	return err;
 }

 static unsigned long long nilfs_max_size(unsigned int blkbits)
 {
 	unsigned int max_bits;
 	unsigned long long res = MAX_LFS_FILESIZE; /* page cache limit */

 	max_bits = blkbits + NILFS_BMAP_KEY_BIT; /* bmap size limit */
 	if (max_bits < 64)
 		res = min_t(unsigned long long, res, (1ULL << max_bits) - 1);
 	return res;
 }

 static int nilfs_store_disk_layout(struct the_nilfs *nilfs,
 				   struct nilfs_super_block *sbp)
 {
 	if (le32_to_cpu(sbp->s_rev_level) != NILFS_CURRENT_REV) {
 		printk(KERN_ERR "NILFS: revision mismatch "
 		       "(superblock rev.=%d.%d, current rev.=%d.%d). "
 		       "Please check the version of mkfs.nilfs.\n",
 		       le32_to_cpu(sbp->s_rev_level),
 		       le16_to_cpu(sbp->s_minor_rev_level),
 		       NILFS_CURRENT_REV, NILFS_MINOR_REV);
 		return -EINVAL;
 	}
 	nilfs->ns_sbsize = le16_to_cpu(sbp->s_bytes);
 	if (nilfs->ns_sbsize > BLOCK_SIZE)
 		return -EINVAL;

 	nilfs->ns_inode_size = le16_to_cpu(sbp->s_inode_size);
 	nilfs->ns_first_ino = le32_to_cpu(sbp->s_first_ino);

 	nilfs->ns_blocks_per_segment = le32_to_cpu(sbp->s_blocks_per_segment);
 	if (nilfs->ns_blocks_per_segment < NILFS_SEG_MIN_BLOCKS) {
 		printk(KERN_ERR "NILFS: too short segment. \n");
 		return -EINVAL;
 	}

 	nilfs->ns_first_data_block = le64_to_cpu(sbp->s_first_data_block);
 	nilfs->ns_nsegments = le64_to_cpu(sbp->s_nsegments);
 	nilfs->ns_r_segments_percentage =
 		le32_to_cpu(sbp->s_r_segments_percentage);
 	nilfs->ns_nrsvsegs =
 		max_t(unsigned long, NILFS_MIN_NRSVSEGS,
 		      DIV_ROUND_UP(nilfs->ns_nsegments *
 				   nilfs->ns_r_segments_percentage, 100));
 	nilfs->ns_crc_seed = le32_to_cpu(sbp->s_crc_seed);
 	return 0;
 }

 static int nilfs_valid_sb(struct nilfs_super_block *sbp)
 {
 	static unsigned char sum[4];
 	const int sumoff = offsetof(struct nilfs_super_block, s_sum);
 	size_t bytes;
 	u32 crc;

 	if (!sbp || le16_to_cpu(sbp->s_magic) != NILFS_SUPER_MAGIC)
 		return 0;
 	bytes = le16_to_cpu(sbp->s_bytes);
 	if (bytes > BLOCK_SIZE)
 		return 0;
 	crc = crc32_le(le32_to_cpu(sbp->s_crc_seed), (unsigned char *)sbp,
 		       sumoff);
 	crc = crc32_le(crc, sum, 4);
 	crc = crc32_le(crc, (unsigned char *)sbp + sumoff + 4,
 		       bytes - sumoff - 4);
 	return crc == le32_to_cpu(sbp->s_sum);
 }

 static int nilfs_sb2_bad_offset(struct nilfs_super_block *sbp, u64 offset)
 {
 	return offset < ((le64_to_cpu(sbp->s_nsegments) *
 			  le32_to_cpu(sbp->s_blocks_per_segment)) <<
 			 (le32_to_cpu(sbp->s_log_block_size) + 10));
 }

 static void nilfs_release_super_block(struct the_nilfs *nilfs)
 {
 	int i;

 	for (i = 0; i < 2; i++) {
 		if (nilfs->ns_sbp[i]) {
 			brelse(nilfs->ns_sbh[i]);
 			nilfs->ns_sbh[i] = NULL;
 			nilfs->ns_sbp[i] = NULL;
 		}
 	}
 }

 void nilfs_fall_back_super_block(struct the_nilfs *nilfs)
 {
 	brelse(nilfs->ns_sbh[0]);
 	nilfs->ns_sbh[0] = nilfs->ns_sbh[1];
 	nilfs->ns_sbp[0] = nilfs->ns_sbp[1];
 	nilfs->ns_sbh[1] = NULL;
 	nilfs->ns_sbp[1] = NULL;
 }

 void nilfs_swap_super_block(struct the_nilfs *nilfs)
 {
 	struct buffer_head *tsbh = nilfs->ns_sbh[0];
 	struct nilfs_super_block *tsbp = nilfs->ns_sbp[0];

 	nilfs->ns_sbh[0] = nilfs->ns_sbh[1];
 	nilfs->ns_sbp[0] = nilfs->ns_sbp[1];
 	nilfs->ns_sbh[1] = tsbh;
 	nilfs->ns_sbp[1] = tsbp;
 }

 static int nilfs_load_super_block(struct the_nilfs *nilfs,
 				  struct super_block *sb, int blocksize,
 				  struct nilfs_super_block **sbpp)
 {
 	struct nilfs_super_block **sbp = nilfs->ns_sbp;
 	struct buffer_head **sbh = nilfs->ns_sbh;
 	u64 sb2off = NILFS_SB2_OFFSET_BYTES(nilfs->ns_bdev->bd_inode->i_size);
 	int valid[2], swp = 0;

 	sbp[0] = nilfs_read_super_block(sb, NILFS_SB_OFFSET_BYTES, blocksize,
 					&sbh[0]);
 	sbp[1] = nilfs_read_super_block(sb, sb2off, blocksize, &sbh[1]);

 	if (!sbp[0]) {
 		if (!sbp[1]) {
 			printk(KERN_ERR "NILFS: unable to read superblock\n");
 			return -EIO;
 		}
 		printk(KERN_WARNING
 		       "NILFS warning: unable to read primary superblock\n");
 	} else if (!sbp[1])
 		printk(KERN_WARNING
 		       "NILFS warning: unable to read secondary superblock\n");

 	valid[0] = nilfs_valid_sb(sbp[0]);
 	valid[1] = nilfs_valid_sb(sbp[1]);
 	swp = valid[1] &&
 		(!valid[0] ||
 		 le64_to_cpu(sbp[1]->s_wtime) > le64_to_cpu(sbp[0]->s_wtime));

 	if (valid[swp] && nilfs_sb2_bad_offset(sbp[swp], sb2off)) {
 		brelse(sbh[1]);
 		sbh[1] = NULL;
 		sbp[1] = NULL;
 		swp = 0;
 	}
 	if (!valid[swp]) {
 		nilfs_release_super_block(nilfs);
 		printk(KERN_ERR "NILFS: Can't find nilfs on dev %s.\n",
 		       sb->s_id);
 		return -EINVAL;
 	}

 	if (swp) {
 		printk(KERN_WARNING "NILFS warning: broken superblock. "
 		       "using spare superblock.\n");
 		nilfs_swap_super_block(nilfs);
 	}

 	nilfs->ns_sbwtime[0] = le64_to_cpu(sbp[0]->s_wtime);
 	nilfs->ns_sbwtime[1] = valid[!swp] ? le64_to_cpu(sbp[1]->s_wtime) : 0;
 	nilfs->ns_prot_seq = le64_to_cpu(sbp[valid[1] & !swp]->s_last_seq);
 	*sbpp = sbp[0];
 	return 0;
 }

 /**
  * init_nilfs - initialize a NILFS instance.
  * @nilfs: the_nilfs structure
  * @sbi: nilfs_sb_info
  * @sb: super block
  * @data: mount options
  *
  * init_nilfs() performs common initialization per block device (e.g.
  * reading the super block, getting disk layout information, initializing
  * shared fields in the_nilfs). It takes on some portion of the jobs
  * typically done by a fill_super() routine. This division arises from
  * the nature that multiple NILFS instances may be simultaneously
  * mounted on a device.
  * For multiple mounts on the same device, only the first mount
  * invokes these tasks.
  *
  * Return Value: On success, 0 is returned. On error, a negative error
  * code is returned.
  */
 int init_nilfs(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi, char *data)
 {
 	struct super_block *sb = sbi->s_super;
 	struct nilfs_super_block *sbp;
 	struct backing_dev_info *bdi;
 	int blocksize;
 	int err;

 	down_write(&nilfs->ns_sem);
 	if (nilfs_init(nilfs)) {
 		/* Load values from existing the_nilfs */
 		sbp = nilfs->ns_sbp[0];
 		err = nilfs_store_magic_and_option(sb, sbp, data);
 		if (err)
 			goto out;

 		blocksize = BLOCK_SIZE << le32_to_cpu(sbp->s_log_block_size);
 		if (sb->s_blocksize != blocksize &&
 		    !sb_set_blocksize(sb, blocksize)) {
 			printk(KERN_ERR "NILFS: blocksize %d unfit to device\n",
 			       blocksize);
 			err = -EINVAL;
 		}
 		sb->s_maxbytes = nilfs_max_size(sb->s_blocksize_bits);
 		goto out;
 	}

 	blocksize = sb_min_blocksize(sb, BLOCK_SIZE);
 	if (!blocksize) {
 		printk(KERN_ERR "NILFS: unable to set blocksize\n");
 		err = -EINVAL;
 		goto out;
 	}
 	err = nilfs_load_super_block(nilfs, sb, blocksize, &sbp);
 	if (err)
 		goto out;

 	err = nilfs_store_magic_and_option(sb, sbp, data);
 	if (err)
 		goto failed_sbh;

 	blocksize = BLOCK_SIZE << le32_to_cpu(sbp->s_log_block_size);
 	if (sb->s_blocksize != blocksize) {
 		int hw_blocksize = bdev_logical_block_size(sb->s_bdev);

 		if (blocksize < hw_blocksize) {
 			printk(KERN_ERR
 			       "NILFS: blocksize %d too small for device "
 			       "(sector-size = %d).\n",
 			       blocksize, hw_blocksize);
 			err = -EINVAL;
 			goto failed_sbh;
 		}
 		nilfs_release_super_block(nilfs);
 		sb_set_blocksize(sb, blocksize);

 		err = nilfs_load_super_block(nilfs, sb, blocksize, &sbp);
 		if (err)
 			goto out;
 			/* not failed_sbh; sbh is released automatically
 			   when reloading fails. */
 	}
 	nilfs->ns_blocksize_bits = sb->s_blocksize_bits;

 	err = nilfs_store_disk_layout(nilfs, sbp);
 	if (err)
 		goto failed_sbh;

 	sb->s_maxbytes = nilfs_max_size(sb->s_blocksize_bits);

 	nilfs->ns_mount_state = le16_to_cpu(sbp->s_state);

 	bdi = nilfs->ns_bdev->bd_inode_backing_dev_info;
 	if (!bdi)
 		bdi = nilfs->ns_bdev->bd_inode->i_mapping->backing_dev_info;
 	nilfs->ns_bdi = bdi ? : &default_backing_dev_info;

 	/* Finding last segment */
 	nilfs->ns_last_pseg = le64_to_cpu(sbp->s_last_pseg);
 	nilfs->ns_last_cno = le64_to_cpu(sbp->s_last_cno);
 	nilfs->ns_last_seq = le64_to_cpu(sbp->s_last_seq);

 	nilfs->ns_seg_seq = nilfs->ns_last_seq;
 	nilfs->ns_segnum =
 		nilfs_get_segnum_of_block(nilfs, nilfs->ns_last_pseg);
 	nilfs->ns_cno = nilfs->ns_last_cno + 1;
 	if (nilfs->ns_segnum >= nilfs->ns_nsegments) {
 		printk(KERN_ERR "NILFS invalid last segment number.\n");
 		err = -EINVAL;
 		goto failed_sbh;
 	}
 	/* Dummy values  */
 	nilfs->ns_free_segments_count =
 		nilfs->ns_nsegments - (nilfs->ns_segnum + 1);

 	/* Initialize gcinode cache */
 	err = nilfs_init_gccache(nilfs);
 	if (err)
 		goto failed_sbh;

 	set_nilfs_init(nilfs);
 	err = 0;
  out:
 	up_write(&nilfs->ns_sem);
 	return err;

  failed_sbh:
 	nilfs_release_super_block(nilfs);
 	goto out;
 }

 int nilfs_count_free_blocks(struct the_nilfs *nilfs, sector_t *nblocks)
 {
 	struct inode *dat = nilfs_dat_inode(nilfs);
 	unsigned long ncleansegs;
 	int err;

 	down_read(&NILFS_MDT(dat)->mi_sem);	/* XXX */
 	err = nilfs_sufile_get_ncleansegs(nilfs->ns_sufile, &ncleansegs);
 	up_read(&NILFS_MDT(dat)->mi_sem);	/* XXX */
 	if (likely(!err))
 		*nblocks = (sector_t)ncleansegs * nilfs->ns_blocks_per_segment;
 	return err;
 }

 int nilfs_near_disk_full(struct the_nilfs *nilfs)
 {
 	struct inode *sufile = nilfs->ns_sufile;
 	unsigned long ncleansegs, nincsegs;
 	int ret;

 	ret = nilfs_sufile_get_ncleansegs(sufile, &ncleansegs);
 	if (likely(!ret)) {
 		nincsegs = atomic_read(&nilfs->ns_ndirtyblks) /
 			nilfs->ns_blocks_per_segment + 1;
 		if (ncleansegs <= nilfs->ns_nrsvsegs + nincsegs)
 			ret++;
 	}
 	return ret;
 }

 /**
  * nilfs_find_sbinfo - find existing nilfs_sb_info structure
  * @nilfs: nilfs object
  * @rw_mount: mount type (non-zero value for read/write mount)
  * @cno: checkpoint number (zero for read-only mount)
  *
  * nilfs_find_sbinfo() returns the nilfs_sb_info structure which
  * @rw_mount and @cno (in case of snapshots) matched.  If no instance
  * was found, NULL is returned.  Although the super block instance can
  * be unmounted after this function returns, the nilfs_sb_info struct
  * is kept on memory until nilfs_put_sbinfo() is called.
  */
 struct nilfs_sb_info *nilfs_find_sbinfo(struct the_nilfs *nilfs,
 					int rw_mount, __u64 cno)
 {
 	struct nilfs_sb_info *sbi;

 	down_read(&nilfs->ns_super_sem);
 	/*
 	 * The SNAPSHOT flag and sb->s_flags are supposed to be
 	 * protected with nilfs->ns_super_sem.
 	 */
 	sbi = nilfs->ns_current;
 	if (rw_mount) {
 		if (sbi && !(sbi->s_super->s_flags & MS_RDONLY))
 			goto found; /* read/write mount */
 		else
 			goto out;
 	} else if (cno == 0) {
 		if (sbi && (sbi->s_super->s_flags & MS_RDONLY))
 			goto found; /* read-only mount */
 		else
 			goto out;
 	}

 	list_for_each_entry(sbi, &nilfs->ns_supers, s_list) {
 		if (nilfs_test_opt(sbi, SNAPSHOT) &&
 		    sbi->s_snapshot_cno == cno)
 			goto found; /* snapshot mount */
 	}
  out:
 	up_read(&nilfs->ns_super_sem);
 	return NULL;

  found:
 	atomic_inc(&sbi->s_count);
 	up_read(&nilfs->ns_super_sem);
 	return sbi;
 }

 int nilfs_checkpoint_is_mounted(struct the_nilfs *nilfs, __u64 cno,
 				int snapshot_mount)
 {
 	struct nilfs_sb_info *sbi;
 	int ret = 0;

 	down_read(&nilfs->ns_super_sem);
 	if (cno == 0 || cno > nilfs->ns_cno)
 		goto out_unlock;

 	list_for_each_entry(sbi, &nilfs->ns_supers, s_list) {
 		if (sbi->s_snapshot_cno == cno &&
 		    (!snapshot_mount || nilfs_test_opt(sbi, SNAPSHOT))) {
 					/* exclude read-only mounts */
 			ret++;
 			break;
 		}
 	}
 	/* for protecting recent checkpoints */
 	if (cno >= nilfs_last_cno(nilfs))
 		ret++;

  out_unlock:
 	up_read(&nilfs->ns_super_sem);
 	return ret;
 }
	/*
	* the_nilfs.c - the_nilfs shared structure.
	*
	* Copyright (C) 2005-2008 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 Ryusuke Konishi <ryusuke@osrg.net>
	*
	*/

	#include <linux/buffer_head.h>
	#include <linux/slab.h>
	#include <linux/blkdev.h>
	#include <linux/backing-dev.h>
	#include <linux/crc32.h>
	#include "nilfs.h"
	#include "segment.h"
	#include "alloc.h"
	#include "cpfile.h"
	#include "sufile.h"
	#include "dat.h"
	#include "segbuf.h"


	static LIST_HEAD(nilfs_objects);
	static DEFINE_SPINLOCK(nilfs_lock);

	void nilfs_set_last_segment(struct the_nilfs *nilfs,
	sector_t start_blocknr, u64 seq, __u64 cno)
	{
	spin_lock(&nilfs->ns_last_segment_lock);
	nilfs->ns_last_pseg = start_blocknr;
	nilfs->ns_last_seq = seq;
	nilfs->ns_last_cno = cno;
	spin_unlock(&nilfs->ns_last_segment_lock);
	}

	/**
	* alloc_nilfs - allocate the_nilfs structure
	* @bdev: block device to which the_nilfs is related
	*
	* alloc_nilfs() allocates memory for the_nilfs and
	* initializes its reference count and locks.
	*
	* Return Value: On success, pointer to the_nilfs is returned.
	* On error, NULL is returned.
	*/
	static struct the_nilfs alloc_nilfs(struct block_device bdev)
	{
	struct the_nilfs *nilfs;

	nilfs = kzalloc(sizeof(*nilfs), GFP_KERNEL);
	if (!nilfs)
	return NULL;

	nilfs->ns_bdev = bdev;
	atomic_set(&nilfs->ns_count, 1);
	atomic_set(&nilfs->ns_writer_refcount, -1);
	atomic_set(&nilfs->ns_ndirtyblks, 0);
	init_rwsem(&nilfs->ns_sem);
	init_rwsem(&nilfs->ns_super_sem);
	mutex_init(&nilfs->ns_mount_mutex);
	mutex_init(&nilfs->ns_writer_mutex);
	INIT_LIST_HEAD(&nilfs->ns_list);
	INIT_LIST_HEAD(&nilfs->ns_supers);
	spin_lock_init(&nilfs->ns_last_segment_lock);
	nilfs->ns_gc_inodes_h = NULL;
	init_rwsem(&nilfs->ns_segctor_sem);

	return nilfs;
	}

	/**
	* find_or_create_nilfs - find or create nilfs object
	* @bdev: block device to which the_nilfs is related
	*
	* find_nilfs() looks up an existent nilfs object created on the
	* device and gets the reference count of the object. If no nilfs object
	* is found on the device, a new nilfs object is allocated.
	*
	* Return Value: On success, pointer to the nilfs object is returned.
	* On error, NULL is returned.
	*/
	struct the_nilfs find_or_create_nilfs(struct block_device bdev)
	{
	struct the_nilfs nilfs, new = NULL;

	retry:
	spin_lock(&nilfs_lock);
	list_for_each_entry(nilfs, &nilfs_objects, ns_list) {
	if (nilfs->ns_bdev == bdev) {
	get_nilfs(nilfs);
	spin_unlock(&nilfs_lock);
	if (new)
	put_nilfs(new);
	return nilfs; /* existing object */
	}
	}
	if (new) {
	list_add_tail(&new->ns_list, &nilfs_objects);
	spin_unlock(&nilfs_lock);
	return new; /* new object */
	}
	spin_unlock(&nilfs_lock);

	new = alloc_nilfs(bdev);
	if (new)
	goto retry;
	return NULL; /* insufficient memory */
	}

	/**
	* put_nilfs - release a reference to the_nilfs
	* @nilfs: the_nilfs structure to be released
	*
	* put_nilfs() decrements a reference counter of the_nilfs.
	* If the reference count reaches zero, the_nilfs is freed.
	*/
	void put_nilfs(struct the_nilfs *nilfs)
	{
	spin_lock(&nilfs_lock);
	if (!atomic_dec_and_test(&nilfs->ns_count)) {
	spin_unlock(&nilfs_lock);
	return;
	}
	list_del_init(&nilfs->ns_list);
	spin_unlock(&nilfs_lock);

	/*
	* Increment of ns_count never occurs below because the caller
	* of get_nilfs() holds at least one reference to the_nilfs.
	* Thus its exclusion control is not required here.
	*/

	might_sleep();
	if (nilfs_loaded(nilfs)) {
	nilfs_mdt_clear(nilfs->ns_sufile);
	nilfs_mdt_destroy(nilfs->ns_sufile);
	nilfs_mdt_clear(nilfs->ns_cpfile);
	nilfs_mdt_destroy(nilfs->ns_cpfile);
	nilfs_mdt_clear(nilfs->ns_dat);
	nilfs_mdt_destroy(nilfs->ns_dat);
	/* XXX: how and when to clear nilfs->ns_gc_dat? */
	nilfs_mdt_destroy(nilfs->ns_gc_dat);
	}
	if (nilfs_init(nilfs)) {
	nilfs_destroy_gccache(nilfs);
	brelse(nilfs->ns_sbh[0]);
	brelse(nilfs->ns_sbh[1]);
	}
	kfree(nilfs);
	}

	static int nilfs_load_super_root(struct the_nilfs *nilfs,
	struct nilfs_sb_info *sbi, sector_t sr_block)
	{
	static struct lock_class_key dat_lock_key;
	struct buffer_head *bh_sr;
	struct nilfs_super_root *raw_sr;
	struct nilfs_super_block **sbp = nilfs->ns_sbp;
	unsigned dat_entry_size, segment_usage_size, checkpoint_size;
	unsigned inode_size;
	int err;

	err = nilfs_read_super_root_block(sbi->s_super, sr_block, &bh_sr, 1);
	if (unlikely(err))
	return err;

	down_read(&nilfs->ns_sem);
	dat_entry_size = le16_to_cpu(sbp[0]->s_dat_entry_size);
	checkpoint_size = le16_to_cpu(sbp[0]->s_checkpoint_size);
	segment_usage_size = le16_to_cpu(sbp[0]->s_segment_usage_size);
	up_read(&nilfs->ns_sem);

	inode_size = nilfs->ns_inode_size;

	err = -ENOMEM;
	nilfs->ns_dat = nilfs_mdt_new(
	nilfs, NULL, NILFS_DAT_INO, NILFS_DAT_GFP);
	if (unlikely(!nilfs->ns_dat))
	goto failed;

	nilfs->ns_gc_dat = nilfs_mdt_new(
	nilfs, NULL, NILFS_DAT_INO, NILFS_DAT_GFP);
	if (unlikely(!nilfs->ns_gc_dat))
	goto failed_dat;

	nilfs->ns_cpfile = nilfs_mdt_new(
	nilfs, NULL, NILFS_CPFILE_INO, NILFS_CPFILE_GFP);
	if (unlikely(!nilfs->ns_cpfile))
	goto failed_gc_dat;

	nilfs->ns_sufile = nilfs_mdt_new(
	nilfs, NULL, NILFS_SUFILE_INO, NILFS_SUFILE_GFP);
	if (unlikely(!nilfs->ns_sufile))
	goto failed_cpfile;

	err = nilfs_palloc_init_blockgroup(nilfs->ns_dat, dat_entry_size);
	if (unlikely(err))
	goto failed_sufile;

	err = nilfs_palloc_init_blockgroup(nilfs->ns_gc_dat, dat_entry_size);
	if (unlikely(err))
	goto failed_sufile;

	lockdep_set_class(&NILFS_MDT(nilfs->ns_dat)->mi_sem, &dat_lock_key);
	lockdep_set_class(&NILFS_MDT(nilfs->ns_gc_dat)->mi_sem, &dat_lock_key);

	nilfs_mdt_set_shadow(nilfs->ns_dat, nilfs->ns_gc_dat);
	nilfs_mdt_set_entry_size(nilfs->ns_cpfile, checkpoint_size,
	sizeof(struct nilfs_cpfile_header));
	nilfs_mdt_set_entry_size(nilfs->ns_sufile, segment_usage_size,
	sizeof(struct nilfs_sufile_header));

	err = nilfs_mdt_read_inode_direct(
	nilfs->ns_dat, bh_sr, NILFS_SR_DAT_OFFSET(inode_size));
	if (unlikely(err))
	goto failed_sufile;

	err = nilfs_mdt_read_inode_direct(
	nilfs->ns_cpfile, bh_sr, NILFS_SR_CPFILE_OFFSET(inode_size));
	if (unlikely(err))
	goto failed_sufile;

	err = nilfs_mdt_read_inode_direct(
	nilfs->ns_sufile, bh_sr, NILFS_SR_SUFILE_OFFSET(inode_size));
	if (unlikely(err))
	goto failed_sufile;

	raw_sr = (struct nilfs_super_root *)bh_sr->b_data;
	nilfs->ns_nongc_ctime = le64_to_cpu(raw_sr->sr_nongc_ctime);

	failed:
	brelse(bh_sr);
	return err;

	failed_sufile:
	nilfs_mdt_destroy(nilfs->ns_sufile);

	failed_cpfile:
	nilfs_mdt_destroy(nilfs->ns_cpfile);

	failed_gc_dat:
	nilfs_mdt_destroy(nilfs->ns_gc_dat);

	failed_dat:
	nilfs_mdt_destroy(nilfs->ns_dat);
	goto failed;
	}

	static void nilfs_init_recovery_info(struct nilfs_recovery_info *ri)
	{
	memset(ri, 0, sizeof(*ri));
	INIT_LIST_HEAD(&ri->ri_used_segments);
	}

	static void nilfs_clear_recovery_info(struct nilfs_recovery_info *ri)
	{
	nilfs_dispose_segment_list(&ri->ri_used_segments);
	}

	/**
	* load_nilfs - load and recover the nilfs
	* @nilfs: the_nilfs structure to be released
	* @sbi: nilfs_sb_info used to recover past segment
	*
	* load_nilfs() searches and load the latest super root,
	* attaches the last segment, and does recovery if needed.
	* The caller must call this exclusively for simultaneous mounts.
	*/
	int load_nilfs(struct the_nilfs nilfs, struct nilfs_sb_info sbi)
	{
	struct nilfs_recovery_info ri;
	unsigned int s_flags = sbi->s_super->s_flags;
	int really_read_only = bdev_read_only(nilfs->ns_bdev);
	unsigned valid_fs;
	int err = 0;

	nilfs_init_recovery_info(&ri);

	down_write(&nilfs->ns_sem);
	valid_fs = (nilfs->ns_mount_state & NILFS_VALID_FS);
	up_write(&nilfs->ns_sem);

	if (!valid_fs && (s_flags & MS_RDONLY)) {
	printk(KERN_INFO "NILFS: INFO: recovery "
	"required for readonly filesystem.\n");
	if (really_read_only) {
	printk(KERN_ERR "NILFS: write access "
	"unavailable, cannot proceed.\n");
	err = -EROFS;
	goto failed;
	}
	printk(KERN_INFO "NILFS: write access will "
	"be enabled during recovery.\n");
	sbi->s_super->s_flags &= ~MS_RDONLY;
	}

	err = nilfs_search_super_root(nilfs, sbi, &ri);
	if (unlikely(err)) {
	printk(KERN_ERR "NILFS: error searching super root.\n");
	goto failed;
	}

	err = nilfs_load_super_root(nilfs, sbi, ri.ri_super_root);
	if (unlikely(err)) {
	printk(KERN_ERR "NILFS: error loading super root.\n");
	goto failed;
	}

	if (!valid_fs) {
	err = nilfs_recover_logical_segments(nilfs, sbi, &ri);
	if (unlikely(err)) {
	nilfs_mdt_destroy(nilfs->ns_cpfile);
	nilfs_mdt_destroy(nilfs->ns_sufile);
	nilfs_mdt_destroy(nilfs->ns_dat);
	goto failed;
	}
	if (ri.ri_need_recovery == NILFS_RECOVERY_SR_UPDATED)
	sbi->s_super->s_dirt = 1;
	}

	set_nilfs_loaded(nilfs);

	failed:
	nilfs_clear_recovery_info(&ri);
	sbi->s_super->s_flags = s_flags;
	return err;
	}

	static unsigned long long nilfs_max_size(unsigned int blkbits)
	{
	unsigned int max_bits;
	unsigned long long res = MAX_LFS_FILESIZE; /* page cache limit */

	max_bits = blkbits + NILFS_BMAP_KEY_BIT; /* bmap size limit */
	if (max_bits < 64)
	res = min_t(unsigned long long, res, (1ULL << max_bits) - 1);
	return res;
	}

	static int nilfs_store_disk_layout(struct the_nilfs *nilfs,
	struct nilfs_super_block *sbp)
	{
	if (le32_to_cpu(sbp->s_rev_level) != NILFS_CURRENT_REV) {
	printk(KERN_ERR "NILFS: revision mismatch "
	"(superblock rev.=%d.%d, current rev.=%d.%d). "
	"Please check the version of mkfs.nilfs.\n",
	le32_to_cpu(sbp->s_rev_level),
	le16_to_cpu(sbp->s_minor_rev_level),
	NILFS_CURRENT_REV, NILFS_MINOR_REV);
	return -EINVAL;
	}
	nilfs->ns_sbsize = le16_to_cpu(sbp->s_bytes);
	if (nilfs->ns_sbsize > BLOCK_SIZE)
	return -EINVAL;

	nilfs->ns_inode_size = le16_to_cpu(sbp->s_inode_size);
	nilfs->ns_first_ino = le32_to_cpu(sbp->s_first_ino);

	nilfs->ns_blocks_per_segment = le32_to_cpu(sbp->s_blocks_per_segment);
	if (nilfs->ns_blocks_per_segment < NILFS_SEG_MIN_BLOCKS) {
	printk(KERN_ERR "NILFS: too short segment. \n");
	return -EINVAL;
	}

	nilfs->ns_first_data_block = le64_to_cpu(sbp->s_first_data_block);
	nilfs->ns_nsegments = le64_to_cpu(sbp->s_nsegments);
	nilfs->ns_r_segments_percentage =
	le32_to_cpu(sbp->s_r_segments_percentage);
	nilfs->ns_nrsvsegs =
	max_t(unsigned long, NILFS_MIN_NRSVSEGS,
	DIV_ROUND_UP(nilfs->ns_nsegments *
	nilfs->ns_r_segments_percentage, 100));
	nilfs->ns_crc_seed = le32_to_cpu(sbp->s_crc_seed);
	return 0;
	}

	static int nilfs_valid_sb(struct nilfs_super_block *sbp)
	{
	static unsigned char sum[4];
	const int sumoff = offsetof(struct nilfs_super_block, s_sum);
	size_t bytes;
	u32 crc;

	if (!sbp \|\| le16_to_cpu(sbp->s_magic) != NILFS_SUPER_MAGIC)
	return 0;
	bytes = le16_to_cpu(sbp->s_bytes);
	if (bytes > BLOCK_SIZE)
	return 0;
	crc = crc32_le(le32_to_cpu(sbp->s_crc_seed), (unsigned char *)sbp,
	sumoff);
	crc = crc32_le(crc, sum, 4);
	crc = crc32_le(crc, (unsigned char *)sbp + sumoff + 4,
	bytes - sumoff - 4);
	return crc == le32_to_cpu(sbp->s_sum);
	}

	static int nilfs_sb2_bad_offset(struct nilfs_super_block *sbp, u64 offset)
	{
	return offset < ((le64_to_cpu(sbp->s_nsegments) *
	le32_to_cpu(sbp->s_blocks_per_segment)) <<
	(le32_to_cpu(sbp->s_log_block_size) + 10));
	}

	static void nilfs_release_super_block(struct the_nilfs *nilfs)
	{
	int i;

	for (i = 0; i < 2; i++) {
	if (nilfs->ns_sbp[i]) {
	brelse(nilfs->ns_sbh[i]);
	nilfs->ns_sbh[i] = NULL;
	nilfs->ns_sbp[i] = NULL;
	}
	}
	}

	void nilfs_fall_back_super_block(struct the_nilfs *nilfs)
	{
	brelse(nilfs->ns_sbh[0]);
	nilfs->ns_sbh[0] = nilfs->ns_sbh[1];
	nilfs->ns_sbp[0] = nilfs->ns_sbp[1];
	nilfs->ns_sbh[1] = NULL;
	nilfs->ns_sbp[1] = NULL;
	}

	void nilfs_swap_super_block(struct the_nilfs *nilfs)
	{
	struct buffer_head *tsbh = nilfs->ns_sbh[0];
	struct nilfs_super_block *tsbp = nilfs->ns_sbp[0];

	nilfs->ns_sbh[0] = nilfs->ns_sbh[1];
	nilfs->ns_sbp[0] = nilfs->ns_sbp[1];
	nilfs->ns_sbh[1] = tsbh;
	nilfs->ns_sbp[1] = tsbp;
	}

	static int nilfs_load_super_block(struct the_nilfs *nilfs,
	struct super_block *sb, int blocksize,
	struct nilfs_super_block **sbpp)
	{
	struct nilfs_super_block **sbp = nilfs->ns_sbp;
	struct buffer_head **sbh = nilfs->ns_sbh;
	u64 sb2off = NILFS_SB2_OFFSET_BYTES(nilfs->ns_bdev->bd_inode->i_size);
	int valid[2], swp = 0;

	sbp[0] = nilfs_read_super_block(sb, NILFS_SB_OFFSET_BYTES, blocksize,
	&sbh[0]);
	sbp[1] = nilfs_read_super_block(sb, sb2off, blocksize, &sbh[1]);

	if (!sbp[0]) {
	if (!sbp[1]) {
	printk(KERN_ERR "NILFS: unable to read superblock\n");
	return -EIO;
	}
	printk(KERN_WARNING
	"NILFS warning: unable to read primary superblock\n");
	} else if (!sbp[1])
	printk(KERN_WARNING
	"NILFS warning: unable to read secondary superblock\n");

	valid[0] = nilfs_valid_sb(sbp[0]);
	valid[1] = nilfs_valid_sb(sbp[1]);
	swp = valid[1] &&
	(!valid[0] \|\|
	le64_to_cpu(sbp[1]->s_wtime) > le64_to_cpu(sbp[0]->s_wtime));

	if (valid[swp] && nilfs_sb2_bad_offset(sbp[swp], sb2off)) {
	brelse(sbh[1]);
	sbh[1] = NULL;
	sbp[1] = NULL;
	swp = 0;
	}
	if (!valid[swp]) {
	nilfs_release_super_block(nilfs);
	printk(KERN_ERR "NILFS: Can't find nilfs on dev %s.\n",
	sb->s_id);
	return -EINVAL;
	}

	if (swp) {
	printk(KERN_WARNING "NILFS warning: broken superblock. "
	"using spare superblock.\n");
	nilfs_swap_super_block(nilfs);
	}

	nilfs->ns_sbwtime[0] = le64_to_cpu(sbp[0]->s_wtime);
	nilfs->ns_sbwtime[1] = valid[!swp] ? le64_to_cpu(sbp[1]->s_wtime) : 0;
	nilfs->ns_prot_seq = le64_to_cpu(sbp[valid[1] & !swp]->s_last_seq);
	*sbpp = sbp[0];
	return 0;
	}

	/**
	* init_nilfs - initialize a NILFS instance.
	* @nilfs: the_nilfs structure
	* @sbi: nilfs_sb_info
	* @sb: super block
	* @data: mount options
	*
	* init_nilfs() performs common initialization per block device (e.g.
	* reading the super block, getting disk layout information, initializing
	* shared fields in the_nilfs). It takes on some portion of the jobs
	* typically done by a fill_super() routine. This division arises from
	* the nature that multiple NILFS instances may be simultaneously
	* mounted on a device.
	* For multiple mounts on the same device, only the first mount
	* invokes these tasks.
	*
	* Return Value: On success, 0 is returned. On error, a negative error
	* code is returned.
	*/
	int init_nilfs(struct the_nilfs nilfs, struct nilfs_sb_info sbi, char *data)
	{
	struct super_block *sb = sbi->s_super;
	struct nilfs_super_block *sbp;
	struct backing_dev_info *bdi;
	int blocksize;
	int err;

	down_write(&nilfs->ns_sem);
	if (nilfs_init(nilfs)) {
	/* Load values from existing the_nilfs */
	sbp = nilfs->ns_sbp[0];
	err = nilfs_store_magic_and_option(sb, sbp, data);
	if (err)
	goto out;

	blocksize = BLOCK_SIZE << le32_to_cpu(sbp->s_log_block_size);
	if (sb->s_blocksize != blocksize &&
	!sb_set_blocksize(sb, blocksize)) {
	printk(KERN_ERR "NILFS: blocksize %d unfit to device\n",
	blocksize);
	err = -EINVAL;
	}
	sb->s_maxbytes = nilfs_max_size(sb->s_blocksize_bits);
	goto out;
	}

	blocksize = sb_min_blocksize(sb, BLOCK_SIZE);
	if (!blocksize) {
	printk(KERN_ERR "NILFS: unable to set blocksize\n");
	err = -EINVAL;
	goto out;
	}
	err = nilfs_load_super_block(nilfs, sb, blocksize, &sbp);
	if (err)
	goto out;

	err = nilfs_store_magic_and_option(sb, sbp, data);
	if (err)
	goto failed_sbh;

	blocksize = BLOCK_SIZE << le32_to_cpu(sbp->s_log_block_size);
	if (sb->s_blocksize != blocksize) {
	int hw_blocksize = bdev_logical_block_size(sb->s_bdev);

	if (blocksize < hw_blocksize) {
	printk(KERN_ERR
	"NILFS: blocksize %d too small for device "
	"(sector-size = %d).\n",
	blocksize, hw_blocksize);
	err = -EINVAL;
	goto failed_sbh;
	}
	nilfs_release_super_block(nilfs);
	sb_set_blocksize(sb, blocksize);

	err = nilfs_load_super_block(nilfs, sb, blocksize, &sbp);
	if (err)
	goto out;
	/* not failed_sbh; sbh is released automatically
	when reloading fails. */
	}
	nilfs->ns_blocksize_bits = sb->s_blocksize_bits;

	err = nilfs_store_disk_layout(nilfs, sbp);
	if (err)
	goto failed_sbh;

	sb->s_maxbytes = nilfs_max_size(sb->s_blocksize_bits);

	nilfs->ns_mount_state = le16_to_cpu(sbp->s_state);

	bdi = nilfs->ns_bdev->bd_inode_backing_dev_info;
	if (!bdi)
	bdi = nilfs->ns_bdev->bd_inode->i_mapping->backing_dev_info;
	nilfs->ns_bdi = bdi ? : &default_backing_dev_info;

	/* Finding last segment */
	nilfs->ns_last_pseg = le64_to_cpu(sbp->s_last_pseg);
	nilfs->ns_last_cno = le64_to_cpu(sbp->s_last_cno);
	nilfs->ns_last_seq = le64_to_cpu(sbp->s_last_seq);

	nilfs->ns_seg_seq = nilfs->ns_last_seq;
	nilfs->ns_segnum =
	nilfs_get_segnum_of_block(nilfs, nilfs->ns_last_pseg);
	nilfs->ns_cno = nilfs->ns_last_cno + 1;
	if (nilfs->ns_segnum >= nilfs->ns_nsegments) {
	printk(KERN_ERR "NILFS invalid last segment number.\n");
	err = -EINVAL;
	goto failed_sbh;
	}
	/* Dummy values */
	nilfs->ns_free_segments_count =
	nilfs->ns_nsegments - (nilfs->ns_segnum + 1);

	/* Initialize gcinode cache */
	err = nilfs_init_gccache(nilfs);
	if (err)
	goto failed_sbh;

	set_nilfs_init(nilfs);
	err = 0;
	out:
	up_write(&nilfs->ns_sem);
	return err;

	failed_sbh:
	nilfs_release_super_block(nilfs);
	goto out;
	}

	int nilfs_count_free_blocks(struct the_nilfs nilfs, sector_t nblocks)
	{
	struct inode *dat = nilfs_dat_inode(nilfs);
	unsigned long ncleansegs;
	int err;

	down_read(&NILFS_MDT(dat)->mi_sem); /* XXX */
	err = nilfs_sufile_get_ncleansegs(nilfs->ns_sufile, &ncleansegs);
	up_read(&NILFS_MDT(dat)->mi_sem); /* XXX */
	if (likely(!err))
	nblocks = (sector_t)ncleansegs nilfs->ns_blocks_per_segment;
	return err;
	}

	int nilfs_near_disk_full(struct the_nilfs *nilfs)
	{
	struct inode *sufile = nilfs->ns_sufile;
	unsigned long ncleansegs, nincsegs;
	int ret;

	ret = nilfs_sufile_get_ncleansegs(sufile, &ncleansegs);
	if (likely(!ret)) {
	nincsegs = atomic_read(&nilfs->ns_ndirtyblks) /
	nilfs->ns_blocks_per_segment + 1;
	if (ncleansegs <= nilfs->ns_nrsvsegs + nincsegs)
	ret++;
	}
	return ret;
	}

	/**
	* nilfs_find_sbinfo - find existing nilfs_sb_info structure
	* @nilfs: nilfs object
	* @rw_mount: mount type (non-zero value for read/write mount)
	* @cno: checkpoint number (zero for read-only mount)
	*
	* nilfs_find_sbinfo() returns the nilfs_sb_info structure which
	* @rw_mount and @cno (in case of snapshots) matched. If no instance
	* was found, NULL is returned. Although the super block instance can
	* be unmounted after this function returns, the nilfs_sb_info struct
	* is kept on memory until nilfs_put_sbinfo() is called.
	*/
	struct nilfs_sb_info nilfs_find_sbinfo(struct the_nilfs nilfs,
	int rw_mount, __u64 cno)
	{
	struct nilfs_sb_info *sbi;

	down_read(&nilfs->ns_super_sem);
	/*
	* The SNAPSHOT flag and sb->s_flags are supposed to be
	* protected with nilfs->ns_super_sem.
	*/
	sbi = nilfs->ns_current;
	if (rw_mount) {
	if (sbi && !(sbi->s_super->s_flags & MS_RDONLY))
	goto found; /* read/write mount */
	else
	goto out;
	} else if (cno == 0) {
	if (sbi && (sbi->s_super->s_flags & MS_RDONLY))
	goto found; /* read-only mount */
	else
	goto out;
	}

	list_for_each_entry(sbi, &nilfs->ns_supers, s_list) {
	if (nilfs_test_opt(sbi, SNAPSHOT) &&
	sbi->s_snapshot_cno == cno)
	goto found; /* snapshot mount */
	}
	out:
	up_read(&nilfs->ns_super_sem);
	return NULL;

	found:
	atomic_inc(&sbi->s_count);
	up_read(&nilfs->ns_super_sem);
	return sbi;
	}

	int nilfs_checkpoint_is_mounted(struct the_nilfs *nilfs, __u64 cno,
	int snapshot_mount)
	{
	struct nilfs_sb_info *sbi;
	int ret = 0;

	down_read(&nilfs->ns_super_sem);
	if (cno == 0 \|\| cno > nilfs->ns_cno)
	goto out_unlock;

	list_for_each_entry(sbi, &nilfs->ns_supers, s_list) {
	if (sbi->s_snapshot_cno == cno &&
	(!snapshot_mount \|\| nilfs_test_opt(sbi, SNAPSHOT))) {
	/* exclude read-only mounts */
	ret++;
	break;
	}
	}
	/* for protecting recent checkpoints */
	if (cno >= nilfs_last_cno(nilfs))
	ret++;

	out_unlock:
	up_read(&nilfs->ns_super_sem);
	return ret;
	}