AFS: Documentation updates

[linux-2.6/mini2440.git] / fs / nilfs2 / the_nilfs.c

/*
 * 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;
}