the_nilfs.c

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/*
 * 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 <[email protected]>
 *
 */

#include <linux/buffer_head.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/random.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 int nilfs_valid_sb(struct nilfs_super_block *sbp);

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;

    if (!nilfs_sb_dirty(nilfs)) {
        if (nilfs->ns_prev_seq == nilfs->ns_last_seq)
            goto stay_cursor;

        set_nilfs_sb_dirty(nilfs);
    }
    nilfs->ns_prev_seq = nilfs->ns_last_seq;

 stay_cursor:
    spin_unlock(&nilfs->ns_last_segment_lock);
}

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_ndirtyblks, 0);
    init_rwsem(&nilfs->ns_sem);
    mutex_init(&nilfs->ns_snapshot_mount_mutex);
    INIT_LIST_HEAD(&nilfs->ns_dirty_files);
    INIT_LIST_HEAD(&nilfs->ns_gc_inodes);
    spin_lock_init(&nilfs->ns_inode_lock);
    spin_lock_init(&nilfs->ns_next_gen_lock);
    spin_lock_init(&nilfs->ns_last_segment_lock);
    nilfs->ns_cptree = RB_ROOT;
    spin_lock_init(&nilfs->ns_cptree_lock);
    init_rwsem(&nilfs->ns_segctor_sem);

    return nilfs;
}

void destroy_nilfs(struct the_nilfs *nilfs)
{
    might_sleep();
    if (nilfs_init(nilfs)) {
        brelse(nilfs->ns_sbh[0]);
        brelse(nilfs->ns_sbh[1]);
    }
    kfree(nilfs);
}

static int nilfs_load_super_root(struct the_nilfs *nilfs,
                 struct super_block *sb, sector_t sr_block)
{
    struct buffer_head *bh_sr;
    struct nilfs_super_root *raw_sr;
    struct nilfs_super_block **sbp = nilfs->ns_sbp;
    struct nilfs_inode *rawi;
    unsigned dat_entry_size, segment_usage_size, checkpoint_size;
    unsigned inode_size;
    int err;

    err = nilfs_read_super_root_block(nilfs, 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;

    rawi = (void *)bh_sr->b_data + NILFS_SR_DAT_OFFSET(inode_size);
    err = nilfs_dat_read(sb, dat_entry_size, rawi, &nilfs->ns_dat);
    if (err)
        goto failed;

    rawi = (void *)bh_sr->b_data + NILFS_SR_CPFILE_OFFSET(inode_size);
    err = nilfs_cpfile_read(sb, checkpoint_size, rawi, &nilfs->ns_cpfile);
    if (err)
        goto failed_dat;

    rawi = (void *)bh_sr->b_data + NILFS_SR_SUFILE_OFFSET(inode_size);
    err = nilfs_sufile_read(sb, segment_usage_size, rawi,
                &nilfs->ns_sufile);
    if (err)
        goto failed_cpfile;

    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_cpfile:
    iput(nilfs->ns_cpfile);

 failed_dat:
    iput(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);
}

static int nilfs_store_log_cursor(struct the_nilfs *nilfs,
                  struct nilfs_super_block *sbp)
{
    int ret = 0;

    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_prev_seq = nilfs->ns_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");
        ret = -EINVAL;
    }
    return ret;
}

int load_nilfs(struct the_nilfs *nilfs, struct super_block *sb)
{
    struct nilfs_recovery_info ri;
    unsigned int s_flags = sb->s_flags;
    int really_read_only = bdev_read_only(nilfs->ns_bdev);
    int valid_fs = nilfs_valid_fs(nilfs);
    int err;

    if (!valid_fs) {
        printk(KERN_WARNING "NILFS warning: mounting unchecked fs\n");
        if (s_flags & MS_RDONLY) {
            printk(KERN_INFO "NILFS: INFO: recovery "
                   "required for readonly filesystem.\n");
            printk(KERN_INFO "NILFS: write access will "
                   "be enabled during recovery.\n");
        }
    }

    nilfs_init_recovery_info(&ri);

    err = nilfs_search_super_root(nilfs, &ri);
    if (unlikely(err)) {
        struct nilfs_super_block **sbp = nilfs->ns_sbp;
        int blocksize;

        if (err != -EINVAL)
            goto scan_error;

        if (!nilfs_valid_sb(sbp[1])) {
            printk(KERN_WARNING
                   "NILFS warning: unable to fall back to spare"
                   "super block\n");
            goto scan_error;
        }
        printk(KERN_INFO
               "NILFS: try rollback from an earlier position\n");

        /*
         * restore super block with its spare and reconfigure
         * relevant states of the nilfs object.
         */
        memcpy(sbp[0], sbp[1], nilfs->ns_sbsize);
        nilfs->ns_crc_seed = le32_to_cpu(sbp[0]->s_crc_seed);
        nilfs->ns_sbwtime = le64_to_cpu(sbp[0]->s_wtime);

        /* verify consistency between two super blocks */
        blocksize = BLOCK_SIZE << le32_to_cpu(sbp[0]->s_log_block_size);
        if (blocksize != nilfs->ns_blocksize) {
            printk(KERN_WARNING
                   "NILFS warning: blocksize differs between "
                   "two super blocks (%d != %d)\n",
                   blocksize, nilfs->ns_blocksize);
            goto scan_error;
        }

        err = nilfs_store_log_cursor(nilfs, sbp[0]);
        if (err)
            goto scan_error;

        /* drop clean flag to allow roll-forward and recovery */
        nilfs->ns_mount_state &= ~NILFS_VALID_FS;
        valid_fs = 0;

        err = nilfs_search_super_root(nilfs, &ri);
        if (err)
            goto scan_error;
    }

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

    if (valid_fs)
        goto skip_recovery;

    if (s_flags & MS_RDONLY) {
        __u64 features;

        if (nilfs_test_opt(nilfs, NORECOVERY)) {
            printk(KERN_INFO "NILFS: norecovery option specified. "
                   "skipping roll-forward recovery\n");
            goto skip_recovery;
        }
        features = le64_to_cpu(nilfs->ns_sbp[0]->s_feature_compat_ro) &
            ~NILFS_FEATURE_COMPAT_RO_SUPP;
        if (features) {
            printk(KERN_ERR "NILFS: couldn't proceed with "
                   "recovery because of unsupported optional "
                   "features (%llx)\n",
                   (unsigned long long)features);
            err = -EROFS;
            goto failed_unload;
        }
        if (really_read_only) {
            printk(KERN_ERR "NILFS: write access "
                   "unavailable, cannot proceed.\n");
            err = -EROFS;
            goto failed_unload;
        }
        sb->s_flags &= ~MS_RDONLY;
    } else if (nilfs_test_opt(nilfs, NORECOVERY)) {
        printk(KERN_ERR "NILFS: recovery cancelled because norecovery "
               "option was specified for a read/write mount\n");
        err = -EINVAL;
        goto failed_unload;
    }

    err = nilfs_salvage_orphan_logs(nilfs, sb, &ri);
    if (err)
        goto failed_unload;

    down_write(&nilfs->ns_sem);
    nilfs->ns_mount_state |= NILFS_VALID_FS; /* set "clean" flag */
    err = nilfs_cleanup_super(sb);
    up_write(&nilfs->ns_sem);

    if (err) {
        printk(KERN_ERR "NILFS: failed to update super block. "
               "recovery unfinished.\n");
        goto failed_unload;
    }
    printk(KERN_INFO "NILFS: recovery complete.\n");

 skip_recovery:
    nilfs_clear_recovery_info(&ri);
    sb->s_flags = s_flags;
    return 0;

 scan_error:
    printk(KERN_ERR "NILFS: error searching super root.\n");
    goto failed;

 failed_unload:
    iput(nilfs->ns_cpfile);
    iput(nilfs->ns_sufile);
    iput(nilfs->ns_dat);

 failed:
    nilfs_clear_recovery_info(&ri);
    sb->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;
}

unsigned long nilfs_nrsvsegs(struct the_nilfs *nilfs, unsigned long nsegs)
{
    return max_t(unsigned long, NILFS_MIN_NRSVSEGS,
             DIV_ROUND_UP(nsegs * nilfs->ns_r_segments_percentage,
                  100));
}

void nilfs_set_nsegments(struct the_nilfs *nilfs, unsigned long nsegs)
{
    nilfs->ns_nsegments = nsegs;
    nilfs->ns_nrsvsegs = nilfs_nrsvsegs(nilfs, nsegs);
}

static int nilfs_store_disk_layout(struct the_nilfs *nilfs,
                   struct nilfs_super_block *sbp)
{
    if (le32_to_cpu(sbp->s_rev_level) < NILFS_MIN_SUPP_REV) {
        printk(KERN_ERR "NILFS: unsupported revision "
               "(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_r_segments_percentage =
        le32_to_cpu(sbp->s_r_segments_percentage);
    if (nilfs->ns_r_segments_percentage < 1 ||
        nilfs->ns_r_segments_percentage > 99) {
        printk(KERN_ERR "NILFS: invalid reserved segments percentage.\n");
        return -EINVAL;
    }

    nilfs_set_nsegments(nilfs, le64_to_cpu(sbp->s_nsegments));
    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 "
               "(blocksize = %d)\n", blocksize);
    } else if (!sbp[1]) {
        printk(KERN_WARNING
               "NILFS warning: unable to read secondary superblock "
               "(blocksize = %d)\n", blocksize);
    }

    /*
     * Compare two super blocks and set 1 in swp if the secondary
     * super block is valid and newer.  Otherwise, set 0 in swp.
     */
    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_last_cno) >
               le64_to_cpu(sbp[0]->s_last_cno));

    if (valid[swp] && nilfs_sb2_bad_offset(sbp[swp], sb2off)) {
        brelse(sbh[1]);
        sbh[1] = NULL;
        sbp[1] = NULL;
        valid[1] = 0;
        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 (!valid[!swp])
        printk(KERN_WARNING "NILFS warning: broken superblock. "
               "using spare superblock (blocksize = %d).\n", blocksize);
    if (swp)
        nilfs_swap_super_block(nilfs);

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

int init_nilfs(struct the_nilfs *nilfs, struct super_block *sb, char *data)
{
    struct nilfs_super_block *sbp;
    int blocksize;
    int err;

    down_write(&nilfs->ns_sem);

    blocksize = sb_min_blocksize(sb, NILFS_MIN_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;

    err = nilfs_check_feature_compatibility(sb, sbp);
    if (err)
        goto failed_sbh;

    blocksize = BLOCK_SIZE << le32_to_cpu(sbp->s_log_block_size);
    if (blocksize < NILFS_MIN_BLOCK_SIZE ||
        blocksize > NILFS_MAX_BLOCK_SIZE) {
        printk(KERN_ERR "NILFS: couldn't mount because of unsupported "
               "filesystem blocksize %d\n", blocksize);
        err = -EINVAL;
        goto failed_sbh;
    }
    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;
    nilfs->ns_blocksize = blocksize;

    get_random_bytes(&nilfs->ns_next_generation,
             sizeof(nilfs->ns_next_generation));

    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);

    err = nilfs_store_log_cursor(nilfs, sbp);
    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_discard_segments(struct the_nilfs *nilfs, __u64 *segnump,
                size_t nsegs)
{
    sector_t seg_start, seg_end;
    sector_t start = 0, nblocks = 0;
    unsigned int sects_per_block;
    __u64 *sn;
    int ret = 0;

    sects_per_block = (1 << nilfs->ns_blocksize_bits) /
        bdev_logical_block_size(nilfs->ns_bdev);
    for (sn = segnump; sn < segnump + nsegs; sn++) {
        nilfs_get_segment_range(nilfs, *sn, &seg_start, &seg_end);

        if (!nblocks) {
            start = seg_start;
            nblocks = seg_end - seg_start + 1;
        } else if (start + nblocks == seg_start) {
            nblocks += seg_end - seg_start + 1;
        } else {
            ret = blkdev_issue_discard(nilfs->ns_bdev,
                           start * sects_per_block,
                           nblocks * sects_per_block,
                           GFP_NOFS, 0);
            if (ret < 0)
                return ret;
            nblocks = 0;
        }
    }
    if (nblocks)
        ret = blkdev_issue_discard(nilfs->ns_bdev,
                       start * sects_per_block,
                       nblocks * sects_per_block,
                       GFP_NOFS, 0);
    return ret;
}

int nilfs_count_free_blocks(struct the_nilfs *nilfs, sector_t *nblocks)
{
    unsigned long ncleansegs;

    down_read(&NILFS_MDT(nilfs->ns_dat)->mi_sem);
    ncleansegs = nilfs_sufile_get_ncleansegs(nilfs->ns_sufile);
    up_read(&NILFS_MDT(nilfs->ns_dat)->mi_sem);
    *nblocks = (sector_t)ncleansegs * nilfs->ns_blocks_per_segment;
    return 0;
}

int nilfs_near_disk_full(struct the_nilfs *nilfs)
{
    unsigned long ncleansegs, nincsegs;

    ncleansegs = nilfs_sufile_get_ncleansegs(nilfs->ns_sufile);
    nincsegs = atomic_read(&nilfs->ns_ndirtyblks) /
        nilfs->ns_blocks_per_segment + 1;

    return ncleansegs <= nilfs->ns_nrsvsegs + nincsegs;
}

struct nilfs_root *nilfs_lookup_root(struct the_nilfs *nilfs, __u64 cno)
{
    struct rb_node *n;
    struct nilfs_root *root;

    spin_lock(&nilfs->ns_cptree_lock);
    n = nilfs->ns_cptree.rb_node;
    while (n) {
        root = rb_entry(n, struct nilfs_root, rb_node);

        if (cno < root->cno) {
            n = n->rb_left;
        } else if (cno > root->cno) {
            n = n->rb_right;
        } else {
            atomic_inc(&root->count);
            spin_unlock(&nilfs->ns_cptree_lock);
            return root;
        }
    }
    spin_unlock(&nilfs->ns_cptree_lock);

    return NULL;
}

struct nilfs_root *
nilfs_find_or_create_root(struct the_nilfs *nilfs, __u64 cno)
{
    struct rb_node **p, *parent;
    struct nilfs_root *root, *new;

    root = nilfs_lookup_root(nilfs, cno);
    if (root)
        return root;

    new = kmalloc(sizeof(*root), GFP_KERNEL);
    if (!new)
        return NULL;

    spin_lock(&nilfs->ns_cptree_lock);

    p = &nilfs->ns_cptree.rb_node;
    parent = NULL;

    while (*p) {
        parent = *p;
        root = rb_entry(parent, struct nilfs_root, rb_node);

        if (cno < root->cno) {
            p = &(*p)->rb_left;
        } else if (cno > root->cno) {
            p = &(*p)->rb_right;
        } else {
            atomic_inc(&root->count);
            spin_unlock(&nilfs->ns_cptree_lock);
            kfree(new);
            return root;
        }
    }

    new->cno = cno;
    new->ifile = NULL;
    new->nilfs = nilfs;
    atomic_set(&new->count, 1);
    atomic_set(&new->inodes_count, 0);
    atomic_set(&new->blocks_count, 0);

    rb_link_node(&new->rb_node, parent, p);
    rb_insert_color(&new->rb_node, &nilfs->ns_cptree);

    spin_unlock(&nilfs->ns_cptree_lock);

    return new;
}

void nilfs_put_root(struct nilfs_root *root)
{
    if (atomic_dec_and_test(&root->count)) {
        struct the_nilfs *nilfs = root->nilfs;

        spin_lock(&nilfs->ns_cptree_lock);
        rb_erase(&root->rb_node, &nilfs->ns_cptree);
        spin_unlock(&nilfs->ns_cptree_lock);
        if (root->ifile)
            iput(root->ifile);

        kfree(root);
    }
}