// SPDX-License-Identifier: GPL-2.0+
/*
 * the_nilfs shared structure.
 *
 * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
 *
 * Written by Ryusuke Konishi.
 *
 */

#include <linux/buffer_head.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/log2.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);
}

/**
 * alloc_nilfs - allocate a nilfs object
 * @sb: super block instance
 *
 * Return: a pointer to the allocated nilfs object on success, or NULL on
 * failure.
 */
struct the_nilfs *alloc_nilfs(struct super_block *sb)
{
        struct the_nilfs *nilfs;

        nilfs = kzalloc_obj(*nilfs);
        if (!nilfs)
                return NULL;

        nilfs->ns_sb = sb;
        nilfs->ns_bdev = sb->s_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_last_segment_lock);
        nilfs->ns_cptree = RB_ROOT;
        spin_lock_init(&nilfs->ns_cptree_lock);
        init_rwsem(&nilfs->ns_segctor_sem);
        nilfs->ns_sb_update_freq = NILFS_SB_FREQ;

        return nilfs;
}

/**
 * destroy_nilfs - destroy nilfs object
 * @nilfs: nilfs object to be released
 */
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 int dat_entry_size, segment_usage_size, checkpoint_size;
        unsigned int 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);
}

/**
 * nilfs_store_log_cursor - load log cursor from a super block
 * @nilfs: nilfs object
 * @sbp: buffer storing super block to be read
 *
 * nilfs_store_log_cursor() reads the last position of the log
 * containing a super root from a given super block, and initializes
 * relevant information on the nilfs object preparatory for log
 * scanning and recovery.
 *
 * Return: 0 on success, or %-EINVAL if current segment number is out
 * of range.
 */
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) {
                nilfs_err(nilfs->ns_sb,
                          "pointed segment number is out of range: segnum=%llu, nsegments=%lu",
                          (unsigned long long)nilfs->ns_segnum,
                          nilfs->ns_nsegments);
                ret = -EINVAL;
        }
        return ret;
}

/**
 * nilfs_get_blocksize - get block size from raw superblock data
 * @sb: super block instance
 * @sbp: superblock raw data buffer
 * @blocksize: place to store block size
 *
 * nilfs_get_blocksize() calculates the block size from the block size
 * exponent information written in @sbp and stores it in @blocksize,
 * or aborts with an error message if it's too large.
 *
 * Return: 0 on success, or %-EINVAL if the block size is too large.
 */
static int nilfs_get_blocksize(struct super_block *sb,
                               struct nilfs_super_block *sbp, int *blocksize)
{
        unsigned int shift_bits = le32_to_cpu(sbp->s_log_block_size);

        if (unlikely(shift_bits >
                     ilog2(NILFS_MAX_BLOCK_SIZE) - BLOCK_SIZE_BITS)) {
                nilfs_err(sb, "too large filesystem blocksize: 2 ^ %u KiB",
                          shift_bits);
                return -EINVAL;
        }
        *blocksize = BLOCK_SIZE << shift_bits;
        return 0;
}

/**
 * load_nilfs - load and recover the nilfs
 * @nilfs: the_nilfs structure to be released
 * @sb: super block instance 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.
 *
 * Return: 0 on success, or one of the following negative error codes on
 * failure:
 * * %-EINVAL   - No valid segment found.
 * * %-EIO      - I/O error.
 * * %-ENOMEM   - Insufficient memory available.
 * * %-EROFS    - Read only device or RO compat mode (if recovery is required)
 */
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) {
                nilfs_warn(sb, "mounting unchecked fs");
                if (s_flags & SB_RDONLY) {
                        nilfs_info(sb,
                                   "recovery required for readonly filesystem");
                        nilfs_info(sb,
                                   "write access will be enabled during recovery");
                }
        }

        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])) {
                        nilfs_warn(sb,
                                   "unable to fall back to spare super block");
                        goto scan_error;
                }
                nilfs_info(sb, "trying rollback from an earlier position");

                /*
                 * 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 */
                err = nilfs_get_blocksize(sb, sbp[0], &blocksize);
                if (err)
                        goto scan_error;

                if (blocksize != nilfs->ns_blocksize) {
                        nilfs_warn(sb,
                                   "blocksize differs between two super blocks (%d != %d)",
                                   blocksize, nilfs->ns_blocksize);
                        err = -EINVAL;
                        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)) {
                nilfs_err(sb, "error %d while loading super root", err);
                goto failed;
        }

        err = nilfs_sysfs_create_device_group(sb);
        if (unlikely(err))
                goto sysfs_error;

        if (valid_fs)
                goto skip_recovery;

        if (s_flags & SB_RDONLY) {
                __u64 features;

                if (nilfs_test_opt(nilfs, NORECOVERY)) {
                        nilfs_info(sb,
                                   "norecovery option specified, skipping roll-forward recovery");
                        goto skip_recovery;
                }
                features = le64_to_cpu(nilfs->ns_sbp[0]->s_feature_compat_ro) &
                        ~NILFS_FEATURE_COMPAT_RO_SUPP;
                if (features) {
                        nilfs_err(sb,
                                  "couldn't proceed with recovery because of unsupported optional features (%llx)",
                                  (unsigned long long)features);
                        err = -EROFS;
                        goto failed_unload;
                }
                if (really_read_only) {
                        nilfs_err(sb,
                                  "write access unavailable, cannot proceed");
                        err = -EROFS;
                        goto failed_unload;
                }
                sb->s_flags &= ~SB_RDONLY;
        } else if (nilfs_test_opt(nilfs, NORECOVERY)) {
                nilfs_err(sb,
                          "recovery cancelled because norecovery option was specified for a read/write mount");
                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) {
                nilfs_err(sb,
                          "error %d updating super block. recovery unfinished.",
                          err);
                goto failed_unload;
        }
        nilfs_info(sb, "recovery complete");

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

 scan_error:
        nilfs_err(sb, "error %d while searching super root", err);
        goto failed;

 failed_unload:
        nilfs_sysfs_delete_device_group(nilfs);

 sysfs_error:
        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;
}

/**
 * nilfs_nrsvsegs - calculate the number of reserved segments
 * @nilfs: nilfs object
 * @nsegs: total number of segments
 *
 * Return: Number of reserved segments.
 */
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));
}

/**
 * nilfs_max_segment_count - calculate the maximum number of segments
 * @nilfs: nilfs object
 *
 * Return: Maximum number of segments
 */
static u64 nilfs_max_segment_count(struct the_nilfs *nilfs)
{
        u64 max_count = U64_MAX;

        max_count = div64_ul(max_count, nilfs->ns_blocks_per_segment);
        return min_t(u64, max_count, ULONG_MAX);
}

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)
{
        u64 nsegments, nblocks;

        if (le32_to_cpu(sbp->s_rev_level) < NILFS_MIN_SUPP_REV) {
                nilfs_err(nilfs->ns_sb,
                          "unsupported revision (superblock rev.=%d.%d, current rev.=%d.%d). Please check the version of mkfs.nilfs(2).",
                          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);
        if (nilfs->ns_inode_size > nilfs->ns_blocksize) {
                nilfs_err(nilfs->ns_sb, "too large inode size: %d bytes",
                          nilfs->ns_inode_size);
                return -EINVAL;
        } else if (nilfs->ns_inode_size < NILFS_MIN_INODE_SIZE) {
                nilfs_err(nilfs->ns_sb, "too small inode size: %d bytes",
                          nilfs->ns_inode_size);
                return -EINVAL;
        }

        nilfs->ns_first_ino = le32_to_cpu(sbp->s_first_ino);
        if (nilfs->ns_first_ino < NILFS_USER_INO) {
                nilfs_err(nilfs->ns_sb,
                          "too small lower limit for non-reserved inode numbers: %u",
                          nilfs->ns_first_ino);
                return -EINVAL;
        }

        nilfs->ns_blocks_per_segment = le32_to_cpu(sbp->s_blocks_per_segment);
        if (nilfs->ns_blocks_per_segment < NILFS_SEG_MIN_BLOCKS) {
                nilfs_err(nilfs->ns_sb, "too short segment: %lu blocks",
                          nilfs->ns_blocks_per_segment);
                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) {
                nilfs_err(nilfs->ns_sb,
                          "invalid reserved segments percentage: %lu",
                          nilfs->ns_r_segments_percentage);
                return -EINVAL;
        }

        nsegments = le64_to_cpu(sbp->s_nsegments);
        if (nsegments > nilfs_max_segment_count(nilfs)) {
                nilfs_err(nilfs->ns_sb,
                          "segment count %llu exceeds upper limit (%llu segments)",
                          (unsigned long long)nsegments,
                          (unsigned long long)nilfs_max_segment_count(nilfs));
                return -EINVAL;
        }

        nblocks = sb_bdev_nr_blocks(nilfs->ns_sb);
        if (nblocks) {
                u64 min_block_count = nsegments * nilfs->ns_blocks_per_segment;
                /*
                 * To avoid failing to mount early device images without a
                 * second superblock, exclude that block count from the
                 * "min_block_count" calculation.
                 */

                if (nblocks < min_block_count) {
                        nilfs_err(nilfs->ns_sb,
                                  "total number of segment blocks %llu exceeds device size (%llu blocks)",
                                  (unsigned long long)min_block_count,
                                  (unsigned long long)nblocks);
                        return -EINVAL;
                }
        }

        nilfs_set_nsegments(nilfs, 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 < sumoff + 4 || 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);
}

/**
 * nilfs_sb2_bad_offset - check the location of the second superblock
 * @sbp: superblock raw data buffer
 * @offset: byte offset of second superblock calculated from device size
 *
 * nilfs_sb2_bad_offset() checks if the position on the second
 * superblock is valid or not based on the filesystem parameters
 * stored in @sbp.  If @offset points to a location within the segment
 * area, or if the parameters themselves are not normal, it is
 * determined to be invalid.
 *
 * Return: true if invalid, false if valid.
 */
static bool nilfs_sb2_bad_offset(struct nilfs_super_block *sbp, u64 offset)
{
        unsigned int shift_bits = le32_to_cpu(sbp->s_log_block_size);
        u32 blocks_per_segment = le32_to_cpu(sbp->s_blocks_per_segment);
        u64 nsegments = le64_to_cpu(sbp->s_nsegments);
        u64 index;

        if (blocks_per_segment < NILFS_SEG_MIN_BLOCKS ||
            shift_bits > ilog2(NILFS_MAX_BLOCK_SIZE) - BLOCK_SIZE_BITS)
                return true;

        index = offset >> (shift_bits + BLOCK_SIZE_BITS);
        do_div(index, blocks_per_segment);
        return index < nsegments;
}

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, devsize = bdev_nr_bytes(nilfs->ns_bdev);
        int valid[2], swp = 0, older;

        if (devsize < NILFS_SEG_MIN_BLOCKS * NILFS_MIN_BLOCK_SIZE + 4096) {
                nilfs_err(sb, "device size too small");
                return -EINVAL;
        }
        sb2off = NILFS_SB2_OFFSET_BYTES(devsize);

        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]) {
                        nilfs_err(sb, "unable to read superblock");
                        return -EIO;
                }
                nilfs_warn(sb,
                           "unable to read primary superblock (blocksize = %d)",
                           blocksize);
        } else if (!sbp[1]) {
                nilfs_warn(sb,
                           "unable to read secondary superblock (blocksize = %d)",
                           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);
                nilfs_err(sb, "couldn't find nilfs on the device");
                return -EINVAL;
        }

        if (!valid[!swp])
                nilfs_warn(sb,
                           "broken superblock, retrying with spare superblock (blocksize = %d)",
                           blocksize);
        if (swp)
                nilfs_swap_super_block(nilfs);

        /*
         * Calculate the array index of the older superblock data.
         * If one has been dropped, set index 0 pointing to the remaining one,
         * otherwise set index 1 pointing to the old one (including if both
         * are the same).
         *
         *  Divided case             valid[0]  valid[1]  swp  ->  older
         *  -------------------------------------------------------------
         *  Both SBs are invalid        0         0       N/A (Error)
         *  SB1 is invalid              0         1       1         0
         *  SB2 is invalid              1         0       0         0
         *  SB2 is newer                1         1       1         0
         *  SB2 is older or the same    1         1       0         1
         */
        older = valid[1] ^ swp;

        nilfs->ns_sbwcount = 0;
        nilfs->ns_sbwtime = le64_to_cpu(sbp[0]->s_wtime);
        nilfs->ns_prot_seq = le64_to_cpu(sbp[older]->s_last_seq);
        *sbpp = sbp[0];
        return 0;
}

/**
 * init_nilfs - initialize a NILFS instance.
 * @nilfs: the_nilfs structure
 * @sb: super block
 *
 * init_nilfs() performs common initialization per block device (e.g.
 * reading the super block, getting disk layout information, initializing
 * shared fields in the_nilfs).
 *
 * Return: 0 on success, or a negative error code on failure.
 */
int init_nilfs(struct the_nilfs *nilfs, struct super_block *sb)
{
        struct nilfs_super_block *sbp;
        int blocksize;
        int err;

        blocksize = sb_min_blocksize(sb, NILFS_MIN_BLOCK_SIZE);
        if (!blocksize) {
                nilfs_err(sb, "unable to set blocksize");
                err = -EINVAL;
                goto out;
        }
        err = nilfs_load_super_block(nilfs, sb, blocksize, &sbp);
        if (err)
                goto out;

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

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

        err = nilfs_get_blocksize(sb, sbp, &blocksize);
        if (err)
                goto failed_sbh;

        if (blocksize < NILFS_MIN_BLOCK_SIZE) {
                nilfs_err(sb,
                          "couldn't mount because of unsupported filesystem blocksize %d",
                          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) {
                        nilfs_err(sb,
                                  "blocksize %d too small for device (sector-size = %d)",
                                  blocksize, hw_blocksize);
                        err = -EINVAL;
                        goto failed_sbh;
                }
                nilfs_release_super_block(nilfs);
                if (!sb_set_blocksize(sb, blocksize)) {
                        nilfs_err(sb, "bad blocksize %d", blocksize);
                        err = -EINVAL;
                        goto out;
                }

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

        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:
        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);
                        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);
        return ret;
}

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

        ncleansegs = nilfs_sufile_get_ncleansegs(nilfs->ns_sufile);
        *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 {
                        refcount_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;
        int err;

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

        new = kzalloc_obj(*root);
        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 {
                        refcount_inc(&root->count);
                        spin_unlock(&nilfs->ns_cptree_lock);
                        kfree(new);
                        return root;
                }
        }

        new->cno = cno;
        new->ifile = NULL;
        new->nilfs = nilfs;
        refcount_set(&new->count, 1);
        atomic64_set(&new->inodes_count, 0);
        atomic64_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);

        err = nilfs_sysfs_create_snapshot_group(new);
        if (err) {
                kfree(new);
                new = NULL;
        }

        return new;
}

void nilfs_put_root(struct nilfs_root *root)
{
        struct the_nilfs *nilfs = root->nilfs;

        if (refcount_dec_and_lock(&root->count, &nilfs->ns_cptree_lock)) {
                rb_erase(&root->rb_node, &nilfs->ns_cptree);
                spin_unlock(&nilfs->ns_cptree_lock);

                nilfs_sysfs_delete_snapshot_group(root);
                iput(root->ifile);

                kfree(root);
        }
}