/*
 * recovery.c - NILFS recovery logic
 *
 * 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.
 *
 * Written by Ryusuke Konishi.
 */

#include <linux/buffer_head.h>
#include <linux/blkdev.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/crc32.h>
#include "nilfs.h"
#include "segment.h"
#include "sufile.h"
#include "page.h"
#include "segbuf.h"

/*
 * Segment check result
 */
enum {
        NILFS_SEG_VALID,
        NILFS_SEG_NO_SUPER_ROOT,
        NILFS_SEG_FAIL_IO,
        NILFS_SEG_FAIL_MAGIC,
        NILFS_SEG_FAIL_SEQ,
        NILFS_SEG_FAIL_CHECKSUM_SUPER_ROOT,
        NILFS_SEG_FAIL_CHECKSUM_FULL,
        NILFS_SEG_FAIL_CONSISTENCY,
};

/* work structure for recovery */
struct nilfs_recovery_block {
        ino_t ino;              /*
                                 * Inode number of the file that this block
                                 * belongs to
                                 */
        sector_t blocknr;       /* block number */
        __u64 vblocknr;         /* virtual block number */
        unsigned long blkoff;   /* File offset of the data block (per block) */
        struct list_head list;
};


static int nilfs_warn_segment_error(struct super_block *sb, int err)
{
        const char *msg = NULL;

        switch (err) {
        case NILFS_SEG_FAIL_IO:
                nilfs_msg(sb, KERN_ERR, "I/O error reading segment");
                return -EIO;
        case NILFS_SEG_FAIL_MAGIC:
                msg = "Magic number mismatch";
                break;
        case NILFS_SEG_FAIL_SEQ:
                msg = "Sequence number mismatch";
                break;
        case NILFS_SEG_FAIL_CHECKSUM_SUPER_ROOT:
                msg = "Checksum error in super root";
                break;
        case NILFS_SEG_FAIL_CHECKSUM_FULL:
                msg = "Checksum error in segment payload";
                break;
        case NILFS_SEG_FAIL_CONSISTENCY:
                msg = "Inconsistency found";
                break;
        case NILFS_SEG_NO_SUPER_ROOT:
                msg = "No super root in the last segment";
                break;
        default:
                nilfs_msg(sb, KERN_ERR, "unrecognized segment error %d", err);
                return -EINVAL;
        }
        nilfs_msg(sb, KERN_WARNING, "invalid segment: %s", msg);
        return -EINVAL;
}

/**
 * nilfs_compute_checksum - compute checksum of blocks continuously
 * @nilfs: nilfs object
 * @bhs: buffer head of start block
 * @sum: place to store result
 * @offset: offset bytes in the first block
 * @check_bytes: number of bytes to be checked
 * @start: DBN of start block
 * @nblock: number of blocks to be checked
 */
static int nilfs_compute_checksum(struct the_nilfs *nilfs,
                                  struct buffer_head *bhs, u32 *sum,
                                  unsigned long offset, u64 check_bytes,
                                  sector_t start, unsigned long nblock)
{
        unsigned int blocksize = nilfs->ns_blocksize;
        unsigned long size;
        u32 crc;

        BUG_ON(offset >= blocksize);
        check_bytes -= offset;
        size = min_t(u64, check_bytes, blocksize - offset);
        crc = crc32_le(nilfs->ns_crc_seed,
                       (unsigned char *)bhs->b_data + offset, size);
        if (--nblock > 0) {
                do {
                        struct buffer_head *bh;

                        bh = __bread(nilfs->ns_bdev, ++start, blocksize);
                        if (!bh)
                                return -EIO;
                        check_bytes -= size;
                        size = min_t(u64, check_bytes, blocksize);
                        crc = crc32_le(crc, bh->b_data, size);
                        brelse(bh);
                } while (--nblock > 0);
        }
        *sum = crc;
        return 0;
}

/**
 * nilfs_read_super_root_block - read super root block
 * @nilfs: nilfs object
 * @sr_block: disk block number of the super root block
 * @pbh: address of a buffer_head pointer to return super root buffer
 * @check: CRC check flag
 */
int nilfs_read_super_root_block(struct the_nilfs *nilfs, sector_t sr_block,
                                struct buffer_head **pbh, int check)
{
        struct buffer_head *bh_sr;
        struct nilfs_super_root *sr;
        u32 crc;
        int ret;

        *pbh = NULL;
        bh_sr = __bread(nilfs->ns_bdev, sr_block, nilfs->ns_blocksize);
        if (unlikely(!bh_sr)) {
                ret = NILFS_SEG_FAIL_IO;
                goto failed;
        }

        sr = (struct nilfs_super_root *)bh_sr->b_data;
        if (check) {
                unsigned int bytes = le16_to_cpu(sr->sr_bytes);

                if (bytes == 0 || bytes > nilfs->ns_blocksize) {
                        ret = NILFS_SEG_FAIL_CHECKSUM_SUPER_ROOT;
                        goto failed_bh;
                }
                if (nilfs_compute_checksum(
                            nilfs, bh_sr, &crc, sizeof(sr->sr_sum), bytes,
                            sr_block, 1)) {
                        ret = NILFS_SEG_FAIL_IO;
                        goto failed_bh;
                }
                if (crc != le32_to_cpu(sr->sr_sum)) {
                        ret = NILFS_SEG_FAIL_CHECKSUM_SUPER_ROOT;
                        goto failed_bh;
                }
        }
        *pbh = bh_sr;
        return 0;

 failed_bh:
        brelse(bh_sr);

 failed:
        return nilfs_warn_segment_error(nilfs->ns_sb, ret);
}

/**
 * nilfs_read_log_header - read summary header of the specified log
 * @nilfs: nilfs object
 * @start_blocknr: start block number of the log
 * @sum: pointer to return segment summary structure
 */
static struct buffer_head *
nilfs_read_log_header(struct the_nilfs *nilfs, sector_t start_blocknr,
                      struct nilfs_segment_summary **sum)
{
        struct buffer_head *bh_sum;

        bh_sum = __bread(nilfs->ns_bdev, start_blocknr, nilfs->ns_blocksize);
        if (bh_sum)
                *sum = (struct nilfs_segment_summary *)bh_sum->b_data;
        return bh_sum;
}

/**
 * nilfs_validate_log - verify consistency of log
 * @nilfs: nilfs object
 * @seg_seq: sequence number of segment
 * @bh_sum: buffer head of summary block
 * @sum: segment summary struct
 */
static int nilfs_validate_log(struct the_nilfs *nilfs, u64 seg_seq,
                              struct buffer_head *bh_sum,
                              struct nilfs_segment_summary *sum)
{
        unsigned long nblock;
        u32 crc;
        int ret;

        ret = NILFS_SEG_FAIL_MAGIC;
        if (le32_to_cpu(sum->ss_magic) != NILFS_SEGSUM_MAGIC)
                goto out;

        ret = NILFS_SEG_FAIL_SEQ;
        if (le64_to_cpu(sum->ss_seq) != seg_seq)
                goto out;

        nblock = le32_to_cpu(sum->ss_nblocks);
        ret = NILFS_SEG_FAIL_CONSISTENCY;
        if (unlikely(nblock == 0 || nblock > nilfs->ns_blocks_per_segment))
                /* This limits the number of blocks read in the CRC check */
                goto out;

        ret = NILFS_SEG_FAIL_IO;
        if (nilfs_compute_checksum(nilfs, bh_sum, &crc, sizeof(sum->ss_datasum),
                                   ((u64)nblock << nilfs->ns_blocksize_bits),
                                   bh_sum->b_blocknr, nblock))
                goto out;

        ret = NILFS_SEG_FAIL_CHECKSUM_FULL;
        if (crc != le32_to_cpu(sum->ss_datasum))
                goto out;
        ret = 0;
out:
        return ret;
}

/**
 * nilfs_read_summary_info - read an item on summary blocks of a log
 * @nilfs: nilfs object
 * @pbh: the current buffer head on summary blocks [in, out]
 * @offset: the current byte offset on summary blocks [in, out]
 * @bytes: byte size of the item to be read
 */
static void *nilfs_read_summary_info(struct the_nilfs *nilfs,
                                     struct buffer_head **pbh,
                                     unsigned int *offset, unsigned int bytes)
{
        void *ptr;
        sector_t blocknr;

        BUG_ON((*pbh)->b_size < *offset);
        if (bytes > (*pbh)->b_size - *offset) {
                blocknr = (*pbh)->b_blocknr;
                brelse(*pbh);
                *pbh = __bread(nilfs->ns_bdev, blocknr + 1,
                               nilfs->ns_blocksize);
                if (unlikely(!*pbh))
                        return NULL;
                *offset = 0;
        }
        ptr = (*pbh)->b_data + *offset;
        *offset += bytes;
        return ptr;
}

/**
 * nilfs_skip_summary_info - skip items on summary blocks of a log
 * @nilfs: nilfs object
 * @pbh: the current buffer head on summary blocks [in, out]
 * @offset: the current byte offset on summary blocks [in, out]
 * @bytes: byte size of the item to be skipped
 * @count: number of items to be skipped
 */
static void nilfs_skip_summary_info(struct the_nilfs *nilfs,
                                    struct buffer_head **pbh,
                                    unsigned int *offset, unsigned int bytes,
                                    unsigned long count)
{
        unsigned int rest_item_in_current_block
                = ((*pbh)->b_size - *offset) / bytes;

        if (count <= rest_item_in_current_block) {
                *offset += bytes * count;
        } else {
                sector_t blocknr = (*pbh)->b_blocknr;
                unsigned int nitem_per_block = (*pbh)->b_size / bytes;
                unsigned int bcnt;

                count -= rest_item_in_current_block;
                bcnt = DIV_ROUND_UP(count, nitem_per_block);
                *offset = bytes * (count - (bcnt - 1) * nitem_per_block);

                brelse(*pbh);
                *pbh = __bread(nilfs->ns_bdev, blocknr + bcnt,
                               nilfs->ns_blocksize);
        }
}

/**
 * nilfs_scan_dsync_log - get block information of a log written for data sync
 * @nilfs: nilfs object
 * @start_blocknr: start block number of the log
 * @sum: log summary information
 * @head: list head to add nilfs_recovery_block struct
 */
static int nilfs_scan_dsync_log(struct the_nilfs *nilfs, sector_t start_blocknr,
                                struct nilfs_segment_summary *sum,
                                struct list_head *head)
{
        struct buffer_head *bh;
        unsigned int offset;
        u32 nfinfo, sumbytes;
        sector_t blocknr;
        ino_t ino;
        int err = -EIO;

        nfinfo = le32_to_cpu(sum->ss_nfinfo);
        if (!nfinfo)
                return 0;

        sumbytes = le32_to_cpu(sum->ss_sumbytes);
        blocknr = start_blocknr + DIV_ROUND_UP(sumbytes, nilfs->ns_blocksize);
        bh = __bread(nilfs->ns_bdev, start_blocknr, nilfs->ns_blocksize);
        if (unlikely(!bh))
                goto out;

        offset = le16_to_cpu(sum->ss_bytes);
        for (;;) {
                unsigned long nblocks, ndatablk, nnodeblk;
                struct nilfs_finfo *finfo;

                finfo = nilfs_read_summary_info(nilfs, &bh, &offset,
                                                sizeof(*finfo));
                if (unlikely(!finfo))
                        goto out;

                ino = le64_to_cpu(finfo->fi_ino);
                nblocks = le32_to_cpu(finfo->fi_nblocks);
                ndatablk = le32_to_cpu(finfo->fi_ndatablk);
                nnodeblk = nblocks - ndatablk;

                while (ndatablk-- > 0) {
                        struct nilfs_recovery_block *rb;
                        struct nilfs_binfo_v *binfo;

                        binfo = nilfs_read_summary_info(nilfs, &bh, &offset,
                                                        sizeof(*binfo));
                        if (unlikely(!binfo))
                                goto out;

                        rb = kmalloc(sizeof(*rb), GFP_NOFS);
                        if (unlikely(!rb)) {
                                err = -ENOMEM;
                                goto out;
                        }
                        rb->ino = ino;
                        rb->blocknr = blocknr++;
                        rb->vblocknr = le64_to_cpu(binfo->bi_vblocknr);
                        rb->blkoff = le64_to_cpu(binfo->bi_blkoff);
                        /* INIT_LIST_HEAD(&rb->list); */
                        list_add_tail(&rb->list, head);
                }
                if (--nfinfo == 0)
                        break;
                blocknr += nnodeblk; /* always 0 for data sync logs */
                nilfs_skip_summary_info(nilfs, &bh, &offset, sizeof(__le64),
                                        nnodeblk);
                if (unlikely(!bh))
                        goto out;
        }
        err = 0;
 out:
        brelse(bh);   /* brelse(NULL) is just ignored */
        return err;
}

static void dispose_recovery_list(struct list_head *head)
{
        while (!list_empty(head)) {
                struct nilfs_recovery_block *rb;

                rb = list_first_entry(head, struct nilfs_recovery_block, list);
                list_del(&rb->list);
                kfree(rb);
        }
}

struct nilfs_segment_entry {
        struct list_head        list;
        __u64                   segnum;
};

static int nilfs_segment_list_add(struct list_head *head, __u64 segnum)
{
        struct nilfs_segment_entry *ent = kmalloc(sizeof(*ent), GFP_NOFS);

        if (unlikely(!ent))
                return -ENOMEM;

        ent->segnum = segnum;
        INIT_LIST_HEAD(&ent->list);
        list_add_tail(&ent->list, head);
        return 0;
}

void nilfs_dispose_segment_list(struct list_head *head)
{
        while (!list_empty(head)) {
                struct nilfs_segment_entry *ent;

                ent = list_first_entry(head, struct nilfs_segment_entry, list);
                list_del(&ent->list);
                kfree(ent);
        }
}

static int nilfs_prepare_segment_for_recovery(struct the_nilfs *nilfs,
                                              struct super_block *sb,
                                              struct nilfs_recovery_info *ri)
{
        struct list_head *head = &ri->ri_used_segments;
        struct nilfs_segment_entry *ent, *n;
        struct inode *sufile = nilfs->ns_sufile;
        __u64 segnum[4];
        int err;
        int i;

        segnum[0] = nilfs->ns_segnum;
        segnum[1] = nilfs->ns_nextnum;
        segnum[2] = ri->ri_segnum;
        segnum[3] = ri->ri_nextnum;

        /*
         * Releasing the next segment of the latest super root.
         * The next segment is invalidated by this recovery.
         */
        err = nilfs_sufile_free(sufile, segnum[1]);
        if (unlikely(err))
                goto failed;

        for (i = 1; i < 4; i++) {
                err = nilfs_segment_list_add(head, segnum[i]);
                if (unlikely(err))
                        goto failed;
        }

        /*
         * Collecting segments written after the latest super root.
         * These are marked dirty to avoid being reallocated in the next write.
         */
        list_for_each_entry_safe(ent, n, head, list) {
                if (ent->segnum != segnum[0]) {
                        err = nilfs_sufile_scrap(sufile, ent->segnum);
                        if (unlikely(err))
                                goto failed;
                }
                list_del(&ent->list);
                kfree(ent);
        }

        /* Allocate new segments for recovery */
        err = nilfs_sufile_alloc(sufile, &segnum[0]);
        if (unlikely(err))
                goto failed;

        nilfs->ns_pseg_offset = 0;
        nilfs->ns_seg_seq = ri->ri_seq + 2;
        nilfs->ns_nextnum = nilfs->ns_segnum = segnum[0];

 failed:
        /* No need to recover sufile because it will be destroyed on error */
        return err;
}

static int nilfs_recovery_copy_block(struct the_nilfs *nilfs,
                                     struct nilfs_recovery_block *rb,
                                     struct page *page)
{
        struct buffer_head *bh_org;
        void *kaddr;

        bh_org = __bread(nilfs->ns_bdev, rb->blocknr, nilfs->ns_blocksize);
        if (unlikely(!bh_org))
                return -EIO;

        kaddr = kmap_atomic(page);
        memcpy(kaddr + bh_offset(bh_org), bh_org->b_data, bh_org->b_size);
        kunmap_atomic(kaddr);
        brelse(bh_org);
        return 0;
}

static int nilfs_recover_dsync_blocks(struct the_nilfs *nilfs,
                                      struct super_block *sb,
                                      struct nilfs_root *root,
                                      struct list_head *head,
                                      unsigned long *nr_salvaged_blocks)
{
        struct inode *inode;
        struct nilfs_recovery_block *rb, *n;
        unsigned int blocksize = nilfs->ns_blocksize;
        struct page *page;
        loff_t pos;
        int err = 0, err2 = 0;

        list_for_each_entry_safe(rb, n, head, list) {
                inode = nilfs_iget(sb, root, rb->ino);
                if (IS_ERR(inode)) {
                        err = PTR_ERR(inode);
                        inode = NULL;
                        goto failed_inode;
                }

                pos = rb->blkoff << inode->i_blkbits;
                err = block_write_begin(inode->i_mapping, pos, blocksize,
                                        0, &page, nilfs_get_block);
                if (unlikely(err)) {
                        loff_t isize = inode->i_size;

                        if (pos + blocksize > isize)
                                nilfs_write_failed(inode->i_mapping,
                                                        pos + blocksize);
                        goto failed_inode;
                }

                err = nilfs_recovery_copy_block(nilfs, rb, page);
                if (unlikely(err))
                        goto failed_page;

                err = nilfs_set_file_dirty(inode, 1);
                if (unlikely(err))
                        goto failed_page;

                block_write_end(NULL, inode->i_mapping, pos, blocksize,
                                blocksize, page, NULL);

                unlock_page(page);
                put_page(page);

                (*nr_salvaged_blocks)++;
                goto next;

 failed_page:
                unlock_page(page);
                put_page(page);

 failed_inode:
                nilfs_msg(sb, KERN_WARNING,
                          "error %d recovering data block (ino=%lu, block-offset=%llu)",
                          err, (unsigned long)rb->ino,
                          (unsigned long long)rb->blkoff);
                if (!err2)
                        err2 = err;
 next:
                iput(inode); /* iput(NULL) is just ignored */
                list_del_init(&rb->list);
                kfree(rb);
        }
        return err2;
}

/**
 * nilfs_do_roll_forward - salvage logical segments newer than the latest
 * checkpoint
 * @nilfs: nilfs object
 * @sb: super block instance
 * @ri: pointer to a nilfs_recovery_info
 */
static int nilfs_do_roll_forward(struct the_nilfs *nilfs,
                                 struct super_block *sb,
                                 struct nilfs_root *root,
                                 struct nilfs_recovery_info *ri)
{
        struct buffer_head *bh_sum = NULL;
        struct nilfs_segment_summary *sum = NULL;
        sector_t pseg_start;
        sector_t seg_start, seg_end;  /* Starting/ending DBN of full segment */
        unsigned long nsalvaged_blocks = 0;
        unsigned int flags;
        u64 seg_seq;
        __u64 segnum, nextnum = 0;
        int empty_seg = 0;
        int err = 0, ret;
        LIST_HEAD(dsync_blocks);  /* list of data blocks to be recovered */
        enum {
                RF_INIT_ST,
                RF_DSYNC_ST,   /* scanning data-sync segments */
        };
        int state = RF_INIT_ST;

        pseg_start = ri->ri_lsegs_start;
        seg_seq = ri->ri_lsegs_start_seq;
        segnum = nilfs_get_segnum_of_block(nilfs, pseg_start);
        nilfs_get_segment_range(nilfs, segnum, &seg_start, &seg_end);

        while (segnum != ri->ri_segnum || pseg_start <= ri->ri_pseg_start) {
                brelse(bh_sum);
                bh_sum = nilfs_read_log_header(nilfs, pseg_start, &sum);
                if (!bh_sum) {
                        err = -EIO;
                        goto failed;
                }

                ret = nilfs_validate_log(nilfs, seg_seq, bh_sum, sum);
                if (ret) {
                        if (ret == NILFS_SEG_FAIL_IO) {
                                err = -EIO;
                                goto failed;
                        }
                        goto strayed;
                }

                flags = le16_to_cpu(sum->ss_flags);
                if (flags & NILFS_SS_SR)
                        goto confused;

                /* Found a valid partial segment; do recovery actions */
                nextnum = nilfs_get_segnum_of_block(nilfs,
                                                    le64_to_cpu(sum->ss_next));
                empty_seg = 0;
                nilfs->ns_ctime = le64_to_cpu(sum->ss_create);
                if (!(flags & NILFS_SS_GC))
                        nilfs->ns_nongc_ctime = nilfs->ns_ctime;

                switch (state) {
                case RF_INIT_ST:
                        if (!(flags & NILFS_SS_LOGBGN) ||
                            !(flags & NILFS_SS_SYNDT))
                                goto try_next_pseg;
                        state = RF_DSYNC_ST;
                        /* Fall through */
                case RF_DSYNC_ST:
                        if (!(flags & NILFS_SS_SYNDT))
                                goto confused;

                        err = nilfs_scan_dsync_log(nilfs, pseg_start, sum,
                                                   &dsync_blocks);
                        if (unlikely(err))
                                goto failed;
                        if (flags & NILFS_SS_LOGEND) {
                                err = nilfs_recover_dsync_blocks(
                                        nilfs, sb, root, &dsync_blocks,
                                        &nsalvaged_blocks);
                                if (unlikely(err))
                                        goto failed;
                                state = RF_INIT_ST;
                        }
                        break; /* Fall through to try_next_pseg */
                }

 try_next_pseg:
                if (pseg_start == ri->ri_lsegs_end)
                        break;
                pseg_start += le32_to_cpu(sum->ss_nblocks);
                if (pseg_start < seg_end)
                        continue;
                goto feed_segment;

 strayed:
                if (pseg_start == ri->ri_lsegs_end)
                        break;

 feed_segment:
                /* Looking to the next full segment */
                if (empty_seg++)
                        break;
                seg_seq++;
                segnum = nextnum;
                nilfs_get_segment_range(nilfs, segnum, &seg_start, &seg_end);
                pseg_start = seg_start;
        }

        if (nsalvaged_blocks) {
                nilfs_msg(sb, KERN_INFO, "salvaged %lu blocks",
                          nsalvaged_blocks);
                ri->ri_need_recovery = NILFS_RECOVERY_ROLLFORWARD_DONE;
        }
 out:
        brelse(bh_sum);
        dispose_recovery_list(&dsync_blocks);
        return err;

 confused:
        err = -EINVAL;
 failed:
        nilfs_msg(sb, KERN_ERR,
                  "error %d roll-forwarding partial segment at blocknr = %llu",
                  err, (unsigned long long)pseg_start);
        goto out;
}

static void nilfs_finish_roll_forward(struct the_nilfs *nilfs,
                                      struct nilfs_recovery_info *ri)
{
        struct buffer_head *bh;
        int err;

        if (nilfs_get_segnum_of_block(nilfs, ri->ri_lsegs_start) !=
            nilfs_get_segnum_of_block(nilfs, ri->ri_super_root))
                return;

        bh = __getblk(nilfs->ns_bdev, ri->ri_lsegs_start, nilfs->ns_blocksize);
        BUG_ON(!bh);
        memset(bh->b_data, 0, bh->b_size);
        set_buffer_dirty(bh);
        err = sync_dirty_buffer(bh);
        if (unlikely(err))
                nilfs_msg(nilfs->ns_sb, KERN_WARNING,
                          "buffer sync write failed during post-cleaning of recovery.");
        brelse(bh);
}

/**
 * nilfs_salvage_orphan_logs - salvage logs written after the latest checkpoint
 * @nilfs: nilfs object
 * @sb: super block instance
 * @ri: pointer to a nilfs_recovery_info struct to store search results.
 *
 * Return Value: On success, 0 is returned.  On error, one of the following
 * negative error code is returned.
 *
 * %-EINVAL - Inconsistent filesystem state.
 *
 * %-EIO - I/O error
 *
 * %-ENOSPC - No space left on device (only in a panic state).
 *
 * %-ERESTARTSYS - Interrupted.
 *
 * %-ENOMEM - Insufficient memory available.
 */
int nilfs_salvage_orphan_logs(struct the_nilfs *nilfs,
                              struct super_block *sb,
                              struct nilfs_recovery_info *ri)
{
        struct nilfs_root *root;
        int err;

        if (ri->ri_lsegs_start == 0 || ri->ri_lsegs_end == 0)
                return 0;

        err = nilfs_attach_checkpoint(sb, ri->ri_cno, true, &root);
        if (unlikely(err)) {
                nilfs_msg(sb, KERN_ERR,
                          "error %d loading the latest checkpoint", err);
                return err;
        }

        err = nilfs_do_roll_forward(nilfs, sb, root, ri);
        if (unlikely(err))
                goto failed;

        if (ri->ri_need_recovery == NILFS_RECOVERY_ROLLFORWARD_DONE) {
                err = nilfs_prepare_segment_for_recovery(nilfs, sb, ri);
                if (unlikely(err)) {
                        nilfs_msg(sb, KERN_ERR,
                                  "error %d preparing segment for recovery",
                                  err);
                        goto failed;
                }

                err = nilfs_attach_log_writer(sb, root);
                if (unlikely(err))
                        goto failed;

                set_nilfs_discontinued(nilfs);
                err = nilfs_construct_segment(sb);
                nilfs_detach_log_writer(sb);

                if (unlikely(err)) {
                        nilfs_msg(sb, KERN_ERR,
                                  "error %d writing segment for recovery",
                                  err);
                        goto failed;
                }

                nilfs_finish_roll_forward(nilfs, ri);
        }

 failed:
        nilfs_put_root(root);
        return err;
}

/**
 * nilfs_search_super_root - search the latest valid super root
 * @nilfs: the_nilfs
 * @ri: pointer to a nilfs_recovery_info struct to store search results.
 *
 * nilfs_search_super_root() looks for the latest super-root from a partial
 * segment pointed by the superblock.  It sets up struct the_nilfs through
 * this search. It fills nilfs_recovery_info (ri) required for recovery.
 *
 * Return Value: On success, 0 is returned.  On error, one of the following
 * negative error code is returned.
 *
 * %-EINVAL - No valid segment found
 *
 * %-EIO - I/O error
 *
 * %-ENOMEM - Insufficient memory available.
 */
int nilfs_search_super_root(struct the_nilfs *nilfs,
                            struct nilfs_recovery_info *ri)
{
        struct buffer_head *bh_sum = NULL;
        struct nilfs_segment_summary *sum = NULL;
        sector_t pseg_start, pseg_end, sr_pseg_start = 0;
        sector_t seg_start, seg_end; /* range of full segment (block number) */
        sector_t b, end;
        unsigned long nblocks;
        unsigned int flags;
        u64 seg_seq;
        __u64 segnum, nextnum = 0;
        __u64 cno;
        LIST_HEAD(segments);
        int empty_seg = 0, scan_newer = 0;
        int ret;

        pseg_start = nilfs->ns_last_pseg;
        seg_seq = nilfs->ns_last_seq;
        cno = nilfs->ns_last_cno;
        segnum = nilfs_get_segnum_of_block(nilfs, pseg_start);

        /* Calculate range of segment */
        nilfs_get_segment_range(nilfs, segnum, &seg_start, &seg_end);

        /* Read ahead segment */
        b = seg_start;
        while (b <= seg_end)
                __breadahead(nilfs->ns_bdev, b++, nilfs->ns_blocksize);

        for (;;) {
                brelse(bh_sum);
                ret = NILFS_SEG_FAIL_IO;
                bh_sum = nilfs_read_log_header(nilfs, pseg_start, &sum);
                if (!bh_sum)
                        goto failed;

                ret = nilfs_validate_log(nilfs, seg_seq, bh_sum, sum);
                if (ret) {
                        if (ret == NILFS_SEG_FAIL_IO)
                                goto failed;
                        goto strayed;
                }

                nblocks = le32_to_cpu(sum->ss_nblocks);
                pseg_end = pseg_start + nblocks - 1;
                if (unlikely(pseg_end > seg_end)) {
                        ret = NILFS_SEG_FAIL_CONSISTENCY;
                        goto strayed;
                }

                /* A valid partial segment */
                ri->ri_pseg_start = pseg_start;
                ri->ri_seq = seg_seq;
                ri->ri_segnum = segnum;
                nextnum = nilfs_get_segnum_of_block(nilfs,
                                                    le64_to_cpu(sum->ss_next));
                ri->ri_nextnum = nextnum;
                empty_seg = 0;

                flags = le16_to_cpu(sum->ss_flags);
                if (!(flags & NILFS_SS_SR) && !scan_newer) {
                        /*
                         * This will never happen because a superblock
                         * (last_segment) always points to a pseg with
                         * a super root.
                         */
                        ret = NILFS_SEG_FAIL_CONSISTENCY;
                        goto failed;
                }

                if (pseg_start == seg_start) {
                        nilfs_get_segment_range(nilfs, nextnum, &b, &end);
                        while (b <= end)
                                __breadahead(nilfs->ns_bdev, b++,
                                             nilfs->ns_blocksize);
                }
                if (!(flags & NILFS_SS_SR)) {
                        if (!ri->ri_lsegs_start && (flags & NILFS_SS_LOGBGN)) {
                                ri->ri_lsegs_start = pseg_start;
                                ri->ri_lsegs_start_seq = seg_seq;
                        }
                        if (flags & NILFS_SS_LOGEND)
                                ri->ri_lsegs_end = pseg_start;
                        goto try_next_pseg;
                }

                /* A valid super root was found. */
                ri->ri_cno = cno++;
                ri->ri_super_root = pseg_end;
                ri->ri_lsegs_start = ri->ri_lsegs_end = 0;

                nilfs_dispose_segment_list(&segments);
                sr_pseg_start = pseg_start;
                nilfs->ns_pseg_offset = pseg_start + nblocks - seg_start;
                nilfs->ns_seg_seq = seg_seq;
                nilfs->ns_segnum = segnum;
                nilfs->ns_cno = cno;  /* nilfs->ns_cno = ri->ri_cno + 1 */
                nilfs->ns_ctime = le64_to_cpu(sum->ss_create);
                nilfs->ns_nextnum = nextnum;

                if (scan_newer)
                        ri->ri_need_recovery = NILFS_RECOVERY_SR_UPDATED;
                else {
                        if (nilfs->ns_mount_state & NILFS_VALID_FS)
                                goto super_root_found;
                        scan_newer = 1;
                }

 try_next_pseg:
                /* Standing on a course, or met an inconsistent state */
                pseg_start += nblocks;
                if (pseg_start < seg_end)
                        continue;
                goto feed_segment;

 strayed:
                /* Off the trail */
                if (!scan_newer)
                        /*
                         * This can happen if a checkpoint was written without
                         * barriers, or as a result of an I/O failure.
                         */
                        goto failed;

 feed_segment:
                /* Looking to the next full segment */
                if (empty_seg++)
                        goto super_root_found; /* found a valid super root */

                ret = nilfs_segment_list_add(&segments, segnum);
                if (unlikely(ret))
                        goto failed;

                seg_seq++;
                segnum = nextnum;
                nilfs_get_segment_range(nilfs, segnum, &seg_start, &seg_end);
                pseg_start = seg_start;
        }

 super_root_found:
        /* Updating pointers relating to the latest checkpoint */
        brelse(bh_sum);
        list_splice_tail(&segments, &ri->ri_used_segments);
        nilfs->ns_last_pseg = sr_pseg_start;
        nilfs->ns_last_seq = nilfs->ns_seg_seq;
        nilfs->ns_last_cno = ri->ri_cno;
        return 0;

 failed:
        brelse(bh_sum);
        nilfs_dispose_segment_list(&segments);
        return ret < 0 ? ret : nilfs_warn_segment_error(nilfs->ns_sb, ret);
}