Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 954 insertions, 0 deletions

diff --git a/fs/nilfs2/recovery.c b/fs/nilfs2/recovery.c
new file mode 100644
index 000000000..140b663e9
--- /dev/null
+++ b/fs/nilfs2/recovery.c
@@ -0,0 +1,954 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * recovery.c - NILFS recovery logic
+ *
+ * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
+ *
+ * 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);
+}