Initial import

1 files changed, 2758 insertions, 0 deletions

diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
new file mode 100644
index 000000000..c6abbad9b
--- /dev/null
+++ b/fs/nilfs2/segment.c
@@ -0,0 +1,2758 @@
+/*
+ * segment.c - NILFS segment constructor.
+ *
+ * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Written by Ryusuke Konishi <ryusuke@osrg.net>
+ *
+ */
+
+#include <linux/pagemap.h>
+#include <linux/buffer_head.h>
+#include <linux/writeback.h>
+#include <linux/bitops.h>
+#include <linux/bio.h>
+#include <linux/completion.h>
+#include <linux/blkdev.h>
+#include <linux/backing-dev.h>
+#include <linux/freezer.h>
+#include <linux/kthread.h>
+#include <linux/crc32.h>
+#include <linux/pagevec.h>
+#include <linux/slab.h>
+#include "nilfs.h"
+#include "btnode.h"
+#include "page.h"
+#include "segment.h"
+#include "sufile.h"
+#include "cpfile.h"
+#include "ifile.h"
+#include "segbuf.h"
+
+
+/*
+ * Segment constructor
+ */
+#define SC_N_INODEVEC	16   /* Size of locally allocated inode vector */
+
+#define SC_MAX_SEGDELTA 64   /* Upper limit of the number of segments
+				appended in collection retry loop */
+
+/* Construction mode */
+enum {
+	SC_LSEG_SR = 1,	/* Make a logical segment having a super root */
+	SC_LSEG_DSYNC,	/* Flush data blocks of a given file and make
+			   a logical segment without a super root */
+	SC_FLUSH_FILE,	/* Flush data files, leads to segment writes without
+			   creating a checkpoint */
+	SC_FLUSH_DAT,	/* Flush DAT file. This also creates segments without
+			   a checkpoint */
+};
+
+/* Stage numbers of dirty block collection */
+enum {
+	NILFS_ST_INIT = 0,
+	NILFS_ST_GC,		/* Collecting dirty blocks for GC */
+	NILFS_ST_FILE,
+	NILFS_ST_IFILE,
+	NILFS_ST_CPFILE,
+	NILFS_ST_SUFILE,
+	NILFS_ST_DAT,
+	NILFS_ST_SR,		/* Super root */
+	NILFS_ST_DSYNC,		/* Data sync blocks */
+	NILFS_ST_DONE,
+};
+
+/* State flags of collection */
+#define NILFS_CF_NODE		0x0001	/* Collecting node blocks */
+#define NILFS_CF_IFILE_STARTED	0x0002	/* IFILE stage has started */
+#define NILFS_CF_SUFREED	0x0004	/* segment usages has been freed */
+#define NILFS_CF_HISTORY_MASK	(NILFS_CF_IFILE_STARTED | NILFS_CF_SUFREED)
+
+/* Operations depending on the construction mode and file type */
+struct nilfs_sc_operations {
+	int (*collect_data)(struct nilfs_sc_info *, struct buffer_head *,
+			    struct inode *);
+	int (*collect_node)(struct nilfs_sc_info *, struct buffer_head *,
+			    struct inode *);
+	int (*collect_bmap)(struct nilfs_sc_info *, struct buffer_head *,
+			    struct inode *);
+	void (*write_data_binfo)(struct nilfs_sc_info *,
+				 struct nilfs_segsum_pointer *,
+				 union nilfs_binfo *);
+	void (*write_node_binfo)(struct nilfs_sc_info *,
+				 struct nilfs_segsum_pointer *,
+				 union nilfs_binfo *);
+};
+
+/*
+ * Other definitions
+ */
+static void nilfs_segctor_start_timer(struct nilfs_sc_info *);
+static void nilfs_segctor_do_flush(struct nilfs_sc_info *, int);
+static void nilfs_segctor_do_immediate_flush(struct nilfs_sc_info *);
+static void nilfs_dispose_list(struct the_nilfs *, struct list_head *, int);
+
+#define nilfs_cnt32_gt(a, b)   \
+	(typecheck(__u32, a) && typecheck(__u32, b) && \
+	 ((__s32)(b) - (__s32)(a) < 0))
+#define nilfs_cnt32_ge(a, b)   \
+	(typecheck(__u32, a) && typecheck(__u32, b) && \
+	 ((__s32)(a) - (__s32)(b) >= 0))
+#define nilfs_cnt32_lt(a, b)  nilfs_cnt32_gt(b, a)
+#define nilfs_cnt32_le(a, b)  nilfs_cnt32_ge(b, a)
+
+static int nilfs_prepare_segment_lock(struct nilfs_transaction_info *ti)
+{
+	struct nilfs_transaction_info *cur_ti = current->journal_info;
+	void *save = NULL;
+
+	if (cur_ti) {
+		if (cur_ti->ti_magic == NILFS_TI_MAGIC)
+			return ++cur_ti->ti_count;
+		else {
+			/*
+			 * If journal_info field is occupied by other FS,
+			 * it is saved and will be restored on
+			 * nilfs_transaction_commit().
+			 */
+			printk(KERN_WARNING
+			       "NILFS warning: journal info from a different "
+			       "FS\n");
+			save = current->journal_info;
+		}
+	}
+	if (!ti) {
+		ti = kmem_cache_alloc(nilfs_transaction_cachep, GFP_NOFS);
+		if (!ti)
+			return -ENOMEM;
+		ti->ti_flags = NILFS_TI_DYNAMIC_ALLOC;
+	} else {
+		ti->ti_flags = 0;
+	}
+	ti->ti_count = 0;
+	ti->ti_save = save;
+	ti->ti_magic = NILFS_TI_MAGIC;
+	current->journal_info = ti;
+	return 0;
+}
+
+/**
+ * nilfs_transaction_begin - start indivisible file operations.
+ * @sb: super block
+ * @ti: nilfs_transaction_info
+ * @vacancy_check: flags for vacancy rate checks
+ *
+ * nilfs_transaction_begin() acquires a reader/writer semaphore, called
+ * the segment semaphore, to make a segment construction and write tasks
+ * exclusive.  The function is used with nilfs_transaction_commit() in pairs.
+ * The region enclosed by these two functions can be nested.  To avoid a
+ * deadlock, the semaphore is only acquired or released in the outermost call.
+ *
+ * This function allocates a nilfs_transaction_info struct to keep context
+ * information on it.  It is initialized and hooked onto the current task in
+ * the outermost call.  If a pre-allocated struct is given to @ti, it is used
+ * instead; otherwise a new struct is assigned from a slab.
+ *
+ * When @vacancy_check flag is set, this function will check the amount of
+ * free space, and will wait for the GC to reclaim disk space if low capacity.
+ *
+ * Return Value: On success, 0 is returned. On error, one of the following
+ * negative error code is returned.
+ *
+ * %-ENOMEM - Insufficient memory available.
+ *
+ * %-ENOSPC - No space left on device
+ */
+int nilfs_transaction_begin(struct super_block *sb,
+			    struct nilfs_transaction_info *ti,
+			    int vacancy_check)
+{
+	struct the_nilfs *nilfs;
+	int ret = nilfs_prepare_segment_lock(ti);
+
+	if (unlikely(ret < 0))
+		return ret;
+	if (ret > 0)
+		return 0;
+
+	sb_start_intwrite(sb);
+
+	nilfs = sb->s_fs_info;
+	down_read(&nilfs->ns_segctor_sem);
+	if (vacancy_check && nilfs_near_disk_full(nilfs)) {
+		up_read(&nilfs->ns_segctor_sem);
+		ret = -ENOSPC;
+		goto failed;
+	}
+	return 0;
+
+ failed:
+	ti = current->journal_info;
+	current->journal_info = ti->ti_save;
+	if (ti->ti_flags & NILFS_TI_DYNAMIC_ALLOC)
+		kmem_cache_free(nilfs_transaction_cachep, ti);
+	sb_end_intwrite(sb);
+	return ret;
+}
+
+/**
+ * nilfs_transaction_commit - commit indivisible file operations.
+ * @sb: super block
+ *
+ * nilfs_transaction_commit() releases the read semaphore which is
+ * acquired by nilfs_transaction_begin(). This is only performed
+ * in outermost call of this function.  If a commit flag is set,
+ * nilfs_transaction_commit() sets a timer to start the segment
+ * constructor.  If a sync flag is set, it starts construction
+ * directly.
+ */
+int nilfs_transaction_commit(struct super_block *sb)
+{
+	struct nilfs_transaction_info *ti = current->journal_info;
+	struct the_nilfs *nilfs = sb->s_fs_info;
+	int err = 0;
+
+	BUG_ON(ti == NULL || ti->ti_magic != NILFS_TI_MAGIC);
+	ti->ti_flags |= NILFS_TI_COMMIT;
+	if (ti->ti_count > 0) {
+		ti->ti_count--;
+		return 0;
+	}
+	if (nilfs->ns_writer) {
+		struct nilfs_sc_info *sci = nilfs->ns_writer;
+
+		if (ti->ti_flags & NILFS_TI_COMMIT)
+			nilfs_segctor_start_timer(sci);
+		if (atomic_read(&nilfs->ns_ndirtyblks) > sci->sc_watermark)
+			nilfs_segctor_do_flush(sci, 0);
+	}
+	up_read(&nilfs->ns_segctor_sem);
+	current->journal_info = ti->ti_save;
+
+	if (ti->ti_flags & NILFS_TI_SYNC)
+		err = nilfs_construct_segment(sb);
+	if (ti->ti_flags & NILFS_TI_DYNAMIC_ALLOC)
+		kmem_cache_free(nilfs_transaction_cachep, ti);
+	sb_end_intwrite(sb);
+	return err;
+}
+
+void nilfs_transaction_abort(struct super_block *sb)
+{
+	struct nilfs_transaction_info *ti = current->journal_info;
+	struct the_nilfs *nilfs = sb->s_fs_info;
+
+	BUG_ON(ti == NULL || ti->ti_magic != NILFS_TI_MAGIC);
+	if (ti->ti_count > 0) {
+		ti->ti_count--;
+		return;
+	}
+	up_read(&nilfs->ns_segctor_sem);
+
+	current->journal_info = ti->ti_save;
+	if (ti->ti_flags & NILFS_TI_DYNAMIC_ALLOC)
+		kmem_cache_free(nilfs_transaction_cachep, ti);
+	sb_end_intwrite(sb);
+}
+
+void nilfs_relax_pressure_in_lock(struct super_block *sb)
+{
+	struct the_nilfs *nilfs = sb->s_fs_info;
+	struct nilfs_sc_info *sci = nilfs->ns_writer;
+
+	if (!sci || !sci->sc_flush_request)
+		return;
+
+	set_bit(NILFS_SC_PRIOR_FLUSH, &sci->sc_flags);
+	up_read(&nilfs->ns_segctor_sem);
+
+	down_write(&nilfs->ns_segctor_sem);
+	if (sci->sc_flush_request &&
+	    test_bit(NILFS_SC_PRIOR_FLUSH, &sci->sc_flags)) {
+		struct nilfs_transaction_info *ti = current->journal_info;
+
+		ti->ti_flags |= NILFS_TI_WRITER;
+		nilfs_segctor_do_immediate_flush(sci);
+		ti->ti_flags &= ~NILFS_TI_WRITER;
+	}
+	downgrade_write(&nilfs->ns_segctor_sem);
+}
+
+static void nilfs_transaction_lock(struct super_block *sb,
+				   struct nilfs_transaction_info *ti,
+				   int gcflag)
+{
+	struct nilfs_transaction_info *cur_ti = current->journal_info;
+	struct the_nilfs *nilfs = sb->s_fs_info;
+	struct nilfs_sc_info *sci = nilfs->ns_writer;
+
+	WARN_ON(cur_ti);
+	ti->ti_flags = NILFS_TI_WRITER;
+	ti->ti_count = 0;
+	ti->ti_save = cur_ti;
+	ti->ti_magic = NILFS_TI_MAGIC;
+	current->journal_info = ti;
+
+	for (;;) {
+		down_write(&nilfs->ns_segctor_sem);
+		if (!test_bit(NILFS_SC_PRIOR_FLUSH, &sci->sc_flags))
+			break;
+
+		nilfs_segctor_do_immediate_flush(sci);
+
+		up_write(&nilfs->ns_segctor_sem);
+		yield();
+	}
+	if (gcflag)
+		ti->ti_flags |= NILFS_TI_GC;
+}
+
+static void nilfs_transaction_unlock(struct super_block *sb)
+{
+	struct nilfs_transaction_info *ti = current->journal_info;
+	struct the_nilfs *nilfs = sb->s_fs_info;
+
+	BUG_ON(ti == NULL || ti->ti_magic != NILFS_TI_MAGIC);
+	BUG_ON(ti->ti_count > 0);
+
+	up_write(&nilfs->ns_segctor_sem);
+	current->journal_info = ti->ti_save;
+}
+
+static void *nilfs_segctor_map_segsum_entry(struct nilfs_sc_info *sci,
+					    struct nilfs_segsum_pointer *ssp,
+					    unsigned bytes)
+{
+	struct nilfs_segment_buffer *segbuf = sci->sc_curseg;
+	unsigned blocksize = sci->sc_super->s_blocksize;
+	void *p;
+
+	if (unlikely(ssp->offset + bytes > blocksize)) {
+		ssp->offset = 0;
+		BUG_ON(NILFS_SEGBUF_BH_IS_LAST(ssp->bh,
+					       &segbuf->sb_segsum_buffers));
+		ssp->bh = NILFS_SEGBUF_NEXT_BH(ssp->bh);
+	}
+	p = ssp->bh->b_data + ssp->offset;
+	ssp->offset += bytes;
+	return p;
+}
+
+/**
+ * nilfs_segctor_reset_segment_buffer - reset the current segment buffer
+ * @sci: nilfs_sc_info
+ */
+static int nilfs_segctor_reset_segment_buffer(struct nilfs_sc_info *sci)
+{
+	struct nilfs_segment_buffer *segbuf = sci->sc_curseg;
+	struct buffer_head *sumbh;
+	unsigned sumbytes;
+	unsigned flags = 0;
+	int err;
+
+	if (nilfs_doing_gc())
+		flags = NILFS_SS_GC;
+	err = nilfs_segbuf_reset(segbuf, flags, sci->sc_seg_ctime, sci->sc_cno);
+	if (unlikely(err))
+		return err;
+
+	sumbh = NILFS_SEGBUF_FIRST_BH(&segbuf->sb_segsum_buffers);
+	sumbytes = segbuf->sb_sum.sumbytes;
+	sci->sc_finfo_ptr.bh = sumbh;  sci->sc_finfo_ptr.offset = sumbytes;
+	sci->sc_binfo_ptr.bh = sumbh;  sci->sc_binfo_ptr.offset = sumbytes;
+	sci->sc_blk_cnt = sci->sc_datablk_cnt = 0;
+	return 0;
+}
+
+static int nilfs_segctor_feed_segment(struct nilfs_sc_info *sci)
+{
+	sci->sc_nblk_this_inc += sci->sc_curseg->sb_sum.nblocks;
+	if (NILFS_SEGBUF_IS_LAST(sci->sc_curseg, &sci->sc_segbufs))
+		return -E2BIG; /* The current segment is filled up
+				  (internal code) */
+	sci->sc_curseg = NILFS_NEXT_SEGBUF(sci->sc_curseg);
+	return nilfs_segctor_reset_segment_buffer(sci);
+}
+
+static int nilfs_segctor_add_super_root(struct nilfs_sc_info *sci)
+{
+	struct nilfs_segment_buffer *segbuf = sci->sc_curseg;
+	int err;
+
+	if (segbuf->sb_sum.nblocks >= segbuf->sb_rest_blocks) {
+		err = nilfs_segctor_feed_segment(sci);
+		if (err)
+			return err;
+		segbuf = sci->sc_curseg;
+	}
+	err = nilfs_segbuf_extend_payload(segbuf, &segbuf->sb_super_root);
+	if (likely(!err))
+		segbuf->sb_sum.flags |= NILFS_SS_SR;
+	return err;
+}
+
+/*
+ * Functions for making segment summary and payloads
+ */
+static int nilfs_segctor_segsum_block_required(
+	struct nilfs_sc_info *sci, const struct nilfs_segsum_pointer *ssp,
+	unsigned binfo_size)
+{
+	unsigned blocksize = sci->sc_super->s_blocksize;
+	/* Size of finfo and binfo is enough small against blocksize */
+
+	return ssp->offset + binfo_size +
+		(!sci->sc_blk_cnt ? sizeof(struct nilfs_finfo) : 0) >
+		blocksize;
+}
+
+static void nilfs_segctor_begin_finfo(struct nilfs_sc_info *sci,
+				      struct inode *inode)
+{
+	sci->sc_curseg->sb_sum.nfinfo++;
+	sci->sc_binfo_ptr = sci->sc_finfo_ptr;
+	nilfs_segctor_map_segsum_entry(
+		sci, &sci->sc_binfo_ptr, sizeof(struct nilfs_finfo));
+
+	if (NILFS_I(inode)->i_root &&
+	    !test_bit(NILFS_SC_HAVE_DELTA, &sci->sc_flags))
+		set_bit(NILFS_SC_HAVE_DELTA, &sci->sc_flags);
+	/* skip finfo */
+}
+
+static void nilfs_segctor_end_finfo(struct nilfs_sc_info *sci,
+				    struct inode *inode)
+{
+	struct nilfs_finfo *finfo;
+	struct nilfs_inode_info *ii;
+	struct nilfs_segment_buffer *segbuf;
+	__u64 cno;
+
+	if (sci->sc_blk_cnt == 0)
+		return;
+
+	ii = NILFS_I(inode);
+
+	if (test_bit(NILFS_I_GCINODE, &ii->i_state))
+		cno = ii->i_cno;
+	else if (NILFS_ROOT_METADATA_FILE(inode->i_ino))
+		cno = 0;
+	else
+		cno = sci->sc_cno;
+
+	finfo = nilfs_segctor_map_segsum_entry(sci, &sci->sc_finfo_ptr,
+						 sizeof(*finfo));
+	finfo->fi_ino = cpu_to_le64(inode->i_ino);
+	finfo->fi_nblocks = cpu_to_le32(sci->sc_blk_cnt);
+	finfo->fi_ndatablk = cpu_to_le32(sci->sc_datablk_cnt);
+	finfo->fi_cno = cpu_to_le64(cno);
+
+	segbuf = sci->sc_curseg;
+	segbuf->sb_sum.sumbytes = sci->sc_binfo_ptr.offset +
+		sci->sc_super->s_blocksize * (segbuf->sb_sum.nsumblk - 1);
+	sci->sc_finfo_ptr = sci->sc_binfo_ptr;
+	sci->sc_blk_cnt = sci->sc_datablk_cnt = 0;
+}
+
+static int nilfs_segctor_add_file_block(struct nilfs_sc_info *sci,
+					struct buffer_head *bh,
+					struct inode *inode,
+					unsigned binfo_size)
+{
+	struct nilfs_segment_buffer *segbuf;
+	int required, err = 0;
+
+ retry:
+	segbuf = sci->sc_curseg;
+	required = nilfs_segctor_segsum_block_required(
+		sci, &sci->sc_binfo_ptr, binfo_size);
+	if (segbuf->sb_sum.nblocks + required + 1 > segbuf->sb_rest_blocks) {
+		nilfs_segctor_end_finfo(sci, inode);
+		err = nilfs_segctor_feed_segment(sci);
+		if (err)
+			return err;
+		goto retry;
+	}
+	if (unlikely(required)) {
+		err = nilfs_segbuf_extend_segsum(segbuf);
+		if (unlikely(err))
+			goto failed;
+	}
+	if (sci->sc_blk_cnt == 0)
+		nilfs_segctor_begin_finfo(sci, inode);
+
+	nilfs_segctor_map_segsum_entry(sci, &sci->sc_binfo_ptr, binfo_size);
+	/* Substitution to vblocknr is delayed until update_blocknr() */
+	nilfs_segbuf_add_file_buffer(segbuf, bh);
+	sci->sc_blk_cnt++;
+ failed:
+	return err;
+}
+
+/*
+ * Callback functions that enumerate, mark, and collect dirty blocks
+ */
+static int nilfs_collect_file_data(struct nilfs_sc_info *sci,
+				   struct buffer_head *bh, struct inode *inode)
+{
+	int err;
+
+	err = nilfs_bmap_propagate(NILFS_I(inode)->i_bmap, bh);
+	if (err < 0)
+		return err;
+
+	err = nilfs_segctor_add_file_block(sci, bh, inode,
+					   sizeof(struct nilfs_binfo_v));
+	if (!err)
+		sci->sc_datablk_cnt++;
+	return err;
+}
+
+static int nilfs_collect_file_node(struct nilfs_sc_info *sci,
+				   struct buffer_head *bh,
+				   struct inode *inode)
+{
+	return nilfs_bmap_propagate(NILFS_I(inode)->i_bmap, bh);
+}
+
+static int nilfs_collect_file_bmap(struct nilfs_sc_info *sci,
+				   struct buffer_head *bh,
+				   struct inode *inode)
+{
+	WARN_ON(!buffer_dirty(bh));
+	return nilfs_segctor_add_file_block(sci, bh, inode, sizeof(__le64));
+}
+
+static void nilfs_write_file_data_binfo(struct nilfs_sc_info *sci,
+					struct nilfs_segsum_pointer *ssp,
+					union nilfs_binfo *binfo)
+{
+	struct nilfs_binfo_v *binfo_v = nilfs_segctor_map_segsum_entry(
+		sci, ssp, sizeof(*binfo_v));
+	*binfo_v = binfo->bi_v;
+}
+
+static void nilfs_write_file_node_binfo(struct nilfs_sc_info *sci,
+					struct nilfs_segsum_pointer *ssp,
+					union nilfs_binfo *binfo)
+{
+	__le64 *vblocknr = nilfs_segctor_map_segsum_entry(
+		sci, ssp, sizeof(*vblocknr));
+	*vblocknr = binfo->bi_v.bi_vblocknr;
+}
+
+static struct nilfs_sc_operations nilfs_sc_file_ops = {
+	.collect_data = nilfs_collect_file_data,
+	.collect_node = nilfs_collect_file_node,
+	.collect_bmap = nilfs_collect_file_bmap,
+	.write_data_binfo = nilfs_write_file_data_binfo,
+	.write_node_binfo = nilfs_write_file_node_binfo,
+};
+
+static int nilfs_collect_dat_data(struct nilfs_sc_info *sci,
+				  struct buffer_head *bh, struct inode *inode)
+{
+	int err;
+
+	err = nilfs_bmap_propagate(NILFS_I(inode)->i_bmap, bh);
+	if (err < 0)
+		return err;
+
+	err = nilfs_segctor_add_file_block(sci, bh, inode, sizeof(__le64));
+	if (!err)
+		sci->sc_datablk_cnt++;
+	return err;
+}
+
+static int nilfs_collect_dat_bmap(struct nilfs_sc_info *sci,
+				  struct buffer_head *bh, struct inode *inode)
+{
+	WARN_ON(!buffer_dirty(bh));
+	return nilfs_segctor_add_file_block(sci, bh, inode,
+					    sizeof(struct nilfs_binfo_dat));
+}
+
+static void nilfs_write_dat_data_binfo(struct nilfs_sc_info *sci,
+				       struct nilfs_segsum_pointer *ssp,
+				       union nilfs_binfo *binfo)
+{
+	__le64 *blkoff = nilfs_segctor_map_segsum_entry(sci, ssp,
+							  sizeof(*blkoff));
+	*blkoff = binfo->bi_dat.bi_blkoff;
+}
+
+static void nilfs_write_dat_node_binfo(struct nilfs_sc_info *sci,
+				       struct nilfs_segsum_pointer *ssp,
+				       union nilfs_binfo *binfo)
+{
+	struct nilfs_binfo_dat *binfo_dat =
+		nilfs_segctor_map_segsum_entry(sci, ssp, sizeof(*binfo_dat));
+	*binfo_dat = binfo->bi_dat;
+}
+
+static struct nilfs_sc_operations nilfs_sc_dat_ops = {
+	.collect_data = nilfs_collect_dat_data,
+	.collect_node = nilfs_collect_file_node,
+	.collect_bmap = nilfs_collect_dat_bmap,
+	.write_data_binfo = nilfs_write_dat_data_binfo,
+	.write_node_binfo = nilfs_write_dat_node_binfo,
+};
+
+static struct nilfs_sc_operations nilfs_sc_dsync_ops = {
+	.collect_data = nilfs_collect_file_data,
+	.collect_node = NULL,
+	.collect_bmap = NULL,
+	.write_data_binfo = nilfs_write_file_data_binfo,
+	.write_node_binfo = NULL,
+};
+
+static size_t nilfs_lookup_dirty_data_buffers(struct inode *inode,
+					      struct list_head *listp,
+					      size_t nlimit,
+					      loff_t start, loff_t end)
+{
+	struct address_space *mapping = inode->i_mapping;
+	struct pagevec pvec;
+	pgoff_t index = 0, last = ULONG_MAX;
+	size_t ndirties = 0;
+	int i;
+
+	if (unlikely(start != 0 || end != LLONG_MAX)) {
+		/*
+		 * A valid range is given for sync-ing data pages. The
+		 * range is rounded to per-page; extra dirty buffers
+		 * may be included if blocksize < pagesize.
+		 */
+		index = start >> PAGE_SHIFT;
+		last = end >> PAGE_SHIFT;
+	}
+	pagevec_init(&pvec, 0);
+ repeat:
+	if (unlikely(index > last) ||
+	    !pagevec_lookup_tag(&pvec, mapping, &index, PAGECACHE_TAG_DIRTY,
+				min_t(pgoff_t, last - index,
+				      PAGEVEC_SIZE - 1) + 1))
+		return ndirties;
+
+	for (i = 0; i < pagevec_count(&pvec); i++) {
+		struct buffer_head *bh, *head;
+		struct page *page = pvec.pages[i];
+
+		if (unlikely(page->index > last))
+			break;
+
+		lock_page(page);
+		if (!page_has_buffers(page))
+			create_empty_buffers(page, 1 << inode->i_blkbits, 0);
+		unlock_page(page);
+
+		bh = head = page_buffers(page);
+		do {
+			if (!buffer_dirty(bh) || buffer_async_write(bh))
+				continue;
+			get_bh(bh);
+			list_add_tail(&bh->b_assoc_buffers, listp);
+			ndirties++;
+			if (unlikely(ndirties >= nlimit)) {
+				pagevec_release(&pvec);
+				cond_resched();
+				return ndirties;
+			}
+		} while (bh = bh->b_this_page, bh != head);
+	}
+	pagevec_release(&pvec);
+	cond_resched();
+	goto repeat;
+}
+
+static void nilfs_lookup_dirty_node_buffers(struct inode *inode,
+					    struct list_head *listp)
+{
+	struct nilfs_inode_info *ii = NILFS_I(inode);
+	struct address_space *mapping = &ii->i_btnode_cache;
+	struct pagevec pvec;
+	struct buffer_head *bh, *head;
+	unsigned int i;
+	pgoff_t index = 0;
+
+	pagevec_init(&pvec, 0);
+
+	while (pagevec_lookup_tag(&pvec, mapping, &index, PAGECACHE_TAG_DIRTY,
+				  PAGEVEC_SIZE)) {
+		for (i = 0; i < pagevec_count(&pvec); i++) {
+			bh = head = page_buffers(pvec.pages[i]);
+			do {
+				if (buffer_dirty(bh) &&
+						!buffer_async_write(bh)) {
+					get_bh(bh);
+					list_add_tail(&bh->b_assoc_buffers,
+						      listp);
+				}
+				bh = bh->b_this_page;
+			} while (bh != head);
+		}
+		pagevec_release(&pvec);
+		cond_resched();
+	}
+}
+
+static void nilfs_dispose_list(struct the_nilfs *nilfs,
+			       struct list_head *head, int force)
+{
+	struct nilfs_inode_info *ii, *n;
+	struct nilfs_inode_info *ivec[SC_N_INODEVEC], **pii;
+	unsigned nv = 0;
+
+	while (!list_empty(head)) {
+		spin_lock(&nilfs->ns_inode_lock);
+		list_for_each_entry_safe(ii, n, head, i_dirty) {
+			list_del_init(&ii->i_dirty);
+			if (force) {
+				if (unlikely(ii->i_bh)) {
+					brelse(ii->i_bh);
+					ii->i_bh = NULL;
+				}
+			} else if (test_bit(NILFS_I_DIRTY, &ii->i_state)) {
+				set_bit(NILFS_I_QUEUED, &ii->i_state);
+				list_add_tail(&ii->i_dirty,
+					      &nilfs->ns_dirty_files);
+				continue;
+			}
+			ivec[nv++] = ii;
+			if (nv == SC_N_INODEVEC)
+				break;
+		}
+		spin_unlock(&nilfs->ns_inode_lock);
+
+		for (pii = ivec; nv > 0; pii++, nv--)
+			iput(&(*pii)->vfs_inode);
+	}
+}
+
+static void nilfs_iput_work_func(struct work_struct *work)
+{
+	struct nilfs_sc_info *sci = container_of(work, struct nilfs_sc_info,
+						 sc_iput_work);
+	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+
+	nilfs_dispose_list(nilfs, &sci->sc_iput_queue, 0);
+}
+
+static int nilfs_test_metadata_dirty(struct the_nilfs *nilfs,
+				     struct nilfs_root *root)
+{
+	int ret = 0;
+
+	if (nilfs_mdt_fetch_dirty(root->ifile))
+		ret++;
+	if (nilfs_mdt_fetch_dirty(nilfs->ns_cpfile))
+		ret++;
+	if (nilfs_mdt_fetch_dirty(nilfs->ns_sufile))
+		ret++;
+	if ((ret || nilfs_doing_gc()) && nilfs_mdt_fetch_dirty(nilfs->ns_dat))
+		ret++;
+	return ret;
+}
+
+static int nilfs_segctor_clean(struct nilfs_sc_info *sci)
+{
+	return list_empty(&sci->sc_dirty_files) &&
+		!test_bit(NILFS_SC_DIRTY, &sci->sc_flags) &&
+		sci->sc_nfreesegs == 0 &&
+		(!nilfs_doing_gc() || list_empty(&sci->sc_gc_inodes));
+}
+
+static int nilfs_segctor_confirm(struct nilfs_sc_info *sci)
+{
+	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+	int ret = 0;
+
+	if (nilfs_test_metadata_dirty(nilfs, sci->sc_root))
+		set_bit(NILFS_SC_DIRTY, &sci->sc_flags);
+
+	spin_lock(&nilfs->ns_inode_lock);
+	if (list_empty(&nilfs->ns_dirty_files) && nilfs_segctor_clean(sci))
+		ret++;
+
+	spin_unlock(&nilfs->ns_inode_lock);
+	return ret;
+}
+
+static void nilfs_segctor_clear_metadata_dirty(struct nilfs_sc_info *sci)
+{
+	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+
+	nilfs_mdt_clear_dirty(sci->sc_root->ifile);
+	nilfs_mdt_clear_dirty(nilfs->ns_cpfile);
+	nilfs_mdt_clear_dirty(nilfs->ns_sufile);
+	nilfs_mdt_clear_dirty(nilfs->ns_dat);
+}
+
+static int nilfs_segctor_create_checkpoint(struct nilfs_sc_info *sci)
+{
+	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+	struct buffer_head *bh_cp;
+	struct nilfs_checkpoint *raw_cp;
+	int err;
+
+	/* XXX: this interface will be changed */
+	err = nilfs_cpfile_get_checkpoint(nilfs->ns_cpfile, nilfs->ns_cno, 1,
+					  &raw_cp, &bh_cp);
+	if (likely(!err)) {
+		/* The following code is duplicated with cpfile.  But, it is
+		   needed to collect the checkpoint even if it was not newly
+		   created */
+		mark_buffer_dirty(bh_cp);
+		nilfs_mdt_mark_dirty(nilfs->ns_cpfile);
+		nilfs_cpfile_put_checkpoint(
+			nilfs->ns_cpfile, nilfs->ns_cno, bh_cp);
+	} else
+		WARN_ON(err == -EINVAL || err == -ENOENT);
+
+	return err;
+}
+
+static int nilfs_segctor_fill_in_checkpoint(struct nilfs_sc_info *sci)
+{
+	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+	struct buffer_head *bh_cp;
+	struct nilfs_checkpoint *raw_cp;
+	int err;
+
+	err = nilfs_cpfile_get_checkpoint(nilfs->ns_cpfile, nilfs->ns_cno, 0,
+					  &raw_cp, &bh_cp);
+	if (unlikely(err)) {
+		WARN_ON(err == -EINVAL || err == -ENOENT);
+		goto failed_ibh;
+	}
+	raw_cp->cp_snapshot_list.ssl_next = 0;
+	raw_cp->cp_snapshot_list.ssl_prev = 0;
+	raw_cp->cp_inodes_count =
+		cpu_to_le64(atomic64_read(&sci->sc_root->inodes_count));
+	raw_cp->cp_blocks_count =
+		cpu_to_le64(atomic64_read(&sci->sc_root->blocks_count));
+	raw_cp->cp_nblk_inc =
+		cpu_to_le64(sci->sc_nblk_inc + sci->sc_nblk_this_inc);
+	raw_cp->cp_create = cpu_to_le64(sci->sc_seg_ctime);
+	raw_cp->cp_cno = cpu_to_le64(nilfs->ns_cno);
+
+	if (test_bit(NILFS_SC_HAVE_DELTA, &sci->sc_flags))
+		nilfs_checkpoint_clear_minor(raw_cp);
+	else
+		nilfs_checkpoint_set_minor(raw_cp);
+
+	nilfs_write_inode_common(sci->sc_root->ifile,
+				 &raw_cp->cp_ifile_inode, 1);
+	nilfs_cpfile_put_checkpoint(nilfs->ns_cpfile, nilfs->ns_cno, bh_cp);
+	return 0;
+
+ failed_ibh:
+	return err;
+}
+
+static void nilfs_fill_in_file_bmap(struct inode *ifile,
+				    struct nilfs_inode_info *ii)
+
+{
+	struct buffer_head *ibh;
+	struct nilfs_inode *raw_inode;
+
+	if (test_bit(NILFS_I_BMAP, &ii->i_state)) {
+		ibh = ii->i_bh;
+		BUG_ON(!ibh);
+		raw_inode = nilfs_ifile_map_inode(ifile, ii->vfs_inode.i_ino,
+						  ibh);
+		nilfs_bmap_write(ii->i_bmap, raw_inode);
+		nilfs_ifile_unmap_inode(ifile, ii->vfs_inode.i_ino, ibh);
+	}
+}
+
+static void nilfs_segctor_fill_in_file_bmap(struct nilfs_sc_info *sci)
+{
+	struct nilfs_inode_info *ii;
+
+	list_for_each_entry(ii, &sci->sc_dirty_files, i_dirty) {
+		nilfs_fill_in_file_bmap(sci->sc_root->ifile, ii);
+		set_bit(NILFS_I_COLLECTED, &ii->i_state);
+	}
+}
+
+static void nilfs_segctor_fill_in_super_root(struct nilfs_sc_info *sci,
+					     struct the_nilfs *nilfs)
+{
+	struct buffer_head *bh_sr;
+	struct nilfs_super_root *raw_sr;
+	unsigned isz, srsz;
+
+	bh_sr = NILFS_LAST_SEGBUF(&sci->sc_segbufs)->sb_super_root;
+	raw_sr = (struct nilfs_super_root *)bh_sr->b_data;
+	isz = nilfs->ns_inode_size;
+	srsz = NILFS_SR_BYTES(isz);
+
+	raw_sr->sr_bytes = cpu_to_le16(srsz);
+	raw_sr->sr_nongc_ctime
+		= cpu_to_le64(nilfs_doing_gc() ?
+			      nilfs->ns_nongc_ctime : sci->sc_seg_ctime);
+	raw_sr->sr_flags = 0;
+
+	nilfs_write_inode_common(nilfs->ns_dat, (void *)raw_sr +
+				 NILFS_SR_DAT_OFFSET(isz), 1);
+	nilfs_write_inode_common(nilfs->ns_cpfile, (void *)raw_sr +
+				 NILFS_SR_CPFILE_OFFSET(isz), 1);
+	nilfs_write_inode_common(nilfs->ns_sufile, (void *)raw_sr +
+				 NILFS_SR_SUFILE_OFFSET(isz), 1);
+	memset((void *)raw_sr + srsz, 0, nilfs->ns_blocksize - srsz);
+}
+
+static void nilfs_redirty_inodes(struct list_head *head)
+{
+	struct nilfs_inode_info *ii;
+
+	list_for_each_entry(ii, head, i_dirty) {
+		if (test_bit(NILFS_I_COLLECTED, &ii->i_state))
+			clear_bit(NILFS_I_COLLECTED, &ii->i_state);
+	}
+}
+
+static void nilfs_drop_collected_inodes(struct list_head *head)
+{
+	struct nilfs_inode_info *ii;
+
+	list_for_each_entry(ii, head, i_dirty) {
+		if (!test_and_clear_bit(NILFS_I_COLLECTED, &ii->i_state))
+			continue;
+
+		clear_bit(NILFS_I_INODE_SYNC, &ii->i_state);
+		set_bit(NILFS_I_UPDATED, &ii->i_state);
+	}
+}
+
+static int nilfs_segctor_apply_buffers(struct nilfs_sc_info *sci,
+				       struct inode *inode,
+				       struct list_head *listp,
+				       int (*collect)(struct nilfs_sc_info *,
+						      struct buffer_head *,
+						      struct inode *))
+{
+	struct buffer_head *bh, *n;
+	int err = 0;
+
+	if (collect) {
+		list_for_each_entry_safe(bh, n, listp, b_assoc_buffers) {
+			list_del_init(&bh->b_assoc_buffers);
+			err = collect(sci, bh, inode);
+			brelse(bh);
+			if (unlikely(err))
+				goto dispose_buffers;
+		}
+		return 0;
+	}
+
+ dispose_buffers:
+	while (!list_empty(listp)) {
+		bh = list_first_entry(listp, struct buffer_head,
+				      b_assoc_buffers);
+		list_del_init(&bh->b_assoc_buffers);
+		brelse(bh);
+	}
+	return err;
+}
+
+static size_t nilfs_segctor_buffer_rest(struct nilfs_sc_info *sci)
+{
+	/* Remaining number of blocks within segment buffer */
+	return sci->sc_segbuf_nblocks -
+		(sci->sc_nblk_this_inc + sci->sc_curseg->sb_sum.nblocks);
+}
+
+static int nilfs_segctor_scan_file(struct nilfs_sc_info *sci,
+				   struct inode *inode,
+				   struct nilfs_sc_operations *sc_ops)
+{
+	LIST_HEAD(data_buffers);
+	LIST_HEAD(node_buffers);
+	int err;
+
+	if (!(sci->sc_stage.flags & NILFS_CF_NODE)) {
+		size_t n, rest = nilfs_segctor_buffer_rest(sci);
+
+		n = nilfs_lookup_dirty_data_buffers(
+			inode, &data_buffers, rest + 1, 0, LLONG_MAX);
+		if (n > rest) {
+			err = nilfs_segctor_apply_buffers(
+				sci, inode, &data_buffers,
+				sc_ops->collect_data);
+			BUG_ON(!err); /* always receive -E2BIG or true error */
+			goto break_or_fail;
+		}
+	}
+	nilfs_lookup_dirty_node_buffers(inode, &node_buffers);
+
+	if (!(sci->sc_stage.flags & NILFS_CF_NODE)) {
+		err = nilfs_segctor_apply_buffers(
+			sci, inode, &data_buffers, sc_ops->collect_data);
+		if (unlikely(err)) {
+			/* dispose node list */
+			nilfs_segctor_apply_buffers(
+				sci, inode, &node_buffers, NULL);
+			goto break_or_fail;
+		}
+		sci->sc_stage.flags |= NILFS_CF_NODE;
+	}
+	/* Collect node */
+	err = nilfs_segctor_apply_buffers(
+		sci, inode, &node_buffers, sc_ops->collect_node);
+	if (unlikely(err))
+		goto break_or_fail;
+
+	nilfs_bmap_lookup_dirty_buffers(NILFS_I(inode)->i_bmap, &node_buffers);
+	err = nilfs_segctor_apply_buffers(
+		sci, inode, &node_buffers, sc_ops->collect_bmap);
+	if (unlikely(err))
+		goto break_or_fail;
+
+	nilfs_segctor_end_finfo(sci, inode);
+	sci->sc_stage.flags &= ~NILFS_CF_NODE;
+
+ break_or_fail:
+	return err;
+}
+
+static int nilfs_segctor_scan_file_dsync(struct nilfs_sc_info *sci,
+					 struct inode *inode)
+{
+	LIST_HEAD(data_buffers);
+	size_t n, rest = nilfs_segctor_buffer_rest(sci);
+	int err;
+
+	n = nilfs_lookup_dirty_data_buffers(inode, &data_buffers, rest + 1,
+					    sci->sc_dsync_start,
+					    sci->sc_dsync_end);
+
+	err = nilfs_segctor_apply_buffers(sci, inode, &data_buffers,
+					  nilfs_collect_file_data);
+	if (!err) {
+		nilfs_segctor_end_finfo(sci, inode);
+		BUG_ON(n > rest);
+		/* always receive -E2BIG or true error if n > rest */
+	}
+	return err;
+}
+
+static int nilfs_segctor_collect_blocks(struct nilfs_sc_info *sci, int mode)
+{
+	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+	struct list_head *head;
+	struct nilfs_inode_info *ii;
+	size_t ndone;
+	int err = 0;
+
+	switch (sci->sc_stage.scnt) {
+	case NILFS_ST_INIT:
+		/* Pre-processes */
+		sci->sc_stage.flags = 0;
+
+		if (!test_bit(NILFS_SC_UNCLOSED, &sci->sc_flags)) {
+			sci->sc_nblk_inc = 0;
+			sci->sc_curseg->sb_sum.flags = NILFS_SS_LOGBGN;
+			if (mode == SC_LSEG_DSYNC) {
+				sci->sc_stage.scnt = NILFS_ST_DSYNC;
+				goto dsync_mode;
+			}
+		}
+
+		sci->sc_stage.dirty_file_ptr = NULL;
+		sci->sc_stage.gc_inode_ptr = NULL;
+		if (mode == SC_FLUSH_DAT) {
+			sci->sc_stage.scnt = NILFS_ST_DAT;
+			goto dat_stage;
+		}
+		sci->sc_stage.scnt++;  /* Fall through */
+	case NILFS_ST_GC:
+		if (nilfs_doing_gc()) {
+			head = &sci->sc_gc_inodes;
+			ii = list_prepare_entry(sci->sc_stage.gc_inode_ptr,
+						head, i_dirty);
+			list_for_each_entry_continue(ii, head, i_dirty) {
+				err = nilfs_segctor_scan_file(
+					sci, &ii->vfs_inode,
+					&nilfs_sc_file_ops);
+				if (unlikely(err)) {
+					sci->sc_stage.gc_inode_ptr = list_entry(
+						ii->i_dirty.prev,
+						struct nilfs_inode_info,
+						i_dirty);
+					goto break_or_fail;
+				}
+				set_bit(NILFS_I_COLLECTED, &ii->i_state);
+			}
+			sci->sc_stage.gc_inode_ptr = NULL;
+		}
+		sci->sc_stage.scnt++;  /* Fall through */
+	case NILFS_ST_FILE:
+		head = &sci->sc_dirty_files;
+		ii = list_prepare_entry(sci->sc_stage.dirty_file_ptr, head,
+					i_dirty);
+		list_for_each_entry_continue(ii, head, i_dirty) {
+			clear_bit(NILFS_I_DIRTY, &ii->i_state);
+
+			err = nilfs_segctor_scan_file(sci, &ii->vfs_inode,
+						      &nilfs_sc_file_ops);
+			if (unlikely(err)) {
+				sci->sc_stage.dirty_file_ptr =
+					list_entry(ii->i_dirty.prev,
+						   struct nilfs_inode_info,
+						   i_dirty);
+				goto break_or_fail;
+			}
+			/* sci->sc_stage.dirty_file_ptr = NILFS_I(inode); */
+			/* XXX: required ? */
+		}
+		sci->sc_stage.dirty_file_ptr = NULL;
+		if (mode == SC_FLUSH_FILE) {
+			sci->sc_stage.scnt = NILFS_ST_DONE;
+			return 0;
+		}
+		sci->sc_stage.scnt++;
+		sci->sc_stage.flags |= NILFS_CF_IFILE_STARTED;
+		/* Fall through */
+	case NILFS_ST_IFILE:
+		err = nilfs_segctor_scan_file(sci, sci->sc_root->ifile,
+					      &nilfs_sc_file_ops);
+		if (unlikely(err))
+			break;
+		sci->sc_stage.scnt++;
+		/* Creating a checkpoint */
+		err = nilfs_segctor_create_checkpoint(sci);
+		if (unlikely(err))
+			break;
+		/* Fall through */
+	case NILFS_ST_CPFILE:
+		err = nilfs_segctor_scan_file(sci, nilfs->ns_cpfile,
+					      &nilfs_sc_file_ops);
+		if (unlikely(err))
+			break;
+		sci->sc_stage.scnt++;  /* Fall through */
+	case NILFS_ST_SUFILE:
+		err = nilfs_sufile_freev(nilfs->ns_sufile, sci->sc_freesegs,
+					 sci->sc_nfreesegs, &ndone);
+		if (unlikely(err)) {
+			nilfs_sufile_cancel_freev(nilfs->ns_sufile,
+						  sci->sc_freesegs, ndone,
+						  NULL);
+			break;
+		}
+		sci->sc_stage.flags |= NILFS_CF_SUFREED;
+
+		err = nilfs_segctor_scan_file(sci, nilfs->ns_sufile,
+					      &nilfs_sc_file_ops);
+		if (unlikely(err))
+			break;
+		sci->sc_stage.scnt++;  /* Fall through */
+	case NILFS_ST_DAT:
+ dat_stage:
+		err = nilfs_segctor_scan_file(sci, nilfs->ns_dat,
+					      &nilfs_sc_dat_ops);
+		if (unlikely(err))
+			break;
+		if (mode == SC_FLUSH_DAT) {
+			sci->sc_stage.scnt = NILFS_ST_DONE;
+			return 0;
+		}
+		sci->sc_stage.scnt++;  /* Fall through */
+	case NILFS_ST_SR:
+		if (mode == SC_LSEG_SR) {
+			/* Appending a super root */
+			err = nilfs_segctor_add_super_root(sci);
+			if (unlikely(err))
+				break;
+		}
+		/* End of a logical segment */
+		sci->sc_curseg->sb_sum.flags |= NILFS_SS_LOGEND;
+		sci->sc_stage.scnt = NILFS_ST_DONE;
+		return 0;
+	case NILFS_ST_DSYNC:
+ dsync_mode:
+		sci->sc_curseg->sb_sum.flags |= NILFS_SS_SYNDT;
+		ii = sci->sc_dsync_inode;
+		if (!test_bit(NILFS_I_BUSY, &ii->i_state))
+			break;
+
+		err = nilfs_segctor_scan_file_dsync(sci, &ii->vfs_inode);
+		if (unlikely(err))
+			break;
+		sci->sc_curseg->sb_sum.flags |= NILFS_SS_LOGEND;
+		sci->sc_stage.scnt = NILFS_ST_DONE;
+		return 0;
+	case NILFS_ST_DONE:
+		return 0;
+	default:
+		BUG();
+	}
+
+ break_or_fail:
+	return err;
+}
+
+/**
+ * nilfs_segctor_begin_construction - setup segment buffer to make a new log
+ * @sci: nilfs_sc_info
+ * @nilfs: nilfs object
+ */
+static int nilfs_segctor_begin_construction(struct nilfs_sc_info *sci,
+					    struct the_nilfs *nilfs)
+{
+	struct nilfs_segment_buffer *segbuf, *prev;
+	__u64 nextnum;
+	int err, alloc = 0;
+
+	segbuf = nilfs_segbuf_new(sci->sc_super);
+	if (unlikely(!segbuf))
+		return -ENOMEM;
+
+	if (list_empty(&sci->sc_write_logs)) {
+		nilfs_segbuf_map(segbuf, nilfs->ns_segnum,
+				 nilfs->ns_pseg_offset, nilfs);
+		if (segbuf->sb_rest_blocks < NILFS_PSEG_MIN_BLOCKS) {
+			nilfs_shift_to_next_segment(nilfs);
+			nilfs_segbuf_map(segbuf, nilfs->ns_segnum, 0, nilfs);
+		}
+
+		segbuf->sb_sum.seg_seq = nilfs->ns_seg_seq;
+		nextnum = nilfs->ns_nextnum;
+
+		if (nilfs->ns_segnum == nilfs->ns_nextnum)
+			/* Start from the head of a new full segment */
+			alloc++;
+	} else {
+		/* Continue logs */
+		prev = NILFS_LAST_SEGBUF(&sci->sc_write_logs);
+		nilfs_segbuf_map_cont(segbuf, prev);
+		segbuf->sb_sum.seg_seq = prev->sb_sum.seg_seq;
+		nextnum = prev->sb_nextnum;
+
+		if (segbuf->sb_rest_blocks < NILFS_PSEG_MIN_BLOCKS) {
+			nilfs_segbuf_map(segbuf, prev->sb_nextnum, 0, nilfs);
+			segbuf->sb_sum.seg_seq++;
+			alloc++;
+		}
+	}
+
+	err = nilfs_sufile_mark_dirty(nilfs->ns_sufile, segbuf->sb_segnum);
+	if (err)
+		goto failed;
+
+	if (alloc) {
+		err = nilfs_sufile_alloc(nilfs->ns_sufile, &nextnum);
+		if (err)
+			goto failed;
+	}
+	nilfs_segbuf_set_next_segnum(segbuf, nextnum, nilfs);
+
+	BUG_ON(!list_empty(&sci->sc_segbufs));
+	list_add_tail(&segbuf->sb_list, &sci->sc_segbufs);
+	sci->sc_segbuf_nblocks = segbuf->sb_rest_blocks;
+	return 0;
+
+ failed:
+	nilfs_segbuf_free(segbuf);
+	return err;
+}
+
+static int nilfs_segctor_extend_segments(struct nilfs_sc_info *sci,
+					 struct the_nilfs *nilfs, int nadd)
+{
+	struct nilfs_segment_buffer *segbuf, *prev;
+	struct inode *sufile = nilfs->ns_sufile;
+	__u64 nextnextnum;
+	LIST_HEAD(list);
+	int err, ret, i;
+
+	prev = NILFS_LAST_SEGBUF(&sci->sc_segbufs);
+	/*
+	 * Since the segment specified with nextnum might be allocated during
+	 * the previous construction, the buffer including its segusage may
+	 * not be dirty.  The following call ensures that the buffer is dirty
+	 * and will pin the buffer on memory until the sufile is written.
+	 */
+	err = nilfs_sufile_mark_dirty(sufile, prev->sb_nextnum);
+	if (unlikely(err))
+		return err;
+
+	for (i = 0; i < nadd; i++) {
+		/* extend segment info */
+		err = -ENOMEM;
+		segbuf = nilfs_segbuf_new(sci->sc_super);
+		if (unlikely(!segbuf))
+			goto failed;
+
+		/* map this buffer to region of segment on-disk */
+		nilfs_segbuf_map(segbuf, prev->sb_nextnum, 0, nilfs);
+		sci->sc_segbuf_nblocks += segbuf->sb_rest_blocks;
+
+		/* allocate the next next full segment */
+		err = nilfs_sufile_alloc(sufile, &nextnextnum);
+		if (unlikely(err))
+			goto failed_segbuf;
+
+		segbuf->sb_sum.seg_seq = prev->sb_sum.seg_seq + 1;
+		nilfs_segbuf_set_next_segnum(segbuf, nextnextnum, nilfs);
+
+		list_add_tail(&segbuf->sb_list, &list);
+		prev = segbuf;
+	}
+	list_splice_tail(&list, &sci->sc_segbufs);
+	return 0;
+
+ failed_segbuf:
+	nilfs_segbuf_free(segbuf);
+ failed:
+	list_for_each_entry(segbuf, &list, sb_list) {
+		ret = nilfs_sufile_free(sufile, segbuf->sb_nextnum);
+		WARN_ON(ret); /* never fails */
+	}
+	nilfs_destroy_logs(&list);
+	return err;
+}
+
+static void nilfs_free_incomplete_logs(struct list_head *logs,
+				       struct the_nilfs *nilfs)
+{
+	struct nilfs_segment_buffer *segbuf, *prev;
+	struct inode *sufile = nilfs->ns_sufile;
+	int ret;
+
+	segbuf = NILFS_FIRST_SEGBUF(logs);
+	if (nilfs->ns_nextnum != segbuf->sb_nextnum) {
+		ret = nilfs_sufile_free(sufile, segbuf->sb_nextnum);
+		WARN_ON(ret); /* never fails */
+	}
+	if (atomic_read(&segbuf->sb_err)) {
+		/* Case 1: The first segment failed */
+		if (segbuf->sb_pseg_start != segbuf->sb_fseg_start)
+			/* Case 1a:  Partial segment appended into an existing
+			   segment */
+			nilfs_terminate_segment(nilfs, segbuf->sb_fseg_start,
+						segbuf->sb_fseg_end);
+		else /* Case 1b:  New full segment */
+			set_nilfs_discontinued(nilfs);
+	}
+
+	prev = segbuf;
+	list_for_each_entry_continue(segbuf, logs, sb_list) {
+		if (prev->sb_nextnum != segbuf->sb_nextnum) {
+			ret = nilfs_sufile_free(sufile, segbuf->sb_nextnum);
+			WARN_ON(ret); /* never fails */
+		}
+		if (atomic_read(&segbuf->sb_err) &&
+		    segbuf->sb_segnum != nilfs->ns_nextnum)
+			/* Case 2: extended segment (!= next) failed */
+			nilfs_sufile_set_error(sufile, segbuf->sb_segnum);
+		prev = segbuf;
+	}
+}
+
+static void nilfs_segctor_update_segusage(struct nilfs_sc_info *sci,
+					  struct inode *sufile)
+{
+	struct nilfs_segment_buffer *segbuf;
+	unsigned long live_blocks;
+	int ret;
+
+	list_for_each_entry(segbuf, &sci->sc_segbufs, sb_list) {
+		live_blocks = segbuf->sb_sum.nblocks +
+			(segbuf->sb_pseg_start - segbuf->sb_fseg_start);
+		ret = nilfs_sufile_set_segment_usage(sufile, segbuf->sb_segnum,
+						     live_blocks,
+						     sci->sc_seg_ctime);
+		WARN_ON(ret); /* always succeed because the segusage is dirty */
+	}
+}
+
+static void nilfs_cancel_segusage(struct list_head *logs, struct inode *sufile)
+{
+	struct nilfs_segment_buffer *segbuf;
+	int ret;
+
+	segbuf = NILFS_FIRST_SEGBUF(logs);
+	ret = nilfs_sufile_set_segment_usage(sufile, segbuf->sb_segnum,
+					     segbuf->sb_pseg_start -
+					     segbuf->sb_fseg_start, 0);
+	WARN_ON(ret); /* always succeed because the segusage is dirty */
+
+	list_for_each_entry_continue(segbuf, logs, sb_list) {
+		ret = nilfs_sufile_set_segment_usage(sufile, segbuf->sb_segnum,
+						     0, 0);
+		WARN_ON(ret); /* always succeed */
+	}
+}
+
+static void nilfs_segctor_truncate_segments(struct nilfs_sc_info *sci,
+					    struct nilfs_segment_buffer *last,
+					    struct inode *sufile)
+{
+	struct nilfs_segment_buffer *segbuf = last;
+	int ret;
+
+	list_for_each_entry_continue(segbuf, &sci->sc_segbufs, sb_list) {
+		sci->sc_segbuf_nblocks -= segbuf->sb_rest_blocks;
+		ret = nilfs_sufile_free(sufile, segbuf->sb_nextnum);
+		WARN_ON(ret);
+	}
+	nilfs_truncate_logs(&sci->sc_segbufs, last);
+}
+
+
+static int nilfs_segctor_collect(struct nilfs_sc_info *sci,
+				 struct the_nilfs *nilfs, int mode)
+{
+	struct nilfs_cstage prev_stage = sci->sc_stage;
+	int err, nadd = 1;
+
+	/* Collection retry loop */
+	for (;;) {
+		sci->sc_nblk_this_inc = 0;
+		sci->sc_curseg = NILFS_FIRST_SEGBUF(&sci->sc_segbufs);
+
+		err = nilfs_segctor_reset_segment_buffer(sci);
+		if (unlikely(err))
+			goto failed;
+
+		err = nilfs_segctor_collect_blocks(sci, mode);
+		sci->sc_nblk_this_inc += sci->sc_curseg->sb_sum.nblocks;
+		if (!err)
+			break;
+
+		if (unlikely(err != -E2BIG))
+			goto failed;
+
+		/* The current segment is filled up */
+		if (mode != SC_LSEG_SR || sci->sc_stage.scnt < NILFS_ST_CPFILE)
+			break;
+
+		nilfs_clear_logs(&sci->sc_segbufs);
+
+		if (sci->sc_stage.flags & NILFS_CF_SUFREED) {
+			err = nilfs_sufile_cancel_freev(nilfs->ns_sufile,
+							sci->sc_freesegs,
+							sci->sc_nfreesegs,
+							NULL);
+			WARN_ON(err); /* do not happen */
+			sci->sc_stage.flags &= ~NILFS_CF_SUFREED;
+		}
+
+		err = nilfs_segctor_extend_segments(sci, nilfs, nadd);
+		if (unlikely(err))
+			return err;
+
+		nadd = min_t(int, nadd << 1, SC_MAX_SEGDELTA);
+		sci->sc_stage = prev_stage;
+	}
+	nilfs_segctor_truncate_segments(sci, sci->sc_curseg, nilfs->ns_sufile);
+	return 0;
+
+ failed:
+	return err;
+}
+
+static void nilfs_list_replace_buffer(struct buffer_head *old_bh,
+				      struct buffer_head *new_bh)
+{
+	BUG_ON(!list_empty(&new_bh->b_assoc_buffers));
+
+	list_replace_init(&old_bh->b_assoc_buffers, &new_bh->b_assoc_buffers);
+	/* The caller must release old_bh */
+}
+
+static int
+nilfs_segctor_update_payload_blocknr(struct nilfs_sc_info *sci,
+				     struct nilfs_segment_buffer *segbuf,
+				     int mode)
+{
+	struct inode *inode = NULL;
+	sector_t blocknr;
+	unsigned long nfinfo = segbuf->sb_sum.nfinfo;
+	unsigned long nblocks = 0, ndatablk = 0;
+	struct nilfs_sc_operations *sc_op = NULL;
+	struct nilfs_segsum_pointer ssp;
+	struct nilfs_finfo *finfo = NULL;
+	union nilfs_binfo binfo;
+	struct buffer_head *bh, *bh_org;
+	ino_t ino = 0;
+	int err = 0;
+
+	if (!nfinfo)
+		goto out;
+
+	blocknr = segbuf->sb_pseg_start + segbuf->sb_sum.nsumblk;
+	ssp.bh = NILFS_SEGBUF_FIRST_BH(&segbuf->sb_segsum_buffers);
+	ssp.offset = sizeof(struct nilfs_segment_summary);
+
+	list_for_each_entry(bh, &segbuf->sb_payload_buffers, b_assoc_buffers) {
+		if (bh == segbuf->sb_super_root)
+			break;
+		if (!finfo) {
+			finfo =	nilfs_segctor_map_segsum_entry(
+				sci, &ssp, sizeof(*finfo));
+			ino = le64_to_cpu(finfo->fi_ino);
+			nblocks = le32_to_cpu(finfo->fi_nblocks);
+			ndatablk = le32_to_cpu(finfo->fi_ndatablk);
+
+			inode = bh->b_page->mapping->host;
+
+			if (mode == SC_LSEG_DSYNC)
+				sc_op = &nilfs_sc_dsync_ops;
+			else if (ino == NILFS_DAT_INO)
+				sc_op = &nilfs_sc_dat_ops;
+			else /* file blocks */
+				sc_op = &nilfs_sc_file_ops;
+		}
+		bh_org = bh;
+		get_bh(bh_org);
+		err = nilfs_bmap_assign(NILFS_I(inode)->i_bmap, &bh, blocknr,
+					&binfo);
+		if (bh != bh_org)
+			nilfs_list_replace_buffer(bh_org, bh);
+		brelse(bh_org);
+		if (unlikely(err))
+			goto failed_bmap;
+
+		if (ndatablk > 0)
+			sc_op->write_data_binfo(sci, &ssp, &binfo);
+		else
+			sc_op->write_node_binfo(sci, &ssp, &binfo);
+
+		blocknr++;
+		if (--nblocks == 0) {
+			finfo = NULL;
+			if (--nfinfo == 0)
+				break;
+		} else if (ndatablk > 0)
+			ndatablk--;
+	}
+ out:
+	return 0;
+
+ failed_bmap:
+	return err;
+}
+
+static int nilfs_segctor_assign(struct nilfs_sc_info *sci, int mode)
+{
+	struct nilfs_segment_buffer *segbuf;
+	int err;
+
+	list_for_each_entry(segbuf, &sci->sc_segbufs, sb_list) {
+		err = nilfs_segctor_update_payload_blocknr(sci, segbuf, mode);
+		if (unlikely(err))
+			return err;
+		nilfs_segbuf_fill_in_segsum(segbuf);
+	}
+	return 0;
+}
+
+static void nilfs_begin_page_io(struct page *page)
+{
+	if (!page || PageWriteback(page))
+		/* For split b-tree node pages, this function may be called
+		   twice.  We ignore the 2nd or later calls by this check. */
+		return;
+
+	lock_page(page);
+	clear_page_dirty_for_io(page);
+	set_page_writeback(page);
+	unlock_page(page);
+}
+
+static void nilfs_segctor_prepare_write(struct nilfs_sc_info *sci)
+{
+	struct nilfs_segment_buffer *segbuf;
+	struct page *bd_page = NULL, *fs_page = NULL;
+
+	list_for_each_entry(segbuf, &sci->sc_segbufs, sb_list) {
+		struct buffer_head *bh;
+
+		list_for_each_entry(bh, &segbuf->sb_segsum_buffers,
+				    b_assoc_buffers) {
+			if (bh->b_page != bd_page) {
+				if (bd_page) {
+					lock_page(bd_page);
+					clear_page_dirty_for_io(bd_page);
+					set_page_writeback(bd_page);
+					unlock_page(bd_page);
+				}
+				bd_page = bh->b_page;
+			}
+		}
+
+		list_for_each_entry(bh, &segbuf->sb_payload_buffers,
+				    b_assoc_buffers) {
+			set_buffer_async_write(bh);
+			if (bh == segbuf->sb_super_root) {
+				if (bh->b_page != bd_page) {
+					lock_page(bd_page);
+					clear_page_dirty_for_io(bd_page);
+					set_page_writeback(bd_page);
+					unlock_page(bd_page);
+					bd_page = bh->b_page;
+				}
+				break;
+			}
+			if (bh->b_page != fs_page) {
+				nilfs_begin_page_io(fs_page);
+				fs_page = bh->b_page;
+			}
+		}
+	}
+	if (bd_page) {
+		lock_page(bd_page);
+		clear_page_dirty_for_io(bd_page);
+		set_page_writeback(bd_page);
+		unlock_page(bd_page);
+	}
+	nilfs_begin_page_io(fs_page);
+}
+
+static int nilfs_segctor_write(struct nilfs_sc_info *sci,
+			       struct the_nilfs *nilfs)
+{
+	int ret;
+
+	ret = nilfs_write_logs(&sci->sc_segbufs, nilfs);
+	list_splice_tail_init(&sci->sc_segbufs, &sci->sc_write_logs);
+	return ret;
+}
+
+static void nilfs_end_page_io(struct page *page, int err)
+{
+	if (!page)
+		return;
+
+	if (buffer_nilfs_node(page_buffers(page)) && !PageWriteback(page)) {
+		/*
+		 * For b-tree node pages, this function may be called twice
+		 * or more because they might be split in a segment.
+		 */
+		if (PageDirty(page)) {
+			/*
+			 * For pages holding split b-tree node buffers, dirty
+			 * flag on the buffers may be cleared discretely.
+			 * In that case, the page is once redirtied for
+			 * remaining buffers, and it must be cancelled if
+			 * all the buffers get cleaned later.
+			 */
+			lock_page(page);
+			if (nilfs_page_buffers_clean(page))
+				__nilfs_clear_page_dirty(page);
+			unlock_page(page);
+		}
+		return;
+	}
+
+	if (!err) {
+		if (!nilfs_page_buffers_clean(page))
+			__set_page_dirty_nobuffers(page);
+		ClearPageError(page);
+	} else {
+		__set_page_dirty_nobuffers(page);
+		SetPageError(page);
+	}
+
+	end_page_writeback(page);
+}
+
+static void nilfs_abort_logs(struct list_head *logs, int err)
+{
+	struct nilfs_segment_buffer *segbuf;
+	struct page *bd_page = NULL, *fs_page = NULL;
+	struct buffer_head *bh;
+
+	if (list_empty(logs))
+		return;
+
+	list_for_each_entry(segbuf, logs, sb_list) {
+		list_for_each_entry(bh, &segbuf->sb_segsum_buffers,
+				    b_assoc_buffers) {
+			if (bh->b_page != bd_page) {
+				if (bd_page)
+					end_page_writeback(bd_page);
+				bd_page = bh->b_page;
+			}
+		}
+
+		list_for_each_entry(bh, &segbuf->sb_payload_buffers,
+				    b_assoc_buffers) {
+			clear_buffer_async_write(bh);
+			if (bh == segbuf->sb_super_root) {
+				if (bh->b_page != bd_page) {
+					end_page_writeback(bd_page);
+					bd_page = bh->b_page;
+				}
+				break;
+			}
+			if (bh->b_page != fs_page) {
+				nilfs_end_page_io(fs_page, err);
+				fs_page = bh->b_page;
+			}
+		}
+	}
+	if (bd_page)
+		end_page_writeback(bd_page);
+
+	nilfs_end_page_io(fs_page, err);
+}
+
+static void nilfs_segctor_abort_construction(struct nilfs_sc_info *sci,
+					     struct the_nilfs *nilfs, int err)
+{
+	LIST_HEAD(logs);
+	int ret;
+
+	list_splice_tail_init(&sci->sc_write_logs, &logs);
+	ret = nilfs_wait_on_logs(&logs);
+	nilfs_abort_logs(&logs, ret ? : err);
+
+	list_splice_tail_init(&sci->sc_segbufs, &logs);
+	nilfs_cancel_segusage(&logs, nilfs->ns_sufile);
+	nilfs_free_incomplete_logs(&logs, nilfs);
+
+	if (sci->sc_stage.flags & NILFS_CF_SUFREED) {
+		ret = nilfs_sufile_cancel_freev(nilfs->ns_sufile,
+						sci->sc_freesegs,
+						sci->sc_nfreesegs,
+						NULL);
+		WARN_ON(ret); /* do not happen */
+	}
+
+	nilfs_destroy_logs(&logs);
+}
+
+static void nilfs_set_next_segment(struct the_nilfs *nilfs,
+				   struct nilfs_segment_buffer *segbuf)
+{
+	nilfs->ns_segnum = segbuf->sb_segnum;
+	nilfs->ns_nextnum = segbuf->sb_nextnum;
+	nilfs->ns_pseg_offset = segbuf->sb_pseg_start - segbuf->sb_fseg_start
+		+ segbuf->sb_sum.nblocks;
+	nilfs->ns_seg_seq = segbuf->sb_sum.seg_seq;
+	nilfs->ns_ctime = segbuf->sb_sum.ctime;
+}
+
+static void nilfs_segctor_complete_write(struct nilfs_sc_info *sci)
+{
+	struct nilfs_segment_buffer *segbuf;
+	struct page *bd_page = NULL, *fs_page = NULL;
+	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+	int update_sr = false;
+
+	list_for_each_entry(segbuf, &sci->sc_write_logs, sb_list) {
+		struct buffer_head *bh;
+
+		list_for_each_entry(bh, &segbuf->sb_segsum_buffers,
+				    b_assoc_buffers) {
+			set_buffer_uptodate(bh);
+			clear_buffer_dirty(bh);
+			if (bh->b_page != bd_page) {
+				if (bd_page)
+					end_page_writeback(bd_page);
+				bd_page = bh->b_page;
+			}
+		}
+		/*
+		 * We assume that the buffers which belong to the same page
+		 * continue over the buffer list.
+		 * Under this assumption, the last BHs of pages is
+		 * identifiable by the discontinuity of bh->b_page
+		 * (page != fs_page).
+		 *
+		 * For B-tree node blocks, however, this assumption is not
+		 * guaranteed.  The cleanup code of B-tree node pages needs
+		 * special care.
+		 */
+		list_for_each_entry(bh, &segbuf->sb_payload_buffers,
+				    b_assoc_buffers) {
+			const unsigned long set_bits = (1 << BH_Uptodate);
+			const unsigned long clear_bits =
+				(1 << BH_Dirty | 1 << BH_Async_Write |
+				 1 << BH_Delay | 1 << BH_NILFS_Volatile |
+				 1 << BH_NILFS_Redirected);
+
+			set_mask_bits(&bh->b_state, clear_bits, set_bits);
+			if (bh == segbuf->sb_super_root) {
+				if (bh->b_page != bd_page) {
+					end_page_writeback(bd_page);
+					bd_page = bh->b_page;
+				}
+				update_sr = true;
+				break;
+			}
+			if (bh->b_page != fs_page) {
+				nilfs_end_page_io(fs_page, 0);
+				fs_page = bh->b_page;
+			}
+		}
+
+		if (!nilfs_segbuf_simplex(segbuf)) {
+			if (segbuf->sb_sum.flags & NILFS_SS_LOGBGN) {
+				set_bit(NILFS_SC_UNCLOSED, &sci->sc_flags);
+				sci->sc_lseg_stime = jiffies;
+			}
+			if (segbuf->sb_sum.flags & NILFS_SS_LOGEND)
+				clear_bit(NILFS_SC_UNCLOSED, &sci->sc_flags);
+		}
+	}
+	/*
+	 * Since pages may continue over multiple segment buffers,
+	 * end of the last page must be checked outside of the loop.
+	 */
+	if (bd_page)
+		end_page_writeback(bd_page);
+
+	nilfs_end_page_io(fs_page, 0);
+
+	nilfs_drop_collected_inodes(&sci->sc_dirty_files);
+
+	if (nilfs_doing_gc())
+		nilfs_drop_collected_inodes(&sci->sc_gc_inodes);
+	else
+		nilfs->ns_nongc_ctime = sci->sc_seg_ctime;
+
+	sci->sc_nblk_inc += sci->sc_nblk_this_inc;
+
+	segbuf = NILFS_LAST_SEGBUF(&sci->sc_write_logs);
+	nilfs_set_next_segment(nilfs, segbuf);
+
+	if (update_sr) {
+		nilfs->ns_flushed_device = 0;
+		nilfs_set_last_segment(nilfs, segbuf->sb_pseg_start,
+				       segbuf->sb_sum.seg_seq, nilfs->ns_cno++);
+
+		clear_bit(NILFS_SC_HAVE_DELTA, &sci->sc_flags);
+		clear_bit(NILFS_SC_DIRTY, &sci->sc_flags);
+		set_bit(NILFS_SC_SUPER_ROOT, &sci->sc_flags);
+		nilfs_segctor_clear_metadata_dirty(sci);
+	} else
+		clear_bit(NILFS_SC_SUPER_ROOT, &sci->sc_flags);
+}
+
+static int nilfs_segctor_wait(struct nilfs_sc_info *sci)
+{
+	int ret;
+
+	ret = nilfs_wait_on_logs(&sci->sc_write_logs);
+	if (!ret) {
+		nilfs_segctor_complete_write(sci);
+		nilfs_destroy_logs(&sci->sc_write_logs);
+	}
+	return ret;
+}
+
+static int nilfs_segctor_collect_dirty_files(struct nilfs_sc_info *sci,
+					     struct the_nilfs *nilfs)
+{
+	struct nilfs_inode_info *ii, *n;
+	struct inode *ifile = sci->sc_root->ifile;
+
+	spin_lock(&nilfs->ns_inode_lock);
+ retry:
+	list_for_each_entry_safe(ii, n, &nilfs->ns_dirty_files, i_dirty) {
+		if (!ii->i_bh) {
+			struct buffer_head *ibh;
+			int err;
+
+			spin_unlock(&nilfs->ns_inode_lock);
+			err = nilfs_ifile_get_inode_block(
+				ifile, ii->vfs_inode.i_ino, &ibh);
+			if (unlikely(err)) {
+				nilfs_warning(sci->sc_super, __func__,
+					      "failed to get inode block.\n");
+				return err;
+			}
+			mark_buffer_dirty(ibh);
+			nilfs_mdt_mark_dirty(ifile);
+			spin_lock(&nilfs->ns_inode_lock);
+			if (likely(!ii->i_bh))
+				ii->i_bh = ibh;
+			else
+				brelse(ibh);
+			goto retry;
+		}
+
+		clear_bit(NILFS_I_QUEUED, &ii->i_state);
+		set_bit(NILFS_I_BUSY, &ii->i_state);
+		list_move_tail(&ii->i_dirty, &sci->sc_dirty_files);
+	}
+	spin_unlock(&nilfs->ns_inode_lock);
+
+	return 0;
+}
+
+static void nilfs_segctor_drop_written_files(struct nilfs_sc_info *sci,
+					     struct the_nilfs *nilfs)
+{
+	struct nilfs_inode_info *ii, *n;
+	int during_mount = !(sci->sc_super->s_flags & MS_ACTIVE);
+	int defer_iput = false;
+
+	spin_lock(&nilfs->ns_inode_lock);
+	list_for_each_entry_safe(ii, n, &sci->sc_dirty_files, i_dirty) {
+		if (!test_and_clear_bit(NILFS_I_UPDATED, &ii->i_state) ||
+		    test_bit(NILFS_I_DIRTY, &ii->i_state))
+			continue;
+
+		clear_bit(NILFS_I_BUSY, &ii->i_state);
+		brelse(ii->i_bh);
+		ii->i_bh = NULL;
+		list_del_init(&ii->i_dirty);
+		if (!ii->vfs_inode.i_nlink || during_mount) {
+			/*
+			 * Defer calling iput() to avoid deadlocks if
+			 * i_nlink == 0 or mount is not yet finished.
+			 */
+			list_add_tail(&ii->i_dirty, &sci->sc_iput_queue);
+			defer_iput = true;
+		} else {
+			spin_unlock(&nilfs->ns_inode_lock);
+			iput(&ii->vfs_inode);
+			spin_lock(&nilfs->ns_inode_lock);
+		}
+	}
+	spin_unlock(&nilfs->ns_inode_lock);
+
+	if (defer_iput)
+		schedule_work(&sci->sc_iput_work);
+}
+
+/*
+ * Main procedure of segment constructor
+ */
+static int nilfs_segctor_do_construct(struct nilfs_sc_info *sci, int mode)
+{
+	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+	int err;
+
+	sci->sc_stage.scnt = NILFS_ST_INIT;
+	sci->sc_cno = nilfs->ns_cno;
+
+	err = nilfs_segctor_collect_dirty_files(sci, nilfs);
+	if (unlikely(err))
+		goto out;
+
+	if (nilfs_test_metadata_dirty(nilfs, sci->sc_root))
+		set_bit(NILFS_SC_DIRTY, &sci->sc_flags);
+
+	if (nilfs_segctor_clean(sci))
+		goto out;
+
+	do {
+		sci->sc_stage.flags &= ~NILFS_CF_HISTORY_MASK;
+
+		err = nilfs_segctor_begin_construction(sci, nilfs);
+		if (unlikely(err))
+			goto out;
+
+		/* Update time stamp */
+		sci->sc_seg_ctime = get_seconds();
+
+		err = nilfs_segctor_collect(sci, nilfs, mode);
+		if (unlikely(err))
+			goto failed;
+
+		/* Avoid empty segment */
+		if (sci->sc_stage.scnt == NILFS_ST_DONE &&
+		    nilfs_segbuf_empty(sci->sc_curseg)) {
+			nilfs_segctor_abort_construction(sci, nilfs, 1);
+			goto out;
+		}
+
+		err = nilfs_segctor_assign(sci, mode);
+		if (unlikely(err))
+			goto failed;
+
+		if (sci->sc_stage.flags & NILFS_CF_IFILE_STARTED)
+			nilfs_segctor_fill_in_file_bmap(sci);
+
+		if (mode == SC_LSEG_SR &&
+		    sci->sc_stage.scnt >= NILFS_ST_CPFILE) {
+			err = nilfs_segctor_fill_in_checkpoint(sci);
+			if (unlikely(err))
+				goto failed_to_write;
+
+			nilfs_segctor_fill_in_super_root(sci, nilfs);
+		}
+		nilfs_segctor_update_segusage(sci, nilfs->ns_sufile);
+
+		/* Write partial segments */
+		nilfs_segctor_prepare_write(sci);
+
+		nilfs_add_checksums_on_logs(&sci->sc_segbufs,
+					    nilfs->ns_crc_seed);
+
+		err = nilfs_segctor_write(sci, nilfs);
+		if (unlikely(err))
+			goto failed_to_write;
+
+		if (sci->sc_stage.scnt == NILFS_ST_DONE ||
+		    nilfs->ns_blocksize_bits != PAGE_CACHE_SHIFT) {
+			/*
+			 * At this point, we avoid double buffering
+			 * for blocksize < pagesize because page dirty
+			 * flag is turned off during write and dirty
+			 * buffers are not properly collected for
+			 * pages crossing over segments.
+			 */
+			err = nilfs_segctor_wait(sci);
+			if (err)
+				goto failed_to_write;
+		}
+	} while (sci->sc_stage.scnt != NILFS_ST_DONE);
+
+ out:
+	nilfs_segctor_drop_written_files(sci, nilfs);
+	return err;
+
+ failed_to_write:
+	if (sci->sc_stage.flags & NILFS_CF_IFILE_STARTED)
+		nilfs_redirty_inodes(&sci->sc_dirty_files);
+
+ failed:
+	if (nilfs_doing_gc())
+		nilfs_redirty_inodes(&sci->sc_gc_inodes);
+	nilfs_segctor_abort_construction(sci, nilfs, err);
+	goto out;
+}
+
+/**
+ * nilfs_segctor_start_timer - set timer of background write
+ * @sci: nilfs_sc_info
+ *
+ * If the timer has already been set, it ignores the new request.
+ * This function MUST be called within a section locking the segment
+ * semaphore.
+ */
+static void nilfs_segctor_start_timer(struct nilfs_sc_info *sci)
+{
+	spin_lock(&sci->sc_state_lock);
+	if (!(sci->sc_state & NILFS_SEGCTOR_COMMIT)) {
+		sci->sc_timer.expires = jiffies + sci->sc_interval;
+		add_timer(&sci->sc_timer);
+		sci->sc_state |= NILFS_SEGCTOR_COMMIT;
+	}
+	spin_unlock(&sci->sc_state_lock);
+}
+
+static void nilfs_segctor_do_flush(struct nilfs_sc_info *sci, int bn)
+{
+	spin_lock(&sci->sc_state_lock);
+	if (!(sci->sc_flush_request & (1 << bn))) {
+		unsigned long prev_req = sci->sc_flush_request;
+
+		sci->sc_flush_request |= (1 << bn);
+		if (!prev_req)
+			wake_up(&sci->sc_wait_daemon);
+	}
+	spin_unlock(&sci->sc_state_lock);
+}
+
+/**
+ * nilfs_flush_segment - trigger a segment construction for resource control
+ * @sb: super block
+ * @ino: inode number of the file to be flushed out.
+ */
+void nilfs_flush_segment(struct super_block *sb, ino_t ino)
+{
+	struct the_nilfs *nilfs = sb->s_fs_info;
+	struct nilfs_sc_info *sci = nilfs->ns_writer;
+
+	if (!sci || nilfs_doing_construction())
+		return;
+	nilfs_segctor_do_flush(sci, NILFS_MDT_INODE(sb, ino) ? ino : 0);
+					/* assign bit 0 to data files */
+}
+
+struct nilfs_segctor_wait_request {
+	wait_queue_t	wq;
+	__u32		seq;
+	int		err;
+	atomic_t	done;
+};
+
+static int nilfs_segctor_sync(struct nilfs_sc_info *sci)
+{
+	struct nilfs_segctor_wait_request wait_req;
+	int err = 0;
+
+	spin_lock(&sci->sc_state_lock);
+	init_wait(&wait_req.wq);
+	wait_req.err = 0;
+	atomic_set(&wait_req.done, 0);
+	wait_req.seq = ++sci->sc_seq_request;
+	spin_unlock(&sci->sc_state_lock);
+
+	init_waitqueue_entry(&wait_req.wq, current);
+	add_wait_queue(&sci->sc_wait_request, &wait_req.wq);
+	set_current_state(TASK_INTERRUPTIBLE);
+	wake_up(&sci->sc_wait_daemon);
+
+	for (;;) {
+		if (atomic_read(&wait_req.done)) {
+			err = wait_req.err;
+			break;
+		}
+		if (!signal_pending(current)) {
+			schedule();
+			continue;
+		}
+		err = -ERESTARTSYS;
+		break;
+	}
+	finish_wait(&sci->sc_wait_request, &wait_req.wq);
+	return err;
+}
+
+static void nilfs_segctor_wakeup(struct nilfs_sc_info *sci, int err)
+{
+	struct nilfs_segctor_wait_request *wrq, *n;
+	unsigned long flags;
+
+	spin_lock_irqsave(&sci->sc_wait_request.lock, flags);
+	list_for_each_entry_safe(wrq, n, &sci->sc_wait_request.task_list,
+				 wq.task_list) {
+		if (!atomic_read(&wrq->done) &&
+		    nilfs_cnt32_ge(sci->sc_seq_done, wrq->seq)) {
+			wrq->err = err;
+			atomic_set(&wrq->done, 1);
+		}
+		if (atomic_read(&wrq->done)) {
+			wrq->wq.func(&wrq->wq,
+				     TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE,
+				     0, NULL);
+		}
+	}
+	spin_unlock_irqrestore(&sci->sc_wait_request.lock, flags);
+}
+
+/**
+ * nilfs_construct_segment - construct a logical segment
+ * @sb: super block
+ *
+ * Return Value: On success, 0 is retured. On errors, one of the following
+ * negative error code is returned.
+ *
+ * %-EROFS - Read only filesystem.
+ *
+ * %-EIO - I/O error
+ *
+ * %-ENOSPC - No space left on device (only in a panic state).
+ *
+ * %-ERESTARTSYS - Interrupted.
+ *
+ * %-ENOMEM - Insufficient memory available.
+ */
+int nilfs_construct_segment(struct super_block *sb)
+{
+	struct the_nilfs *nilfs = sb->s_fs_info;
+	struct nilfs_sc_info *sci = nilfs->ns_writer;
+	struct nilfs_transaction_info *ti;
+	int err;
+
+	if (!sci)
+		return -EROFS;
+
+	/* A call inside transactions causes a deadlock. */
+	BUG_ON((ti = current->journal_info) && ti->ti_magic == NILFS_TI_MAGIC);
+
+	err = nilfs_segctor_sync(sci);
+	return err;
+}
+
+/**
+ * nilfs_construct_dsync_segment - construct a data-only logical segment
+ * @sb: super block
+ * @inode: inode whose data blocks should be written out
+ * @start: start byte offset
+ * @end: end byte offset (inclusive)
+ *
+ * Return Value: On success, 0 is retured. On errors, one of the following
+ * negative error code is returned.
+ *
+ * %-EROFS - Read only filesystem.
+ *
+ * %-EIO - I/O error
+ *
+ * %-ENOSPC - No space left on device (only in a panic state).
+ *
+ * %-ERESTARTSYS - Interrupted.
+ *
+ * %-ENOMEM - Insufficient memory available.
+ */
+int nilfs_construct_dsync_segment(struct super_block *sb, struct inode *inode,
+				  loff_t start, loff_t end)
+{
+	struct the_nilfs *nilfs = sb->s_fs_info;
+	struct nilfs_sc_info *sci = nilfs->ns_writer;
+	struct nilfs_inode_info *ii;
+	struct nilfs_transaction_info ti;
+	int err = 0;
+
+	if (!sci)
+		return -EROFS;
+
+	nilfs_transaction_lock(sb, &ti, 0);
+
+	ii = NILFS_I(inode);
+	if (test_bit(NILFS_I_INODE_SYNC, &ii->i_state) ||
+	    nilfs_test_opt(nilfs, STRICT_ORDER) ||
+	    test_bit(NILFS_SC_UNCLOSED, &sci->sc_flags) ||
+	    nilfs_discontinued(nilfs)) {
+		nilfs_transaction_unlock(sb);
+		err = nilfs_segctor_sync(sci);
+		return err;
+	}
+
+	spin_lock(&nilfs->ns_inode_lock);
+	if (!test_bit(NILFS_I_QUEUED, &ii->i_state) &&
+	    !test_bit(NILFS_I_BUSY, &ii->i_state)) {
+		spin_unlock(&nilfs->ns_inode_lock);
+		nilfs_transaction_unlock(sb);
+		return 0;
+	}
+	spin_unlock(&nilfs->ns_inode_lock);
+	sci->sc_dsync_inode = ii;
+	sci->sc_dsync_start = start;
+	sci->sc_dsync_end = end;
+
+	err = nilfs_segctor_do_construct(sci, SC_LSEG_DSYNC);
+	if (!err)
+		nilfs->ns_flushed_device = 0;
+
+	nilfs_transaction_unlock(sb);
+	return err;
+}
+
+#define FLUSH_FILE_BIT	(0x1) /* data file only */
+#define FLUSH_DAT_BIT	(1 << NILFS_DAT_INO) /* DAT only */
+
+/**
+ * nilfs_segctor_accept - record accepted sequence count of log-write requests
+ * @sci: segment constructor object
+ */
+static void nilfs_segctor_accept(struct nilfs_sc_info *sci)
+{
+	spin_lock(&sci->sc_state_lock);
+	sci->sc_seq_accepted = sci->sc_seq_request;
+	spin_unlock(&sci->sc_state_lock);
+	del_timer_sync(&sci->sc_timer);
+}
+
+/**
+ * nilfs_segctor_notify - notify the result of request to caller threads
+ * @sci: segment constructor object
+ * @mode: mode of log forming
+ * @err: error code to be notified
+ */
+static void nilfs_segctor_notify(struct nilfs_sc_info *sci, int mode, int err)
+{
+	/* Clear requests (even when the construction failed) */
+	spin_lock(&sci->sc_state_lock);
+
+	if (mode == SC_LSEG_SR) {
+		sci->sc_state &= ~NILFS_SEGCTOR_COMMIT;
+		sci->sc_seq_done = sci->sc_seq_accepted;
+		nilfs_segctor_wakeup(sci, err);
+		sci->sc_flush_request = 0;
+	} else {
+		if (mode == SC_FLUSH_FILE)
+			sci->sc_flush_request &= ~FLUSH_FILE_BIT;
+		else if (mode == SC_FLUSH_DAT)
+			sci->sc_flush_request &= ~FLUSH_DAT_BIT;
+
+		/* re-enable timer if checkpoint creation was not done */
+		if ((sci->sc_state & NILFS_SEGCTOR_COMMIT) &&
+		    time_before(jiffies, sci->sc_timer.expires))
+			add_timer(&sci->sc_timer);
+	}
+	spin_unlock(&sci->sc_state_lock);
+}
+
+/**
+ * nilfs_segctor_construct - form logs and write them to disk
+ * @sci: segment constructor object
+ * @mode: mode of log forming
+ */
+static int nilfs_segctor_construct(struct nilfs_sc_info *sci, int mode)
+{
+	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+	struct nilfs_super_block **sbp;
+	int err = 0;
+
+	nilfs_segctor_accept(sci);
+
+	if (nilfs_discontinued(nilfs))
+		mode = SC_LSEG_SR;
+	if (!nilfs_segctor_confirm(sci))
+		err = nilfs_segctor_do_construct(sci, mode);
+
+	if (likely(!err)) {
+		if (mode != SC_FLUSH_DAT)
+			atomic_set(&nilfs->ns_ndirtyblks, 0);
+		if (test_bit(NILFS_SC_SUPER_ROOT, &sci->sc_flags) &&
+		    nilfs_discontinued(nilfs)) {
+			down_write(&nilfs->ns_sem);
+			err = -EIO;
+			sbp = nilfs_prepare_super(sci->sc_super,
+						  nilfs_sb_will_flip(nilfs));
+			if (likely(sbp)) {
+				nilfs_set_log_cursor(sbp[0], nilfs);
+				err = nilfs_commit_super(sci->sc_super,
+							 NILFS_SB_COMMIT);
+			}
+			up_write(&nilfs->ns_sem);
+		}
+	}
+
+	nilfs_segctor_notify(sci, mode, err);
+	return err;
+}
+
+static void nilfs_construction_timeout(unsigned long data)
+{
+	struct task_struct *p = (struct task_struct *)data;
+	wake_up_process(p);
+}
+
+static void
+nilfs_remove_written_gcinodes(struct the_nilfs *nilfs, struct list_head *head)
+{
+	struct nilfs_inode_info *ii, *n;
+
+	list_for_each_entry_safe(ii, n, head, i_dirty) {
+		if (!test_bit(NILFS_I_UPDATED, &ii->i_state))
+			continue;
+		list_del_init(&ii->i_dirty);
+		truncate_inode_pages(&ii->vfs_inode.i_data, 0);
+		nilfs_btnode_cache_clear(&ii->i_btnode_cache);
+		iput(&ii->vfs_inode);
+	}
+}
+
+int nilfs_clean_segments(struct super_block *sb, struct nilfs_argv *argv,
+			 void **kbufs)
+{
+	struct the_nilfs *nilfs = sb->s_fs_info;
+	struct nilfs_sc_info *sci = nilfs->ns_writer;
+	struct nilfs_transaction_info ti;
+	int err;
+
+	if (unlikely(!sci))
+		return -EROFS;
+
+	nilfs_transaction_lock(sb, &ti, 1);
+
+	err = nilfs_mdt_save_to_shadow_map(nilfs->ns_dat);
+	if (unlikely(err))
+		goto out_unlock;
+
+	err = nilfs_ioctl_prepare_clean_segments(nilfs, argv, kbufs);
+	if (unlikely(err)) {
+		nilfs_mdt_restore_from_shadow_map(nilfs->ns_dat);
+		goto out_unlock;
+	}
+
+	sci->sc_freesegs = kbufs[4];
+	sci->sc_nfreesegs = argv[4].v_nmembs;
+	list_splice_tail_init(&nilfs->ns_gc_inodes, &sci->sc_gc_inodes);
+
+	for (;;) {
+		err = nilfs_segctor_construct(sci, SC_LSEG_SR);
+		nilfs_remove_written_gcinodes(nilfs, &sci->sc_gc_inodes);
+
+		if (likely(!err))
+			break;
+
+		nilfs_warning(sb, __func__,
+			      "segment construction failed. (err=%d)", err);
+		set_current_state(TASK_INTERRUPTIBLE);
+		schedule_timeout(sci->sc_interval);
+	}
+	if (nilfs_test_opt(nilfs, DISCARD)) {
+		int ret = nilfs_discard_segments(nilfs, sci->sc_freesegs,
+						 sci->sc_nfreesegs);
+		if (ret) {
+			printk(KERN_WARNING
+			       "NILFS warning: error %d on discard request, "
+			       "turning discards off for the device\n", ret);
+			nilfs_clear_opt(nilfs, DISCARD);
+		}
+	}
+
+ out_unlock:
+	sci->sc_freesegs = NULL;
+	sci->sc_nfreesegs = 0;
+	nilfs_mdt_clear_shadow_map(nilfs->ns_dat);
+	nilfs_transaction_unlock(sb);
+	return err;
+}
+
+static void nilfs_segctor_thread_construct(struct nilfs_sc_info *sci, int mode)
+{
+	struct nilfs_transaction_info ti;
+
+	nilfs_transaction_lock(sci->sc_super, &ti, 0);
+	nilfs_segctor_construct(sci, mode);
+
+	/*
+	 * Unclosed segment should be retried.  We do this using sc_timer.
+	 * Timeout of sc_timer will invoke complete construction which leads
+	 * to close the current logical segment.
+	 */
+	if (test_bit(NILFS_SC_UNCLOSED, &sci->sc_flags))
+		nilfs_segctor_start_timer(sci);
+
+	nilfs_transaction_unlock(sci->sc_super);
+}
+
+static void nilfs_segctor_do_immediate_flush(struct nilfs_sc_info *sci)
+{
+	int mode = 0;
+	int err;
+
+	spin_lock(&sci->sc_state_lock);
+	mode = (sci->sc_flush_request & FLUSH_DAT_BIT) ?
+		SC_FLUSH_DAT : SC_FLUSH_FILE;
+	spin_unlock(&sci->sc_state_lock);
+
+	if (mode) {
+		err = nilfs_segctor_do_construct(sci, mode);
+
+		spin_lock(&sci->sc_state_lock);
+		sci->sc_flush_request &= (mode == SC_FLUSH_FILE) ?
+			~FLUSH_FILE_BIT : ~FLUSH_DAT_BIT;
+		spin_unlock(&sci->sc_state_lock);
+	}
+	clear_bit(NILFS_SC_PRIOR_FLUSH, &sci->sc_flags);
+}
+
+static int nilfs_segctor_flush_mode(struct nilfs_sc_info *sci)
+{
+	if (!test_bit(NILFS_SC_UNCLOSED, &sci->sc_flags) ||
+	    time_before(jiffies, sci->sc_lseg_stime + sci->sc_mjcp_freq)) {
+		if (!(sci->sc_flush_request & ~FLUSH_FILE_BIT))
+			return SC_FLUSH_FILE;
+		else if (!(sci->sc_flush_request & ~FLUSH_DAT_BIT))
+			return SC_FLUSH_DAT;
+	}
+	return SC_LSEG_SR;
+}
+
+/**
+ * nilfs_segctor_thread - main loop of the segment constructor thread.
+ * @arg: pointer to a struct nilfs_sc_info.
+ *
+ * nilfs_segctor_thread() initializes a timer and serves as a daemon
+ * to execute segment constructions.
+ */
+static int nilfs_segctor_thread(void *arg)
+{
+	struct nilfs_sc_info *sci = (struct nilfs_sc_info *)arg;
+	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+	int timeout = 0;
+
+	sci->sc_timer.data = (unsigned long)current;
+	sci->sc_timer.function = nilfs_construction_timeout;
+
+	/* start sync. */
+	sci->sc_task = current;
+	wake_up(&sci->sc_wait_task); /* for nilfs_segctor_start_thread() */
+	printk(KERN_INFO
+	       "segctord starting. Construction interval = %lu seconds, "
+	       "CP frequency < %lu seconds\n",
+	       sci->sc_interval / HZ, sci->sc_mjcp_freq / HZ);
+
+	spin_lock(&sci->sc_state_lock);
+ loop:
+	for (;;) {
+		int mode;
+
+		if (sci->sc_state & NILFS_SEGCTOR_QUIT)
+			goto end_thread;
+
+		if (timeout || sci->sc_seq_request != sci->sc_seq_done)
+			mode = SC_LSEG_SR;
+		else if (!sci->sc_flush_request)
+			break;
+		else
+			mode = nilfs_segctor_flush_mode(sci);
+
+		spin_unlock(&sci->sc_state_lock);
+		nilfs_segctor_thread_construct(sci, mode);
+		spin_lock(&sci->sc_state_lock);
+		timeout = 0;
+	}
+
+
+	if (freezing(current)) {
+		spin_unlock(&sci->sc_state_lock);
+		try_to_freeze();
+		spin_lock(&sci->sc_state_lock);
+	} else {
+		DEFINE_WAIT(wait);
+		int should_sleep = 1;
+
+		prepare_to_wait(&sci->sc_wait_daemon, &wait,
+				TASK_INTERRUPTIBLE);
+
+		if (sci->sc_seq_request != sci->sc_seq_done)
+			should_sleep = 0;
+		else if (sci->sc_flush_request)
+			should_sleep = 0;
+		else if (sci->sc_state & NILFS_SEGCTOR_COMMIT)
+			should_sleep = time_before(jiffies,
+					sci->sc_timer.expires);
+
+		if (should_sleep) {
+			spin_unlock(&sci->sc_state_lock);
+			schedule();
+			spin_lock(&sci->sc_state_lock);
+		}
+		finish_wait(&sci->sc_wait_daemon, &wait);
+		timeout = ((sci->sc_state & NILFS_SEGCTOR_COMMIT) &&
+			   time_after_eq(jiffies, sci->sc_timer.expires));
+
+		if (nilfs_sb_dirty(nilfs) && nilfs_sb_need_update(nilfs))
+			set_nilfs_discontinued(nilfs);
+	}
+	goto loop;
+
+ end_thread:
+	spin_unlock(&sci->sc_state_lock);
+
+	/* end sync. */
+	sci->sc_task = NULL;
+	wake_up(&sci->sc_wait_task); /* for nilfs_segctor_kill_thread() */
+	return 0;
+}
+
+static int nilfs_segctor_start_thread(struct nilfs_sc_info *sci)
+{
+	struct task_struct *t;
+
+	t = kthread_run(nilfs_segctor_thread, sci, "segctord");
+	if (IS_ERR(t)) {
+		int err = PTR_ERR(t);
+
+		printk(KERN_ERR "NILFS: error %d creating segctord thread\n",
+		       err);
+		return err;
+	}
+	wait_event(sci->sc_wait_task, sci->sc_task != NULL);
+	return 0;
+}
+
+static void nilfs_segctor_kill_thread(struct nilfs_sc_info *sci)
+	__acquires(&sci->sc_state_lock)
+	__releases(&sci->sc_state_lock)
+{
+	sci->sc_state |= NILFS_SEGCTOR_QUIT;
+
+	while (sci->sc_task) {
+		wake_up(&sci->sc_wait_daemon);
+		spin_unlock(&sci->sc_state_lock);
+		wait_event(sci->sc_wait_task, sci->sc_task == NULL);
+		spin_lock(&sci->sc_state_lock);
+	}
+}
+
+/*
+ * Setup & clean-up functions
+ */
+static struct nilfs_sc_info *nilfs_segctor_new(struct super_block *sb,
+					       struct nilfs_root *root)
+{
+	struct the_nilfs *nilfs = sb->s_fs_info;
+	struct nilfs_sc_info *sci;
+
+	sci = kzalloc(sizeof(*sci), GFP_KERNEL);
+	if (!sci)
+		return NULL;
+
+	sci->sc_super = sb;
+
+	nilfs_get_root(root);
+	sci->sc_root = root;
+
+	init_waitqueue_head(&sci->sc_wait_request);
+	init_waitqueue_head(&sci->sc_wait_daemon);
+	init_waitqueue_head(&sci->sc_wait_task);
+	spin_lock_init(&sci->sc_state_lock);
+	INIT_LIST_HEAD(&sci->sc_dirty_files);
+	INIT_LIST_HEAD(&sci->sc_segbufs);
+	INIT_LIST_HEAD(&sci->sc_write_logs);
+	INIT_LIST_HEAD(&sci->sc_gc_inodes);
+	INIT_LIST_HEAD(&sci->sc_iput_queue);
+	INIT_WORK(&sci->sc_iput_work, nilfs_iput_work_func);
+	init_timer(&sci->sc_timer);
+
+	sci->sc_interval = HZ * NILFS_SC_DEFAULT_TIMEOUT;
+	sci->sc_mjcp_freq = HZ * NILFS_SC_DEFAULT_SR_FREQ;
+	sci->sc_watermark = NILFS_SC_DEFAULT_WATERMARK;
+
+	if (nilfs->ns_interval)
+		sci->sc_interval = HZ * nilfs->ns_interval;
+	if (nilfs->ns_watermark)
+		sci->sc_watermark = nilfs->ns_watermark;
+	return sci;
+}
+
+static void nilfs_segctor_write_out(struct nilfs_sc_info *sci)
+{
+	int ret, retrycount = NILFS_SC_CLEANUP_RETRY;
+
+	/* The segctord thread was stopped and its timer was removed.
+	   But some tasks remain. */
+	do {
+		struct nilfs_transaction_info ti;
+
+		nilfs_transaction_lock(sci->sc_super, &ti, 0);
+		ret = nilfs_segctor_construct(sci, SC_LSEG_SR);
+		nilfs_transaction_unlock(sci->sc_super);
+
+		flush_work(&sci->sc_iput_work);
+
+	} while (ret && retrycount-- > 0);
+}
+
+/**
+ * nilfs_segctor_destroy - destroy the segment constructor.
+ * @sci: nilfs_sc_info
+ *
+ * nilfs_segctor_destroy() kills the segctord thread and frees
+ * the nilfs_sc_info struct.
+ * Caller must hold the segment semaphore.
+ */
+static void nilfs_segctor_destroy(struct nilfs_sc_info *sci)
+{
+	struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
+	int flag;
+
+	up_write(&nilfs->ns_segctor_sem);
+
+	spin_lock(&sci->sc_state_lock);
+	nilfs_segctor_kill_thread(sci);
+	flag = ((sci->sc_state & NILFS_SEGCTOR_COMMIT) || sci->sc_flush_request
+		|| sci->sc_seq_request != sci->sc_seq_done);
+	spin_unlock(&sci->sc_state_lock);
+
+	if (flush_work(&sci->sc_iput_work))
+		flag = true;
+
+	if (flag || !nilfs_segctor_confirm(sci))
+		nilfs_segctor_write_out(sci);
+
+	if (!list_empty(&sci->sc_dirty_files)) {
+		nilfs_warning(sci->sc_super, __func__,
+			      "dirty file(s) after the final construction\n");
+		nilfs_dispose_list(nilfs, &sci->sc_dirty_files, 1);
+	}
+
+	if (!list_empty(&sci->sc_iput_queue)) {
+		nilfs_warning(sci->sc_super, __func__,
+			      "iput queue is not empty\n");
+		nilfs_dispose_list(nilfs, &sci->sc_iput_queue, 1);
+	}
+
+	WARN_ON(!list_empty(&sci->sc_segbufs));
+	WARN_ON(!list_empty(&sci->sc_write_logs));
+
+	nilfs_put_root(sci->sc_root);
+
+	down_write(&nilfs->ns_segctor_sem);
+
+	del_timer_sync(&sci->sc_timer);
+	kfree(sci);
+}
+
+/**
+ * nilfs_attach_log_writer - attach log writer
+ * @sb: super block instance
+ * @root: root object of the current filesystem tree
+ *
+ * This allocates a log writer object, initializes it, and starts the
+ * log writer.
+ *
+ * Return Value: On success, 0 is returned. On error, one of the following
+ * negative error code is returned.
+ *
+ * %-ENOMEM - Insufficient memory available.
+ */
+int nilfs_attach_log_writer(struct super_block *sb, struct nilfs_root *root)
+{
+	struct the_nilfs *nilfs = sb->s_fs_info;
+	int err;
+
+	if (nilfs->ns_writer) {
+		/*
+		 * This happens if the filesystem was remounted
+		 * read/write after nilfs_error degenerated it into a
+		 * read-only mount.
+		 */
+		nilfs_detach_log_writer(sb);
+	}
+
+	nilfs->ns_writer = nilfs_segctor_new(sb, root);
+	if (!nilfs->ns_writer)
+		return -ENOMEM;
+
+	err = nilfs_segctor_start_thread(nilfs->ns_writer);
+	if (err) {
+		kfree(nilfs->ns_writer);
+		nilfs->ns_writer = NULL;
+	}
+	return err;
+}
+
+/**
+ * nilfs_detach_log_writer - destroy log writer
+ * @sb: super block instance
+ *
+ * This kills log writer daemon, frees the log writer object, and
+ * destroys list of dirty files.
+ */
+void nilfs_detach_log_writer(struct super_block *sb)
+{
+	struct the_nilfs *nilfs = sb->s_fs_info;
+	LIST_HEAD(garbage_list);
+
+	down_write(&nilfs->ns_segctor_sem);
+	if (nilfs->ns_writer) {
+		nilfs_segctor_destroy(nilfs->ns_writer);
+		nilfs->ns_writer = NULL;
+	}
+
+	/* Force to free the list of dirty files */
+	spin_lock(&nilfs->ns_inode_lock);
+	if (!list_empty(&nilfs->ns_dirty_files)) {
+		list_splice_init(&nilfs->ns_dirty_files, &garbage_list);
+		nilfs_warning(sb, __func__,
+			      "Hit dirty file after stopped log writer\n");
+	}
+	spin_unlock(&nilfs->ns_inode_lock);
+	up_write(&nilfs->ns_segctor_sem);
+
+	nilfs_dispose_list(nilfs, &garbage_list, 1);
+}