fs/nilfs2/segbuf.c - fp2-dev/kernel/msm - Gitiles

 /*
  * segbuf.c - NILFS segment buffer
  *
  * 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/buffer_head.h>
 #include <linux/writeback.h>
 #include <linux/crc32.h>
 #include <linux/backing-dev.h>
 #include "page.h"
 #include "segbuf.h"


 struct nilfs_write_info {
 	struct the_nilfs       *nilfs;
 	struct bio	       *bio;
 	int 			start, end; /* The region to be submitted */
 	int			rest_blocks;
 	int			max_pages;
 	int			nr_vecs;
 	sector_t		blocknr;
 };


 static struct kmem_cache *nilfs_segbuf_cachep;

 static void nilfs_segbuf_init_once(void *obj)
 {
 	memset(obj, 0, sizeof(struct nilfs_segment_buffer));
 }

 int __init nilfs_init_segbuf_cache(void)
 {
 	nilfs_segbuf_cachep =
 		kmem_cache_create("nilfs2_segbuf_cache",
 				  sizeof(struct nilfs_segment_buffer),
 				  0, SLAB_RECLAIM_ACCOUNT,
 				  nilfs_segbuf_init_once);

 	return (nilfs_segbuf_cachep == NULL) ? -ENOMEM : 0;
 }

 void nilfs_destroy_segbuf_cache(void)
 {
 	kmem_cache_destroy(nilfs_segbuf_cachep);
 }

 struct nilfs_segment_buffer *nilfs_segbuf_new(struct super_block *sb)
 {
 	struct nilfs_segment_buffer *segbuf;

 	segbuf = kmem_cache_alloc(nilfs_segbuf_cachep, GFP_NOFS);
 	if (unlikely(!segbuf))
 		return NULL;

 	segbuf->sb_super = sb;
 	INIT_LIST_HEAD(&segbuf->sb_list);
 	INIT_LIST_HEAD(&segbuf->sb_segsum_buffers);
 	INIT_LIST_HEAD(&segbuf->sb_payload_buffers);

 	init_completion(&segbuf->sb_bio_event);
 	atomic_set(&segbuf->sb_err, 0);
 	segbuf->sb_nbio = 0;

 	return segbuf;
 }

 void nilfs_segbuf_free(struct nilfs_segment_buffer *segbuf)
 {
 	kmem_cache_free(nilfs_segbuf_cachep, segbuf);
 }

 void nilfs_segbuf_map(struct nilfs_segment_buffer *segbuf, __u64 segnum,
 		     unsigned long offset, struct the_nilfs *nilfs)
 {
 	segbuf->sb_segnum = segnum;
 	nilfs_get_segment_range(nilfs, segnum, &segbuf->sb_fseg_start,
 				&segbuf->sb_fseg_end);

 	segbuf->sb_pseg_start = segbuf->sb_fseg_start + offset;
 	segbuf->sb_rest_blocks =
 		segbuf->sb_fseg_end - segbuf->sb_pseg_start + 1;
 }

 void nilfs_segbuf_set_next_segnum(struct nilfs_segment_buffer *segbuf,
 				  __u64 nextnum, struct the_nilfs *nilfs)
 {
 	segbuf->sb_nextnum = nextnum;
 	segbuf->sb_sum.next = nilfs_get_segment_start_blocknr(nilfs, nextnum);
 }

 int nilfs_segbuf_extend_segsum(struct nilfs_segment_buffer *segbuf)
 {
 	struct buffer_head *bh;

 	bh = sb_getblk(segbuf->sb_super,
 		       segbuf->sb_pseg_start + segbuf->sb_sum.nsumblk);
 	if (unlikely(!bh))
 		return -ENOMEM;

 	nilfs_segbuf_add_segsum_buffer(segbuf, bh);
 	return 0;
 }

 int nilfs_segbuf_extend_payload(struct nilfs_segment_buffer *segbuf,
 				struct buffer_head **bhp)
 {
 	struct buffer_head *bh;

 	bh = sb_getblk(segbuf->sb_super,
 		       segbuf->sb_pseg_start + segbuf->sb_sum.nblocks);
 	if (unlikely(!bh))
 		return -ENOMEM;

 	nilfs_segbuf_add_payload_buffer(segbuf, bh);
 	*bhp = bh;
 	return 0;
 }

 int nilfs_segbuf_reset(struct nilfs_segment_buffer *segbuf, unsigned flags,
 		       time_t ctime)
 {
 	int err;

 	segbuf->sb_sum.nblocks = segbuf->sb_sum.nsumblk = 0;
 	err = nilfs_segbuf_extend_segsum(segbuf);
 	if (unlikely(err))
 		return err;

 	segbuf->sb_sum.flags = flags;
 	segbuf->sb_sum.sumbytes = sizeof(struct nilfs_segment_summary);
 	segbuf->sb_sum.nfinfo = segbuf->sb_sum.nfileblk = 0;
 	segbuf->sb_sum.ctime = ctime;
 	return 0;
 }

 /*
  * Setup segument summary
  */
 void nilfs_segbuf_fill_in_segsum(struct nilfs_segment_buffer *segbuf)
 {
 	struct nilfs_segment_summary *raw_sum;
 	struct buffer_head *bh_sum;

 	bh_sum = list_entry(segbuf->sb_segsum_buffers.next,
 			    struct buffer_head, b_assoc_buffers);
 	raw_sum = (struct nilfs_segment_summary *)bh_sum->b_data;

 	raw_sum->ss_magic    = cpu_to_le32(NILFS_SEGSUM_MAGIC);
 	raw_sum->ss_bytes    = cpu_to_le16(sizeof(*raw_sum));
 	raw_sum->ss_flags    = cpu_to_le16(segbuf->sb_sum.flags);
 	raw_sum->ss_seq      = cpu_to_le64(segbuf->sb_sum.seg_seq);
 	raw_sum->ss_create   = cpu_to_le64(segbuf->sb_sum.ctime);
 	raw_sum->ss_next     = cpu_to_le64(segbuf->sb_sum.next);
 	raw_sum->ss_nblocks  = cpu_to_le32(segbuf->sb_sum.nblocks);
 	raw_sum->ss_nfinfo   = cpu_to_le32(segbuf->sb_sum.nfinfo);
 	raw_sum->ss_sumbytes = cpu_to_le32(segbuf->sb_sum.sumbytes);
 	raw_sum->ss_pad      = 0;
 }

 /*
  * CRC calculation routines
  */
 void nilfs_segbuf_fill_in_segsum_crc(struct nilfs_segment_buffer *segbuf,
 				     u32 seed)
 {
 	struct buffer_head *bh;
 	struct nilfs_segment_summary *raw_sum;
 	unsigned long size, bytes = segbuf->sb_sum.sumbytes;
 	u32 crc;

 	bh = list_entry(segbuf->sb_segsum_buffers.next, struct buffer_head,
 			b_assoc_buffers);

 	raw_sum = (struct nilfs_segment_summary *)bh->b_data;
 	size = min_t(unsigned long, bytes, bh->b_size);
 	crc = crc32_le(seed,
 		       (unsigned char *)raw_sum +
 		       sizeof(raw_sum->ss_datasum) + sizeof(raw_sum->ss_sumsum),
 		       size - (sizeof(raw_sum->ss_datasum) +
 			       sizeof(raw_sum->ss_sumsum)));

 	list_for_each_entry_continue(bh, &segbuf->sb_segsum_buffers,
 				     b_assoc_buffers) {
 		bytes -= size;
 		size = min_t(unsigned long, bytes, bh->b_size);
 		crc = crc32_le(crc, bh->b_data, size);
 	}
 	raw_sum->ss_sumsum = cpu_to_le32(crc);
 }

 void nilfs_segbuf_fill_in_data_crc(struct nilfs_segment_buffer *segbuf,
 				   u32 seed)
 {
 	struct buffer_head *bh;
 	struct nilfs_segment_summary *raw_sum;
 	void *kaddr;
 	u32 crc;

 	bh = list_entry(segbuf->sb_segsum_buffers.next, struct buffer_head,
 			b_assoc_buffers);
 	raw_sum = (struct nilfs_segment_summary *)bh->b_data;
 	crc = crc32_le(seed,
 		       (unsigned char *)raw_sum + sizeof(raw_sum->ss_datasum),
 		       bh->b_size - sizeof(raw_sum->ss_datasum));

 	list_for_each_entry_continue(bh, &segbuf->sb_segsum_buffers,
 				     b_assoc_buffers) {
 		crc = crc32_le(crc, bh->b_data, bh->b_size);
 	}
 	list_for_each_entry(bh, &segbuf->sb_payload_buffers, b_assoc_buffers) {
 		kaddr = kmap_atomic(bh->b_page, KM_USER0);
 		crc = crc32_le(crc, kaddr + bh_offset(bh), bh->b_size);
 		kunmap_atomic(kaddr, KM_USER0);
 	}
 	raw_sum->ss_datasum = cpu_to_le32(crc);
 }

 void nilfs_release_buffers(struct list_head *list)
 {
 	struct buffer_head *bh, *n;

 	list_for_each_entry_safe(bh, n, list, b_assoc_buffers) {
 		list_del_init(&bh->b_assoc_buffers);
 		if (buffer_nilfs_allocated(bh)) {
 			struct page *clone_page = bh->b_page;

 			/* remove clone page */
 			brelse(bh);
 			page_cache_release(clone_page); /* for each bh */
 			if (page_count(clone_page) <= 2) {
 				lock_page(clone_page);
 				nilfs_free_private_page(clone_page);
 			}
 			continue;
 		}
 		brelse(bh);
 	}
 }

 /*
  * BIO operations
  */
 static void nilfs_end_bio_write(struct bio *bio, int err)
 {
 	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
 	struct nilfs_segment_buffer *segbuf = bio->bi_private;

 	if (err == -EOPNOTSUPP) {
 		set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
 		bio_put(bio);
 		/* to be detected by submit_seg_bio() */
 	}

 	if (!uptodate)
 		atomic_inc(&segbuf->sb_err);

 	bio_put(bio);
 	complete(&segbuf->sb_bio_event);
 }

 static int nilfs_segbuf_submit_bio(struct nilfs_segment_buffer *segbuf,
 				   struct nilfs_write_info *wi, int mode)
 {
 	struct bio *bio = wi->bio;
 	int err;

 	if (segbuf->sb_nbio > 0 && bdi_write_congested(wi->nilfs->ns_bdi)) {
 		wait_for_completion(&segbuf->sb_bio_event);
 		segbuf->sb_nbio--;
 		if (unlikely(atomic_read(&segbuf->sb_err))) {
 			bio_put(bio);
 			err = -EIO;
 			goto failed;
 		}
 	}

 	bio->bi_end_io = nilfs_end_bio_write;
 	bio->bi_private = segbuf;
 	bio_get(bio);
 	submit_bio(mode, bio);
 	if (bio_flagged(bio, BIO_EOPNOTSUPP)) {
 		bio_put(bio);
 		err = -EOPNOTSUPP;
 		goto failed;
 	}
 	segbuf->sb_nbio++;
 	bio_put(bio);

 	wi->bio = NULL;
 	wi->rest_blocks -= wi->end - wi->start;
 	wi->nr_vecs = min(wi->max_pages, wi->rest_blocks);
 	wi->start = wi->end;
 	return 0;

  failed:
 	wi->bio = NULL;
 	return err;
 }

 /**
  * nilfs_alloc_seg_bio - allocate a new bio for writing log
  * @nilfs: nilfs object
  * @start: start block number of the bio
  * @nr_vecs: request size of page vector.
  *
  * Return Value: On success, pointer to the struct bio is returned.
  * On error, NULL is returned.
  */
 static struct bio *nilfs_alloc_seg_bio(struct the_nilfs *nilfs, sector_t start,
 				       int nr_vecs)
 {
 	struct bio *bio;

 	bio = bio_alloc(GFP_NOIO, nr_vecs);
 	if (bio == NULL) {
 		while (!bio && (nr_vecs >>= 1))
 			bio = bio_alloc(GFP_NOIO, nr_vecs);
 	}
 	if (likely(bio)) {
 		bio->bi_bdev = nilfs->ns_bdev;
 		bio->bi_sector = start << (nilfs->ns_blocksize_bits - 9);
 	}
 	return bio;
 }

 static void nilfs_segbuf_prepare_write(struct nilfs_segment_buffer *segbuf,
 				       struct nilfs_write_info *wi)
 {
 	wi->bio = NULL;
 	wi->rest_blocks = segbuf->sb_sum.nblocks;
 	wi->max_pages = bio_get_nr_vecs(wi->nilfs->ns_bdev);
 	wi->nr_vecs = min(wi->max_pages, wi->rest_blocks);
 	wi->start = wi->end = 0;
 	wi->blocknr = segbuf->sb_pseg_start;
 }

 static int nilfs_segbuf_submit_bh(struct nilfs_segment_buffer *segbuf,
 				  struct nilfs_write_info *wi,
 				  struct buffer_head *bh, int mode)
 {
 	int len, err;

 	BUG_ON(wi->nr_vecs <= 0);
  repeat:
 	if (!wi->bio) {
 		wi->bio = nilfs_alloc_seg_bio(wi->nilfs, wi->blocknr + wi->end,
 					      wi->nr_vecs);
 		if (unlikely(!wi->bio))
 			return -ENOMEM;
 	}

 	len = bio_add_page(wi->bio, bh->b_page, bh->b_size, bh_offset(bh));
 	if (len == bh->b_size) {
 		wi->end++;
 		return 0;
 	}
 	/* bio is FULL */
 	err = nilfs_segbuf_submit_bio(segbuf, wi, mode);
 	/* never submit current bh */
 	if (likely(!err))
 		goto repeat;
 	return err;
 }

 /**
  * nilfs_segbuf_write - submit write requests of a log
  * @segbuf: buffer storing a log to be written
  * @nilfs: nilfs object
  *
  * Return Value: On Success, 0 is returned. On Error, one of the following
  * negative error code is returned.
  *
  * %-EIO - I/O error
  *
  * %-ENOMEM - Insufficient memory available.
  */
 int nilfs_segbuf_write(struct nilfs_segment_buffer *segbuf,
 		       struct the_nilfs *nilfs)
 {
 	struct nilfs_write_info wi;
 	struct buffer_head *bh;
 	int res = 0, rw = WRITE;

 	wi.nilfs = nilfs;
 	nilfs_segbuf_prepare_write(segbuf, &wi);

 	list_for_each_entry(bh, &segbuf->sb_segsum_buffers, b_assoc_buffers) {
 		res = nilfs_segbuf_submit_bh(segbuf, &wi, bh, rw);
 		if (unlikely(res))
 			goto failed_bio;
 	}

 	list_for_each_entry(bh, &segbuf->sb_payload_buffers, b_assoc_buffers) {
 		res = nilfs_segbuf_submit_bh(segbuf, &wi, bh, rw);
 		if (unlikely(res))
 			goto failed_bio;
 	}

 	if (wi.bio) {
 		/*
 		 * Last BIO is always sent through the following
 		 * submission.
 		 */
 		rw |= (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG);
 		res = nilfs_segbuf_submit_bio(segbuf, &wi, rw);
 	}

  failed_bio:
 	return res;
 }

 /**
  * nilfs_segbuf_wait - wait for completion of requested BIOs
  * @segbuf: segment buffer
  *
  * Return Value: On Success, 0 is returned. On Error, one of the following
  * negative error code is returned.
  *
  * %-EIO - I/O error
  */
 int nilfs_segbuf_wait(struct nilfs_segment_buffer *segbuf)
 {
 	int err = 0;

 	if (!segbuf->sb_nbio)
 		return 0;

 	do {
 		wait_for_completion(&segbuf->sb_bio_event);
 	} while (--segbuf->sb_nbio > 0);

 	if (unlikely(atomic_read(&segbuf->sb_err) > 0)) {
 		printk(KERN_ERR "NILFS: IO error writing segment\n");
 		err = -EIO;
 	}
 	return err;
 }
	/*
	* segbuf.c - NILFS segment buffer
	*
	* 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/buffer_head.h>
	#include <linux/writeback.h>
	#include <linux/crc32.h>
	#include <linux/backing-dev.h>
	#include "page.h"
	#include "segbuf.h"


	struct nilfs_write_info {
	struct the_nilfs *nilfs;
	struct bio *bio;
	int start, end; /* The region to be submitted */
	int rest_blocks;
	int max_pages;
	int nr_vecs;
	sector_t blocknr;
	};


	static struct kmem_cache *nilfs_segbuf_cachep;

	static void nilfs_segbuf_init_once(void *obj)
	{
	memset(obj, 0, sizeof(struct nilfs_segment_buffer));
	}

	int __init nilfs_init_segbuf_cache(void)
	{
	nilfs_segbuf_cachep =
	kmem_cache_create("nilfs2_segbuf_cache",
	sizeof(struct nilfs_segment_buffer),
	0, SLAB_RECLAIM_ACCOUNT,
	nilfs_segbuf_init_once);

	return (nilfs_segbuf_cachep == NULL) ? -ENOMEM : 0;
	}

	void nilfs_destroy_segbuf_cache(void)
	{
	kmem_cache_destroy(nilfs_segbuf_cachep);
	}

	struct nilfs_segment_buffer nilfs_segbuf_new(struct super_block sb)
	{
	struct nilfs_segment_buffer *segbuf;

	segbuf = kmem_cache_alloc(nilfs_segbuf_cachep, GFP_NOFS);
	if (unlikely(!segbuf))
	return NULL;

	segbuf->sb_super = sb;
	INIT_LIST_HEAD(&segbuf->sb_list);
	INIT_LIST_HEAD(&segbuf->sb_segsum_buffers);
	INIT_LIST_HEAD(&segbuf->sb_payload_buffers);

	init_completion(&segbuf->sb_bio_event);
	atomic_set(&segbuf->sb_err, 0);
	segbuf->sb_nbio = 0;

	return segbuf;
	}

	void nilfs_segbuf_free(struct nilfs_segment_buffer *segbuf)
	{
	kmem_cache_free(nilfs_segbuf_cachep, segbuf);
	}

	void nilfs_segbuf_map(struct nilfs_segment_buffer *segbuf, __u64 segnum,
	unsigned long offset, struct the_nilfs *nilfs)
	{
	segbuf->sb_segnum = segnum;
	nilfs_get_segment_range(nilfs, segnum, &segbuf->sb_fseg_start,
	&segbuf->sb_fseg_end);

	segbuf->sb_pseg_start = segbuf->sb_fseg_start + offset;
	segbuf->sb_rest_blocks =
	segbuf->sb_fseg_end - segbuf->sb_pseg_start + 1;
	}

	void nilfs_segbuf_set_next_segnum(struct nilfs_segment_buffer *segbuf,
	__u64 nextnum, struct the_nilfs *nilfs)
	{
	segbuf->sb_nextnum = nextnum;
	segbuf->sb_sum.next = nilfs_get_segment_start_blocknr(nilfs, nextnum);
	}

	int nilfs_segbuf_extend_segsum(struct nilfs_segment_buffer *segbuf)
	{
	struct buffer_head *bh;

	bh = sb_getblk(segbuf->sb_super,
	segbuf->sb_pseg_start + segbuf->sb_sum.nsumblk);
	if (unlikely(!bh))
	return -ENOMEM;

	nilfs_segbuf_add_segsum_buffer(segbuf, bh);
	return 0;
	}

	int nilfs_segbuf_extend_payload(struct nilfs_segment_buffer *segbuf,
	struct buffer_head **bhp)
	{
	struct buffer_head *bh;

	bh = sb_getblk(segbuf->sb_super,
	segbuf->sb_pseg_start + segbuf->sb_sum.nblocks);
	if (unlikely(!bh))
	return -ENOMEM;

	nilfs_segbuf_add_payload_buffer(segbuf, bh);
	*bhp = bh;
	return 0;
	}

	int nilfs_segbuf_reset(struct nilfs_segment_buffer *segbuf, unsigned flags,
	time_t ctime)
	{
	int err;

	segbuf->sb_sum.nblocks = segbuf->sb_sum.nsumblk = 0;
	err = nilfs_segbuf_extend_segsum(segbuf);
	if (unlikely(err))
	return err;

	segbuf->sb_sum.flags = flags;
	segbuf->sb_sum.sumbytes = sizeof(struct nilfs_segment_summary);
	segbuf->sb_sum.nfinfo = segbuf->sb_sum.nfileblk = 0;
	segbuf->sb_sum.ctime = ctime;
	return 0;
	}

	/*
	* Setup segument summary
	*/
	void nilfs_segbuf_fill_in_segsum(struct nilfs_segment_buffer *segbuf)
	{
	struct nilfs_segment_summary *raw_sum;
	struct buffer_head *bh_sum;

	bh_sum = list_entry(segbuf->sb_segsum_buffers.next,
	struct buffer_head, b_assoc_buffers);
	raw_sum = (struct nilfs_segment_summary *)bh_sum->b_data;

	raw_sum->ss_magic = cpu_to_le32(NILFS_SEGSUM_MAGIC);
	raw_sum->ss_bytes = cpu_to_le16(sizeof(*raw_sum));
	raw_sum->ss_flags = cpu_to_le16(segbuf->sb_sum.flags);
	raw_sum->ss_seq = cpu_to_le64(segbuf->sb_sum.seg_seq);
	raw_sum->ss_create = cpu_to_le64(segbuf->sb_sum.ctime);
	raw_sum->ss_next = cpu_to_le64(segbuf->sb_sum.next);
	raw_sum->ss_nblocks = cpu_to_le32(segbuf->sb_sum.nblocks);
	raw_sum->ss_nfinfo = cpu_to_le32(segbuf->sb_sum.nfinfo);
	raw_sum->ss_sumbytes = cpu_to_le32(segbuf->sb_sum.sumbytes);
	raw_sum->ss_pad = 0;
	}

	/*
	* CRC calculation routines
	*/
	void nilfs_segbuf_fill_in_segsum_crc(struct nilfs_segment_buffer *segbuf,
	u32 seed)
	{
	struct buffer_head *bh;
	struct nilfs_segment_summary *raw_sum;
	unsigned long size, bytes = segbuf->sb_sum.sumbytes;
	u32 crc;

	bh = list_entry(segbuf->sb_segsum_buffers.next, struct buffer_head,
	b_assoc_buffers);

	raw_sum = (struct nilfs_segment_summary *)bh->b_data;
	size = min_t(unsigned long, bytes, bh->b_size);
	crc = crc32_le(seed,
	(unsigned char *)raw_sum +
	sizeof(raw_sum->ss_datasum) + sizeof(raw_sum->ss_sumsum),
	size - (sizeof(raw_sum->ss_datasum) +
	sizeof(raw_sum->ss_sumsum)));

	list_for_each_entry_continue(bh, &segbuf->sb_segsum_buffers,
	b_assoc_buffers) {
	bytes -= size;
	size = min_t(unsigned long, bytes, bh->b_size);
	crc = crc32_le(crc, bh->b_data, size);
	}
	raw_sum->ss_sumsum = cpu_to_le32(crc);
	}

	void nilfs_segbuf_fill_in_data_crc(struct nilfs_segment_buffer *segbuf,
	u32 seed)
	{
	struct buffer_head *bh;
	struct nilfs_segment_summary *raw_sum;
	void *kaddr;
	u32 crc;

	bh = list_entry(segbuf->sb_segsum_buffers.next, struct buffer_head,
	b_assoc_buffers);
	raw_sum = (struct nilfs_segment_summary *)bh->b_data;
	crc = crc32_le(seed,
	(unsigned char *)raw_sum + sizeof(raw_sum->ss_datasum),
	bh->b_size - sizeof(raw_sum->ss_datasum));

	list_for_each_entry_continue(bh, &segbuf->sb_segsum_buffers,
	b_assoc_buffers) {
	crc = crc32_le(crc, bh->b_data, bh->b_size);
	}
	list_for_each_entry(bh, &segbuf->sb_payload_buffers, b_assoc_buffers) {
	kaddr = kmap_atomic(bh->b_page, KM_USER0);
	crc = crc32_le(crc, kaddr + bh_offset(bh), bh->b_size);
	kunmap_atomic(kaddr, KM_USER0);
	}
	raw_sum->ss_datasum = cpu_to_le32(crc);
	}

	void nilfs_release_buffers(struct list_head *list)
	{
	struct buffer_head bh, n;

	list_for_each_entry_safe(bh, n, list, b_assoc_buffers) {
	list_del_init(&bh->b_assoc_buffers);
	if (buffer_nilfs_allocated(bh)) {
	struct page *clone_page = bh->b_page;

	/* remove clone page */
	brelse(bh);
	page_cache_release(clone_page); /* for each bh */
	if (page_count(clone_page) <= 2) {
	lock_page(clone_page);
	nilfs_free_private_page(clone_page);
	}
	continue;
	}
	brelse(bh);
	}
	}

	/*
	* BIO operations
	*/
	static void nilfs_end_bio_write(struct bio *bio, int err)
	{
	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
	struct nilfs_segment_buffer *segbuf = bio->bi_private;

	if (err == -EOPNOTSUPP) {
	set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
	bio_put(bio);
	/* to be detected by submit_seg_bio() */
	}

	if (!uptodate)
	atomic_inc(&segbuf->sb_err);

	bio_put(bio);
	complete(&segbuf->sb_bio_event);
	}

	static int nilfs_segbuf_submit_bio(struct nilfs_segment_buffer *segbuf,
	struct nilfs_write_info *wi, int mode)
	{
	struct bio *bio = wi->bio;
	int err;

	if (segbuf->sb_nbio > 0 && bdi_write_congested(wi->nilfs->ns_bdi)) {
	wait_for_completion(&segbuf->sb_bio_event);
	segbuf->sb_nbio--;
	if (unlikely(atomic_read(&segbuf->sb_err))) {
	bio_put(bio);
	err = -EIO;
	goto failed;
	}
	}

	bio->bi_end_io = nilfs_end_bio_write;
	bio->bi_private = segbuf;
	bio_get(bio);
	submit_bio(mode, bio);
	if (bio_flagged(bio, BIO_EOPNOTSUPP)) {
	bio_put(bio);
	err = -EOPNOTSUPP;
	goto failed;
	}
	segbuf->sb_nbio++;
	bio_put(bio);

	wi->bio = NULL;
	wi->rest_blocks -= wi->end - wi->start;
	wi->nr_vecs = min(wi->max_pages, wi->rest_blocks);
	wi->start = wi->end;
	return 0;

	failed:
	wi->bio = NULL;
	return err;
	}

	/**
	* nilfs_alloc_seg_bio - allocate a new bio for writing log
	* @nilfs: nilfs object
	* @start: start block number of the bio
	* @nr_vecs: request size of page vector.
	*
	* Return Value: On success, pointer to the struct bio is returned.
	* On error, NULL is returned.
	*/
	static struct bio nilfs_alloc_seg_bio(struct the_nilfs nilfs, sector_t start,
	int nr_vecs)
	{
	struct bio *bio;

	bio = bio_alloc(GFP_NOIO, nr_vecs);
	if (bio == NULL) {
	while (!bio && (nr_vecs >>= 1))
	bio = bio_alloc(GFP_NOIO, nr_vecs);
	}
	if (likely(bio)) {
	bio->bi_bdev = nilfs->ns_bdev;
	bio->bi_sector = start << (nilfs->ns_blocksize_bits - 9);
	}
	return bio;
	}

	static void nilfs_segbuf_prepare_write(struct nilfs_segment_buffer *segbuf,
	struct nilfs_write_info *wi)
	{
	wi->bio = NULL;
	wi->rest_blocks = segbuf->sb_sum.nblocks;
	wi->max_pages = bio_get_nr_vecs(wi->nilfs->ns_bdev);
	wi->nr_vecs = min(wi->max_pages, wi->rest_blocks);
	wi->start = wi->end = 0;
	wi->blocknr = segbuf->sb_pseg_start;
	}

	static int nilfs_segbuf_submit_bh(struct nilfs_segment_buffer *segbuf,
	struct nilfs_write_info *wi,
	struct buffer_head *bh, int mode)
	{
	int len, err;

	BUG_ON(wi->nr_vecs <= 0);
	repeat:
	if (!wi->bio) {
	wi->bio = nilfs_alloc_seg_bio(wi->nilfs, wi->blocknr + wi->end,
	wi->nr_vecs);
	if (unlikely(!wi->bio))
	return -ENOMEM;
	}

	len = bio_add_page(wi->bio, bh->b_page, bh->b_size, bh_offset(bh));
	if (len == bh->b_size) {
	wi->end++;
	return 0;
	}
	/* bio is FULL */
	err = nilfs_segbuf_submit_bio(segbuf, wi, mode);
	/* never submit current bh */
	if (likely(!err))
	goto repeat;
	return err;
	}

	/**
	* nilfs_segbuf_write - submit write requests of a log
	* @segbuf: buffer storing a log to be written
	* @nilfs: nilfs object
	*
	* Return Value: On Success, 0 is returned. On Error, one of the following
	* negative error code is returned.
	*
	* %-EIO - I/O error
	*
	* %-ENOMEM - Insufficient memory available.
	*/
	int nilfs_segbuf_write(struct nilfs_segment_buffer *segbuf,
	struct the_nilfs *nilfs)
	{
	struct nilfs_write_info wi;
	struct buffer_head *bh;
	int res = 0, rw = WRITE;

	wi.nilfs = nilfs;
	nilfs_segbuf_prepare_write(segbuf, &wi);

	list_for_each_entry(bh, &segbuf->sb_segsum_buffers, b_assoc_buffers) {
	res = nilfs_segbuf_submit_bh(segbuf, &wi, bh, rw);
	if (unlikely(res))
	goto failed_bio;
	}

	list_for_each_entry(bh, &segbuf->sb_payload_buffers, b_assoc_buffers) {
	res = nilfs_segbuf_submit_bh(segbuf, &wi, bh, rw);
	if (unlikely(res))
	goto failed_bio;
	}

	if (wi.bio) {
	/*
	* Last BIO is always sent through the following
	* submission.
	*/
	rw \|= (1 << BIO_RW_SYNCIO) \| (1 << BIO_RW_UNPLUG);
	res = nilfs_segbuf_submit_bio(segbuf, &wi, rw);
	}

	failed_bio:
	return res;
	}

	/**
	* nilfs_segbuf_wait - wait for completion of requested BIOs
	* @segbuf: segment buffer
	*
	* Return Value: On Success, 0 is returned. On Error, one of the following
	* negative error code is returned.
	*
	* %-EIO - I/O error
	*/
	int nilfs_segbuf_wait(struct nilfs_segment_buffer *segbuf)
	{
	int err = 0;

	if (!segbuf->sb_nbio)
	return 0;

	do {
	wait_for_completion(&segbuf->sb_bio_event);
	} while (--segbuf->sb_nbio > 0);

	if (unlikely(atomic_read(&segbuf->sb_err) > 0)) {
	printk(KERN_ERR "NILFS: IO error writing segment\n");
	err = -EIO;
	}
	return err;
	}