void nilfs_sufile_do_cancel_free(struct inode *sufile, __u64 segnum,
				 struct buffer_head *header_bh,
				 struct buffer_head *su_bh)
{
	struct nilfs_segment_usage *su;
	void *kaddr;

	kaddr = kmap_atomic(su_bh->b_page, KM_USER0);
	su = nilfs_sufile_block_get_segment_usage(sufile, segnum, su_bh, kaddr);
	if (unlikely(!nilfs_segment_usage_clean(su))) {
		printk(KERN_WARNING "%s: segment %llu must be clean\n",
		       __func__, (unsigned long long)segnum);
		kunmap_atomic(kaddr, KM_USER0);
		return;
	}
	nilfs_segment_usage_set_dirty(su);
	kunmap_atomic(kaddr, KM_USER0);

	nilfs_sufile_mod_counter(header_bh, -1, 1);
	nilfs_mdt_mark_buffer_dirty(su_bh);
	nilfs_mdt_mark_dirty(sufile);
}
int nilfs_sufile_alloc(struct inode *sufile, __u64 *segnump)
{
	struct buffer_head *header_bh, *su_bh;
	struct nilfs_sufile_header *header;
	struct nilfs_segment_usage *su;
	struct nilfs_sufile_info *sui = NILFS_SUI(sufile);
	size_t susz = NILFS_MDT(sufile)->mi_entry_size;
	__u64 segnum, maxsegnum, last_alloc;
	void *kaddr;
	unsigned long nsegments, ncleansegs, nsus, cnt;
	int ret, j;

	down_write(&NILFS_MDT(sufile)->mi_sem);

	ret = nilfs_sufile_get_header_block(sufile, &header_bh);
	if (ret < 0)
		goto out_sem;
	kaddr = kmap_atomic(header_bh->b_page);
	header = kaddr + bh_offset(header_bh);
	ncleansegs = le64_to_cpu(header->sh_ncleansegs);
	last_alloc = le64_to_cpu(header->sh_last_alloc);
	kunmap_atomic(kaddr);

	nsegments = nilfs_sufile_get_nsegments(sufile);
	maxsegnum = sui->allocmax;
	segnum = last_alloc + 1;
	if (segnum < sui->allocmin || segnum > sui->allocmax)
		segnum = sui->allocmin;

	for (cnt = 0; cnt < nsegments; cnt += nsus) {
		if (segnum > maxsegnum) {
			if (cnt < sui->allocmax - sui->allocmin + 1) {
				segnum = sui->allocmin;
				maxsegnum = last_alloc;
			} else if (segnum > sui->allocmin &&
				   sui->allocmax + 1 < nsegments) {
				segnum = sui->allocmax + 1;
				maxsegnum = nsegments - 1;
			} else if (sui->allocmin > 0)  {
				segnum = 0;
				maxsegnum = sui->allocmin - 1;
			} else {
				break; 
			}
		}
		ret = nilfs_sufile_get_segment_usage_block(sufile, segnum, 1,
							   &su_bh);
		if (ret < 0)
			goto out_header;
		kaddr = kmap_atomic(su_bh->b_page);
		su = nilfs_sufile_block_get_segment_usage(
			sufile, segnum, su_bh, kaddr);

		nsus = nilfs_sufile_segment_usages_in_block(
			sufile, segnum, maxsegnum);
		for (j = 0; j < nsus; j++, su = (void *)su + susz, segnum++) {
			if (!nilfs_segment_usage_clean(su))
				continue;
			
			nilfs_segment_usage_set_dirty(su);
			kunmap_atomic(kaddr);

			kaddr = kmap_atomic(header_bh->b_page);
			header = kaddr + bh_offset(header_bh);
			le64_add_cpu(&header->sh_ncleansegs, -1);
			le64_add_cpu(&header->sh_ndirtysegs, 1);
			header->sh_last_alloc = cpu_to_le64(segnum);
			kunmap_atomic(kaddr);

			sui->ncleansegs--;
			mark_buffer_dirty(header_bh);
			mark_buffer_dirty(su_bh);
			nilfs_mdt_mark_dirty(sufile);
			brelse(su_bh);
			*segnump = segnum;
			goto out_header;
		}

		kunmap_atomic(kaddr);
		brelse(su_bh);
	}

	
	ret = -ENOSPC;

 out_header:
	brelse(header_bh);

 out_sem:
	up_write(&NILFS_MDT(sufile)->mi_sem);
	return ret;
}
/**
 * nilfs_sufile_alloc - allocate a segment
 * @sufile: inode of segment usage file
 * @segnump: pointer to segment number
 *
 * Description: nilfs_sufile_alloc() allocates a clean segment.
 *
 * Return Value: On success, 0 is returned and the segment number of the
 * allocated segment is stored in the place pointed by @segnump. On error, one
 * of the following negative error codes is returned.
 *
 * %-EIO - I/O error.
 *
 * %-ENOMEM - Insufficient amount of memory available.
 *
 * %-ENOSPC - No clean segment left.
 */
int nilfs_sufile_alloc(struct inode *sufile, __u64 *segnump)
{
	struct buffer_head *header_bh, *su_bh;
	struct nilfs_sufile_header *header;
	struct nilfs_segment_usage *su;
	size_t susz = NILFS_MDT(sufile)->mi_entry_size;
	__u64 segnum, maxsegnum, last_alloc;
	void *kaddr;
	unsigned long nsegments, ncleansegs, nsus;
	int ret, i, j;

	down_write(&NILFS_MDT(sufile)->mi_sem);

	ret = nilfs_sufile_get_header_block(sufile, &header_bh);
	if (ret < 0)
		goto out_sem;
	kaddr = kmap_atomic(header_bh->b_page, KM_USER0);
	header = nilfs_sufile_block_get_header(sufile, header_bh, kaddr);
	ncleansegs = le64_to_cpu(header->sh_ncleansegs);
	last_alloc = le64_to_cpu(header->sh_last_alloc);
	kunmap_atomic(kaddr, KM_USER0);

	nsegments = nilfs_sufile_get_nsegments(sufile);
	segnum = last_alloc + 1;
	maxsegnum = nsegments - 1;
	for (i = 0; i < nsegments; i += nsus) {
		if (segnum >= nsegments) {
			/* wrap around */
			segnum = 0;
			maxsegnum = last_alloc;
		}
		ret = nilfs_sufile_get_segment_usage_block(sufile, segnum, 1,
							   &su_bh);
		if (ret < 0)
			goto out_header;
		kaddr = kmap_atomic(su_bh->b_page, KM_USER0);
		su = nilfs_sufile_block_get_segment_usage(
			sufile, segnum, su_bh, kaddr);

		nsus = nilfs_sufile_segment_usages_in_block(
			sufile, segnum, maxsegnum);
		for (j = 0; j < nsus; j++, su = (void *)su + susz, segnum++) {
			if (!nilfs_segment_usage_clean(su))
				continue;
			/* found a clean segment */
			nilfs_segment_usage_set_dirty(su);
			kunmap_atomic(kaddr, KM_USER0);

			kaddr = kmap_atomic(header_bh->b_page, KM_USER0);
			header = nilfs_sufile_block_get_header(
				sufile, header_bh, kaddr);
			le64_add_cpu(&header->sh_ncleansegs, -1);
			le64_add_cpu(&header->sh_ndirtysegs, 1);
			header->sh_last_alloc = cpu_to_le64(segnum);
			kunmap_atomic(kaddr, KM_USER0);

			nilfs_mdt_mark_buffer_dirty(header_bh);
			nilfs_mdt_mark_buffer_dirty(su_bh);
			nilfs_mdt_mark_dirty(sufile);
			brelse(su_bh);
			*segnump = segnum;
			goto out_header;
		}

		kunmap_atomic(kaddr, KM_USER0);
		brelse(su_bh);
	}

	/* no segments left */
	ret = -ENOSPC;

 out_header:
	brelse(header_bh);

 out_sem:
	up_write(&NILFS_MDT(sufile)->mi_sem);
	return ret;
}