text: /*
   * fs/logfs/segment.c	- Handling the Object Store
   *
   * As should be obvious for Linux kernel code, license is GPLv2
   *
   * Copyright (c) 2005-2008 Joern Engel <joern@logfs.org>
   *
   * Object store or ostore makes up the complete device with exception of
   * the superblock and journal areas.  Apart from its own metadata it stores
   * three kinds of objects: inodes, dentries and blocks, both data and indirect.
   */
  #include "logfs.h"
  #include <linux/slab.h>
  
  static int logfs_mark_segment_bad(struct super_block *sb, u32 segno)
  {
  	struct logfs_super *super = logfs_super(sb);
  	struct btree_head32 *head = &super->s_reserved_segments;
  	int err;
  
  	err = btree_insert32(head, segno, (void *)1, GFP_NOFS);
  	if (err)
  		return err;
  	logfs_super(sb)->s_bad_segments++;
  	/* FIXME: write to journal */
  	return 0;
  }
  
  int logfs_erase_segment(struct super_block *sb, u32 segno, int ensure_erase)
  {
  	struct logfs_super *super = logfs_super(sb);
  
  	super->s_gec++;
  
  	return super->s_devops->erase(sb, (u64)segno << super->s_segshift,
  			super->s_segsize, ensure_erase);
  }
  
  static s64 logfs_get_free_bytes(struct logfs_area *area, size_t bytes)
  {
  	s32 ofs;
  
  	logfs_open_area(area, bytes);
  
  	ofs = area->a_used_bytes;
  	area->a_used_bytes += bytes;
  	BUG_ON(area->a_used_bytes >= logfs_super(area->a_sb)->s_segsize);
  
  	return dev_ofs(area->a_sb, area->a_segno, ofs);
  }
  
  static struct page *get_mapping_page(struct super_block *sb, pgoff_t index,
  		int use_filler)
  {
  	struct logfs_super *super = logfs_super(sb);
  	struct address_space *mapping = super->s_mapping_inode->i_mapping;
  	filler_t *filler = super->s_devops->readpage;
  	struct page *page;
  
  	BUG_ON(mapping_gfp_mask(mapping) & __GFP_FS);
  	if (use_filler)
  		page = read_cache_page(mapping, index, filler, sb);
  	else {
  		page = find_or_create_page(mapping, index, GFP_NOFS);
  		unlock_page(page);
  	}
  	return page;
  }
  
  int __logfs_buf_write(struct logfs_area *area, u64 ofs, void *buf, size_t len,
  		int use_filler)
  {
  	pgoff_t index = ofs >> PAGE_SHIFT;
  	struct page *page;
  	long offset = ofs & (PAGE_SIZE-1);
  	long copylen;
  
  	/* Only logfs_wbuf_recover may use len==0 */
  	BUG_ON(!len && !use_filler);
  	do {
  		copylen = min((ulong)len, PAGE_SIZE - offset);
  
  		page = get_mapping_page(area->a_sb, index, use_filler);
  		if (IS_ERR(page))
  			return PTR_ERR(page);
  		BUG_ON(!page); /* FIXME: reserve a pool */
  		SetPageUptodate(page);
  		memcpy(page_address(page) + offset, buf, copylen);
  
  		if (!PagePrivate(page)) {
  			SetPagePrivate(page);
  			page_cache_get(page);
  		}
  		page_cache_release(page);
  
  		buf += copylen;
  		len -= copylen;
  		offset = 0;
  		index++;
  	} while (len);
  	return 0;
  }
  
  static void pad_partial_page(struct logfs_area *area)
  {
  	struct super_block *sb = area->a_sb;
  	struct page *page;
  	u64 ofs = dev_ofs(sb, area->a_segno, area->a_used_bytes);
  	pgoff_t index = ofs >> PAGE_SHIFT;
  	long offset = ofs & (PAGE_SIZE-1);
  	u32 len = PAGE_SIZE - offset;
  
  	if (len % PAGE_SIZE) {
  		page = get_mapping_page(sb, index, 0);
  		BUG_ON(!page); /* FIXME: reserve a pool */
  		memset(page_address(page) + offset, 0xff, len);
  		if (!PagePrivate(page)) {
  			SetPagePrivate(page);
  			page_cache_get(page);
  		}
  		page_cache_release(page);
  	}
  }
  
  static void pad_full_pages(struct logfs_area *area)
  {
  	struct super_block *sb = area->a_sb;
  	struct logfs_super *super = logfs_super(sb);
  	u64 ofs = dev_ofs(sb, area->a_segno, area->a_used_bytes);
  	u32 len = super->s_segsize - area->a_used_bytes;
  	pgoff_t index = PAGE_CACHE_ALIGN(ofs) >> PAGE_CACHE_SHIFT;
  	pgoff_t no_indizes = len >> PAGE_CACHE_SHIFT;
  	struct page *page;
  
  	while (no_indizes) {
  		page = get_mapping_page(sb, index, 0);
  		BUG_ON(!page); /* FIXME: reserve a pool */
  		SetPageUptodate(page);
  		memset(page_address(page), 0xff, PAGE_CACHE_SIZE);
  		if (!PagePrivate(page)) {
  			SetPagePrivate(page);
  			page_cache_get(page);
  		}
  		page_cache_release(page);
  		index++;
  		no_indizes--;
  	}
  }
  
  /*
   * bdev_writeseg will write full pages.  Memset the tail to prevent data leaks.
   * Also make sure we allocate (and memset) all pages for final writeout.
   */
  static void pad_wbuf(struct logfs_area *area, int final)
  {
  	pad_partial_page(area);
  	if (final)
  		pad_full_pages(area);
  }
  
  /*
   * We have to be careful with the alias tree.  Since lookup is done by bix,
   * it needs to be normalized, so 14, 15, 16, etc. all match when dealing with
   * indirect blocks.  So always use it through accessor functions.
   */
  static void *alias_tree_lookup(struct super_block *sb, u64 ino, u64 bix,
  		level_t level)
  {
  	struct btree_head128 *head = &logfs_super(sb)->s_object_alias_tree;
  	pgoff_t index = logfs_pack_index(bix, level);
  
  	return btree_lookup128(head, ino, index);
  }
  
  static int alias_tree_insert(struct super_block *sb, u64 ino, u64 bix,
  		level_t level, void *val)
  {
  	struct btree_head128 *head = &logfs_super(sb)->s_object_alias_tree;
  	pgoff_t index = logfs_pack_index(bix, level);
  
  	return btree_insert128(head, ino, index, val, GFP_NOFS);
  }
  
  static int btree_write_alias(struct super_block *sb, struct logfs_block *block,
  		write_alias_t *write_one_alias)
  {
  	struct object_alias_item *item;
  	int err;
  
  	list_for_each_entry(item, &block->item_list, list) {
  		err = write_alias_journal(sb, block->ino, block->bix,
  				block->level, item->child_no, item->val);
  		if (err)
  			return err;
  	}
  	return 0;
  }
  
  static struct logfs_block_ops btree_block_ops = {
  	.write_block	= btree_write_block,
  	.free_block	= __free_block,
  	.write_alias	= btree_write_alias,
  };
  
  int logfs_load_object_aliases(struct super_block *sb,
  		struct logfs_obj_alias *oa, int count)
  {
  	struct logfs_super *super = logfs_super(sb);
  	struct logfs_block *block;
  	struct object_alias_item *item;
  	u64 ino, bix;
  	level_t level;
  	int i, err;
  
  	super->s_flags |= LOGFS_SB_FLAG_OBJ_ALIAS;
  	count /= sizeof(*oa);
  	for (i = 0; i < count; i++) {
  		item = mempool_alloc(super->s_alias_pool, GFP_NOFS);
  		if (!item)
  			return -ENOMEM;
  		memset(item, 0, sizeof(*item));
  
  		super->s_no_object_aliases++;
  		item->val = oa[i].val;
  		item->child_no = be16_to_cpu(oa[i].child_no);
  
  		ino = be64_to_cpu(oa[i].ino);
  		bix = be64_to_cpu(oa[i].bix);
  		level = LEVEL(oa[i].level);
  
  		log_aliases("logfs_load_object_aliases(%llx, %llx, %x, %x) %llx\n",
  				ino, bix, level, item->child_no,
  				be64_to_cpu(item->val));
  		block = alias_tree_lookup(sb, ino, bix, level);
  		if (!block) {
  			block = __alloc_block(sb, ino, bix, level);
  			block->ops = &btree_block_ops;
  			err = alias_tree_insert(sb, ino, bix, level, block);
  			BUG_ON(err); /* mempool empty */
  		}
  		if (test_and_set_bit(item->child_no, block->alias_map)) {
  			printk(KERN_ERR"LogFS: Alias collision detected\n");
  			return -EIO;
  		}
  		list_move_tail(&block->alias_list, &super->s_object_alias);
  		list_add(&item->list, &block->item_list);
  	}
  	return 0;
  }
  
  static void kill_alias(void *_block, unsigned long ignore0,
  		u64 ignore1, u64 ignore2, size_t ignore3)
  {
  	struct logfs_block *block = _block;
  	struct super_block *sb = block->sb;
  	struct logfs_super *super = logfs_super(sb);
  	struct object_alias_item *item;
  
  	while (!list_empty(&block->item_list)) {
  		item = list_entry(block->item_list.next, typeof(*item), list);
  		list_del(&item->list);
  		mempool_free(item, super->s_alias_pool);
  	}
  	block->ops->free_block(sb, block);
  }
  
  static int obj_type(struct inode *inode, level_t level)
  {
  	if (level == 0) {
  		if (S_ISDIR(inode->i_mode))
  			return OBJ_DENTRY;
  		if (inode->i_ino == LOGFS_INO_MASTER)
  			return OBJ_INODE;
  	}
  	return OBJ_BLOCK;
  }
  
  static int obj_len(struct super_block *sb, int obj_type)
  {
  	switch (obj_type) {
  	case OBJ_DENTRY:
  		return sizeof(struct logfs_disk_dentry);
  	case OBJ_INODE:
  		return sizeof(struct logfs_disk_inode);
  	case OBJ_BLOCK:
  		return sb->s_blocksize;
  	default:
  		BUG();
  	}
  }
  
  static int __logfs_segment_write(struct inode *inode, void *buf,
  		struct logfs_shadow *shadow, int type, int len, int compr)
  {
  	struct logfs_area *area;
  	struct super_block *sb = inode->i_sb;
  	s64 ofs;
  	struct logfs_object_header h;
  	int acc_len;
  
  	if (shadow->gc_level == 0)
  		acc_len = len;
  	else
  		acc_len = obj_len(sb, type);
  
  	area = get_area(sb, shadow->gc_level);
  	ofs = logfs_get_free_bytes(area, len + LOGFS_OBJECT_HEADERSIZE);
  	LOGFS_BUG_ON(ofs <= 0, sb);
  	/*
  	 * Order is important.  logfs_get_free_bytes(), by modifying the
  	 * segment file, may modify the content of the very page we're about
  	 * to write now.  Which is fine, as long as the calculated crc and
  	 * written data still match.  So do the modifications _before_
  	 * calculating the crc.
  	 */
  
  	h.len	= cpu_to_be16(len);
  	h.type	= type;
  	h.compr	= compr;
  	h.ino	= cpu_to_be64(inode->i_ino);
  	h.bix	= cpu_to_be64(shadow->bix);
  	h.crc	= logfs_crc32(&h, sizeof(h) - 4, 4);
  	h.data_crc = logfs_crc32(buf, len, 0);
  
  	logfs_buf_write(area, ofs, &h, sizeof(h));
  	logfs_buf_write(area, ofs + LOGFS_OBJECT_HEADERSIZE, buf, len);
  
  	shadow->new_ofs = ofs;
  	shadow->new_len = acc_len + LOGFS_OBJECT_HEADERSIZE;
  
  	return 0;
  }
  
  static s64 logfs_segment_write_compress(struct inode *inode, void *buf,
  		struct logfs_shadow *shadow, int type, int len)
  {
  	struct super_block *sb = inode->i_sb;
  	void *compressor_buf = logfs_super(sb)->s_compressed_je;
  	ssize_t compr_len;
  	int ret;
  
  	mutex_lock(&logfs_super(sb)->s_journal_mutex);
  	compr_len = logfs_compress(buf, compressor_buf, len, len);
  
  	if (compr_len >= 0) {
  		ret = __logfs_segment_write(inode, compressor_buf, shadow,
  				type, compr_len, COMPR_ZLIB);
  	} else {
  		ret = __logfs_segment_write(inode, buf, shadow, type, len,
  				COMPR_NONE);
  	}
  	mutex_unlock(&logfs_super(sb)->s_journal_mutex);
  	return ret;
  }
  
  /**
   * logfs_segment_write - write data block to object store
   * @inode:		inode containing data
   *
   * Returns an errno or zero.
   */
  int logfs_segment_write(struct inode *inode, struct page *page,
  		struct logfs_shadow *shadow)
  {
  	struct super_block *sb = inode->i_sb;
  	struct logfs_super *super = logfs_super(sb);
  	int do_compress, type, len;
  	int ret;
  	void *buf;
  
  	super->s_flags |= LOGFS_SB_FLAG_DIRTY;
  	BUG_ON(super->s_flags & LOGFS_SB_FLAG_SHUTDOWN);
  	do_compress = logfs_inode(inode)->li_flags & LOGFS_IF_COMPRESSED;
  	if (shadow->gc_level != 0) {
  		/* temporarily disable compression for indirect blocks */
  		do_compress = 0;
  	}
  
  	type = obj_type(inode, shrink_level(shadow->gc_level));
  	len = obj_len(sb, type);
  	buf = kmap(page);
  	if (do_compress)
  		ret = logfs_segment_write_compress(inode, buf, shadow, type,
  				len);
  	else
  		ret = __logfs_segment_write(inode, buf, shadow, type, len,
  				COMPR_NONE);
  	kunmap(page);
  
  	log_segment("logfs_segment_write(%llx, %llx, %x) %llx->%llx %x->%x\n",
  			shadow->ino, shadow->bix, shadow->gc_level,
  			shadow->old_ofs, shadow->new_ofs,
  			shadow->old_len, shadow->new_len);
  	/* this BUG_ON did catch a locking bug.  useful */
  	BUG_ON(!(shadow->new_ofs & (super->s_segsize - 1)));
  	return ret;
  }
  
  int wbuf_read(struct super_block *sb, u64 ofs, size_t len, void *buf)
  {
  	pgoff_t index = ofs >> PAGE_SHIFT;
  	struct page *page;
  	long offset = ofs & (PAGE_SIZE-1);
  	long copylen;
  
  	while (len) {
  		copylen = min((ulong)len, PAGE_SIZE - offset);
  
  		page = get_mapping_page(sb, index, 1);
  		if (IS_ERR(page))
  			return PTR_ERR(page);
  		memcpy(buf, page_address(page) + offset, copylen);
  		page_cache_release(page);
  
  		buf += copylen;
  		len -= copylen;
  		offset = 0;
  		index++;
  	}
  	return 0;
  }
  
  /*
   * The "position" of indirect blocks is ambiguous.  It can be the position
   * of any data block somewhere behind this indirect block.  So we need to
   * normalize the positions through logfs_block_mask() before comparing.
   */
  static int check_pos(struct super_block *sb, u64 pos1, u64 pos2, level_t level)
  {
  	return	(pos1 & logfs_block_mask(sb, level)) !=
  		(pos2 & logfs_block_mask(sb, level));
  }
  
  #if 0
  static int read_seg_header(struct super_block *sb, u64 ofs,
  		struct logfs_segment_header *sh)
  {
  	__be32 crc;
  	int err;
  
  	err = wbuf_read(sb, ofs, sizeof(*sh), sh);
  	if (err)
  		return err;
  	crc = logfs_crc32(sh, sizeof(*sh), 4);
  	if (crc != sh->crc) {
  		printk(KERN_ERR"LOGFS: header crc error at %llx: expected %x, "
  				"got %x\n", ofs, be32_to_cpu(sh->crc),
  				be32_to_cpu(crc));
  		return -EIO;
  	}
  	return 0;
  }
  #endif
  
  static int read_obj_header(struct super_block *sb, u64 ofs,
  		struct logfs_object_header *oh)
  {
  	__be32 crc;
  	int err;
  
  	err = wbuf_read(sb, ofs, sizeof(*oh), oh);
  	if (err)
  		return err;
  	crc = logfs_crc32(oh, sizeof(*oh) - 4, 4);
  	if (crc != oh->crc) {
  		printk(KERN_ERR"LOGFS: header crc error at %llx: expected %x, "
  				"got %x\n", ofs, be32_to_cpu(oh->crc),
  				be32_to_cpu(crc));
  		return -EIO;
  	}
  	return 0;
  }
  
  static void move_btree_to_page(struct inode *inode, struct page *page,
  		__be64 *data)
  {
  	struct super_block *sb = inode->i_sb;
  	struct logfs_super *super = logfs_super(sb);
  	struct btree_head128 *head = &super->s_object_alias_tree;
  	struct logfs_block *block;
  	struct object_alias_item *item, *next;
  
  	if (!(super->s_flags & LOGFS_SB_FLAG_OBJ_ALIAS))
  		return;
  
  	block = btree_remove128(head, inode->i_ino, page->index);
  	if (!block)
  		return;
  
  	log_blockmove("move_btree_to_page(%llx, %llx, %x)\n",
  			block->ino, block->bix, block->level);
  	list_for_each_entry_safe(item, next, &block->item_list, list) {
  		data[item->child_no] = item->val;
  		list_del(&item->list);
  		mempool_free(item, super->s_alias_pool);
  	}
  	block->page = page;
  
  	if (!PagePrivate(page)) {
  		SetPagePrivate(page);
  		page_cache_get(page);
  		set_page_private(page, (unsigned long) block);
  	}
  	block->ops = &indirect_block_ops;
  	initialize_block_counters(page, block, data, 0);
  }
  
  /*
   * This silences a false, yet annoying gcc warning.  I hate it when my editor
   * jumps into bitops.h each time I recompile this file.
   * TODO: Complain to gcc folks about this and upgrade compiler.
   */
  static unsigned long fnb(const unsigned long *addr,
  		unsigned long size, unsigned long offset)
  {
  	return find_next_bit(addr, size, offset);
  }
  
  void move_page_to_btree(struct page *page)
  {
  	struct logfs_block *block = logfs_block(page);
  	struct super_block *sb = block->sb;
  	struct logfs_super *super = logfs_super(sb);
  	struct object_alias_item *item;
  	unsigned long pos;
  	__be64 *child;
  	int err;
  
  	if (super->s_flags & LOGFS_SB_FLAG_SHUTDOWN) {
  		block->ops->free_block(sb, block);
  		return;
  	}
  	log_blockmove("move_page_to_btree(%llx, %llx, %x)\n",
  			block->ino, block->bix, block->level);
  	super->s_flags |= LOGFS_SB_FLAG_OBJ_ALIAS;
  
  	for (pos = 0; ; pos++) {
  		pos = fnb(block->alias_map, LOGFS_BLOCK_FACTOR, pos);
  		if (pos >= LOGFS_BLOCK_FACTOR)
  			break;
  
  		item = mempool_alloc(super->s_alias_pool, GFP_NOFS);
  		BUG_ON(!item); /* mempool empty */
  		memset(item, 0, sizeof(*item));
  
  		child = kmap_atomic(page);
  		item->val = child[pos];
  		kunmap_atomic(child);
  		item->child_no = pos;
  		list_add(&item->list, &block->item_list);
  	}
  	block->page = NULL;
  
  	if (PagePrivate(page)) {
  		ClearPagePrivate(page);
  		page_cache_release(page);
  		set_page_private(page, 0);
  	}
  	block->ops = &btree_block_ops;
  	err = alias_tree_insert(block->sb, block->ino, block->bix, block->level,
  			block);
  	BUG_ON(err); /* mempool empty */
  	ClearPageUptodate(page);
  }
  
  static int __logfs_segment_read(struct inode *inode, void *buf,
  		u64 ofs, u64 bix, level_t level)
  {
  	struct super_block *sb = inode->i_sb;
  	void *compressor_buf = logfs_super(sb)->s_compressed_je;
  	struct logfs_object_header oh;
  	__be32 crc;
  	u16 len;
  	int err, block_len;
  
  	block_len = obj_len(sb, obj_type(inode, level));
  	err = read_obj_header(sb, ofs, &oh);
  	if (err)
  		goto out_err;
  
  	err = -EIO;
  	if (be64_to_cpu(oh.ino) != inode->i_ino
  			|| check_pos(sb, be64_to_cpu(oh.bix), bix, level)) {
  		printk(KERN_ERR"LOGFS: (ino, bix) don't match at %llx: "
  				"expected (%lx, %llx), got (%llx, %llx)\n",
  				ofs, inode->i_ino, bix,
  				be64_to_cpu(oh.ino), be64_to_cpu(oh.bix));
  		goto out_err;
  	}
  
  	len = be16_to_cpu(oh.len);
  
  	switch (oh.compr) {
  	case COMPR_NONE:
  		err = wbuf_read(sb, ofs + LOGFS_OBJECT_HEADERSIZE, len, buf);
  		if (err)
  			goto out_err;
  		crc = logfs_crc32(buf, len, 0);
  		if (crc != oh.data_crc) {
  			printk(KERN_ERR"LOGFS: uncompressed data crc error at "
  					"%llx: expected %x, got %x\n", ofs,
  					be32_to_cpu(oh.data_crc),
  					be32_to_cpu(crc));
  			goto out_err;
  		}
  		break;
  	case COMPR_ZLIB:
  		mutex_lock(&logfs_super(sb)->s_journal_mutex);
  		err = wbuf_read(sb, ofs + LOGFS_OBJECT_HEADERSIZE, len,
  				compressor_buf);
  		if (err) {
  			mutex_unlock(&logfs_super(sb)->s_journal_mutex);
  			goto out_err;
  		}
  		crc = logfs_crc32(compressor_buf, len, 0);
  		if (crc != oh.data_crc) {
  			printk(KERN_ERR"LOGFS: compressed data crc error at "
  					"%llx: expected %x, got %x\n", ofs,
  					be32_to_cpu(oh.data_crc),
  					be32_to_cpu(crc));
  			mutex_unlock(&logfs_super(sb)->s_journal_mutex);
  			goto out_err;
  		}
  		err = logfs_uncompress(compressor_buf, buf, len, block_len);
  		mutex_unlock(&logfs_super(sb)->s_journal_mutex);
  		if (err) {
  			printk(KERN_ERR"LOGFS: uncompress error at %llx\n", ofs);
  			goto out_err;
  		}
  		break;
  	default:
  		LOGFS_BUG(sb);
  		err = -EIO;
  		goto out_err;
  	}
  	return 0;
  
  out_err:
  	logfs_set_ro(sb);
  	printk(KERN_ERR"LOGFS: device is read-only now\n");
  	LOGFS_BUG(sb);
  	return err;
  }
  
  /**
   * logfs_segment_read - read data block from object store
   * @inode:		inode containing data
   * @buf:		data buffer
   * @ofs:		physical data offset
   * @bix:		block index
   * @level:		block level
   *
   * Returns 0 on success or a negative errno.
   */
  int logfs_segment_read(struct inode *inode, struct page *page,
  		u64 ofs, u64 bix, level_t level)
  {
  	int err;
  	void *buf;
  
  	if (PageUptodate(page))
  		return 0;
  
  	ofs &= ~LOGFS_FULLY_POPULATED;
  
  	buf = kmap(page);
  	err = __logfs_segment_read(inode, buf, ofs, bix, level);
  	if (!err) {
  		move_btree_to_page(inode, page, buf);
  		SetPageUptodate(page);
  	}
  	kunmap(page);
  	log_segment("logfs_segment_read(%lx, %llx, %x) %llx (%d)\n",
  			inode->i_ino, bix, level, ofs, err);
  	return err;
  }
  
  int logfs_segment_delete(struct inode *inode, struct logfs_shadow *shadow)
  {
  	struct super_block *sb = inode->i_sb;
  	struct logfs_super *super = logfs_super(sb);
  	struct logfs_object_header h;
  	u16 len;
  	int err;
  
  	super->s_flags |= LOGFS_SB_FLAG_DIRTY;
  	BUG_ON(super->s_flags & LOGFS_SB_FLAG_SHUTDOWN);
  	BUG_ON(shadow->old_ofs & LOGFS_FULLY_POPULATED);
  	if (!shadow->old_ofs)
  		return 0;
  
  	log_segment("logfs_segment_delete(%llx, %llx, %x) %llx->%llx %x->%x\n",
  			shadow->ino, shadow->bix, shadow->gc_level,
  			shadow->old_ofs, shadow->new_ofs,
  			shadow->old_len, shadow->new_len);
  	err = read_obj_header(sb, shadow->old_ofs, &h);
  	LOGFS_BUG_ON(err, sb);
  	LOGFS_BUG_ON(be64_to_cpu(h.ino) != inode->i_ino, sb);
  	LOGFS_BUG_ON(check_pos(sb, shadow->bix, be64_to_cpu(h.bix),
  				shrink_level(shadow->gc_level)), sb);
  
  	if (shadow->gc_level == 0)
  		len = be16_to_cpu(h.len);
  	else
  		len = obj_len(sb, h.type);
  	shadow->old_len = len + sizeof(h);
  	return 0;
  }
  
  void freeseg(struct super_block *sb, u32 segno)
  {
  	struct logfs_super *super = logfs_super(sb);
  	struct address_space *mapping = super->s_mapping_inode->i_mapping;
  	struct page *page;
  	u64 ofs, start, end;
  
  	start = dev_ofs(sb, segno, 0);
  	end = dev_ofs(sb, segno + 1, 0);
  	for (ofs = start; ofs < end; ofs += PAGE_SIZE) {
  		page = find_get_page(mapping, ofs >> PAGE_SHIFT);
  		if (!page)
  			continue;
  		if (PagePrivate(page)) {
  			ClearPagePrivate(page);
  			page_cache_release(page);
  		}
  		page_cache_release(page);
  	}
  }
  
  int logfs_open_area(struct logfs_area *area, size_t bytes)
  {
  	struct super_block *sb = area->a_sb;
  	struct logfs_super *super = logfs_super(sb);
  	int err, closed = 0;
  
  	if (area->a_is_open && area->a_used_bytes + bytes <= super->s_segsize)
  		return 0;
  
  	if (area->a_is_open) {
  		u64 ofs = dev_ofs(sb, area->a_segno, area->a_written_bytes);
  		u32 len = super->s_segsize - area->a_written_bytes;
  
  		log_gc("logfs_close_area(%x)\n", area->a_segno);
  		pad_wbuf(area, 1);
  		super->s_devops->writeseg(area->a_sb, ofs, len);
  		freeseg(sb, area->a_segno);
  		closed = 1;
  	}
  
  	area->a_used_bytes = 0;
  	area->a_written_bytes = 0;
  again:
  	area->a_ops->get_free_segment(area);
  	area->a_ops->get_erase_count(area);
  
  	log_gc("logfs_open_area(%x, %x)\n", area->a_segno, area->a_level);
  	err = area->a_ops->erase_segment(area);
  	if (err) {
  		printk(KERN_WARNING "LogFS: Error erasing segment %x\n",
  				area->a_segno);
  		logfs_mark_segment_bad(sb, area->a_segno);
  		goto again;
  	}
  	area->a_is_open = 1;
  	return closed;
  }
  
  void logfs_sync_area(struct logfs_area *area)
  {
  	struct super_block *sb = area->a_sb;
  	struct logfs_super *super = logfs_super(sb);
  	u64 ofs = dev_ofs(sb, area->a_segno, area->a_written_bytes);
  	u32 len = (area->a_used_bytes - area->a_written_bytes);
  
  	if (super->s_writesize)
  		len &= ~(super->s_writesize - 1);
  	if (len == 0)
  		return;
  	pad_wbuf(area, 0);
  	super->s_devops->writeseg(sb, ofs, len);
  	area->a_written_bytes += len;
  }
  
  void logfs_sync_segments(struct super_block *sb)
  {
  	struct logfs_super *super = logfs_super(sb);
  	int i;
  
  	for_each_area(i)
  		logfs_sync_area(super->s_area[i]);
  }
  
  /*
   * Pick a free segment to be used for this area.  Effectively takes a
   * candidate from the free list (not really a candidate anymore).
   */
  static void ostore_get_free_segment(struct logfs_area *area)
  {
  	struct super_block *sb = area->a_sb;
  	struct logfs_super *super = logfs_super(sb);
  
  	if (super->s_free_list.count == 0) {
  		printk(KERN_ERR"LOGFS: ran out of free segments\n");
  		LOGFS_BUG(sb);
  	}
  
  	area->a_segno = get_best_cand(sb, &super->s_free_list, NULL);
  }
  
  static void ostore_get_erase_count(struct logfs_area *area)
  {
  	struct logfs_segment_entry se;
  	u32 ec_level;
  
  	logfs_get_segment_entry(area->a_sb, area->a_segno, &se);
  	BUG_ON(se.ec_level == cpu_to_be32(BADSEG) ||
  			se.valid == cpu_to_be32(RESERVED));
  
  	ec_level = be32_to_cpu(se.ec_level);
  	area->a_erase_count = (ec_level >> 4) + 1;
  }
  
  static int ostore_erase_segment(struct logfs_area *area)
  {
  	struct super_block *sb = area->a_sb;
  	struct logfs_segment_header sh;
  	u64 ofs;
  	int err;
  
  	err = logfs_erase_segment(sb, area->a_segno, 0);
  	if (err)
  		return err;
  
  	sh.pad = 0;
  	sh.type = SEG_OSTORE;
  	sh.level = (__force u8)area->a_level;
  	sh.segno = cpu_to_be32(area->a_segno);
  	sh.ec = cpu_to_be32(area->a_erase_count);
  	sh.gec = cpu_to_be64(logfs_super(sb)->s_gec);
  	sh.crc = logfs_crc32(&sh, sizeof(sh), 4);
  
  	logfs_set_segment_erased(sb, area->a_segno, area->a_erase_count,
  			area->a_level);
  
  	ofs = dev_ofs(sb, area->a_segno, 0);
  	area->a_used_bytes = sizeof(sh);
  	logfs_buf_write(area, ofs, &sh, sizeof(sh));
  	return 0;
  }
  
  static const struct logfs_area_ops ostore_area_ops = {
  	.get_free_segment	= ostore_get_free_segment,
  	.get_erase_count	= ostore_get_erase_count,
  	.erase_segment		= ostore_erase_segment,
  };
  
  static void free_area(struct logfs_area *area)
  {
  	if (area)
  		freeseg(area->a_sb, area->a_segno);
  	kfree(area);
  }
  
  void free_areas(struct super_block *sb)
  {
  	struct logfs_super *super = logfs_super(sb);
  	int i;
  
  	for_each_area(i)
  		free_area(super->s_area[i]);
  	free_area(super->s_journal_area);
  }
  
  static struct logfs_area *alloc_area(struct super_block *sb)
  {
  	struct logfs_area *area;
  
  	area = kzalloc(sizeof(*area), GFP_KERNEL);
  	if (!area)
  		return NULL;
  
  	area->a_sb = sb;
  	return area;
  }
  
  static void map_invalidatepage(struct page *page, unsigned long l)
  {
  	return;
  }
  
  static int map_releasepage(struct page *page, gfp_t g)
  {
  	/* Don't release these pages */
  	return 0;
  }
  
  static const struct address_space_operations mapping_aops = {
  	.invalidatepage = map_invalidatepage,
  	.releasepage	= map_releasepage,
  	.set_page_dirty = __set_page_dirty_nobuffers,
  };
  
  int logfs_init_mapping(struct super_block *sb)
  {
  	struct logfs_super *super = logfs_super(sb);
  	struct address_space *mapping;
  	struct inode *inode;
  
  	inode = logfs_new_meta_inode(sb, LOGFS_INO_MAPPING);
  	if (IS_ERR(inode))
  		return PTR_ERR(inode);
  	super->s_mapping_inode = inode;
  	mapping = inode->i_mapping;
  	mapping->a_ops = &mapping_aops;
  	/* Would it be possible to use __GFP_HIGHMEM as well? */
  	mapping_set_gfp_mask(mapping, GFP_NOFS);
  	return 0;
  }
  
  int logfs_init_areas(struct super_block *sb)
  {
  	struct logfs_super *super = logfs_super(sb);
  	int i = -1;
  
  	super->s_alias_pool = mempool_create_kmalloc_pool(600,
  			sizeof(struct object_alias_item));
  	if (!super->s_alias_pool)
  		return -ENOMEM;
  
  	super->s_journal_area = alloc_area(sb);
  	if (!super->s_journal_area)
  		goto err;
  
  	for_each_area(i) {
  		super->s_area[i] = alloc_area(sb);
  		if (!super->s_area[i])
  			goto err;
  		super->s_area[i]->a_level = GC_LEVEL(i);
  		super->s_area[i]->a_ops = &ostore_area_ops;
  	}
  	btree_init_mempool128(&super->s_object_alias_tree,
  			super->s_btree_pool);
  	return 0;
  
  err:
  	for (i--; i >= 0; i--)
  		free_area(super->s_area[i]);
  	free_area(super->s_journal_area);
  	logfs_mempool_destroy(super->s_alias_pool);
  	return -ENOMEM;
  }
  
  void logfs_cleanup_areas(struct super_block *sb)
  {
  	struct logfs_super *super = logfs_super(sb);
  
  	btree_grim_visitor128(&super->s_object_alias_tree, 0, kill_alias);
  }
  