[LogFS] add new flash file system

This is a new flash file system. See
Documentation/filesystems/logfs.txt

Signed-off-by: Joern Engel <joern@logfs.org>

1 files changed, 924 insertions, 0 deletions

diff --git a/fs/logfs/segment.c b/fs/logfs/segment.c
new file mode 100644
index 0000000..5f58b74
--- /dev/null
+++ b/fs/logfs/segment.c
@@ -0,0 +1,924 @@
+/*
+ * 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"
+
+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)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	super->s_gec++;
+
+	return super->s_devops->erase(sb, (u64)segno << super->s_segshift,
+			super->s_segsize);
+}
+
+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;
+}
+
+void __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);
+		SetPageUptodate(page);
+		BUG_ON(!page); /* FIXME: reserve a pool */
+		memcpy(page_address(page) + offset, buf, copylen);
+		SetPagePrivate(page);
+		page_cache_release(page);
+
+		buf += copylen;
+		len -= copylen;
+		offset = 0;
+		index++;
+	} while (len);
+}
+
+/*
+ * bdev_writeseg will write full pages.  Memset the tail to prevent data leaks.
+ */
+static void pad_wbuf(struct logfs_area *area, int final)
+{
+	struct super_block *sb = area->a_sb;
+	struct logfs_super *super = logfs_super(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) {
+		/* The math in this function can surely use some love */
+		len = 0;
+	}
+	if (len) {
+		BUG_ON(area->a_used_bytes >= super->s_segsize);
+
+		page = get_mapping_page(area->a_sb, index, 0);
+		BUG_ON(!page); /* FIXME: reserve a pool */
+		memset(page_address(page) + offset, 0xff, len);
+		SetPagePrivate(page);
+		page_cache_release(page);
+	}
+
+	if (!final)
+		return;
+
+	area->a_used_bytes += len;
+	for ( ; area->a_used_bytes < super->s_segsize;
+			area->a_used_bytes += PAGE_SIZE) {
+		/* Memset another page */
+		index++;
+		page = get_mapping_page(area->a_sb, index, 0);
+		BUG_ON(!page); /* FIXME: reserve a pool */
+		memset(page_address(page), 0xff, PAGE_SIZE);
+		SetPagePrivate(page);
+		page_cache_release(page);
+	}
+}
+
+/*
+ * 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 gc_level_t btree_block_level(struct logfs_block *block)
+{
+	return expand_level(block->ino, block->level);
+}
+
+static struct logfs_block_ops btree_block_ops = {
+	.write_block	= btree_write_block,
+	.block_level	= btree_block_level,
+	.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;
+
+	BUG_ON(logfs_super(sb)->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;
+	SetPagePrivate(page);
+	page->private = (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, KM_USER0);
+		item->val = child[pos];
+		kunmap_atomic(child, KM_USER0);
+		item->child_no = pos;
+		list_add(&item->list, &block->item_list);
+	}
+	block->page = NULL;
+	ClearPagePrivate(page);
+	page->private = 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_object_header h;
+	u16 len;
+	int err;
+
+	BUG_ON(logfs_super(sb)->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;
+}
+
+static 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;
+		ClearPagePrivate(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);
+	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);
+}
+
+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)
+{
+	BUG();
+}
+
+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);
+	mempool_destroy(super->s_alias_pool);
+	return -ENOMEM;
+}
+
+void logfs_cleanup_areas(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int i;
+
+	btree_grim_visitor128(&super->s_object_alias_tree, 0, kill_alias);
+	for_each_area(i)
+		free_area(super->s_area[i]);
+	free_area(super->s_journal_area);
+	destroy_meta_inode(super->s_mapping_inode);
+}