Linux 3.16-rc2

[linux/fpc-iii.git] / fs / logfs / segment.c

/*
 * 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);
                if (page)
                        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 int o,
                               unsigned int 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);
}