Prevent data corruption in logfs_rewrite_block()

[deliverable/linux.git] / fs / logfs / readwrite.c

/*
 * fs/logfs/readwrite.c
 *
 * As should be obvious for Linux kernel code, license is GPLv2
 *
 * Copyright (c) 2005-2008 Joern Engel <joern@logfs.org>
 *
 *
 * Actually contains five sets of very similar functions:
 * read         read blocks from a file
 * seek_hole    find next hole
 * seek_data    find next data block
 * valid        check whether a block still belongs to a file
 * write        write blocks to a file
 * delete       delete a block (for directories and ifile)
 * rewrite      move existing blocks of a file to a new location (gc helper)
 * truncate     truncate a file
 */
#include "logfs.h"
#include <linux/sched.h>

static u64 adjust_bix(u64 bix, level_t level)
{
        switch (level) {
        case 0:
                return bix;
        case LEVEL(1):
                return max_t(u64, bix, I0_BLOCKS);
        case LEVEL(2):
                return max_t(u64, bix, I1_BLOCKS);
        case LEVEL(3):
                return max_t(u64, bix, I2_BLOCKS);
        case LEVEL(4):
                return max_t(u64, bix, I3_BLOCKS);
        case LEVEL(5):
                return max_t(u64, bix, I4_BLOCKS);
        default:
                WARN_ON(1);
                return bix;
        }
}

static inline u64 maxbix(u8 height)
{
        return 1ULL << (LOGFS_BLOCK_BITS * height);
}

/**
 * The inode address space is cut in two halves.  Lower half belongs to data
 * pages, upper half to indirect blocks.  If the high bit (INDIRECT_BIT) is
 * set, the actual block index (bix) and level can be derived from the page
 * index.
 *
 * The lowest three bits of the block index are set to 0 after packing and
 * unpacking.  Since the lowest n bits (9 for 4KiB blocksize) are ignored
 * anyway this is harmless.
 */
#define ARCH_SHIFT      (BITS_PER_LONG - 32)
#define INDIRECT_BIT    (0x80000000UL << ARCH_SHIFT)
#define LEVEL_SHIFT     (28 + ARCH_SHIFT)
static inline pgoff_t first_indirect_block(void)
{
        return INDIRECT_BIT | (1ULL << LEVEL_SHIFT);
}

pgoff_t logfs_pack_index(u64 bix, level_t level)
{
        pgoff_t index;

        BUG_ON(bix >= INDIRECT_BIT);
        if (level == 0)
                return bix;

        index  = INDIRECT_BIT;
        index |= (__force long)level << LEVEL_SHIFT;
        index |= bix >> ((__force u8)level * LOGFS_BLOCK_BITS);
        return index;
}

void logfs_unpack_index(pgoff_t index, u64 *bix, level_t *level)
{
        u8 __level;

        if (!(index & INDIRECT_BIT)) {
                *bix = index;
                *level = 0;
                return;
        }

        __level = (index & ~INDIRECT_BIT) >> LEVEL_SHIFT;
        *level = LEVEL(__level);
        *bix = (index << (__level * LOGFS_BLOCK_BITS)) & ~INDIRECT_BIT;
        *bix = adjust_bix(*bix, *level);
        return;
}
#undef ARCH_SHIFT
#undef INDIRECT_BIT
#undef LEVEL_SHIFT

/*
 * Time is stored as nanoseconds since the epoch.
 */
static struct timespec be64_to_timespec(__be64 betime)
{
        return ns_to_timespec(be64_to_cpu(betime));
}

static __be64 timespec_to_be64(struct timespec tsp)
{
        return cpu_to_be64((u64)tsp.tv_sec * NSEC_PER_SEC + tsp.tv_nsec);
}

static void logfs_disk_to_inode(struct logfs_disk_inode *di, struct inode*inode)
{
        struct logfs_inode *li = logfs_inode(inode);
        int i;

        inode->i_mode   = be16_to_cpu(di->di_mode);
        li->li_height   = di->di_height;
        li->li_flags    = be32_to_cpu(di->di_flags);
        inode->i_uid    = be32_to_cpu(di->di_uid);
        inode->i_gid    = be32_to_cpu(di->di_gid);
        inode->i_size   = be64_to_cpu(di->di_size);
        logfs_set_blocks(inode, be64_to_cpu(di->di_used_bytes));
        inode->i_atime  = be64_to_timespec(di->di_atime);
        inode->i_ctime  = be64_to_timespec(di->di_ctime);
        inode->i_mtime  = be64_to_timespec(di->di_mtime);
        inode->i_nlink  = be32_to_cpu(di->di_refcount);
        inode->i_generation = be32_to_cpu(di->di_generation);

        switch (inode->i_mode & S_IFMT) {
        case S_IFSOCK:  /* fall through */
        case S_IFBLK:   /* fall through */
        case S_IFCHR:   /* fall through */
        case S_IFIFO:
                inode->i_rdev = be64_to_cpu(di->di_data[0]);
                break;
        case S_IFDIR:   /* fall through */
        case S_IFREG:   /* fall through */
        case S_IFLNK:
                for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
                        li->li_data[i] = be64_to_cpu(di->di_data[i]);
                break;
        default:
                BUG();
        }
}

static void logfs_inode_to_disk(struct inode *inode, struct logfs_disk_inode*di)
{
        struct logfs_inode *li = logfs_inode(inode);
        int i;

        di->di_mode     = cpu_to_be16(inode->i_mode);
        di->di_height   = li->li_height;
        di->di_pad      = 0;
        di->di_flags    = cpu_to_be32(li->li_flags);
        di->di_uid      = cpu_to_be32(inode->i_uid);
        di->di_gid      = cpu_to_be32(inode->i_gid);
        di->di_size     = cpu_to_be64(i_size_read(inode));
        di->di_used_bytes = cpu_to_be64(li->li_used_bytes);
        di->di_atime    = timespec_to_be64(inode->i_atime);
        di->di_ctime    = timespec_to_be64(inode->i_ctime);
        di->di_mtime    = timespec_to_be64(inode->i_mtime);
        di->di_refcount = cpu_to_be32(inode->i_nlink);
        di->di_generation = cpu_to_be32(inode->i_generation);

        switch (inode->i_mode & S_IFMT) {
        case S_IFSOCK:  /* fall through */
        case S_IFBLK:   /* fall through */
        case S_IFCHR:   /* fall through */
        case S_IFIFO:
                di->di_data[0] = cpu_to_be64(inode->i_rdev);
                break;
        case S_IFDIR:   /* fall through */
        case S_IFREG:   /* fall through */
        case S_IFLNK:
                for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
                        di->di_data[i] = cpu_to_be64(li->li_data[i]);
                break;
        default:
                BUG();
        }
}

static void __logfs_set_blocks(struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        struct logfs_inode *li = logfs_inode(inode);

        inode->i_blocks = ULONG_MAX;
        if (li->li_used_bytes >> sb->s_blocksize_bits < ULONG_MAX)
                inode->i_blocks = ALIGN(li->li_used_bytes, 512) >> 9;
}

void logfs_set_blocks(struct inode *inode, u64 bytes)
{
        struct logfs_inode *li = logfs_inode(inode);

        li->li_used_bytes = bytes;
        __logfs_set_blocks(inode);
}

static void prelock_page(struct super_block *sb, struct page *page, int lock)
{
        struct logfs_super *super = logfs_super(sb);

        BUG_ON(!PageLocked(page));
        if (lock) {
                BUG_ON(PagePreLocked(page));
                SetPagePreLocked(page);
        } else {
                /* We are in GC path. */
                if (PagePreLocked(page))
                        super->s_lock_count++;
                else
                        SetPagePreLocked(page);
        }
}

static void preunlock_page(struct super_block *sb, struct page *page, int lock)
{
        struct logfs_super *super = logfs_super(sb);

        BUG_ON(!PageLocked(page));
        if (lock)
                ClearPagePreLocked(page);
        else {
                /* We are in GC path. */
                BUG_ON(!PagePreLocked(page));
                if (super->s_lock_count)
                        super->s_lock_count--;
                else
                        ClearPagePreLocked(page);
        }
}

/*
 * Logfs is prone to an AB-BA deadlock where one task tries to acquire
 * s_write_mutex with a locked page and GC tries to get that page while holding
 * s_write_mutex.
 * To solve this issue logfs will ignore the page lock iff the page in question
 * is waiting for s_write_mutex.  We annotate this fact by setting PG_pre_locked
 * in addition to PG_locked.
 */
static void logfs_get_wblocks(struct super_block *sb, struct page *page,
                int lock)
{
        struct logfs_super *super = logfs_super(sb);

        if (page)
                prelock_page(sb, page, lock);

        if (lock) {
                mutex_lock(&super->s_write_mutex);
                logfs_gc_pass(sb);
                /* FIXME: We also have to check for shadowed space
                 * and mempool fill grade */
        }
}

static void logfs_put_wblocks(struct super_block *sb, struct page *page,
                int lock)
{
        struct logfs_super *super = logfs_super(sb);

        if (page)
                preunlock_page(sb, page, lock);
        /* Order matters - we must clear PG_pre_locked before releasing
         * s_write_mutex or we could race against another task. */
        if (lock)
                mutex_unlock(&super->s_write_mutex);
}

static struct page *logfs_get_read_page(struct inode *inode, u64 bix,
                level_t level)
{
        return find_or_create_page(inode->i_mapping,
                        logfs_pack_index(bix, level), GFP_NOFS);
}

static void logfs_put_read_page(struct page *page)
{
        unlock_page(page);
        page_cache_release(page);
}

static void logfs_lock_write_page(struct page *page)
{
        int loop = 0;

        while (unlikely(!trylock_page(page))) {
                if (loop++ > 0x1000) {
                        /* Has been observed once so far... */
                        printk(KERN_ERR "stack at %p\n", &loop);
                        BUG();
                }
                if (PagePreLocked(page)) {
                        /* Holder of page lock is waiting for us, it
                         * is safe to use this page. */
                        break;
                }
                /* Some other process has this page locked and has
                 * nothing to do with us.  Wait for it to finish.
                 */
                schedule();
        }
        BUG_ON(!PageLocked(page));
}

static struct page *logfs_get_write_page(struct inode *inode, u64 bix,
                level_t level)
{
        struct address_space *mapping = inode->i_mapping;
        pgoff_t index = logfs_pack_index(bix, level);
        struct page *page;
        int err;

repeat:
        page = find_get_page(mapping, index);
        if (!page) {
                page = __page_cache_alloc(GFP_NOFS);
                if (!page)
                        return NULL;
                err = add_to_page_cache_lru(page, mapping, index, GFP_NOFS);
                if (unlikely(err)) {
                        page_cache_release(page);
                        if (err == -EEXIST)
                                goto repeat;
                        return NULL;
                }
        } else logfs_lock_write_page(page);
        BUG_ON(!PageLocked(page));
        return page;
}

static void logfs_unlock_write_page(struct page *page)
{
        if (!PagePreLocked(page))
                unlock_page(page);
}

static void logfs_put_write_page(struct page *page)
{
        logfs_unlock_write_page(page);
        page_cache_release(page);
}

static struct page *logfs_get_page(struct inode *inode, u64 bix, level_t level,
                int rw)
{
        if (rw == READ)
                return logfs_get_read_page(inode, bix, level);
        else
                return logfs_get_write_page(inode, bix, level);
}

static void logfs_put_page(struct page *page, int rw)
{
        if (rw == READ)
                logfs_put_read_page(page);
        else
                logfs_put_write_page(page);
}

static unsigned long __get_bits(u64 val, int skip, int no)
{
        u64 ret = val;

        ret >>= skip * no;
        ret <<= 64 - no;
        ret >>= 64 - no;
        return ret;
}

static unsigned long get_bits(u64 val, level_t skip)
{
        return __get_bits(val, (__force int)skip, LOGFS_BLOCK_BITS);
}

static inline void init_shadow_tree(struct super_block *sb,
                struct shadow_tree *tree)
{
        struct logfs_super *super = logfs_super(sb);

        btree_init_mempool64(&tree->new, super->s_btree_pool);
        btree_init_mempool64(&tree->old, super->s_btree_pool);
}

static void indirect_write_block(struct logfs_block *block)
{
        struct page *page;
        struct inode *inode;
        int ret;

        page = block->page;
        inode = page->mapping->host;
        logfs_lock_write_page(page);
        ret = logfs_write_buf(inode, page, 0);
        logfs_unlock_write_page(page);
        /*
         * This needs some rework.  Unless you want your filesystem to run
         * completely synchronously (you don't), the filesystem will always
         * report writes as 'successful' before the actual work has been
         * done.  The actual work gets done here and this is where any errors
         * will show up.  And there isn't much we can do about it, really.
         *
         * Some attempts to fix the errors (move from bad blocks, retry io,...)
         * have already been done, so anything left should be either a broken
         * device or a bug somewhere in logfs itself.  Being relatively new,
         * the odds currently favor a bug, so for now the line below isn't
         * entirely tasteles.
         */
        BUG_ON(ret);
}

static void inode_write_block(struct logfs_block *block)
{
        struct inode *inode;
        int ret;

        inode = block->inode;
        if (inode->i_ino == LOGFS_INO_MASTER)
                logfs_write_anchor(inode->i_sb);
        else {
                ret = __logfs_write_inode(inode, 0);
                /* see indirect_write_block comment */
                BUG_ON(ret);
        }
}

static gc_level_t inode_block_level(struct logfs_block *block)
{
        BUG_ON(block->inode->i_ino == LOGFS_INO_MASTER);
        return GC_LEVEL(LOGFS_MAX_LEVELS);
}

static gc_level_t indirect_block_level(struct logfs_block *block)
{
        struct page *page;
        struct inode *inode;
        u64 bix;
        level_t level;

        page = block->page;
        inode = page->mapping->host;
        logfs_unpack_index(page->index, &bix, &level);
        return expand_level(inode->i_ino, level);
}

/*
 * 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);
}

static __be64 inode_val0(struct inode *inode)
{
        struct logfs_inode *li = logfs_inode(inode);
        u64 val;

        /*
         * Explicit shifting generates good code, but must match the format
         * of the structure.  Add some paranoia just in case.
         */
        BUILD_BUG_ON(offsetof(struct logfs_disk_inode, di_mode) != 0);
        BUILD_BUG_ON(offsetof(struct logfs_disk_inode, di_height) != 2);
        BUILD_BUG_ON(offsetof(struct logfs_disk_inode, di_flags) != 4);

        val =   (u64)inode->i_mode << 48 |
                (u64)li->li_height << 40 |
                (u64)li->li_flags;
        return cpu_to_be64(val);
}

static int inode_write_alias(struct super_block *sb,
                struct logfs_block *block, write_alias_t *write_one_alias)
{
        struct inode *inode = block->inode;
        struct logfs_inode *li = logfs_inode(inode);
        unsigned long pos;
        u64 ino , bix;
        __be64 val;
        level_t level;
        int err;

        for (pos = 0; ; pos++) {
                pos = fnb(block->alias_map, LOGFS_BLOCK_FACTOR, pos);
                if (pos >= LOGFS_EMBEDDED_FIELDS + INODE_POINTER_OFS)
                        return 0;

                switch (pos) {
                case INODE_HEIGHT_OFS:
                        val = inode_val0(inode);
                        break;
                case INODE_USED_OFS:
                        val = cpu_to_be64(li->li_used_bytes);;
                        break;
                case INODE_SIZE_OFS:
                        val = cpu_to_be64(i_size_read(inode));
                        break;
                case INODE_POINTER_OFS ... INODE_POINTER_OFS + LOGFS_EMBEDDED_FIELDS - 1:
                        val = cpu_to_be64(li->li_data[pos - INODE_POINTER_OFS]);
                        break;
                default:
                        BUG();
                }

                ino = LOGFS_INO_MASTER;
                bix = inode->i_ino;
                level = LEVEL(0);
                err = write_one_alias(sb, ino, bix, level, pos, val);
                if (err)
                        return err;
        }
}

static int indirect_write_alias(struct super_block *sb,
                struct logfs_block *block, write_alias_t *write_one_alias)
{
        unsigned long pos;
        struct page *page = block->page;
        u64 ino , bix;
        __be64 *child, val;
        level_t level;
        int err;

        for (pos = 0; ; pos++) {
                pos = fnb(block->alias_map, LOGFS_BLOCK_FACTOR, pos);
                if (pos >= LOGFS_BLOCK_FACTOR)
                        return 0;

                ino = page->mapping->host->i_ino;
                logfs_unpack_index(page->index, &bix, &level);
                child = kmap_atomic(page, KM_USER0);
                val = child[pos];
                kunmap_atomic(child, KM_USER0);
                err = write_one_alias(sb, ino, bix, level, pos, val);
                if (err)
                        return err;
        }
}

int logfs_write_obj_aliases_pagecache(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_block *block;
        int err;

        list_for_each_entry(block, &super->s_object_alias, alias_list) {
                err = block->ops->write_alias(sb, block, write_alias_journal);
                if (err)
                        return err;
        }
        return 0;
}

void __free_block(struct super_block *sb, struct logfs_block *block)
{
        BUG_ON(!list_empty(&block->item_list));
        list_del(&block->alias_list);
        mempool_free(block, logfs_super(sb)->s_block_pool);
}

static void inode_free_block(struct super_block *sb, struct logfs_block *block)
{
        struct inode *inode = block->inode;

        logfs_inode(inode)->li_block = NULL;
        __free_block(sb, block);
}

static void indirect_free_block(struct super_block *sb,
                struct logfs_block *block)
{
        ClearPagePrivate(block->page);
        block->page->private = 0;
        __free_block(sb, block);
}


static struct logfs_block_ops inode_block_ops = {
        .write_block = inode_write_block,
        .block_level = inode_block_level,
        .free_block = inode_free_block,
        .write_alias = inode_write_alias,
};

struct logfs_block_ops indirect_block_ops = {
        .write_block = indirect_write_block,
        .block_level = indirect_block_level,
        .free_block = indirect_free_block,
        .write_alias = indirect_write_alias,
};

struct logfs_block *__alloc_block(struct super_block *sb,
                u64 ino, u64 bix, level_t level)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_block *block;

        block = mempool_alloc(super->s_block_pool, GFP_NOFS);
        memset(block, 0, sizeof(*block));
        INIT_LIST_HEAD(&block->alias_list);
        INIT_LIST_HEAD(&block->item_list);
        block->sb = sb;
        block->ino = ino;
        block->bix = bix;
        block->level = level;
        return block;
}

static void alloc_inode_block(struct inode *inode)
{
        struct logfs_inode *li = logfs_inode(inode);
        struct logfs_block *block;

        if (li->li_block)
                return;

        block = __alloc_block(inode->i_sb, LOGFS_INO_MASTER, inode->i_ino, 0);
        block->inode = inode;
        li->li_block = block;
        block->ops = &inode_block_ops;
}

void initialize_block_counters(struct page *page, struct logfs_block *block,
                __be64 *array, int page_is_empty)
{
        u64 ptr;
        int i, start;

        block->partial = 0;
        block->full = 0;
        start = 0;
        if (page->index < first_indirect_block()) {
                /* Counters are pointless on level 0 */
                return;
        }
        if (page->index == first_indirect_block()) {
                /* Skip unused pointers */
                start = I0_BLOCKS;
                block->full = I0_BLOCKS;
        }
        if (!page_is_empty) {
                for (i = start; i < LOGFS_BLOCK_FACTOR; i++) {
                        ptr = be64_to_cpu(array[i]);
                        if (ptr)
                                block->partial++;
                        if (ptr & LOGFS_FULLY_POPULATED)
                                block->full++;
                }
        }
}

static void alloc_data_block(struct inode *inode, struct page *page)
{
        struct logfs_block *block;
        u64 bix;
        level_t level;

        if (PagePrivate(page))
                return;

        logfs_unpack_index(page->index, &bix, &level);
        block = __alloc_block(inode->i_sb, inode->i_ino, bix, level);
        block->page = page;
        SetPagePrivate(page);
        page->private = (unsigned long)block;
        block->ops = &indirect_block_ops;
}

static void alloc_indirect_block(struct inode *inode, struct page *page,
                int page_is_empty)
{
        struct logfs_block *block;
        __be64 *array;

        if (PagePrivate(page))
                return;

        alloc_data_block(inode, page);

        block = logfs_block(page);
        array = kmap_atomic(page, KM_USER0);
        initialize_block_counters(page, block, array, page_is_empty);
        kunmap_atomic(array, KM_USER0);
}

static void block_set_pointer(struct page *page, int index, u64 ptr)
{
        struct logfs_block *block = logfs_block(page);
        __be64 *array;
        u64 oldptr;

        BUG_ON(!block);
        array = kmap_atomic(page, KM_USER0);
        oldptr = be64_to_cpu(array[index]);
        array[index] = cpu_to_be64(ptr);
        kunmap_atomic(array, KM_USER0);
        SetPageUptodate(page);

        block->full += !!(ptr & LOGFS_FULLY_POPULATED)
                - !!(oldptr & LOGFS_FULLY_POPULATED);
        block->partial += !!ptr - !!oldptr;
}

static u64 block_get_pointer(struct page *page, int index)
{
        __be64 *block;
        u64 ptr;

        block = kmap_atomic(page, KM_USER0);
        ptr = be64_to_cpu(block[index]);
        kunmap_atomic(block, KM_USER0);
        return ptr;
}

static int logfs_read_empty(struct page *page)
{
        zero_user_segment(page, 0, PAGE_CACHE_SIZE);
        return 0;
}

static int logfs_read_direct(struct inode *inode, struct page *page)
{
        struct logfs_inode *li = logfs_inode(inode);
        pgoff_t index = page->index;
        u64 block;

        block = li->li_data[index];
        if (!block)
                return logfs_read_empty(page);

        return logfs_segment_read(inode, page, block, index, 0);
}

static int logfs_read_loop(struct inode *inode, struct page *page,
                int rw_context)
{
        struct logfs_inode *li = logfs_inode(inode);
        u64 bix, bofs = li->li_data[INDIRECT_INDEX];
        level_t level, target_level;
        int ret;
        struct page *ipage;

        logfs_unpack_index(page->index, &bix, &target_level);
        if (!bofs)
                return logfs_read_empty(page);

        if (bix >= maxbix(li->li_height))
                return logfs_read_empty(page);

        for (level = LEVEL(li->li_height);
                        (__force u8)level > (__force u8)target_level;
                        level = SUBLEVEL(level)){
                ipage = logfs_get_page(inode, bix, level, rw_context);
                if (!ipage)
                        return -ENOMEM;

                ret = logfs_segment_read(inode, ipage, bofs, bix, level);
                if (ret) {
                        logfs_put_read_page(ipage);
                        return ret;
                }

                bofs = block_get_pointer(ipage, get_bits(bix, SUBLEVEL(level)));
                logfs_put_page(ipage, rw_context);
                if (!bofs)
                        return logfs_read_empty(page);
        }

        return logfs_segment_read(inode, page, bofs, bix, 0);
}

static int logfs_read_block(struct inode *inode, struct page *page,
                int rw_context)
{
        pgoff_t index = page->index;

        if (index < I0_BLOCKS)
                return logfs_read_direct(inode, page);
        return logfs_read_loop(inode, page, rw_context);
}

static int logfs_exist_loop(struct inode *inode, u64 bix)
{
        struct logfs_inode *li = logfs_inode(inode);
        u64 bofs = li->li_data[INDIRECT_INDEX];
        level_t level;
        int ret;
        struct page *ipage;

        if (!bofs)
                return 0;
        if (bix >= maxbix(li->li_height))
                return 0;

        for (level = LEVEL(li->li_height); level != 0; level = SUBLEVEL(level)) {
                ipage = logfs_get_read_page(inode, bix, level);
                if (!ipage)
                        return -ENOMEM;

                ret = logfs_segment_read(inode, ipage, bofs, bix, level);
                if (ret) {
                        logfs_put_read_page(ipage);
                        return ret;
                }

                bofs = block_get_pointer(ipage, get_bits(bix, SUBLEVEL(level)));
                logfs_put_read_page(ipage);
                if (!bofs)
                        return 0;
        }

        return 1;
}

int logfs_exist_block(struct inode *inode, u64 bix)
{
        struct logfs_inode *li = logfs_inode(inode);

        if (bix < I0_BLOCKS)
                return !!li->li_data[bix];
        return logfs_exist_loop(inode, bix);
}

static u64 seek_holedata_direct(struct inode *inode, u64 bix, int data)
{
        struct logfs_inode *li = logfs_inode(inode);

        for (; bix < I0_BLOCKS; bix++)
                if (data ^ (li->li_data[bix] == 0))
                        return bix;
        return I0_BLOCKS;
}

static u64 seek_holedata_loop(struct inode *inode, u64 bix, int data)
{
        struct logfs_inode *li = logfs_inode(inode);
        __be64 *rblock;
        u64 increment, bofs = li->li_data[INDIRECT_INDEX];
        level_t level;
        int ret, slot;
        struct page *page;

        BUG_ON(!bofs);

        for (level = LEVEL(li->li_height); level != 0; level = SUBLEVEL(level)) {
                increment = 1 << (LOGFS_BLOCK_BITS * ((__force u8)level-1));
                page = logfs_get_read_page(inode, bix, level);
                if (!page)
                        return bix;

                ret = logfs_segment_read(inode, page, bofs, bix, level);
                if (ret) {
                        logfs_put_read_page(page);
                        return bix;
                }

                slot = get_bits(bix, SUBLEVEL(level));
                rblock = kmap_atomic(page, KM_USER0);
                while (slot < LOGFS_BLOCK_FACTOR) {
                        if (data && (rblock[slot] != 0))
                                break;
                        if (!data && !(be64_to_cpu(rblock[slot]) & LOGFS_FULLY_POPULATED))
                                break;
                        slot++;
                        bix += increment;
                        bix &= ~(increment - 1);
                }
                if (slot >= LOGFS_BLOCK_FACTOR) {
                        kunmap_atomic(rblock, KM_USER0);
                        logfs_put_read_page(page);
                        return bix;
                }
                bofs = be64_to_cpu(rblock[slot]);
                kunmap_atomic(rblock, KM_USER0);
                logfs_put_read_page(page);
                if (!bofs) {
                        BUG_ON(data);
                        return bix;
                }
        }
        return bix;
}

/**
 * logfs_seek_hole - find next hole starting at a given block index
 * @inode:              inode to search in
 * @bix:                block index to start searching
 *
 * Returns next hole.  If the file doesn't contain any further holes, the
 * block address next to eof is returned instead.
 */
u64 logfs_seek_hole(struct inode *inode, u64 bix)
{
        struct logfs_inode *li = logfs_inode(inode);

        if (bix < I0_BLOCKS) {
                bix = seek_holedata_direct(inode, bix, 0);
                if (bix < I0_BLOCKS)
                        return bix;
        }

        if (!li->li_data[INDIRECT_INDEX])
                return bix;
        else if (li->li_data[INDIRECT_INDEX] & LOGFS_FULLY_POPULATED)
                bix = maxbix(li->li_height);
        else {
                bix = seek_holedata_loop(inode, bix, 0);
                if (bix < maxbix(li->li_height))
                        return bix;
                /* Should not happen anymore.  But if some port writes semi-
                 * corrupt images (as this one used to) we might run into it.
                 */
                WARN_ON_ONCE(bix == maxbix(li->li_height));
        }

        return bix;
}

static u64 __logfs_seek_data(struct inode *inode, u64 bix)
{
        struct logfs_inode *li = logfs_inode(inode);

        if (bix < I0_BLOCKS) {
                bix = seek_holedata_direct(inode, bix, 1);
                if (bix < I0_BLOCKS)
                        return bix;
        }

        if (bix < maxbix(li->li_height)) {
                if (!li->li_data[INDIRECT_INDEX])
                        bix = maxbix(li->li_height);
                else
                        return seek_holedata_loop(inode, bix, 1);
        }

        return bix;
}

/**
 * logfs_seek_data - find next data block after a given block index
 * @inode:              inode to search in
 * @bix:                block index to start searching
 *
 * Returns next data block.  If the file doesn't contain any further data
 * blocks, the last block in the file is returned instead.
 */
u64 logfs_seek_data(struct inode *inode, u64 bix)
{
        struct super_block *sb = inode->i_sb;
        u64 ret, end;

        ret = __logfs_seek_data(inode, bix);
        end = i_size_read(inode) >> sb->s_blocksize_bits;
        if (ret >= end)
                ret = max(bix, end);
        return ret;
}

static int logfs_is_valid_direct(struct logfs_inode *li, u64 bix, u64 ofs)
{
        return pure_ofs(li->li_data[bix]) == ofs;
}

static int __logfs_is_valid_loop(struct inode *inode, u64 bix,
                u64 ofs, u64 bofs)
{
        struct logfs_inode *li = logfs_inode(inode);
        level_t level;
        int ret;
        struct page *page;

        for (level = LEVEL(li->li_height); level != 0; level = SUBLEVEL(level)){
                page = logfs_get_write_page(inode, bix, level);
                BUG_ON(!page);

                ret = logfs_segment_read(inode, page, bofs, bix, level);
                if (ret) {
                        logfs_put_write_page(page);
                        return 0;
                }

                bofs = block_get_pointer(page, get_bits(bix, SUBLEVEL(level)));
                logfs_put_write_page(page);
                if (!bofs)
                        return 0;

                if (pure_ofs(bofs) == ofs)
                        return 1;
        }
        return 0;
}

static int logfs_is_valid_loop(struct inode *inode, u64 bix, u64 ofs)
{
        struct logfs_inode *li = logfs_inode(inode);
        u64 bofs = li->li_data[INDIRECT_INDEX];

        if (!bofs)
                return 0;

        if (bix >= maxbix(li->li_height))
                return 0;

        if (pure_ofs(bofs) == ofs)
                return 1;

        return __logfs_is_valid_loop(inode, bix, ofs, bofs);
}

static int __logfs_is_valid_block(struct inode *inode, u64 bix, u64 ofs)
{
        struct logfs_inode *li = logfs_inode(inode);

        if ((inode->i_nlink == 0) && atomic_read(&inode->i_count) == 1)
                return 0;

        if (bix < I0_BLOCKS)
                return logfs_is_valid_direct(li, bix, ofs);
        return logfs_is_valid_loop(inode, bix, ofs);
}

/**
 * logfs_is_valid_block - check whether this block is still valid
 *
 * @sb  - superblock
 * @ofs - block physical offset
 * @ino - block inode number
 * @bix - block index
 * @level - block level
 *
 * Returns 0 if the block is invalid, 1 if it is valid and 2 if it will
 * become invalid once the journal is written.
 */
int logfs_is_valid_block(struct super_block *sb, u64 ofs, u64 ino, u64 bix,
                gc_level_t gc_level)
{
        struct logfs_super *super = logfs_super(sb);
        struct inode *inode;
        int ret, cookie;

        /* Umount closes a segment with free blocks remaining.  Those
         * blocks are by definition invalid. */
        if (ino == -1)
                return 0;

        LOGFS_BUG_ON((u64)(u_long)ino != ino, sb);

        inode = logfs_safe_iget(sb, ino, &cookie);
        if (IS_ERR(inode))
                goto invalid;

        ret = __logfs_is_valid_block(inode, bix, ofs);
        logfs_safe_iput(inode, cookie);
        if (ret)
                return ret;

invalid:
        /* Block is nominally invalid, but may still sit in the shadow tree,
         * waiting for a journal commit.
         */
        if (btree_lookup64(&super->s_shadow_tree.old, ofs))
                return 2;
        return 0;
}

int logfs_readpage_nolock(struct page *page)
{
        struct inode *inode = page->mapping->host;
        int ret = -EIO;

        ret = logfs_read_block(inode, page, READ);

        if (ret) {
                ClearPageUptodate(page);
                SetPageError(page);
        } else {
                SetPageUptodate(page);
                ClearPageError(page);
        }
        flush_dcache_page(page);

        return ret;
}

static int logfs_reserve_bytes(struct inode *inode, int bytes)
{
        struct logfs_super *super = logfs_super(inode->i_sb);
        u64 available = super->s_free_bytes + super->s_dirty_free_bytes
                        - super->s_dirty_used_bytes - super->s_dirty_pages;

        if (!bytes)
                return 0;

        if (available < bytes)
                return -ENOSPC;

        if (available < bytes + super->s_root_reserve &&
                        !capable(CAP_SYS_RESOURCE))
                return -ENOSPC;

        return 0;
}

int get_page_reserve(struct inode *inode, struct page *page)
{
        struct logfs_super *super = logfs_super(inode->i_sb);
        int ret;

        if (logfs_block(page) && logfs_block(page)->reserved_bytes)
                return 0;

        logfs_get_wblocks(inode->i_sb, page, WF_LOCK);
        ret = logfs_reserve_bytes(inode, 6 * LOGFS_MAX_OBJECTSIZE);
        if (!ret) {
                alloc_data_block(inode, page);
                logfs_block(page)->reserved_bytes += 6 * LOGFS_MAX_OBJECTSIZE;
                super->s_dirty_pages += 6 * LOGFS_MAX_OBJECTSIZE;
        }
        logfs_put_wblocks(inode->i_sb, page, WF_LOCK);
        return ret;
}

/*
 * We are protected by write lock.  Push victims up to superblock level
 * and release transaction when appropriate.
 */
/* FIXME: This is currently called from the wrong spots. */
static void logfs_handle_transaction(struct inode *inode,
                struct logfs_transaction *ta)
{
        struct logfs_super *super = logfs_super(inode->i_sb);

        if (!ta)
                return;
        logfs_inode(inode)->li_block->ta = NULL;

        if (inode->i_ino != LOGFS_INO_MASTER) {
                BUG(); /* FIXME: Yes, this needs more thought */
                /* just remember the transaction until inode is written */
                //BUG_ON(logfs_inode(inode)->li_transaction);
                //logfs_inode(inode)->li_transaction = ta;
                return;
        }

        switch (ta->state) {
        case CREATE_1: /* fall through */
        case UNLINK_1:
                BUG_ON(super->s_victim_ino);
                super->s_victim_ino = ta->ino;
                break;
        case CREATE_2: /* fall through */
        case UNLINK_2:
                BUG_ON(super->s_victim_ino != ta->ino);
                super->s_victim_ino = 0;
                /* transaction ends here - free it */
                kfree(ta);
                break;
        case CROSS_RENAME_1:
                BUG_ON(super->s_rename_dir);
                BUG_ON(super->s_rename_pos);
                super->s_rename_dir = ta->dir;
                super->s_rename_pos = ta->pos;
                break;
        case CROSS_RENAME_2:
                BUG_ON(super->s_rename_dir != ta->dir);
                BUG_ON(super->s_rename_pos != ta->pos);
                super->s_rename_dir = 0;
                super->s_rename_pos = 0;
                kfree(ta);
                break;
        case TARGET_RENAME_1:
                BUG_ON(super->s_rename_dir);
                BUG_ON(super->s_rename_pos);
                BUG_ON(super->s_victim_ino);
                super->s_rename_dir = ta->dir;
                super->s_rename_pos = ta->pos;
                super->s_victim_ino = ta->ino;
                break;
        case TARGET_RENAME_2:
                BUG_ON(super->s_rename_dir != ta->dir);
                BUG_ON(super->s_rename_pos != ta->pos);
                BUG_ON(super->s_victim_ino != ta->ino);
                super->s_rename_dir = 0;
                super->s_rename_pos = 0;
                break;
        case TARGET_RENAME_3:
                BUG_ON(super->s_rename_dir);
                BUG_ON(super->s_rename_pos);
                BUG_ON(super->s_victim_ino != ta->ino);
                super->s_victim_ino = 0;
                kfree(ta);
                break;
        default:
                BUG();
        }
}

/*
 * Not strictly a reservation, but rather a check that we still have enough
 * space to satisfy the write.
 */
static int logfs_reserve_blocks(struct inode *inode, int blocks)
{
        return logfs_reserve_bytes(inode, blocks * LOGFS_MAX_OBJECTSIZE);
}

struct write_control {
        u64 ofs;
        long flags;
};

static struct logfs_shadow *alloc_shadow(struct inode *inode, u64 bix,
                level_t level, u64 old_ofs)
{
        struct logfs_super *super = logfs_super(inode->i_sb);
        struct logfs_shadow *shadow;

        shadow = mempool_alloc(super->s_shadow_pool, GFP_NOFS);
        memset(shadow, 0, sizeof(*shadow));
        shadow->ino = inode->i_ino;
        shadow->bix = bix;
        shadow->gc_level = expand_level(inode->i_ino, level);
        shadow->old_ofs = old_ofs & ~LOGFS_FULLY_POPULATED;
        return shadow;
}

static void free_shadow(struct inode *inode, struct logfs_shadow *shadow)
{
        struct logfs_super *super = logfs_super(inode->i_sb);

        mempool_free(shadow, super->s_shadow_pool);
}

/**
 * fill_shadow_tree - Propagate shadow tree changes due to a write
 * @inode:      Inode owning the page
 * @page:       Struct page that was written
 * @shadow:     Shadow for the current write
 *
 * Writes in logfs can result in two semi-valid objects.  The old object
 * is still valid as long as it can be reached by following pointers on
 * the medium.  Only when writes propagate all the way up to the journal
 * has the new object safely replaced the old one.
 *
 * To handle this problem, a struct logfs_shadow is used to represent
 * every single write.  It is attached to the indirect block, which is
 * marked dirty.  When the indirect block is written, its shadows are
 * handed up to the next indirect block (or inode).  Untimately they
 * will reach the master inode and be freed upon journal commit.
 *
 * This function handles a single step in the propagation.  It adds the
 * shadow for the current write to the tree, along with any shadows in
 * the page's tree, in case it was an indirect block.  If a page is
 * written, the inode parameter is left NULL, if an inode is written,
 * the page parameter is left NULL.
 */
static void fill_shadow_tree(struct inode *inode, struct page *page,
                struct logfs_shadow *shadow)
{
        struct logfs_super *super = logfs_super(inode->i_sb);
        struct logfs_block *block = logfs_block(page);
        struct shadow_tree *tree = &super->s_shadow_tree;

        if (PagePrivate(page)) {
                if (block->alias_map)
                        super->s_no_object_aliases -= bitmap_weight(
                                        block->alias_map, LOGFS_BLOCK_FACTOR);
                logfs_handle_transaction(inode, block->ta);
                block->ops->free_block(inode->i_sb, block);
        }
        if (shadow) {
                if (shadow->old_ofs)
                        btree_insert64(&tree->old, shadow->old_ofs, shadow,
                                        GFP_NOFS);
                else
                        btree_insert64(&tree->new, shadow->new_ofs, shadow,
                                        GFP_NOFS);

                super->s_dirty_used_bytes += shadow->new_len;
                super->s_dirty_free_bytes += shadow->old_len;
        }
}

static void logfs_set_alias(struct super_block *sb, struct logfs_block *block,
                long child_no)
{
        struct logfs_super *super = logfs_super(sb);

        if (block->inode && block->inode->i_ino == LOGFS_INO_MASTER) {
                /* Aliases in the master inode are pointless. */
                return;
        }

        if (!test_bit(child_no, block->alias_map)) {
                set_bit(child_no, block->alias_map);
                super->s_no_object_aliases++;
        }
        list_move_tail(&block->alias_list, &super->s_object_alias);
}

/*
 * Object aliases can and often do change the size and occupied space of a
 * file.  So not only do we have to change the pointers, we also have to
 * change inode->i_size and li->li_used_bytes.  Which is done by setting
 * another two object aliases for the inode itself.
 */
static void set_iused(struct inode *inode, struct logfs_shadow *shadow)
{
        struct logfs_inode *li = logfs_inode(inode);

        if (shadow->new_len == shadow->old_len)
                return;

        alloc_inode_block(inode);
        li->li_used_bytes += shadow->new_len - shadow->old_len;
        __logfs_set_blocks(inode);
        logfs_set_alias(inode->i_sb, li->li_block, INODE_USED_OFS);
        logfs_set_alias(inode->i_sb, li->li_block, INODE_SIZE_OFS);
}

static int logfs_write_i0(struct inode *inode, struct page *page,
                struct write_control *wc)
{
        struct logfs_shadow *shadow;
        u64 bix;
        level_t level;
        int full, err = 0;

        logfs_unpack_index(page->index, &bix, &level);
        if (wc->ofs == 0)
                if (logfs_reserve_blocks(inode, 1))
                        return -ENOSPC;

        shadow = alloc_shadow(inode, bix, level, wc->ofs);
        if (wc->flags & WF_WRITE)
                err = logfs_segment_write(inode, page, shadow);
        if (wc->flags & WF_DELETE)
                logfs_segment_delete(inode, shadow);
        if (err) {
                free_shadow(inode, shadow);
                return err;
        }

        set_iused(inode, shadow);
        full = 1;
        if (level != 0) {
                alloc_indirect_block(inode, page, 0);
                full = logfs_block(page)->full == LOGFS_BLOCK_FACTOR;
        }
        fill_shadow_tree(inode, page, shadow);
        wc->ofs = shadow->new_ofs;
        if (wc->ofs && full)
                wc->ofs |= LOGFS_FULLY_POPULATED;
        return 0;
}

static int logfs_write_direct(struct inode *inode, struct page *page,
                long flags)
{
        struct logfs_inode *li = logfs_inode(inode);
        struct write_control wc = {
                .ofs = li->li_data[page->index],
                .flags = flags,
        };
        int err;

        alloc_inode_block(inode);

        err = logfs_write_i0(inode, page, &wc);
        if (err)
                return err;

        li->li_data[page->index] = wc.ofs;
        logfs_set_alias(inode->i_sb, li->li_block,
                        page->index + INODE_POINTER_OFS);
        return 0;
}

static int ptr_change(u64 ofs, struct page *page)
{
        struct logfs_block *block = logfs_block(page);
        int empty0, empty1, full0, full1;

        empty0 = ofs == 0;
        empty1 = block->partial == 0;
        if (empty0 != empty1)
                return 1;

        /* The !! is necessary to shrink result to int */
        full0 = !!(ofs & LOGFS_FULLY_POPULATED);
        full1 = block->full == LOGFS_BLOCK_FACTOR;
        if (full0 != full1)
                return 1;
        return 0;
}

static int __logfs_write_rec(struct inode *inode, struct page *page,
                struct write_control *this_wc,
                pgoff_t bix, level_t target_level, level_t level)
{
        int ret, page_empty = 0;
        int child_no = get_bits(bix, SUBLEVEL(level));
        struct page *ipage;
        struct write_control child_wc = {
                .flags = this_wc->flags,
        };

        ipage = logfs_get_write_page(inode, bix, level);
        if (!ipage)
                return -ENOMEM;

        if (this_wc->ofs) {
                ret = logfs_segment_read(inode, ipage, this_wc->ofs, bix, level);
                if (ret)
                        goto out;
        } else if (!PageUptodate(ipage)) {
                page_empty = 1;
                logfs_read_empty(ipage);
        }

        child_wc.ofs = block_get_pointer(ipage, child_no);

        if ((__force u8)level-1 > (__force u8)target_level)
                ret = __logfs_write_rec(inode, page, &child_wc, bix,
                                target_level, SUBLEVEL(level));
        else
                ret = logfs_write_i0(inode, page, &child_wc);

        if (ret)
                goto out;

        alloc_indirect_block(inode, ipage, page_empty);
        block_set_pointer(ipage, child_no, child_wc.ofs);
        /* FIXME: first condition seems superfluous */
        if (child_wc.ofs || logfs_block(ipage)->partial)
                this_wc->flags |= WF_WRITE;
        /* the condition on this_wc->ofs ensures that we won't consume extra
         * space for indirect blocks in the future, which we cannot reserve */
        if (!this_wc->ofs || ptr_change(this_wc->ofs, ipage))
                ret = logfs_write_i0(inode, ipage, this_wc);
        else
                logfs_set_alias(inode->i_sb, logfs_block(ipage), child_no);
out:
        logfs_put_write_page(ipage);
        return ret;
}

static int logfs_write_rec(struct inode *inode, struct page *page,
                pgoff_t bix, level_t target_level, long flags)
{
        struct logfs_inode *li = logfs_inode(inode);
        struct write_control wc = {
                .ofs = li->li_data[INDIRECT_INDEX],
                .flags = flags,
        };
        int ret;

        alloc_inode_block(inode);

        if (li->li_height > (__force u8)target_level)
                ret = __logfs_write_rec(inode, page, &wc, bix, target_level,
                                LEVEL(li->li_height));
        else
                ret = logfs_write_i0(inode, page, &wc);
        if (ret)
                return ret;

        if (li->li_data[INDIRECT_INDEX] != wc.ofs) {
                li->li_data[INDIRECT_INDEX] = wc.ofs;
                logfs_set_alias(inode->i_sb, li->li_block,
                                INDIRECT_INDEX + INODE_POINTER_OFS);
        }
        return ret;
}

void logfs_add_transaction(struct inode *inode, struct logfs_transaction *ta)
{
        alloc_inode_block(inode);
        logfs_inode(inode)->li_block->ta = ta;
}

void logfs_del_transaction(struct inode *inode, struct logfs_transaction *ta)
{
        struct logfs_block *block = logfs_inode(inode)->li_block;

        if (block && block->ta)
                block->ta = NULL;
}

static int grow_inode(struct inode *inode, u64 bix, level_t level)
{
        struct logfs_inode *li = logfs_inode(inode);
        u8 height = (__force u8)level;
        struct page *page;
        struct write_control wc = {
                .flags = WF_WRITE,
        };
        int err;

        BUG_ON(height > 5 || li->li_height > 5);
        while (height > li->li_height || bix >= maxbix(li->li_height)) {
                page = logfs_get_write_page(inode, I0_BLOCKS + 1,
                                LEVEL(li->li_height + 1));
                if (!page)
                        return -ENOMEM;
                logfs_read_empty(page);
                alloc_indirect_block(inode, page, 1);
                block_set_pointer(page, 0, li->li_data[INDIRECT_INDEX]);
                err = logfs_write_i0(inode, page, &wc);
                logfs_put_write_page(page);
                if (err)
                        return err;
                li->li_data[INDIRECT_INDEX] = wc.ofs;
                wc.ofs = 0;
                li->li_height++;
                logfs_set_alias(inode->i_sb, li->li_block, INODE_HEIGHT_OFS);
        }
        return 0;
}

static int __logfs_write_buf(struct inode *inode, struct page *page, long flags)
{
        struct logfs_super *super = logfs_super(inode->i_sb);
        pgoff_t index = page->index;
        u64 bix;
        level_t level;
        int err;

        flags |= WF_WRITE | WF_DELETE;
        inode->i_ctime = inode->i_mtime = CURRENT_TIME;

        logfs_unpack_index(index, &bix, &level);
        if (logfs_block(page) && logfs_block(page)->reserved_bytes)
                super->s_dirty_pages -= logfs_block(page)->reserved_bytes;

        if (index < I0_BLOCKS)
                return logfs_write_direct(inode, page, flags);

        bix = adjust_bix(bix, level);
        err = grow_inode(inode, bix, level);
        if (err)
                return err;
        return logfs_write_rec(inode, page, bix, level, flags);
}

int logfs_write_buf(struct inode *inode, struct page *page, long flags)
{
        struct super_block *sb = inode->i_sb;
        int ret;

        logfs_get_wblocks(sb, page, flags & WF_LOCK);
        ret = __logfs_write_buf(inode, page, flags);
        logfs_put_wblocks(sb, page, flags & WF_LOCK);
        return ret;
}

static int __logfs_delete(struct inode *inode, struct page *page)
{
        long flags = WF_DELETE;

        inode->i_ctime = inode->i_mtime = CURRENT_TIME;

        if (page->index < I0_BLOCKS)
                return logfs_write_direct(inode, page, flags);
        return logfs_write_rec(inode, page, page->index, 0, flags);
}

int logfs_delete(struct inode *inode, pgoff_t index,
                struct shadow_tree *shadow_tree)
{
        struct super_block *sb = inode->i_sb;
        struct page *page;
        int ret;

        page = logfs_get_read_page(inode, index, 0);
        if (!page)
                return -ENOMEM;

        logfs_get_wblocks(sb, page, 1);
        ret = __logfs_delete(inode, page);
        logfs_put_wblocks(sb, page, 1);

        logfs_put_read_page(page);

        return ret;
}

int logfs_rewrite_block(struct inode *inode, u64 bix, u64 ofs,
                gc_level_t gc_level, long flags)
{
        level_t level = shrink_level(gc_level);
        struct page *page;
        int err;

        page = logfs_get_write_page(inode, bix, level);
        if (!page)
                return -ENOMEM;

        err = logfs_segment_read(inode, page, ofs, bix, level);
        if (!err) {
                if (level != 0)
                        alloc_indirect_block(inode, page, 0);
                err = logfs_write_buf(inode, page, flags);
                if (!err && shrink_level(gc_level) == 0) {
                        /* Rewrite cannot mark the inode dirty but has to
                         * write it immediatly.
                         * Q: Can't we just create an alias for the inode
                         * instead?  And if not, why not?
                         */
                        if (inode->i_ino == LOGFS_INO_MASTER)
                                logfs_write_anchor(inode->i_sb);
                        else {
                                err = __logfs_write_inode(inode, flags);
                        }
                }
        }
        logfs_put_write_page(page);
        return err;
}

static int truncate_data_block(struct inode *inode, struct page *page,
                u64 ofs, struct logfs_shadow *shadow, u64 size)
{
        loff_t pageofs = page->index << inode->i_sb->s_blocksize_bits;
        u64 bix;
        level_t level;
        int err;

        /* Does truncation happen within this page? */
        if (size <= pageofs || size - pageofs >= PAGE_SIZE)
                return 0;

        logfs_unpack_index(page->index, &bix, &level);
        BUG_ON(level != 0);

        err = logfs_segment_read(inode, page, ofs, bix, level);
        if (err)
                return err;

        zero_user_segment(page, size - pageofs, PAGE_CACHE_SIZE);
        return logfs_segment_write(inode, page, shadow);
}

static int logfs_truncate_i0(struct inode *inode, struct page *page,
                struct write_control *wc, u64 size)
{
        struct logfs_shadow *shadow;
        u64 bix;
        level_t level;
        int err = 0;

        logfs_unpack_index(page->index, &bix, &level);
        BUG_ON(level != 0);
        shadow = alloc_shadow(inode, bix, level, wc->ofs);

        err = truncate_data_block(inode, page, wc->ofs, shadow, size);
        if (err) {
                free_shadow(inode, shadow);
                return err;
        }

        logfs_segment_delete(inode, shadow);
        set_iused(inode, shadow);
        fill_shadow_tree(inode, page, shadow);
        wc->ofs = shadow->new_ofs;
        return 0;
}

static int logfs_truncate_direct(struct inode *inode, u64 size)
{
        struct logfs_inode *li = logfs_inode(inode);
        struct write_control wc;
        struct page *page;
        int e;
        int err;

        alloc_inode_block(inode);

        for (e = I0_BLOCKS - 1; e >= 0; e--) {
                if (size > (e+1) * LOGFS_BLOCKSIZE)
                        break;

                wc.ofs = li->li_data[e];
                if (!wc.ofs)
                        continue;

                page = logfs_get_write_page(inode, e, 0);
                if (!page)
                        return -ENOMEM;
                err = logfs_segment_read(inode, page, wc.ofs, e, 0);
                if (err) {
                        logfs_put_write_page(page);
                        return err;
                }
                err = logfs_truncate_i0(inode, page, &wc, size);
                logfs_put_write_page(page);
                if (err)
                        return err;

                li->li_data[e] = wc.ofs;
        }
        return 0;
}

/* FIXME: these need to become per-sb once we support different blocksizes */
static u64 __logfs_step[] = {
        1,
        I1_BLOCKS,
        I2_BLOCKS,
        I3_BLOCKS,
};

static u64 __logfs_start_index[] = {
        I0_BLOCKS,
        I1_BLOCKS,
        I2_BLOCKS,
        I3_BLOCKS
};

static inline u64 logfs_step(level_t level)
{
        return __logfs_step[(__force u8)level];
}

static inline u64 logfs_factor(u8 level)
{
        return __logfs_step[level] * LOGFS_BLOCKSIZE;
}

static inline u64 logfs_start_index(level_t level)
{
        return __logfs_start_index[(__force u8)level];
}

static void logfs_unpack_raw_index(pgoff_t index, u64 *bix, level_t *level)
{
        logfs_unpack_index(index, bix, level);
        if (*bix <= logfs_start_index(SUBLEVEL(*level)))
                *bix = 0;
}

static int __logfs_truncate_rec(struct inode *inode, struct page *ipage,
                struct write_control *this_wc, u64 size)
{
        int truncate_happened = 0;
        int e, err = 0;
        u64 bix, child_bix, next_bix;
        level_t level;
        struct page *page;
        struct write_control child_wc = { /* FIXME: flags */ };

        logfs_unpack_raw_index(ipage->index, &bix, &level);
        err = logfs_segment_read(inode, ipage, this_wc->ofs, bix, level);
        if (err)
                return err;

        for (e = LOGFS_BLOCK_FACTOR - 1; e >= 0; e--) {
                child_bix = bix + e * logfs_step(SUBLEVEL(level));
                next_bix = child_bix + logfs_step(SUBLEVEL(level));
                if (size > next_bix * LOGFS_BLOCKSIZE)
                        break;

                child_wc.ofs = pure_ofs(block_get_pointer(ipage, e));
                if (!child_wc.ofs)
                        continue;

                page = logfs_get_write_page(inode, child_bix, SUBLEVEL(level));
                if (!page)
                        return -ENOMEM;

                if ((__force u8)level > 1)
                        err = __logfs_truncate_rec(inode, page, &child_wc, size);
                else
                        err = logfs_truncate_i0(inode, page, &child_wc, size);
                logfs_put_write_page(page);
                if (err)
                        return err;

                truncate_happened = 1;
                alloc_indirect_block(inode, ipage, 0);
                block_set_pointer(ipage, e, child_wc.ofs);
        }

        if (!truncate_happened) {
                printk("ineffectual truncate (%lx, %lx, %llx)\n", inode->i_ino, ipage->index, size);
                return 0;
        }

        this_wc->flags = WF_DELETE;
        if (logfs_block(ipage)->partial)
                this_wc->flags |= WF_WRITE;

        return logfs_write_i0(inode, ipage, this_wc);
}

static int logfs_truncate_rec(struct inode *inode, u64 size)
{
        struct logfs_inode *li = logfs_inode(inode);
        struct write_control wc = {
                .ofs = li->li_data[INDIRECT_INDEX],
        };
        struct page *page;
        int err;

        alloc_inode_block(inode);

        if (!wc.ofs)
                return 0;

        page = logfs_get_write_page(inode, 0, LEVEL(li->li_height));
        if (!page)
                return -ENOMEM;

        err = __logfs_truncate_rec(inode, page, &wc, size);
        logfs_put_write_page(page);
        if (err)
                return err;

        if (li->li_data[INDIRECT_INDEX] != wc.ofs)
                li->li_data[INDIRECT_INDEX] = wc.ofs;
        return 0;
}

static int __logfs_truncate(struct inode *inode, u64 size)
{
        int ret;

        if (size >= logfs_factor(logfs_inode(inode)->li_height))
                return 0;

        ret = logfs_truncate_rec(inode, size);
        if (ret)
                return ret;

        return logfs_truncate_direct(inode, size);
}

int logfs_truncate(struct inode *inode, u64 size)
{
        struct super_block *sb = inode->i_sb;
        int err;

        logfs_get_wblocks(sb, NULL, 1);
        err = __logfs_truncate(inode, size);
        if (!err)
                err = __logfs_write_inode(inode, 0);
        logfs_put_wblocks(sb, NULL, 1);

        if (!err)
                err = vmtruncate(inode, size);

        /* I don't trust error recovery yet. */
        WARN_ON(err);
        return err;
}

static void move_page_to_inode(struct inode *inode, struct page *page)
{
        struct logfs_inode *li = logfs_inode(inode);
        struct logfs_block *block = logfs_block(page);

        if (!block)
                return;

        log_blockmove("move_page_to_inode(%llx, %llx, %x)\n",
                        block->ino, block->bix, block->level);
        BUG_ON(li->li_block);
        block->ops = &inode_block_ops;
        block->inode = inode;
        li->li_block = block;

        block->page = NULL;
        page->private = 0;
        ClearPagePrivate(page);
}

static void move_inode_to_page(struct page *page, struct inode *inode)
{
        struct logfs_inode *li = logfs_inode(inode);
        struct logfs_block *block = li->li_block;

        if (!block)
                return;

        log_blockmove("move_inode_to_page(%llx, %llx, %x)\n",
                        block->ino, block->bix, block->level);
        BUG_ON(PagePrivate(page));
        block->ops = &indirect_block_ops;
        block->page = page;
        page->private = (unsigned long)block;
        SetPagePrivate(page);

        block->inode = NULL;
        li->li_block = NULL;
}

int logfs_read_inode(struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        struct logfs_super *super = logfs_super(sb);
        struct inode *master_inode = super->s_master_inode;
        struct page *page;
        struct logfs_disk_inode *di;
        u64 ino = inode->i_ino;

        if (ino << sb->s_blocksize_bits > i_size_read(master_inode))
                return -ENODATA;
        if (!logfs_exist_block(master_inode, ino))
                return -ENODATA;

        page = read_cache_page(master_inode->i_mapping, ino,
                        (filler_t *)logfs_readpage, NULL);
        if (IS_ERR(page))
                return PTR_ERR(page);

        di = kmap_atomic(page, KM_USER0);
        logfs_disk_to_inode(di, inode);
        kunmap_atomic(di, KM_USER0);
        move_page_to_inode(inode, page);
        page_cache_release(page);
        return 0;
}

/* Caller must logfs_put_write_page(page); */
static struct page *inode_to_page(struct inode *inode)
{
        struct inode *master_inode = logfs_super(inode->i_sb)->s_master_inode;
        struct logfs_disk_inode *di;
        struct page *page;

        BUG_ON(inode->i_ino == LOGFS_INO_MASTER);

        page = logfs_get_write_page(master_inode, inode->i_ino, 0);
        if (!page)
                return NULL;

        di = kmap_atomic(page, KM_USER0);
        logfs_inode_to_disk(inode, di);
        kunmap_atomic(di, KM_USER0);
        move_inode_to_page(page, inode);
        return page;
}

/* Cheaper version of write_inode.  All changes are concealed in
 * aliases, which are moved back.  No write to the medium happens.
 */
void logfs_clear_inode(struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        struct logfs_inode *li = logfs_inode(inode);
        struct logfs_block *block = li->li_block;
        struct page *page;

        /* Only deleted files may be dirty at this point */
        BUG_ON(inode->i_state & I_DIRTY && inode->i_nlink);
        if (!block)
                return;
        if ((logfs_super(sb)->s_flags & LOGFS_SB_FLAG_SHUTDOWN)) {
                block->ops->free_block(inode->i_sb, block);
                return;
        }

        BUG_ON(inode->i_ino < LOGFS_RESERVED_INOS);
        page = inode_to_page(inode);
        BUG_ON(!page); /* FIXME: Use emergency page */
        logfs_put_write_page(page);
}

static int do_write_inode(struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        struct inode *master_inode = logfs_super(sb)->s_master_inode;
        loff_t size = (inode->i_ino + 1) << inode->i_sb->s_blocksize_bits;
        struct page *page;
        int err;

        BUG_ON(inode->i_ino == LOGFS_INO_MASTER);
        /* FIXME: lock inode */

        if (i_size_read(master_inode) < size)
                i_size_write(master_inode, size);

        /* TODO: Tell vfs this inode is clean now */

        page = inode_to_page(inode);
        if (!page)
                return -ENOMEM;

        /* FIXME: transaction is part of logfs_block now.  Is that enough? */
        err = logfs_write_buf(master_inode, page, 0);
        logfs_put_write_page(page);
        return err;
}

static void logfs_mod_segment_entry(struct super_block *sb, u32 segno,
                int write,
                void (*change_se)(struct logfs_segment_entry *, long),
                long arg)
{
        struct logfs_super *super = logfs_super(sb);
        struct inode *inode;
        struct page *page;
        struct logfs_segment_entry *se;
        pgoff_t page_no;
        int child_no;

        page_no = segno >> (sb->s_blocksize_bits - 3);
        child_no = segno & ((sb->s_blocksize >> 3) - 1);

        inode = super->s_segfile_inode;
        page = logfs_get_write_page(inode, page_no, 0);
        BUG_ON(!page); /* FIXME: We need some reserve page for this case */
        if (!PageUptodate(page))
                logfs_read_block(inode, page, WRITE);

        if (write)
                alloc_indirect_block(inode, page, 0);
        se = kmap_atomic(page, KM_USER0);
        change_se(se + child_no, arg);
        if (write) {
                logfs_set_alias(sb, logfs_block(page), child_no);
                BUG_ON((int)be32_to_cpu(se[child_no].valid) > super->s_segsize);
        }
        kunmap_atomic(se, KM_USER0);

        logfs_put_write_page(page);
}

static void __get_segment_entry(struct logfs_segment_entry *se, long _target)
{
        struct logfs_segment_entry *target = (void *)_target;

        *target = *se;
}

void logfs_get_segment_entry(struct super_block *sb, u32 segno,
                struct logfs_segment_entry *se)
{
        logfs_mod_segment_entry(sb, segno, 0, __get_segment_entry, (long)se);
}

static void __set_segment_used(struct logfs_segment_entry *se, long increment)
{
        u32 valid;

        valid = be32_to_cpu(se->valid);
        valid += increment;
        se->valid = cpu_to_be32(valid);
}

void logfs_set_segment_used(struct super_block *sb, u64 ofs, int increment)
{
        struct logfs_super *super = logfs_super(sb);
        u32 segno = ofs >> super->s_segshift;

        if (!increment)
                return;

        logfs_mod_segment_entry(sb, segno, 1, __set_segment_used, increment);
}

static void __set_segment_erased(struct logfs_segment_entry *se, long ec_level)
{
        se->ec_level = cpu_to_be32(ec_level);
}

void logfs_set_segment_erased(struct super_block *sb, u32 segno, u32 ec,
                gc_level_t gc_level)
{
        u32 ec_level = ec << 4 | (__force u8)gc_level;

        logfs_mod_segment_entry(sb, segno, 1, __set_segment_erased, ec_level);
}

static void __set_segment_reserved(struct logfs_segment_entry *se, long ignore)
{
        se->valid = cpu_to_be32(RESERVED);
}

void logfs_set_segment_reserved(struct super_block *sb, u32 segno)
{
        logfs_mod_segment_entry(sb, segno, 1, __set_segment_reserved, 0);
}

static void __set_segment_unreserved(struct logfs_segment_entry *se,
                long ec_level)
{
        se->valid = 0;
        se->ec_level = cpu_to_be32(ec_level);
}

void logfs_set_segment_unreserved(struct super_block *sb, u32 segno, u32 ec)
{
        u32 ec_level = ec << 4;

        logfs_mod_segment_entry(sb, segno, 1, __set_segment_unreserved,
                        ec_level);
}

int __logfs_write_inode(struct inode *inode, long flags)
{
        struct super_block *sb = inode->i_sb;
        int ret;

        logfs_get_wblocks(sb, NULL, flags & WF_LOCK);
        ret = do_write_inode(inode);
        logfs_put_wblocks(sb, NULL, flags & WF_LOCK);
        return ret;
}

static int do_delete_inode(struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        struct inode *master_inode = logfs_super(sb)->s_master_inode;
        struct page *page;
        int ret;

        page = logfs_get_write_page(master_inode, inode->i_ino, 0);
        if (!page)
                return -ENOMEM;

        move_inode_to_page(page, inode);

        logfs_get_wblocks(sb, page, 1);
        ret = __logfs_delete(master_inode, page);
        logfs_put_wblocks(sb, page, 1);

        logfs_put_write_page(page);
        return ret;
}

/*
 * ZOMBIE inodes have already been deleted before and should remain dead,
 * if it weren't for valid checking.  No need to kill them again here.
 */
void logfs_delete_inode(struct inode *inode)
{
        struct logfs_inode *li = logfs_inode(inode);

        if (!(li->li_flags & LOGFS_IF_ZOMBIE)) {
                li->li_flags |= LOGFS_IF_ZOMBIE;
                if (i_size_read(inode) > 0)
                        logfs_truncate(inode, 0);
                do_delete_inode(inode);
        }
        truncate_inode_pages(&inode->i_data, 0);
        clear_inode(inode);
}

void btree_write_block(struct logfs_block *block)
{
        struct inode *inode;
        struct page *page;
        int err, cookie;

        inode = logfs_safe_iget(block->sb, block->ino, &cookie);
        page = logfs_get_write_page(inode, block->bix, block->level);

        err = logfs_readpage_nolock(page);
        BUG_ON(err);
        BUG_ON(!PagePrivate(page));
        BUG_ON(logfs_block(page) != block);
        err = __logfs_write_buf(inode, page, 0);
        BUG_ON(err);
        BUG_ON(PagePrivate(page) || page->private);

        logfs_put_write_page(page);
        logfs_safe_iput(inode, cookie);
}

/**
 * logfs_inode_write - write inode or dentry objects
 *
 * @inode:              parent inode (ifile or directory)
 * @buf:                object to write (inode or dentry)
 * @n:                  object size
 * @_pos:               object number (file position in blocks/objects)
 * @flags:              write flags
 * @lock:               0 if write lock is already taken, 1 otherwise
 * @shadow_tree:        shadow below this inode
 *
 * FIXME: All caller of this put a 200-300 byte variable on the stack,
 * only to call here and do a memcpy from that stack variable.  A good
 * example of wasted performance and stack space.
 */
int logfs_inode_write(struct inode *inode, const void *buf, size_t count,
                loff_t bix, long flags, struct shadow_tree *shadow_tree)
{
        loff_t pos = bix << inode->i_sb->s_blocksize_bits;
        int err;
        struct page *page;
        void *pagebuf;

        BUG_ON(pos & (LOGFS_BLOCKSIZE-1));
        BUG_ON(count > LOGFS_BLOCKSIZE);
        page = logfs_get_write_page(inode, bix, 0);
        if (!page)
                return -ENOMEM;

        pagebuf = kmap_atomic(page, KM_USER0);
        memcpy(pagebuf, buf, count);
        flush_dcache_page(page);
        kunmap_atomic(pagebuf, KM_USER0);

        if (i_size_read(inode) < pos + LOGFS_BLOCKSIZE)
                i_size_write(inode, pos + LOGFS_BLOCKSIZE);

        err = logfs_write_buf(inode, page, flags);
        logfs_put_write_page(page);
        return err;
}

int logfs_open_segfile(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        struct inode *inode;

        inode = logfs_read_meta_inode(sb, LOGFS_INO_SEGFILE);
        if (IS_ERR(inode))
                return PTR_ERR(inode);
        super->s_segfile_inode = inode;
        return 0;
}

int logfs_init_rw(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        int min_fill = 3 * super->s_no_blocks;

        INIT_LIST_HEAD(&super->s_object_alias);
        mutex_init(&super->s_write_mutex);
        super->s_block_pool = mempool_create_kmalloc_pool(min_fill,
                        sizeof(struct logfs_block));
        super->s_shadow_pool = mempool_create_kmalloc_pool(min_fill,
                        sizeof(struct logfs_shadow));
        return 0;
}

void logfs_cleanup_rw(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);

        destroy_meta_inode(super->s_segfile_inode);
        if (super->s_block_pool)
                mempool_destroy(super->s_block_pool);
        if (super->s_shadow_pool)
                mempool_destroy(super->s_shadow_pool);
}