indirect.c

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/*
 *  linux/fs/ext4/indirect.c
 *
 *  from
 *
 *  linux/fs/ext4/inode.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card ([email protected])
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/inode.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Goal-directed block allocation by Stephen Tweedie
 *  ([email protected]), 1993, 1998
 */

#include "ext4_jbd2.h"
#include "truncate.h"

#include <trace/events/ext4.h>

typedef struct {
    __le32  *p;
    __le32  key;
    struct buffer_head *bh;
} Indirect;

static inline void add_chain(Indirect *p, struct buffer_head *bh, __le32 *v)
{
    p->key = *(p->p = v);
    p->bh = bh;
}

/*
 * Portability note: the last comparison (check that we fit into triple
 * indirect block) is spelled differently, because otherwise on an
 * architecture with 32-bit longs and 8Kb pages we might get into trouble
 * if our filesystem had 8Kb blocks. We might use long long, but that would
 * kill us on x86. Oh, well, at least the sign propagation does not matter -
 * i_block would have to be negative in the very beginning, so we would not
 * get there at all.
 */

static int ext4_block_to_path(struct inode *inode,
                  ext4_lblk_t i_block,
                  ext4_lblk_t offsets[4], int *boundary)
{
    int ptrs = EXT4_ADDR_PER_BLOCK(inode->i_sb);
    int ptrs_bits = EXT4_ADDR_PER_BLOCK_BITS(inode->i_sb);
    const long direct_blocks = EXT4_NDIR_BLOCKS,
        indirect_blocks = ptrs,
        double_blocks = (1 << (ptrs_bits * 2));
    int n = 0;
    int final = 0;

    if (i_block < direct_blocks) {
        offsets[n++] = i_block;
        final = direct_blocks;
    } else if ((i_block -= direct_blocks) < indirect_blocks) {
        offsets[n++] = EXT4_IND_BLOCK;
        offsets[n++] = i_block;
        final = ptrs;
    } else if ((i_block -= indirect_blocks) < double_blocks) {
        offsets[n++] = EXT4_DIND_BLOCK;
        offsets[n++] = i_block >> ptrs_bits;
        offsets[n++] = i_block & (ptrs - 1);
        final = ptrs;
    } else if (((i_block -= double_blocks) >> (ptrs_bits * 2)) < ptrs) {
        offsets[n++] = EXT4_TIND_BLOCK;
        offsets[n++] = i_block >> (ptrs_bits * 2);
        offsets[n++] = (i_block >> ptrs_bits) & (ptrs - 1);
        offsets[n++] = i_block & (ptrs - 1);
        final = ptrs;
    } else {
        ext4_warning(inode->i_sb, "block %lu > max in inode %lu",
                 i_block + direct_blocks +
                 indirect_blocks + double_blocks, inode->i_ino);
    }
    if (boundary)
        *boundary = final - 1 - (i_block & (ptrs - 1));
    return n;
}

static Indirect *ext4_get_branch(struct inode *inode, int depth,
                 ext4_lblk_t  *offsets,
                 Indirect chain[4], int *err)
{
    struct super_block *sb = inode->i_sb;
    Indirect *p = chain;
    struct buffer_head *bh;

    *err = 0;
    /* i_data is not going away, no lock needed */
    add_chain(chain, NULL, EXT4_I(inode)->i_data + *offsets);
    if (!p->key)
        goto no_block;
    while (--depth) {
        bh = sb_getblk(sb, le32_to_cpu(p->key));
        if (unlikely(!bh))
            goto failure;

        if (!bh_uptodate_or_lock(bh)) {
            if (bh_submit_read(bh) < 0) {
                put_bh(bh);
                goto failure;
            }
            /* validate block references */
            if (ext4_check_indirect_blockref(inode, bh)) {
                put_bh(bh);
                goto failure;
            }
        }

        add_chain(++p, bh, (__le32 *)bh->b_data + *++offsets);
        /* Reader: end */
        if (!p->key)
            goto no_block;
    }
    return NULL;

failure:
    *err = -EIO;
no_block:
    return p;
}

static ext4_fsblk_t ext4_find_near(struct inode *inode, Indirect *ind)
{
    struct ext4_inode_info *ei = EXT4_I(inode);
    __le32 *start = ind->bh ? (__le32 *) ind->bh->b_data : ei->i_data;
    __le32 *p;

    /* Try to find previous block */
    for (p = ind->p - 1; p >= start; p--) {
        if (*p)
            return le32_to_cpu(*p);
    }

    /* No such thing, so let's try location of indirect block */
    if (ind->bh)
        return ind->bh->b_blocknr;

    /*
     * It is going to be referred to from the inode itself? OK, just put it
     * into the same cylinder group then.
     */
    return ext4_inode_to_goal_block(inode);
}

static ext4_fsblk_t ext4_find_goal(struct inode *inode, ext4_lblk_t block,
                   Indirect *partial)
{
    ext4_fsblk_t goal;

    /*
     * XXX need to get goal block from mballoc's data structures
     */

    goal = ext4_find_near(inode, partial);
    goal = goal & EXT4_MAX_BLOCK_FILE_PHYS;
    return goal;
}

static int ext4_blks_to_allocate(Indirect *branch, int k, unsigned int blks,
                 int blocks_to_boundary)
{
    unsigned int count = 0;

    /*
     * Simple case, [t,d]Indirect block(s) has not allocated yet
     * then it's clear blocks on that path have not allocated
     */
    if (k > 0) {
        /* right now we don't handle cross boundary allocation */
        if (blks < blocks_to_boundary + 1)
            count += blks;
        else
            count += blocks_to_boundary + 1;
        return count;
    }

    count++;
    while (count < blks && count <= blocks_to_boundary &&
        le32_to_cpu(*(branch[0].p + count)) == 0) {
        count++;
    }
    return count;
}

static int ext4_alloc_blocks(handle_t *handle, struct inode *inode,
                 ext4_lblk_t iblock, ext4_fsblk_t goal,
                 int indirect_blks, int blks,
                 ext4_fsblk_t new_blocks[4], int *err)
{
    struct ext4_allocation_request ar;
    int target, i;
    unsigned long count = 0, blk_allocated = 0;
    int index = 0;
    ext4_fsblk_t current_block = 0;
    int ret = 0;

    /*
     * Here we try to allocate the requested multiple blocks at once,
     * on a best-effort basis.
     * To build a branch, we should allocate blocks for
     * the indirect blocks(if not allocated yet), and at least
     * the first direct block of this branch.  That's the
     * minimum number of blocks need to allocate(required)
     */
    /* first we try to allocate the indirect blocks */
    target = indirect_blks;
    while (target > 0) {
        count = target;
        /* allocating blocks for indirect blocks and direct blocks */
        current_block = ext4_new_meta_blocks(handle, inode, goal,
                             0, &count, err);
        if (*err)
            goto failed_out;

        if (unlikely(current_block + count > EXT4_MAX_BLOCK_FILE_PHYS)) {
            EXT4_ERROR_INODE(inode,
                     "current_block %llu + count %lu > %d!",
                     current_block, count,
                     EXT4_MAX_BLOCK_FILE_PHYS);
            *err = -EIO;
            goto failed_out;
        }

        target -= count;
        /* allocate blocks for indirect blocks */
        while (index < indirect_blks && count) {
            new_blocks[index++] = current_block++;
            count--;
        }
        if (count > 0) {
            /*
             * save the new block number
             * for the first direct block
             */
            new_blocks[index] = current_block;
            printk(KERN_INFO "%s returned more blocks than "
                        "requested\n", __func__);
            WARN_ON(1);
            break;
        }
    }

    target = blks - count ;
    blk_allocated = count;
    if (!target)
        goto allocated;
    /* Now allocate data blocks */
    memset(&ar, 0, sizeof(ar));
    ar.inode = inode;
    ar.goal = goal;
    ar.len = target;
    ar.logical = iblock;
    if (S_ISREG(inode->i_mode))
        /* enable in-core preallocation only for regular files */
        ar.flags = EXT4_MB_HINT_DATA;

    current_block = ext4_mb_new_blocks(handle, &ar, err);
    if (unlikely(current_block + ar.len > EXT4_MAX_BLOCK_FILE_PHYS)) {
        EXT4_ERROR_INODE(inode,
                 "current_block %llu + ar.len %d > %d!",
                 current_block, ar.len,
                 EXT4_MAX_BLOCK_FILE_PHYS);
        *err = -EIO;
        goto failed_out;
    }

    if (*err && (target == blks)) {
        /*
         * if the allocation failed and we didn't allocate
         * any blocks before
         */
        goto failed_out;
    }
    if (!*err) {
        if (target == blks) {
            /*
             * save the new block number
             * for the first direct block
             */
            new_blocks[index] = current_block;
        }
        blk_allocated += ar.len;
    }
allocated:
    /* total number of blocks allocated for direct blocks */
    ret = blk_allocated;
    *err = 0;
    return ret;
failed_out:
    for (i = 0; i < index; i++)
        ext4_free_blocks(handle, inode, NULL, new_blocks[i], 1, 0);
    return ret;
}

static int ext4_alloc_branch(handle_t *handle, struct inode *inode,
                 ext4_lblk_t iblock, int indirect_blks,
                 int *blks, ext4_fsblk_t goal,
                 ext4_lblk_t *offsets, Indirect *branch)
{
    int blocksize = inode->i_sb->s_blocksize;
    int i, n = 0;
    int err = 0;
    struct buffer_head *bh;
    int num;
    ext4_fsblk_t new_blocks[4];
    ext4_fsblk_t current_block;

    num = ext4_alloc_blocks(handle, inode, iblock, goal, indirect_blks,
                *blks, new_blocks, &err);
    if (err)
        return err;

    branch[0].key = cpu_to_le32(new_blocks[0]);
    /*
     * metadata blocks and data blocks are allocated.
     */
    for (n = 1; n <= indirect_blks;  n++) {
        /*
         * Get buffer_head for parent block, zero it out
         * and set the pointer to new one, then send
         * parent to disk.
         */
        bh = sb_getblk(inode->i_sb, new_blocks[n-1]);
        if (unlikely(!bh)) {
            err = -EIO;
            goto failed;
        }

        branch[n].bh = bh;
        lock_buffer(bh);
        BUFFER_TRACE(bh, "call get_create_access");
        err = ext4_journal_get_create_access(handle, bh);
        if (err) {
            /* Don't brelse(bh) here; it's done in
             * ext4_journal_forget() below */
            unlock_buffer(bh);
            goto failed;
        }

        memset(bh->b_data, 0, blocksize);
        branch[n].p = (__le32 *) bh->b_data + offsets[n];
        branch[n].key = cpu_to_le32(new_blocks[n]);
        *branch[n].p = branch[n].key;
        if (n == indirect_blks) {
            current_block = new_blocks[n];
            /*
             * End of chain, update the last new metablock of
             * the chain to point to the new allocated
             * data blocks numbers
             */
            for (i = 1; i < num; i++)
                *(branch[n].p + i) = cpu_to_le32(++current_block);
        }
        BUFFER_TRACE(bh, "marking uptodate");
        set_buffer_uptodate(bh);
        unlock_buffer(bh);

        BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
        err = ext4_handle_dirty_metadata(handle, inode, bh);
        if (err)
            goto failed;
    }
    *blks = num;
    return err;
failed:
    /* Allocation failed, free what we already allocated */
    ext4_free_blocks(handle, inode, NULL, new_blocks[0], 1, 0);
    for (i = 1; i <= n ; i++) {
        /*
         * branch[i].bh is newly allocated, so there is no
         * need to revoke the block, which is why we don't
         * need to set EXT4_FREE_BLOCKS_METADATA.
         */
        ext4_free_blocks(handle, inode, NULL, new_blocks[i], 1,
                 EXT4_FREE_BLOCKS_FORGET);
    }
    for (i = n+1; i < indirect_blks; i++)
        ext4_free_blocks(handle, inode, NULL, new_blocks[i], 1, 0);

    ext4_free_blocks(handle, inode, NULL, new_blocks[i], num, 0);

    return err;
}

static int ext4_splice_branch(handle_t *handle, struct inode *inode,
                  ext4_lblk_t block, Indirect *where, int num,
                  int blks)
{
    int i;
    int err = 0;
    ext4_fsblk_t current_block;

    /*
     * If we're splicing into a [td]indirect block (as opposed to the
     * inode) then we need to get write access to the [td]indirect block
     * before the splice.
     */
    if (where->bh) {
        BUFFER_TRACE(where->bh, "get_write_access");
        err = ext4_journal_get_write_access(handle, where->bh);
        if (err)
            goto err_out;
    }
    /* That's it */

    *where->p = where->key;

    /*
     * Update the host buffer_head or inode to point to more just allocated
     * direct blocks blocks
     */
    if (num == 0 && blks > 1) {
        current_block = le32_to_cpu(where->key) + 1;
        for (i = 1; i < blks; i++)
            *(where->p + i) = cpu_to_le32(current_block++);
    }

    /* We are done with atomic stuff, now do the rest of housekeeping */
    /* had we spliced it onto indirect block? */
    if (where->bh) {
        /*
         * If we spliced it onto an indirect block, we haven't
         * altered the inode.  Note however that if it is being spliced
         * onto an indirect block at the very end of the file (the
         * file is growing) then we *will* alter the inode to reflect
         * the new i_size.  But that is not done here - it is done in
         * generic_commit_write->__mark_inode_dirty->ext4_dirty_inode.
         */
        jbd_debug(5, "splicing indirect only\n");
        BUFFER_TRACE(where->bh, "call ext4_handle_dirty_metadata");
        err = ext4_handle_dirty_metadata(handle, inode, where->bh);
        if (err)
            goto err_out;
    } else {
        /*
         * OK, we spliced it into the inode itself on a direct block.
         */
        ext4_mark_inode_dirty(handle, inode);
        jbd_debug(5, "splicing direct\n");
    }
    return err;

err_out:
    for (i = 1; i <= num; i++) {
        /*
         * branch[i].bh is newly allocated, so there is no
         * need to revoke the block, which is why we don't
         * need to set EXT4_FREE_BLOCKS_METADATA.
         */
        ext4_free_blocks(handle, inode, where[i].bh, 0, 1,
                 EXT4_FREE_BLOCKS_FORGET);
    }
    ext4_free_blocks(handle, inode, NULL, le32_to_cpu(where[num].key),
             blks, 0);

    return err;
}

/*
 * The ext4_ind_map_blocks() function handles non-extents inodes
 * (i.e., using the traditional indirect/double-indirect i_blocks
 * scheme) for ext4_map_blocks().
 *
 * Allocation strategy is simple: if we have to allocate something, we will
 * have to go the whole way to leaf. So let's do it before attaching anything
 * to tree, set linkage between the newborn blocks, write them if sync is
 * required, recheck the path, free and repeat if check fails, otherwise
 * set the last missing link (that will protect us from any truncate-generated
 * removals - all blocks on the path are immune now) and possibly force the
 * write on the parent block.
 * That has a nice additional property: no special recovery from the failed
 * allocations is needed - we simply release blocks and do not touch anything
 * reachable from inode.
 *
 * `handle' can be NULL if create == 0.
 *
 * return > 0, # of blocks mapped or allocated.
 * return = 0, if plain lookup failed.
 * return < 0, error case.
 *
 * The ext4_ind_get_blocks() function should be called with
 * down_write(&EXT4_I(inode)->i_data_sem) if allocating filesystem
 * blocks (i.e., flags has EXT4_GET_BLOCKS_CREATE set) or
 * down_read(&EXT4_I(inode)->i_data_sem) if not allocating file system
 * blocks.
 */
int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
            struct ext4_map_blocks *map,
            int flags)
{
    int err = -EIO;
    ext4_lblk_t offsets[4];
    Indirect chain[4];
    Indirect *partial;
    ext4_fsblk_t goal;
    int indirect_blks;
    int blocks_to_boundary = 0;
    int depth;
    int count = 0;
    ext4_fsblk_t first_block = 0;

    trace_ext4_ind_map_blocks_enter(inode, map->m_lblk, map->m_len, flags);
    J_ASSERT(!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)));
    J_ASSERT(handle != NULL || (flags & EXT4_GET_BLOCKS_CREATE) == 0);
    depth = ext4_block_to_path(inode, map->m_lblk, offsets,
                   &blocks_to_boundary);

    if (depth == 0)
        goto out;

    partial = ext4_get_branch(inode, depth, offsets, chain, &err);

    /* Simplest case - block found, no allocation needed */
    if (!partial) {
        first_block = le32_to_cpu(chain[depth - 1].key);
        count++;
        /*map more blocks*/
        while (count < map->m_len && count <= blocks_to_boundary) {
            ext4_fsblk_t blk;

            blk = le32_to_cpu(*(chain[depth-1].p + count));

            if (blk == first_block + count)
                count++;
            else
                break;
        }
        goto got_it;
    }

    /* Next simple case - plain lookup or failed read of indirect block */
    if ((flags & EXT4_GET_BLOCKS_CREATE) == 0 || err == -EIO)
        goto cleanup;

    /*
     * Okay, we need to do block allocation.
    */
    if (EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
                       EXT4_FEATURE_RO_COMPAT_BIGALLOC)) {
        EXT4_ERROR_INODE(inode, "Can't allocate blocks for "
                 "non-extent mapped inodes with bigalloc");
        return -ENOSPC;
    }

    goal = ext4_find_goal(inode, map->m_lblk, partial);

    /* the number of blocks need to allocate for [d,t]indirect blocks */
    indirect_blks = (chain + depth) - partial - 1;

    /*
     * Next look up the indirect map to count the totoal number of
     * direct blocks to allocate for this branch.
     */
    count = ext4_blks_to_allocate(partial, indirect_blks,
                      map->m_len, blocks_to_boundary);
    /*
     * Block out ext4_truncate while we alter the tree
     */
    err = ext4_alloc_branch(handle, inode, map->m_lblk, indirect_blks,
                &count, goal,
                offsets + (partial - chain), partial);

    /*
     * The ext4_splice_branch call will free and forget any buffers
     * on the new chain if there is a failure, but that risks using
     * up transaction credits, especially for bitmaps where the
     * credits cannot be returned.  Can we handle this somehow?  We
     * may need to return -EAGAIN upwards in the worst case.  --sct
     */
    if (!err)
        err = ext4_splice_branch(handle, inode, map->m_lblk,
                     partial, indirect_blks, count);
    if (err)
        goto cleanup;

    map->m_flags |= EXT4_MAP_NEW;

    ext4_update_inode_fsync_trans(handle, inode, 1);
got_it:
    map->m_flags |= EXT4_MAP_MAPPED;
    map->m_pblk = le32_to_cpu(chain[depth-1].key);
    map->m_len = count;
    if (count > blocks_to_boundary)
        map->m_flags |= EXT4_MAP_BOUNDARY;
    err = count;
    /* Clean up and exit */
    partial = chain + depth - 1;    /* the whole chain */
cleanup:
    while (partial > chain) {
        BUFFER_TRACE(partial->bh, "call brelse");
        brelse(partial->bh);
        partial--;
    }
out:
    trace_ext4_ind_map_blocks_exit(inode, map->m_lblk,
                map->m_pblk, map->m_len, err);
    return err;
}

/*
 * O_DIRECT for ext3 (or indirect map) based files
 *
 * If the O_DIRECT write will extend the file then add this inode to the
 * orphan list.  So recovery will truncate it back to the original size
 * if the machine crashes during the write.
 *
 * If the O_DIRECT write is intantiating holes inside i_size and the machine
 * crashes then stale disk data _may_ be exposed inside the file. But current
 * VFS code falls back into buffered path in that case so we are safe.
 */
ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb,
               const struct iovec *iov, loff_t offset,
               unsigned long nr_segs)
{
    struct file *file = iocb->ki_filp;
    struct inode *inode = file->f_mapping->host;
    struct ext4_inode_info *ei = EXT4_I(inode);
    handle_t *handle;
    ssize_t ret;
    int orphan = 0;
    size_t count = iov_length(iov, nr_segs);
    int retries = 0;

    if (rw == WRITE) {
        loff_t final_size = offset + count;

        if (final_size > inode->i_size) {
            /* Credits for sb + inode write */
            handle = ext4_journal_start(inode, 2);
            if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                goto out;
            }
            ret = ext4_orphan_add(handle, inode);
            if (ret) {
                ext4_journal_stop(handle);
                goto out;
            }
            orphan = 1;
            ei->i_disksize = inode->i_size;
            ext4_journal_stop(handle);
        }
    }

retry:
    if (rw == READ && ext4_should_dioread_nolock(inode)) {
        if (unlikely(atomic_read(&EXT4_I(inode)->i_unwritten))) {
            mutex_lock(&inode->i_mutex);
            ext4_flush_unwritten_io(inode);
            mutex_unlock(&inode->i_mutex);
        }
        /*
         * Nolock dioread optimization may be dynamically disabled
         * via ext4_inode_block_unlocked_dio(). Check inode's state
         * while holding extra i_dio_count ref.
         */
        atomic_inc(&inode->i_dio_count);
        smp_mb();
        if (unlikely(ext4_test_inode_state(inode,
                            EXT4_STATE_DIOREAD_LOCK))) {
            inode_dio_done(inode);
            goto locked;
        }
        ret = __blockdev_direct_IO(rw, iocb, inode,
                 inode->i_sb->s_bdev, iov,
                 offset, nr_segs,
                 ext4_get_block, NULL, NULL, 0);
        inode_dio_done(inode);
    } else {
locked:
        ret = blockdev_direct_IO(rw, iocb, inode, iov,
                 offset, nr_segs, ext4_get_block);

        if (unlikely((rw & WRITE) && ret < 0)) {
            loff_t isize = i_size_read(inode);
            loff_t end = offset + iov_length(iov, nr_segs);

            if (end > isize)
                ext4_truncate_failed_write(inode);
        }
    }
    if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
        goto retry;

    if (orphan) {
        int err;

        /* Credits for sb + inode write */
        handle = ext4_journal_start(inode, 2);
        if (IS_ERR(handle)) {
            /* This is really bad luck. We've written the data
             * but cannot extend i_size. Bail out and pretend
             * the write failed... */
            ret = PTR_ERR(handle);
            if (inode->i_nlink)
                ext4_orphan_del(NULL, inode);

            goto out;
        }
        if (inode->i_nlink)
            ext4_orphan_del(handle, inode);
        if (ret > 0) {
            loff_t end = offset + ret;
            if (end > inode->i_size) {
                ei->i_disksize = end;
                i_size_write(inode, end);
                /*
                 * We're going to return a positive `ret'
                 * here due to non-zero-length I/O, so there's
                 * no way of reporting error returns from
                 * ext4_mark_inode_dirty() to userspace.  So
                 * ignore it.
                 */
                ext4_mark_inode_dirty(handle, inode);
            }
        }
        err = ext4_journal_stop(handle);
        if (ret == 0)
            ret = err;
    }
out:
    return ret;
}

/*
 * Calculate the number of metadata blocks need to reserve
 * to allocate a new block at @lblocks for non extent file based file
 */
int ext4_ind_calc_metadata_amount(struct inode *inode, sector_t lblock)
{
    struct ext4_inode_info *ei = EXT4_I(inode);
    sector_t dind_mask = ~((sector_t)EXT4_ADDR_PER_BLOCK(inode->i_sb) - 1);
    int blk_bits;

    if (lblock < EXT4_NDIR_BLOCKS)
        return 0;

    lblock -= EXT4_NDIR_BLOCKS;

    if (ei->i_da_metadata_calc_len &&
        (lblock & dind_mask) == ei->i_da_metadata_calc_last_lblock) {
        ei->i_da_metadata_calc_len++;
        return 0;
    }
    ei->i_da_metadata_calc_last_lblock = lblock & dind_mask;
    ei->i_da_metadata_calc_len = 1;
    blk_bits = order_base_2(lblock);
    return (blk_bits / EXT4_ADDR_PER_BLOCK_BITS(inode->i_sb)) + 1;
}

int ext4_ind_trans_blocks(struct inode *inode, int nrblocks, int chunk)
{
    int indirects;

    /* if nrblocks are contiguous */
    if (chunk) {
        /*
         * With N contiguous data blocks, we need at most
         * N/EXT4_ADDR_PER_BLOCK(inode->i_sb) + 1 indirect blocks,
         * 2 dindirect blocks, and 1 tindirect block
         */
        return DIV_ROUND_UP(nrblocks,
                    EXT4_ADDR_PER_BLOCK(inode->i_sb)) + 4;
    }
    /*
     * if nrblocks are not contiguous, worse case, each block touch
     * a indirect block, and each indirect block touch a double indirect
     * block, plus a triple indirect block
     */
    indirects = nrblocks * 2 + 1;
    return indirects;
}

/*
 * Truncate transactions can be complex and absolutely huge.  So we need to
 * be able to restart the transaction at a conventient checkpoint to make
 * sure we don't overflow the journal.
 *
 * start_transaction gets us a new handle for a truncate transaction,
 * and extend_transaction tries to extend the existing one a bit.  If
 * extend fails, we need to propagate the failure up and restart the
 * transaction in the top-level truncate loop. --sct
 */
static handle_t *start_transaction(struct inode *inode)
{
    handle_t *result;

    result = ext4_journal_start(inode, ext4_blocks_for_truncate(inode));
    if (!IS_ERR(result))
        return result;

    ext4_std_error(inode->i_sb, PTR_ERR(result));
    return result;
}

/*
 * Try to extend this transaction for the purposes of truncation.
 *
 * Returns 0 if we managed to create more room.  If we can't create more
 * room, and the transaction must be restarted we return 1.
 */
static int try_to_extend_transaction(handle_t *handle, struct inode *inode)
{
    if (!ext4_handle_valid(handle))
        return 0;
    if (ext4_handle_has_enough_credits(handle, EXT4_RESERVE_TRANS_BLOCKS+1))
        return 0;
    if (!ext4_journal_extend(handle, ext4_blocks_for_truncate(inode)))
        return 0;
    return 1;
}

/*
 * Probably it should be a library function... search for first non-zero word
 * or memcmp with zero_page, whatever is better for particular architecture.
 * Linus?
 */
static inline int all_zeroes(__le32 *p, __le32 *q)
{
    while (p < q)
        if (*p++)
            return 0;
    return 1;
}

static Indirect *ext4_find_shared(struct inode *inode, int depth,
                  ext4_lblk_t offsets[4], Indirect chain[4],
                  __le32 *top)
{
    Indirect *partial, *p;
    int k, err;

    *top = 0;
    /* Make k index the deepest non-null offset + 1 */
    for (k = depth; k > 1 && !offsets[k-1]; k--)
        ;
    partial = ext4_get_branch(inode, k, offsets, chain, &err);
    /* Writer: pointers */
    if (!partial)
        partial = chain + k-1;
    /*
     * If the branch acquired continuation since we've looked at it -
     * fine, it should all survive and (new) top doesn't belong to us.
     */
    if (!partial->key && *partial->p)
        /* Writer: end */
        goto no_top;
    for (p = partial; (p > chain) && all_zeroes((__le32 *) p->bh->b_data, p->p); p--)
        ;
    /*
     * OK, we've found the last block that must survive. The rest of our
     * branch should be detached before unlocking. However, if that rest
     * of branch is all ours and does not grow immediately from the inode
     * it's easier to cheat and just decrement partial->p.
     */
    if (p == chain + k - 1 && p > chain) {
        p->p--;
    } else {
        *top = *p->p;
        /* Nope, don't do this in ext4.  Must leave the tree intact */
#if 0
        *p->p = 0;
#endif
    }
    /* Writer: end */

    while (partial > p) {
        brelse(partial->bh);
        partial--;
    }
no_top:
    return partial;
}

/*
 * Zero a number of block pointers in either an inode or an indirect block.
 * If we restart the transaction we must again get write access to the
 * indirect block for further modification.
 *
 * We release `count' blocks on disk, but (last - first) may be greater
 * than `count' because there can be holes in there.
 *
 * Return 0 on success, 1 on invalid block range
 * and < 0 on fatal error.
 */
static int ext4_clear_blocks(handle_t *handle, struct inode *inode,
                 struct buffer_head *bh,
                 ext4_fsblk_t block_to_free,
                 unsigned long count, __le32 *first,
                 __le32 *last)
{
    __le32 *p;
    int flags = EXT4_FREE_BLOCKS_FORGET | EXT4_FREE_BLOCKS_VALIDATED;
    int err;

    if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
        flags |= EXT4_FREE_BLOCKS_METADATA;

    if (!ext4_data_block_valid(EXT4_SB(inode->i_sb), block_to_free,
                   count)) {
        EXT4_ERROR_INODE(inode, "attempt to clear invalid "
                 "blocks %llu len %lu",
                 (unsigned long long) block_to_free, count);
        return 1;
    }

    if (try_to_extend_transaction(handle, inode)) {
        if (bh) {
            BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
            err = ext4_handle_dirty_metadata(handle, inode, bh);
            if (unlikely(err))
                goto out_err;
        }
        err = ext4_mark_inode_dirty(handle, inode);
        if (unlikely(err))
            goto out_err;
        err = ext4_truncate_restart_trans(handle, inode,
                    ext4_blocks_for_truncate(inode));
        if (unlikely(err))
            goto out_err;
        if (bh) {
            BUFFER_TRACE(bh, "retaking write access");
            err = ext4_journal_get_write_access(handle, bh);
            if (unlikely(err))
                goto out_err;
        }
    }

    for (p = first; p < last; p++)
        *p = 0;

    ext4_free_blocks(handle, inode, NULL, block_to_free, count, flags);
    return 0;
out_err:
    ext4_std_error(inode->i_sb, err);
    return err;
}

static void ext4_free_data(handle_t *handle, struct inode *inode,
               struct buffer_head *this_bh,
               __le32 *first, __le32 *last)
{
    ext4_fsblk_t block_to_free = 0;    /* Starting block # of a run */
    unsigned long count = 0;        /* Number of blocks in the run */
    __le32 *block_to_free_p = NULL;     /* Pointer into inode/ind
                           corresponding to
                           block_to_free */
    ext4_fsblk_t nr;            /* Current block # */
    __le32 *p;              /* Pointer into inode/ind
                           for current block */
    int err = 0;

    if (this_bh) {              /* For indirect block */
        BUFFER_TRACE(this_bh, "get_write_access");
        err = ext4_journal_get_write_access(handle, this_bh);
        /* Important: if we can't update the indirect pointers
         * to the blocks, we can't free them. */
        if (err)
            return;
    }

    for (p = first; p < last; p++) {
        nr = le32_to_cpu(*p);
        if (nr) {
            /* accumulate blocks to free if they're contiguous */
            if (count == 0) {
                block_to_free = nr;
                block_to_free_p = p;
                count = 1;
            } else if (nr == block_to_free + count) {
                count++;
            } else {
                err = ext4_clear_blocks(handle, inode, this_bh,
                                block_to_free, count,
                                block_to_free_p, p);
                if (err)
                    break;
                block_to_free = nr;
                block_to_free_p = p;
                count = 1;
            }
        }
    }

    if (!err && count > 0)
        err = ext4_clear_blocks(handle, inode, this_bh, block_to_free,
                    count, block_to_free_p, p);
    if (err < 0)
        /* fatal error */
        return;

    if (this_bh) {
        BUFFER_TRACE(this_bh, "call ext4_handle_dirty_metadata");

        /*
         * The buffer head should have an attached journal head at this
         * point. However, if the data is corrupted and an indirect
         * block pointed to itself, it would have been detached when
         * the block was cleared. Check for this instead of OOPSing.
         */
        if ((EXT4_JOURNAL(inode) == NULL) || bh2jh(this_bh))
            ext4_handle_dirty_metadata(handle, inode, this_bh);
        else
            EXT4_ERROR_INODE(inode,
                     "circular indirect block detected at "
                     "block %llu",
                (unsigned long long) this_bh->b_blocknr);
    }
}

static void ext4_free_branches(handle_t *handle, struct inode *inode,
                   struct buffer_head *parent_bh,
                   __le32 *first, __le32 *last, int depth)
{
    ext4_fsblk_t nr;
    __le32 *p;

    if (ext4_handle_is_aborted(handle))
        return;

    if (depth--) {
        struct buffer_head *bh;
        int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
        p = last;
        while (--p >= first) {
            nr = le32_to_cpu(*p);
            if (!nr)
                continue;       /* A hole */

            if (!ext4_data_block_valid(EXT4_SB(inode->i_sb),
                           nr, 1)) {
                EXT4_ERROR_INODE(inode,
                         "invalid indirect mapped "
                         "block %lu (level %d)",
                         (unsigned long) nr, depth);
                break;
            }

            /* Go read the buffer for the next level down */
            bh = sb_bread(inode->i_sb, nr);

            /*
             * A read failure? Report error and clear slot
             * (should be rare).
             */
            if (!bh) {
                EXT4_ERROR_INODE_BLOCK(inode, nr,
                               "Read failure");
                continue;
            }

            /* This zaps the entire block.  Bottom up. */
            BUFFER_TRACE(bh, "free child branches");
            ext4_free_branches(handle, inode, bh,
                    (__le32 *) bh->b_data,
                    (__le32 *) bh->b_data + addr_per_block,
                    depth);
            brelse(bh);

            /*
             * Everything below this this pointer has been
             * released.  Now let this top-of-subtree go.
             *
             * We want the freeing of this indirect block to be
             * atomic in the journal with the updating of the
             * bitmap block which owns it.  So make some room in
             * the journal.
             *
             * We zero the parent pointer *after* freeing its
             * pointee in the bitmaps, so if extend_transaction()
             * for some reason fails to put the bitmap changes and
             * the release into the same transaction, recovery
             * will merely complain about releasing a free block,
             * rather than leaking blocks.
             */
            if (ext4_handle_is_aborted(handle))
                return;
            if (try_to_extend_transaction(handle, inode)) {
                ext4_mark_inode_dirty(handle, inode);
                ext4_truncate_restart_trans(handle, inode,
                        ext4_blocks_for_truncate(inode));
            }

            /*
             * The forget flag here is critical because if
             * we are journaling (and not doing data
             * journaling), we have to make sure a revoke
             * record is written to prevent the journal
             * replay from overwriting the (former)
             * indirect block if it gets reallocated as a
             * data block.  This must happen in the same
             * transaction where the data blocks are
             * actually freed.
             */
            ext4_free_blocks(handle, inode, NULL, nr, 1,
                     EXT4_FREE_BLOCKS_METADATA|
                     EXT4_FREE_BLOCKS_FORGET);

            if (parent_bh) {
                /*
                 * The block which we have just freed is
                 * pointed to by an indirect block: journal it
                 */
                BUFFER_TRACE(parent_bh, "get_write_access");
                if (!ext4_journal_get_write_access(handle,
                                   parent_bh)){
                    *p = 0;
                    BUFFER_TRACE(parent_bh,
                    "call ext4_handle_dirty_metadata");
                    ext4_handle_dirty_metadata(handle,
                                   inode,
                                   parent_bh);
                }
            }
        }
    } else {
        /* We have reached the bottom of the tree. */
        BUFFER_TRACE(parent_bh, "free data blocks");
        ext4_free_data(handle, inode, parent_bh, first, last);
    }
}

void ext4_ind_truncate(struct inode *inode)
{
    handle_t *handle;
    struct ext4_inode_info *ei = EXT4_I(inode);
    __le32 *i_data = ei->i_data;
    int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
    struct address_space *mapping = inode->i_mapping;
    ext4_lblk_t offsets[4];
    Indirect chain[4];
    Indirect *partial;
    __le32 nr = 0;
    int n = 0;
    ext4_lblk_t last_block, max_block;
    loff_t page_len;
    unsigned blocksize = inode->i_sb->s_blocksize;
    int err;

    handle = start_transaction(inode);
    if (IS_ERR(handle))
        return;     /* AKPM: return what? */

    last_block = (inode->i_size + blocksize-1)
                    >> EXT4_BLOCK_SIZE_BITS(inode->i_sb);
    max_block = (EXT4_SB(inode->i_sb)->s_bitmap_maxbytes + blocksize-1)
                    >> EXT4_BLOCK_SIZE_BITS(inode->i_sb);

    if (inode->i_size % PAGE_CACHE_SIZE != 0) {
        page_len = PAGE_CACHE_SIZE -
            (inode->i_size & (PAGE_CACHE_SIZE - 1));

        err = ext4_discard_partial_page_buffers(handle,
            mapping, inode->i_size, page_len, 0);

        if (err)
            goto out_stop;
    }

    if (last_block != max_block) {
        n = ext4_block_to_path(inode, last_block, offsets, NULL);
        if (n == 0)
            goto out_stop;  /* error */
    }

    /*
     * OK.  This truncate is going to happen.  We add the inode to the
     * orphan list, so that if this truncate spans multiple transactions,
     * and we crash, we will resume the truncate when the filesystem
     * recovers.  It also marks the inode dirty, to catch the new size.
     *
     * Implication: the file must always be in a sane, consistent
     * truncatable state while each transaction commits.
     */
    if (ext4_orphan_add(handle, inode))
        goto out_stop;

    /*
     * From here we block out all ext4_get_block() callers who want to
     * modify the block allocation tree.
     */
    down_write(&ei->i_data_sem);

    ext4_discard_preallocations(inode);

    /*
     * The orphan list entry will now protect us from any crash which
     * occurs before the truncate completes, so it is now safe to propagate
     * the new, shorter inode size (held for now in i_size) into the
     * on-disk inode. We do this via i_disksize, which is the value which
     * ext4 *really* writes onto the disk inode.
     */
    ei->i_disksize = inode->i_size;

    if (last_block == max_block) {
        /*
         * It is unnecessary to free any data blocks if last_block is
         * equal to the indirect block limit.
         */
        goto out_unlock;
    } else if (n == 1) {        /* direct blocks */
        ext4_free_data(handle, inode, NULL, i_data+offsets[0],
                   i_data + EXT4_NDIR_BLOCKS);
        goto do_indirects;
    }

    partial = ext4_find_shared(inode, n, offsets, chain, &nr);
    /* Kill the top of shared branch (not detached) */
    if (nr) {
        if (partial == chain) {
            /* Shared branch grows from the inode */
            ext4_free_branches(handle, inode, NULL,
                       &nr, &nr+1, (chain+n-1) - partial);
            *partial->p = 0;
            /*
             * We mark the inode dirty prior to restart,
             * and prior to stop.  No need for it here.
             */
        } else {
            /* Shared branch grows from an indirect block */
            BUFFER_TRACE(partial->bh, "get_write_access");
            ext4_free_branches(handle, inode, partial->bh,
                    partial->p,
                    partial->p+1, (chain+n-1) - partial);
        }
    }
    /* Clear the ends of indirect blocks on the shared branch */
    while (partial > chain) {
        ext4_free_branches(handle, inode, partial->bh, partial->p + 1,
                   (__le32*)partial->bh->b_data+addr_per_block,
                   (chain+n-1) - partial);
        BUFFER_TRACE(partial->bh, "call brelse");
        brelse(partial->bh);
        partial--;
    }
do_indirects:
    /* Kill the remaining (whole) subtrees */
    switch (offsets[0]) {
    default:
        nr = i_data[EXT4_IND_BLOCK];
        if (nr) {
            ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 1);
            i_data[EXT4_IND_BLOCK] = 0;
        }
    case EXT4_IND_BLOCK:
        nr = i_data[EXT4_DIND_BLOCK];
        if (nr) {
            ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 2);
            i_data[EXT4_DIND_BLOCK] = 0;
        }
    case EXT4_DIND_BLOCK:
        nr = i_data[EXT4_TIND_BLOCK];
        if (nr) {
            ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 3);
            i_data[EXT4_TIND_BLOCK] = 0;
        }
    case EXT4_TIND_BLOCK:
        ;
    }

out_unlock:
    up_write(&ei->i_data_sem);
    inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
    ext4_mark_inode_dirty(handle, inode);

    /*
     * In a multi-transaction truncate, we only make the final transaction
     * synchronous
     */
    if (IS_SYNC(inode))
        ext4_handle_sync(handle);
out_stop:
    /*
     * If this was a simple ftruncate(), and the file will remain alive
     * then we need to clear up the orphan record which we created above.
     * However, if this was a real unlink then we were called by
     * ext4_delete_inode(), and we allow that function to clean up the
     * orphan info for us.
     */
    if (inode->i_nlink)
        ext4_orphan_del(handle, inode);

    ext4_journal_stop(handle);
    trace_ext4_truncate_exit(inode);
}