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    Subject[PATCH 3/5] ext4: Extent overlap bugfix
    This is a fix for an extent-overlap bug. The fallocate() implementation
    on ext4 depends on this bugfix. Though this fix had been posted earlier,
    but because it is still not part of mainline code, I have attached it
    here too.

    Signed-off-by: Amit Arora <aarora@in.ibm.com>
    ---
    fs/ext4/extents.c | 50 ++++++++++++++++++++++++++++++++++++++--
    include/linux/ext4_fs_extents.h | 1
    2 files changed, 49 insertions(+), 2 deletions(-)

    Index: linux-2.6.21/fs/ext4/extents.c
    ===================================================================
    --- linux-2.6.21.orig/fs/ext4/extents.c
    +++ linux-2.6.21/fs/ext4/extents.c
    @@ -1129,6 +1129,45 @@ ext4_can_extents_be_merged(struct inode
    }

    /*
    + * ext4_ext_check_overlap:
    + * check if a portion of the "newext" extent overlaps with an
    + * existing extent.
    + *
    + * If there is an overlap discovered, it updates the length of the newext
    + * such that there will be no overlap, and then returns 1.
    + * If there is no overlap found, it returns 0.
    + */
    +unsigned int ext4_ext_check_overlap(struct inode *inode,
    + struct ext4_extent *newext,
    + struct ext4_ext_path *path)
    +{
    + unsigned long b1, b2;
    + unsigned int depth, len1;
    +
    + b1 = le32_to_cpu(newext->ee_block);
    + len1 = le16_to_cpu(newext->ee_len);
    + depth = ext_depth(inode);
    + if (!path[depth].p_ext)
    + goto out;
    + b2 = le32_to_cpu(path[depth].p_ext->ee_block);
    +
    + /* get the next allocated block if the extent in the path
    + * is before the requested block(s) */
    + if (b2 < b1) {
    + b2 = ext4_ext_next_allocated_block(path);
    + if (b2 == EXT_MAX_BLOCK)
    + goto out;
    + }
    +
    + if (b1 + len1 > b2) {
    + newext->ee_len = cpu_to_le16(b2 - b1);
    + return 1;
    + }
    +out:
    + return 0;
    +}
    +
    +/*
    * ext4_ext_insert_extent:
    * tries to merge requsted extent into the existing extent or
    * inserts requested extent as new one into the tree,
    @@ -2032,7 +2071,15 @@ int ext4_ext_get_blocks(handle_t *handle

    /* allocate new block */
    goal = ext4_ext_find_goal(inode, path, iblock);
    - allocated = max_blocks;
    +
    + /* Check if we can really insert (iblock)::(iblock+max_blocks) extent */
    + newex.ee_block = cpu_to_le32(iblock);
    + newex.ee_len = cpu_to_le16(max_blocks);
    + err = ext4_ext_check_overlap(inode, &newex, path);
    + if (err)
    + allocated = le16_to_cpu(newex.ee_len);
    + else
    + allocated = max_blocks;
    newblock = ext4_new_blocks(handle, inode, goal, &allocated, &err);
    if (!newblock)
    goto out2;
    @@ -2040,7 +2087,6 @@ int ext4_ext_get_blocks(handle_t *handle
    goal, newblock, allocated);

    /* try to insert new extent into found leaf and return */
    - newex.ee_block = cpu_to_le32(iblock);
    ext4_ext_store_pblock(&newex, newblock);
    newex.ee_len = cpu_to_le16(allocated);
    err = ext4_ext_insert_extent(handle, inode, path, &newex);
    Index: linux-2.6.21/include/linux/ext4_fs_extents.h
    ===================================================================
    --- linux-2.6.21.orig/include/linux/ext4_fs_extents.h
    +++ linux-2.6.21/include/linux/ext4_fs_extents.h
    @@ -190,6 +190,7 @@ ext4_ext_invalidate_cache(struct inode *

    extern int ext4_extent_tree_init(handle_t *, struct inode *);
    extern int ext4_ext_calc_credits_for_insert(struct inode *, struct ext4_ext_path *);
    +extern unsigned int ext4_ext_check_overlap(struct inode *, struct ext4_extent *, struct ext4_ext_path *);
    extern int ext4_ext_insert_extent(handle_t *, struct inode *, struct ext4_ext_path *, struct ext4_extent *);
    extern int ext4_ext_walk_space(struct inode *, unsigned long, unsigned long, ext_prepare_callback, void *);
    extern struct ext4_ext_path * ext4_ext_find_extent(struct inode *, int, struct ext4_ext_path *);
    -
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