fallocate-3-extent-overlap-bugfix

   1 From: "Amit K. Arora" <aarora@linux.vnet.ibm.com>
   2 Subject: [PATCH 3/5] ext4: Extent overlap bugfix
   3 Cc: linux-ext4@vger.kernel.org, suparna@in.ibm.com, cmm@us.ibm.com
   4
   5 This is a fix for an extent-overlap bug. The fallocate() implementation
   6 on ext4 depends on this bugfix. Though this fix had been posted earlier,
   7 but because it is still not part of mainline code, I have attached it
   8 here too.
   9
  10 Signed-off-by: Amit Arora <aarora@in.ibm.com>
  11 ---
  12  fs/ext4/extents.c               |   50 ++++++++++++++++++++++++++++++++++++++--
  13  include/linux/ext4_fs_extents.h |    1
  14  2 files changed, 49 insertions(+), 2 deletions(-)
  15
  16 Index: linux-2.6.21/fs/ext4/extents.c
  17 ===================================================================
  18 --- linux-2.6.21.orig/fs/ext4/extents.c
  19 +++ linux-2.6.21/fs/ext4/extents.c
  20 @@ -1129,6 +1129,45 @@ ext4_can_extents_be_merged(struct inode
  21  }
  22
  23  /*
  24 + * ext4_ext_check_overlap:
  25 + * check if a portion of the "newext" extent overlaps with an
  26 + * existing extent.
  27 + *
  28 + * If there is an overlap discovered, it updates the length of the newext
  29 + * such that there will be no overlap, and then returns 1.
  30 + * If there is no overlap found, it returns 0.
  31 + */
  32 +unsigned int ext4_ext_check_overlap(struct inode *inode,
  33 +                                       struct ext4_extent *newext,
  34 +                                       struct ext4_ext_path *path)
  35 +{
  36 +       unsigned long b1, b2;
  37 +       unsigned int depth, len1;
  38 +
  39 +       b1 = le32_to_cpu(newext->ee_block);
  40 +       len1 = le16_to_cpu(newext->ee_len);
  41 +       depth = ext_depth(inode);
  42 +       if (!path[depth].p_ext)
  43 +               goto out;
  44 +       b2 = le32_to_cpu(path[depth].p_ext->ee_block);
  45 +
  46 +       /* get the next allocated block if the extent in the path
  47 +        * is before the requested block(s) */
  48 +       if (b2 < b1) {
  49 +               b2 = ext4_ext_next_allocated_block(path);
  50 +               if (b2 == EXT_MAX_BLOCK)
  51 +                       goto out;
  52 +       }
  53 +
  54 +       if (b1 + len1 > b2) {
  55 +               newext->ee_len = cpu_to_le16(b2 - b1);
  56 +               return 1;
  57 +       }
  58 +out:
  59 +       return 0;
  60 +}
  61 +
  62 +/*
  63   * ext4_ext_insert_extent:
  64   * tries to merge requsted extent into the existing extent or
  65   * inserts requested extent as new one into the tree,
  66 @@ -2032,7 +2071,15 @@ int ext4_ext_get_blocks(handle_t *handle
  67
  68         /* allocate new block */
  69         goal = ext4_ext_find_goal(inode, path, iblock);
  70 -       allocated = max_blocks;
  71 +
  72 +       /* Check if we can really insert (iblock)::(iblock+max_blocks) extent */
  73 +       newex.ee_block = cpu_to_le32(iblock);
  74 +       newex.ee_len = cpu_to_le16(max_blocks);
  75 +       err = ext4_ext_check_overlap(inode, &newex, path);
  76 +       if (err)
  77 +               allocated = le16_to_cpu(newex.ee_len);
  78 +       else
  79 +               allocated = max_blocks;
  80         newblock = ext4_new_blocks(handle, inode, goal, &allocated, &err);
  81         if (!newblock)
  82                 goto out2;
  83 @@ -2040,7 +2087,6 @@ int ext4_ext_get_blocks(handle_t *handle
  84                         goal, newblock, allocated);
  85
  86         /* try to insert new extent into found leaf and return */
  87 -       newex.ee_block = cpu_to_le32(iblock);
  88         ext4_ext_store_pblock(&newex, newblock);
  89         newex.ee_len = cpu_to_le16(allocated);
  90         err = ext4_ext_insert_extent(handle, inode, path, &newex);
  91 Index: linux-2.6.21/include/linux/ext4_fs_extents.h
  92 ===================================================================
  93 --- linux-2.6.21.orig/include/linux/ext4_fs_extents.h
  94 +++ linux-2.6.21/include/linux/ext4_fs_extents.h
  95 @@ -190,6 +190,7 @@ ext4_ext_invalidate_cache(struct inode *
  96
  97  extern int ext4_extent_tree_init(handle_t *, struct inode *);
  98  extern int ext4_ext_calc_credits_for_insert(struct inode *, struct ext4_ext_path *);
  99 +extern unsigned int ext4_ext_check_overlap(struct inode *, struct ext4_extent *, struct ext4_ext_path *);
 100  extern int ext4_ext_insert_extent(handle_t *, struct inode *, struct ext4_ext_path *, struct ext4_extent *);
 101  extern int ext4_ext_walk_space(struct inode *, unsigned long, unsigned long, ext_prepare_callback, void *);
 102  extern struct ext4_ext_path * ext4_ext_find_extent(struct inode *, int, struct ext4_ext_path *);
 103 -
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