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[PATCH 4/6][TAKE4] ext4: Extent overlap bugfix

To: torvalds@xxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx
Subject: [PATCH 4/6][TAKE4] ext4: Extent overlap bugfix
From: "Amit K. Arora" <aarora@xxxxxxxxxxxxxxxxxx>
Date: Thu, 17 May 2007 19:56:49 +0530
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, suparna@xxxxxxxxxx, cmm@xxxxxxxxxx
In-reply-to: <20070517141458.GA26641@xxxxxxxxxxxxxxxxxxxx>
References: <20070329101010.7a2b8783.akpm@xxxxxxxxxxxxxxxxxxxx> <20070330071417.GI355@xxxxxxxxxxxxxxxxxxxxxxxx> <20070417125514.GA7574@xxxxxxxxxxxxxxxxxxxx> <20070418130600.GW5967@xxxxxxxxxxxxxxxxxxxx> <20070420135146.GA21352@xxxxxxxxxxxxxxxxxxxx> <20070420145918.GY355@xxxxxxxxxxxxxxxxxxxxxxxx> <20070424121632.GA10136@xxxxxxxxxxxxxxxxxxxx> <20070426175056.GA25321@xxxxxxxxxxxxxxxxxxxx> <20070517141115.GA24260@xxxxxxxxxxxxxxxxxxxx> <20070517141458.GA26641@xxxxxxxxxxxxxxxxxxxx>
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This patch adds a check for overlap of extents and cuts short the
new extent to be inserted, if there is a chance of overlap.

Changelog:
---------
Changes from Take3 to Take4:
 - no change -
Changes from Take2 to Take3:
 1) Patch rebased to 2.6.22-rc1 kernel.
Changes from Take1 to Take2:
 1) As suggested by Andrew, a check for wrap though zero has been added.

Here is the new patch:

Signed-off-by: Amit Arora <aarora@xxxxxxxxxx>
---
 fs/ext4/extents.c               |   60 ++++++++++++++++++++++++++++++++++++++--
 include/linux/ext4_fs_extents.h |    1 
 2 files changed, 59 insertions(+), 2 deletions(-)

Index: linux-2.6.22-rc1/fs/ext4/extents.c
===================================================================
--- linux-2.6.22-rc1.orig/fs/ext4/extents.c
+++ linux-2.6.22-rc1/fs/ext4/extents.c
@@ -1128,6 +1128,55 @@ ext4_can_extents_be_merged(struct inode 
 }
 
 /*
+ * 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;
+       unsigned int ret = 0;
+
+       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;
+       }
+
+       /* check for wrap through zero */
+       if (b1 + len1 < b1) {
+               len1 = EXT_MAX_BLOCK - b1;
+               newext->ee_len = cpu_to_le16(len1);
+               ret = 1;
+       }
+
+       /* check for overlap */
+       if (b1 + len1 > b2) {
+               newext->ee_len = cpu_to_le16(b2 - b1);
+               ret = 1;
+       }
+out:
+       return ret;
+}
+
+/*
  * ext4_ext_insert_extent:
  * tries to merge requsted extent into the existing extent or
  * inserts requested extent as new one into the tree,
@@ -2031,7 +2080,15 @@ 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;
@@ -2039,7 +2096,6 @@ 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-2.6.22-rc1/include/linux/ext4_fs_extents.h
===================================================================
--- linux-2.6.22-rc1.orig/include/linux/ext4_fs_extents.h
+++ linux-2.6.22-rc1/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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