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[PATCH 3/5] ext4: Extent overlap bugfix

To: torvalds@xxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx
Subject: [PATCH 3/5] ext4: Extent overlap bugfix
From: "Amit K. Arora" <aarora@xxxxxxxxxxxxxxxxxx>
Date: Thu, 26 Apr 2007 23:41:01 +0530
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, suparna@xxxxxxxxxx, cmm@xxxxxxxxxx
In-reply-to: <20070426175056.GA25321@amitarora.in.ibm.com>
References: <20070321120425.GA27273@amitarora.in.ibm.com> <20070329115126.GB7374@amitarora.in.ibm.com> <20070329101010.7a2b8783.akpm@linux-foundation.org> <20070330071417.GI355@devserv.devel.redhat.com> <20070417125514.GA7574@amitarora.in.ibm.com> <20070418130600.GW5967@schatzie.adilger.int> <20070420135146.GA21352@amitarora.in.ibm.com> <20070420145918.GY355@devserv.devel.redhat.com> <20070424121632.GA10136@amitarora.in.ibm.com> <20070426175056.GA25321@amitarora.in.ibm.com>
Sender: xfs-bounce@xxxxxxxxxxx
User-agent: Mutt/1.4.1i
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@xxxxxxxxxx>
---
 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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