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Commit 25d14f98 authored by Amit Arora's avatar Amit Arora Committed by Theodore Ts'o
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ext4: Extent overlap bugfix 



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.

Signed-off-by: default avatarAmit Arora <aarora@in.ibm.com>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 8a9dc944

fs/ext4/extents.c

+58 −2
Original line number Diff line number Diff line
@@ -1127,6 +1127,55 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1, 
	return 0;

}



/*

 * 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
@@ -2031,6 +2080,14 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode, 


	/* allocate new block */

	goal = ext4_ext_find_goal(inode, path, iblock);



	/* 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)
@@ -2039,7 +2096,6 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode, 
			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);

include/linux/ext4_fs_extents.h

+1 −0
Original line number Diff line number Diff line
@@ -190,6 +190,7 @@ ext4_ext_invalidate_cache(struct inode *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 *);