Commit 7ac8b88e authored by ethanwu's avatar ethanwu Committed by David Sterba
Browse files

btrfs: backref, only collect file extent items matching backref offset 



When resolving one backref of type EXTENT_DATA_REF, we collect all
references that simply reference the EXTENT_ITEM even though their
(file_pos - file_extent_item::offset) are not the same as the
btrfs_extent_data_ref::offset we are searching for.

This patch adds additional check so that we only collect references whose
(file_pos - file_extent_item::offset) == btrfs_extent_data_ref::offset.

Reviewed-by: default avatarJosef Bacik <josef@toxicpanda.com>
Reviewed-by: default avatarJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: default avatarethanwu <ethanwu@synology.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 9da2b242

fs/btrfs/backref.c

+33 −30
Original line number Diff line number Diff line
@@ -347,33 +347,10 @@ static int add_prelim_ref(const struct btrfs_fs_info *fs_info, 
		return -ENOMEM;



	ref->root_id = root_id;

	if (key) {

	if (key)

		ref->key_for_search = *key;

		/*

		 * We can often find data backrefs with an offset that is too

		 * large (>= LLONG_MAX, maximum allowed file offset) due to

		 * underflows when subtracting a file's offset with the data

		 * offset of its corresponding extent data item. This can

		 * happen for example in the clone ioctl.

		 * So if we detect such case we set the search key's offset to

		 * zero to make sure we will find the matching file extent item

		 * at add_all_parents(), otherwise we will miss it because the

		 * offset taken form the backref is much larger then the offset

		 * of the file extent item. This can make us scan a very large

		 * number of file extent items, but at least it will not make

		 * us miss any.

		 * This is an ugly workaround for a behaviour that should have

		 * never existed, but it does and a fix for the clone ioctl

		 * would touch a lot of places, cause backwards incompatibility

		 * and would not fix the problem for extents cloned with older

		 * kernels.

		 */

		if (ref->key_for_search.type == BTRFS_EXTENT_DATA_KEY &&

		    ref->key_for_search.offset >= LLONG_MAX)

			ref->key_for_search.offset = 0;

	} else {

	else

		memset(&ref->key_for_search, 0, sizeof(ref->key_for_search));

	}



	ref->inode_list = NULL;

	ref->level = level;
@@ -424,6 +401,7 @@ static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path, 
	u64 disk_byte;

	u64 wanted_disk_byte = ref->wanted_disk_byte;

	u64 count = 0;

	u64 data_offset;



	if (level != 0) {

		eb = path->nodes[level];
@@ -457,11 +435,15 @@ static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path, 


		fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);

		disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);

		data_offset = btrfs_file_extent_offset(eb, fi);



		if (disk_byte == wanted_disk_byte) {

			eie = NULL;

			old = NULL;

			if (ref->key_for_search.offset == key.offset - data_offset)

				count++;

			else

				goto next;

			if (extent_item_pos) {

				ret = check_extent_in_eb(&key, eb, fi,

						*extent_item_pos,
@@ -513,6 +495,7 @@ static int resolve_indirect_ref(struct btrfs_fs_info *fs_info, 
	int root_level;

	int level = ref->level;

	int index;

	struct btrfs_key search_key = ref->key_for_search;



	root_key.objectid = ref->root_id;

	root_key.type = BTRFS_ROOT_ITEM_KEY;
@@ -545,13 +528,33 @@ static int resolve_indirect_ref(struct btrfs_fs_info *fs_info, 
		goto out;

	}



	/*

	 * We can often find data backrefs with an offset that is too large

	 * (>= LLONG_MAX, maximum allowed file offset) due to underflows when

	 * subtracting a file's offset with the data offset of its

	 * corresponding extent data item. This can happen for example in the

	 * clone ioctl.

	 *

	 * So if we detect such case we set the search key's offset to zero to

	 * make sure we will find the matching file extent item at

	 * add_all_parents(), otherwise we will miss it because the offset

	 * taken form the backref is much larger then the offset of the file

	 * extent item. This can make us scan a very large number of file

	 * extent items, but at least it will not make us miss any.

	 *

	 * This is an ugly workaround for a behaviour that should have never

	 * existed, but it does and a fix for the clone ioctl would touch a lot

	 * of places, cause backwards incompatibility and would not fix the

	 * problem for extents cloned with older kernels.

	 */

	if (search_key.type == BTRFS_EXTENT_DATA_KEY &&

	    search_key.offset >= LLONG_MAX)

		search_key.offset = 0;

	path->lowest_level = level;

	if (time_seq == SEQ_LAST)

		ret = btrfs_search_slot(NULL, root, &ref->key_for_search, path,

					0, 0);

		ret = btrfs_search_slot(NULL, root, &search_key, path, 0, 0);

	else

		ret = btrfs_search_old_slot(root, &ref->key_for_search, path,

					    time_seq);

		ret = btrfs_search_old_slot(root, &search_key, path, time_seq);



	/* root node has been locked, we can release @subvol_srcu safely here */

	srcu_read_unlock(&fs_info->subvol_srcu, index);

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