Btrfs: fix a bug of snapshot-aware defrag to make it work on partial extents (e68afa49) · Commits · 戴 / test

For partial extents, snapshot-aware defrag does not work as expected, since a) we use the wrong logical offset to search for parents, which should be disk_bytenr + extent_offset, not just disk_bytenr, b) 'offset' returned by the backref walking just refers to key.offset, not the 'offset' stored in btrfs_extent_data_ref which is (key.offset - extent_offset). The reproducer: $ mkfs.btrfs sda $ mount sda /mnt $ btrfs sub create /mnt/sub $ for i in `seq 5 -1 1`; do dd if=/dev/zero of=/mnt/sub/foo bs=5k count=1 seek=$i conv=notrunc oflag=sync; done $ btrfs sub snap /mnt/sub /mnt/snap1 $ btrfs sub snap /mnt/sub /mnt/snap2 $ sync; btrfs filesystem defrag /mnt/sub/foo; $ umount /mnt $ btrfs-debug-tree sda (Here we can check whether the defrag operation is snapshot-awared. This addresses the above two problems. Signed-off-by:

Liu Bo <bo.li.liu@oracle.com> Signed-off-by:

Josef Bacik <jbacik@fusionio.com> Signed-off-by:

Chris Mason <chris.mason@fusionio.com>

fs/btrfs/inode.c

+12 −4

Original line number	Diff line number	Diff line
		@@ -2166,16 +2166,23 @@ static noinline int record_one_backref(u64 inum, u64 offset, u64 root_id,
		if (btrfs_file_extent_disk_bytenr(leaf, extent) != old->bytenr)
		continue;

		extent_offset = btrfs_file_extent_offset(leaf, extent);
		if (key.offset - extent_offset != offset)
		/*
		* 'offset' refers to the exact key.offset,
		* NOT the 'offset' field in btrfs_extent_data_ref, ie.
		* (key.offset - extent_offset).
		*/
		if (key.offset != offset)
		continue;

		extent_offset = btrfs_file_extent_offset(leaf, extent);
		num_bytes = btrfs_file_extent_num_bytes(leaf, extent);

		if (extent_offset >= old->extent_offset + old->offset +
		old->len \|\| extent_offset + num_bytes <=
		old->extent_offset + old->offset)
		continue;

		ret = 0;
		break;
		}

		@@ -2187,7 +2194,7 @@ static noinline int record_one_backref(u64 inum, u64 offset, u64 root_id,

		backref->root_id = root_id;
		backref->inum = inum;
		backref->file_pos = offset + extent_offset;
		backref->file_pos = offset;
		backref->num_bytes = num_bytes;
		backref->extent_offset = extent_offset;
		backref->generation = btrfs_file_extent_generation(leaf, extent);
		@@ -2210,7 +2217,8 @@ static noinline bool record_extent_backrefs(struct btrfs_path *path,
		new->path = path;

		list_for_each_entry_safe(old, tmp, &new->head, list) {
		ret = iterate_inodes_from_logical(old->bytenr, fs_info,
		ret = iterate_inodes_from_logical(old->bytenr +
		old->extent_offset, fs_info,
		path, record_one_backref,
		old);
		BUG_ON(ret < 0 && ret != -ENOENT);

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