From e68afa49aec5f0851e550ee1de48fcc3a9bf5ef7 Mon Sep 17 00:00:00 2001 From: Liu Bo Date: Mon, 1 Jul 2013 22:13:26 +0800 Subject: [PATCH 1/1] Btrfs: fix a bug of snapshot-aware defrag to make it work on partial extents 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 Signed-off-by: Josef Bacik Signed-off-by: Chris Mason --- fs/btrfs/inode.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 0fd7647c8932..c72033ee6017 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -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); -- 2.39.2