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....@oracle.com>
---
fs/btrfs/inode.c | 16 ++++++++++++----
1 files changed, 12 insertions(+), 4 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index c931a4d..ab87862 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2134,16 +2134,23 @@ 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;
}
@@ -2155,7 +2162,7 @@ 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);
@@ -2178,7 +2185,8 @@ 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);
--
1.7.7
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