Under some cases the filesystem checker reports an error when it finds
checksum items for an extent that is referenced by an inode as a prealloc
extent. Such cases are not an error when the extent is actually shared
(was cloned/reflinked) with other inodes and was written through one of
those other inodes.
Example:
$ mkfs.btrfs -f /dev/sdb
$ mount /dev/sdb /mnt
$ touch /mnt/foo
$ xfs_io -c "falloc 0 256K" /mnt/foo
$ sync
$ xfs_io -c "pwrite -S 0xab 0 256K" /mnt/foo
$ touch /mnt/bar
$ xfs_io -c "reflink /mnt/foo 0 0 256K" /mnt/bar
$ xfs_io -c "fsync" /mnt/bar
<power fail>
$ mount /dev/sdb /mnt
$ umount /mnt
$ btrfs check /dev/sdc
Checking filesystem on /dev/sdb
UUID: 52d3006e-ee3b-40eb-aa21-e56253a03d39
checking extents
checking free space cache
checking fs roots
root 5 inode 257 errors 800, odd csum item
ERROR: errors found in fs roots
found 688128 bytes used, error(s) found
total csum bytes: 256
total tree bytes: 163840
total fs tree bytes: 65536
total extent tree bytes: 16384
btree space waste bytes: 138819
file data blocks allocated: 10747904
referenced 10747904
$ echo $?
1
So teach check to not report such cases as errors by checking if the
extent is shared with other inodes and if so, consider it an error the
existence of checksum items only if all those other inodes are referencing
the extent as a prealloc extent.
This case can be hit often when running the generic/475 testcase from
fstests.
A test case will follow in a separate patch.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
