Can't cp --reflink files on a Ext4-converted FS w/o checksums

[Roman Mamedov <rm@romanrm.net>]

Hello,

I used btrfs-convert to switch my FS from Ext4 to Btrfs. As it was a rather
large 10 TB filesystem, to save on the conversion time, I used the "-d,
disable data checksum" option of btrfs-convert.

Turns out now I can't "cp --reflink" any files that were already on the FS
prior to conversion. The error message from cp is "failed to clone [...]
Invalid argument".

I assume this is because of the lack of checksums; the only way to make old
files cloneable is to plain copy them to a different place and then delete the
originals, but that's what I was trying to avoid in the first place.

Also I thought maybe defragmenting will help, but nope, doesn't seem to be the
case, even ordering it to recompress data to a different method doesn't fix
the problem. (Even if it did, it's still a lot of unnecessary rewriting).

Is there really a good reason to stop these files without checksums from being
cloneable? It's not like they have the noCoW attribute, so I'd assume any new
write to these files would cause a CoW and proper checksums for all new blocks
anyways.

-- 
With respect,
Roman