Use reflinks in mkfs.btrfs when using --rootdir?

[DaanDeMeyer]

I noticed that when using mkfs.btrfs on a loopback file with --rootdir, it doesn't seem to try to reflink the files into the filesystem. Would this be possible at all to avoid copying the data?

[kdave]

Yeah reflink is not implemented. It could as long as it would work for the source and target. It's in add_file_items, source file is read by sectors and needs the checksum calculated. Reflinking would need to look for longest contiguous extent while still adding the checksums.