On 02/05/2021 18:12, Chris Murphy wrote:
Hi,Fedora 34 user 'adrum' reports that 'cp --reflink=never' is performing a lightweight copy on Btrfs. And filefrag -v shows the extents are shared. Strace shows use of copy_file_range even with --reflink=never The note for copy_file_range() includes: copy_file_range() gives filesystems an opportunity to implement "copy acceleration" techniques, such as the use of reflinks Downstream bug https://bugzilla.redhat.com/show_bug.cgi?id=1956080 The commit that causes the change in behavior: https://src.fedoraproject.org/rpms/coreutils/c/1737e5c81fa82451b510f982499bdedb2a1619d1?branch=rawhide It references five upstream commits.
Thanks for the detailed report. I've fixed this upstream with: https://git.sv.gnu.org/gitweb/?p=coreutils.git;a=commitdiff;h=v8.32-147-gea9af9923 Ideally copy_file_range() would take CAN_REFLINK as a flag, but for now the patch above avoids the call with --reflink=never. Note we've not released an official coreutils release with this change yet, as we've yet to fully test all variations of this new copying logic. There are subtle interactions like this that need to be considered. BTW there has been recent discussions on the non generality of copy_file_range() at https://lwn.net/Articles/846403/ Marking this as done. cheers, Pádraig
