bug#48164: cp --reflink=never no longer works as expected

[Chris Murphy]

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.


-- 
Chris Murphy