Feature or enhancement

fcntl exposes many constants for the fcntl and ioctl system calls. The module should expose FICLONE and FICLONERANGE too; they can be passed to ioctl to share some data of one file with another file by reflinking on some filesystems (e.g., btrfs, OCFS2, and XFS).
https://man7.org/linux/man-pages/man2/ioctl_ficlone.2.html

Pitch

These constants can be used to reflink files in users' code, and they have a potential to be used in shutil in the future #81338.