$ git clone -n https://src.fedoraproject.org/rpms/btrfsd.git /var/lib/mock/f38-build-side-42-init-devel-1407214-31287/root/chroot_tmpdir/scmroot/btrfsd
Cloning into '/var/lib/mock/f38-build-side-42-init-devel-1407214-31287/root/chroot_tmpdir/scmroot/btrfsd'...
$ git fetch origin cb386847a2ef078b4b00cb85a558cc52e8327e8e:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/btrfsd
 * [new ref]         cb386847a2ef078b4b00cb85a558cc52e8327e8e -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at cb38684 Update to 0.2.0