$ git clone -n https://src.fedoraproject.org/rpms/rust-cstr.git /var/lib/mock/f41-build-side-1-3086341-39123/root/chroot_tmpdir/scmroot/rust-cstr
Cloning into '/var/lib/mock/f41-build-side-1-3086341-39123/root/chroot_tmpdir/scmroot/rust-cstr'...
$ git fetch origin ff542de1077fc989e6531ebb3b05459b662646ad:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-cstr
 * [new ref]         ff542de1077fc989e6531ebb3b05459b662646ad -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ff542de no longer needed