$ git clone -n https://src.fedoraproject.org/rpms/rust-readwrite.git /var/lib/mock/f41-build-side-1-2993505-36026/root/chroot_tmpdir/scmroot/rust-readwrite
Cloning into '/var/lib/mock/f41-build-side-1-2993505-36026/root/chroot_tmpdir/scmroot/rust-readwrite'...
$ git fetch origin bb93ff955df123a811b95f5d88054ba1c70e19a5:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-readwrite
 * [new ref]         bb93ff955df123a811b95f5d88054ba1c70e19a5 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at bb93ff9 no longer needed