$ git clone -n https://src.fedoraproject.org/rpms/rust-block-modes.git /var/lib/mock/f42-build-side-1-3539459-46565/root/chroot_tmpdir/scmroot/rust-block-modes
Cloning into '/var/lib/mock/f42-build-side-1-3539459-46565/root/chroot_tmpdir/scmroot/rust-block-modes'...
$ git fetch origin a8ffb685b87ae22a0e7e7573c6c028d62186ba4c:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-block-modes
 * [new ref]         a8ffb685b87ae22a0e7e7573c6c028d62186ba4c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a8ffb68 no longer needed