$ git clone -n https://src.fedoraproject.org/rpms/libguestfs.git /var/lib/mock/f42-build-863088-171404/root/chroot_tmpdir/scmroot/libguestfs
Cloning into '/var/lib/mock/f42-build-863088-171404/root/chroot_tmpdir/scmroot/libguestfs'...
$ git fetch origin ff5b9715aa981d712b281069c260208d21aa40e8:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/libguestfs
 * [new ref]         ff5b9715aa981d712b281069c260208d21aa40e8 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ff5b971 Make perl Guestfs.so writable