$ git clone -n https://src.fedoraproject.org/rpms/xen.git /var/lib/mock/f39-build-1677952-40960/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/f39-build-1677952-40960/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin b5231bddba35ce2daf5df35532b14017b3cda8a2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/xen
 * [new ref]         b5231bddba35ce2daf5df35532b14017b3cda8a2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b5231bd 2 security issues