$ git clone -n https://src.fedoraproject.org/rpms/R-pillar.git /var/lib/mock/f43-build-side-110352-58908160-6569187/root/chroot_tmpdir/scmroot/R-pillar
Cloning into '/var/lib/mock/f43-build-side-110352-58908160-6569187/root/chroot_tmpdir/scmroot/R-pillar'...
$ git fetch origin 987d2fa8997a0a07fe20feb892ce81d6bf43d054:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-pillar
 * [new ref]         987d2fa8997a0a07fe20feb892ce81d6bf43d054 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 987d2fa R-maint-sig mass rebuild