$ git clone -n https://src.fedoraproject.org/rpms/glib2.git /var/lib/mock/f40-build-733723-105363/root/chroot_tmpdir/scmroot/glib2
Cloning into '/var/lib/mock/f40-build-733723-105363/root/chroot_tmpdir/scmroot/glib2'...
$ git fetch origin 79f461e497064703f2c00a64b0da4f4cefeb556b:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/glib2
 * [new ref]         79f461e497064703f2c00a64b0da4f4cefeb556b -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 79f461e Update to 2.78.1