this works,

    <disk type='network' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
        <source protocol='gluster' name='test123/root.qcow2'>
          <host name='127.0.0.1' port='24007'/>
        </source>
      <target dev='vda' bus='virtio'/>
    </disk>

but not this,

    <disk type='network' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
        <source protocol='gluster' name='test123/root.qcow2'>
          <host transport='unix' socket='/var/run/glusterd.socket'/>
        </source>
      <target dev='vda' bus='virtio'/>
    </disk>

error is:

[root@vmos-of1-03 test123]# virsh create test123.gluster.xml-socket --console
error: Failed to create domain from test123.gluster.xml-socket
error: failed to initialize gluster connection to server: '/var/run/glusterd.socket': Transport endpoint is not connected