udisksctl unmount -b /dev/sdc1

udisksctl unmount -b $(mount | grep 1234-5678  | cut -d" "  -f1)

gio mount -l

$ gio mount -l
Drive(0): DA4032
  Type: GProxyDrive (GProxyVolumeMonitorUDisks2)
Volume(0): Canon Digital Camera
  Type: GProxyVolume (GProxyVolumeMonitorGPhoto2)
  Mount(0): Canon Digital Camera -> gphoto2://%5Busb%3A002,002%5D/
    Type: GProxyShadowMount (GProxyVolumeMonitorGPhoto2)
Mount(1): Canon Digital Camera -> gphoto2://%5Busb%3A002,002%5D/
  Type: GDaemonMount

gio mount -u gphoto2://%5Busb%3A002,002%5D/