(use extras srfi-1)
(use udev)

(define (mountable-device? dev)
  (and (equal? (udev-device-type dev) "partition")
       (equal? (udev-device-subsystem dev) "block")))

(define (usb-device? dev)
  (and (udev-device-parent-with-subsystem-devtype dev "usb" "usb_device")
       #t))

(print "===== Mountable USB devices\n")

(pp (filter (conjoin mountable-device? usb-device?)
            (udev-list-devices)))