with

  guix system: error: service 'swap-/dev/mapper/guix-swap' requires 'device-mapping-guix-swap', which is not provided by any service

(define swap-service-type
  (shepherd-service-type
   'swap
   (lambda (device)
     (define requirement
       (if (and (string? device)
                (string-prefix? "/dev/mapper/" device))
           (list (symbol-append 'device-mapping-
                                (string->symbol (basename device))))
           '()))

at

Thanks

/shyam