cups-deviced polls the backends in
/usr/lib/cups/backend for a list of available devices.
It is run by cupsd(8) in response to a
CUPS-Get-Devices request. The output format is an IPP
response message. The request-id argument is the request ID
from the original IPP request, typically 1. The limit
argument is the limit value from the original IPP request - 0
means no limit. The user-id argument is the
requesting-user-name value from the original IPP request.
Finally, the options argument is a space-delimited list of
attributes ("name=value name=value ...") that were passed in
with the request. Currently cups-deviced looks for the
requested-attributes attribute and tailors the output