CUPS- the print spooler that wants to print via IPP-over-USB.
ippusb_manager- service that helps establish communication between the print spooler and
ippusbxd. Developed specifically for IPP-over-USB printing in Chromium OS.
ippusbxd- service that facilitates IPP-over-USB communication. Heavily patched for use in Chromium OS. Known to differ substantially from upstream.
lpadminand to the
ippusb://scheme, then CUPS sends a request to
ippusb_managerto broker a socket for communication with the printer by way of
ippusb://scheme is specific to Chromium OS.
ippusb://scheme in CUPS configuration etc. on-device, but rewrite the URI to use the
ipp://scheme before communicating with the printer.
CUPSwith the basename of the socket over which it can communicate with
ippusbxdto preempt the latter from its timed idle exit.
ippusb_managerlistens for an explicit acknowledgement before declaring
ippusbxdalive and reusing the extant sockets.
ippusb_managertries to wait for the sockets to disappear (i.e. that
ippusbxdhas exited) before spawning a new instance of
ippusb_manager, as mentioned above.
CUPSand the printer.
ippusbinterface on a given printer: one for each direction of communication.
ippusbinterfaces on the printer until exit.
ippusbxdare run from inside minijail instances and retain their own seccomp filters.
ippusbxd, the former seccomp filter must be a superset of the latter.
How much of ippusbxd do we use?
We don't use any of the avahi code.
(WRT ippusb_manager) why Unix sockets; why not D-Bus?
We didn't consider D-Bus at the time. The messages are quite simple and
CUPS already had code for dealing with Unix sockets.
Can a user plug in more than one USB printer?
Yes, as long as they do not appear to be the same (i.e. present identical VIDs and PIDs). We opine that this is an uncommon enough use case to be an issue.
Can ippusb_manager and ippusbxd have multiple clients?
Preliminary testing indicates that this should work. Sockets are connection-oriented.
See the design doc for information about the overall design and how
ippusb_manager fits into it. This is accessible only within google.
This repository contains the following subdirectories:
|Upstart config files for launching |
|udev rules for setting group permissions on ipp-usb printers|