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IPP-USB as a weak dependency of CUPS and sane-airscan

This is a proposed Change for Fedora Linux.
This document represents a proposed Change. As part of the Changes process, proposals are publicly announced in order to receive community feedback. This proposal will only be implemented if approved by the Fedora Engineering Steering Committee.

Summary

Add ipp-usb as a weak dependency of packages which provide support for driverless printing (cups), driverless scanning (sane-airscan) and driverless fax for USB devices capable of using driverless functionality (how to find out whether your USB device is driverless here), so such devices will work without a specific driver. ipp-usb design conflicts with the way how drivers work with the device, so a user intervention is required after upgrade.

Owner

Name: Zdenek Dohnal
Email: zdohnal@redhat.com

Current status

Targeted release: Fedora Linux 38
Last updated: 2023-01-11
FESCo issue: <will be assigned by the Wrangler>
Tracker bug: <will be assigned by the Wrangler>
Release notes tracker: <will be assigned by the Wrangler>

Detailed Description

Nowadays most printers and scanners from common vendors provide a way how to work without a specific driver. This way relies on driverless standards implemented in device's firmware and their support in the operating system user has. At first (in 2010) network driverless standards were implemented in devices and widely spread, such as AirPrint, IPP Everywhere for printers or eSCL (sometimes called AirScan) and WSD (Windows Service Discovery) for scanners. Those network driverless standards and others are already supported in cups (for printing) and sane-airscan packages. Two years later USB devices got their own driverless standard - IPP over USB - which is now implemented by ipp-usb.

The ipp-usb package contains ipp-usb daemon, which works as an HTTP proxy over the claimed USB devices, provides printing (via IPP 2.0+ protocol), scanning (via eSCL and WSD) and fax (via IPP Faxout) support and advertises them on localhost by mDNS protocol. mDNS is the key feature for automatic printer discovery, but it is not required to used it - the virtual printer device provided by ipp-usb can be accessed at URI ipp://localhost:60000/ipp/print and the URI can be used for permanent queue installation - here is the manual. However if mDNS is enabled, the virtual device shared by ipp-usb can be automatically picked up by other services (as cups or sane-airscan), so no further configuration is required to get the printer installed. The feature is called temporary queue in CUPS and it is supported in applications using the up-to-date CUPS API or toolkits using up-to-date CUPS API - f.e. GTK3+ based applications, Libreoffice and Firefox. The fax functionality is available at URI ipp://localhost:60000/ipp/faxout, but the automatic installation doesn't work for it and it has to be installed manually.

As mentioned above, the ipp-usb daemon claims the USB interface of the device which supports IPP over USB standard. This behavior conflicts with the previous driver approach, where the discovery mechanism only scans USB ports for available devices, but doesn't try to claim the device, which is unavailable because ipp-usb has claimed it already. The result is the device can be discovered by classic driver tools, but it won't work once user wants to print or scan. In such cases user intervention is needed, where user has to make a decision whether to use driverless USB support or classic support with drivers. The way how to do it will be explained later in this proposal.

Based on the current ipp-usb design the following specific setups aren't expected to work:

combining driverless and classic driver's support doesn't work on the same device - driverless or classic driver has to be used for whole device's functionality.
if user has several devices of the same model, all of them has to be supported by a single solution - driverless or classic driver - because quirks and SANE backends use model name, vendor ID or product ID, which are the same for all devices of the same model, for denying the support.
if scanner backend does not support disabling support for a specific device (f.e. hpaio, pixma), the whole backend can be disabled to prevent discovering broken scanners - it results in the scanner support provided by the backend will be disabled for all other devices which are in the user's environment - both network and USB.

To provide a possibility to opt-out from driverless USB printing the ipp-usb package will be added as a weak dependency of cups and sane-airscan, so it can be uninstalled without losing the rest of the printing and scanning stack, and ipp-usb check will be added into %post scriptlet of ipp-usb package for users to see whether they have a device claimed by ipp-usb during upgrade process.

Feedback

I've investigated possible solutions for two biggest concerns which adding ipp-usb has raised and consulted it upstream:

1. The current design of claiming the interface of IPP-over-USB device and not releasing it until ipp-usb daemon stops and whether it can be changed - I talked with upstream about it at upstream issue - the reason for it is to prevent potential race conditions/bugs in device's firmware, which is sometimes flaky and updates are not coming to it in regular manner, due combined access for printing or scanning.

2. The design makes impact to an existing setups as well, so the upgrade path has to be taken into consideration - this was mentioned in the upstream ticket too. Based on the following expectations regarding devices:

might have firmware bugs
might have lesser functionality than classic driver

and the expectations above differ from device to device, we can't automatically prefer one solution over the other at the moment and user manual intervention after upgrade is needed.

This feature will explain how to create a quirk for the ipp-usb daemon to ignore the device or disable them in classic drivers to reduce this conflict.

Benefit to Fedora

Modern USB devices will work out of the box without a specific driver, so users don't need to install a driver or the device at all.

Scope

Proposal owners:

The proposal owner will add Recommends: ipp-usb to cups and sane-airscan packages, ipp-usb check call into %post scriptlet of ipp-usb and rebuild all changed packges. The owner will update Fedora Quick Docs with the manual how to create the ipp-usb quirk and how to disable the device in classic drivers if possible.

Other developers:

Release engineering: #Releng issue number

Policies and guidelines: N/A (not needed for this Change)

Trademark approval: N/A (not needed for this Change)

Alignment with Objectives:

Upgrade/compatibility impact

ipp-usb is incompatible with classic printing and scanning drivers for IPP-over-USB devices, so a manual intervention depending on user's choice is required after upgrade. The steps which users have to do are described below.

Choices:

IPP-USB
Classic drivers

Prerequisites: Checking the IPP-over-USB device and its capabilities

update device's firmware if possible
stop and disable cups-browsed service if it is not used for installing printers from remote print server (which means BrowsePoll <server> is used in /etc/cups/cups-browsed.conf)
check if the device is recognized by ipp-usb:

$ sudo ipp-usb check
Configuration files: OK
IPP over USB devices:
 Num  Device              Vndr:Prod  Model
   1. Bus 001 Device 005  04a9:2823  "Canon MF440 Series"

if the device has a printing functionality:

check whether the device is seen by CUPS among existing destinations, but not among installed printers (Canon_MF440_Series_USB is the CUPS temporary queue for IPP-over-USB device called Canon MF430):

$ lpstat -e
Canon_MF440_Series_USB
Canon_MF440_Series
$ lpstat -a
Canon_MF440_Series accepting requests since Wed 16 Mar 2022 11:27:02 AM CET

Note: If the Canon_MF440_Series_USB is shown here, but not in your application, report the issue to the application.

check whether it provides the options you use during printing:

$ ipptool -tv ipp://localhost:60000/ipp/print get-printer-attributes.test
$ lpoptions -p Canon_MF440_Series_USB -l

Note: ipptool command will return all IPP attributes which the device supports - currently common PPD options are generated from some of the attributes, so if your printing option is present in IPP response, but not in lpoptions output, then it is a CUPS issue. lpoptions returns available PPD options, which are used by print dialogs in most cases.

If the device has a scanning functionality:

check whether the device is seen by airscan backend (the HP LaserJet MFP M130fw device here is used for illustration, it does not show its real IPP-over-USB compatibility or its real options shared via AirScan from ipp-usb):

$ scanimage -L
...
device `airscan:e0:HP LaserJet MFP M130fw (E700D6)' is a eSCL HP LaserJet MFP M130fw (E700D6) ip=127.0.0.1

check the device capabilities:

$ scanimage --help -d 'airscan:e0:HP LaserJet MFP M130fw (E700D6)'
...
Options specific to device `airscan:e0:HP LaserJet MFP M130fw (E700D6)':
  Standard:
    --resolution 75|150|200|300|600|1200dpi [300]
        Sets the resolution of the scanned image.
    --mode Color|Gray [Color]
        Selects the scan mode (e.g., lineart, monochrome, or color).
    --source Flatbed|ADF [Flatbed]
        Selects the scan source (such as a document-feeder).
  Geometry:
    -l 0..215.9mm [0]
        Top-left x position of scan area.
    -t 0..297.011mm [0]
        Top-left y position of scan area.
    -x 0..215.9mm [215.9]
        Width of scan-area.
    -y 0..297.011mm [297.011]
        Height of scan-area.
  Enhancement:
    --brightness -100..100% (in steps of 1) [0]
        Controls the brightness of the acquired image.
    --contrast -100..100% (in steps of 1) [0]
        Controls the contrast of the acquired image.
    --shadow 0..100% (in steps of 1) [0]
        Selects what radiance level should be considered "black".
    --highlight 0..100% (in steps of 1) [100]
        Selects what radiance level should be considered "white".
    --analog-gamma 0.0999908..4 [1]
        Analog gamma-correction
    --negative[=(yes|no)] [no]
        Swap black and white
...

if the device has a fax functionality and user requires it:

check its capabilities via ipptool command:

$ ipptool -tv ipp://localhost:60000/ipp/faxout get-printer-attributes.test

User can see the available printing, scanning and fax capabilities with the command above and can decide which solution - driverless or classic drivers - he wants to pursue. The recommendation is to use driverless if it provides the set of options required by user - the device is not bound to a driver being available in the distribution and, if mDNS works, the device is automatically installed and no other intervention will be needed in the future, when classic drivers will be covered by printer applications and permanent queues will turn into printer profiles on desktops.

1. If IPP-USB is chosen to support the device

if the device has a printing functionality:

Remove any existing printers installed for the device in the past:

find out the printer name:

$ lpstat -a
Canon_MF440_Series accepting requests since Wed 16 Mar 2022 11:27:02 AM CET

remove the printer:

$ lpadmin -x Canon_MF440_Series

if the device has a scanning functionality:

Disable the device in a SANE backend, disable the backend as whole or uninstall the driver:

$ scanimage -L
device `hpaio:/usb/laserjet_mfp_m129-m134?serial=XXXX' is a Hewlett-Packard laserjet_mfp_m129-m134 all-in-one
device `airscan:e0:HP LaserJet MFP M130fw (E700D6)' is a eSCL HP LaserJet MFP M130fw (E700D6) ip=127.0.0.1
$ sudo sed -i 's,^\s*hpaio$,#hpaio,' /etc/sane.d/dll.d/hpaio                                                  # disables backend

if the device has a fax functionality:

remove the old fax queue if exists:

$ lpadmin -x <fax_queue>

install a new fax queue:

$ lpadmin -p <fax_name> -v ipp://localhost:60000/ipp/faxout -m driverless-fax:ipp://localhost:60000/ipp/faxout -E

After this user is able to send fax via lp command and the chosen fax queue.

If a classic driver is chosen to support the device

create a quirk for ipp-usb:

get device's model name:

$ sudo ipp-usb check
$ sudo ipp-usb check
Configuration files: OK
IPP over USB devices:
 Num  Device              Vndr:Prod  Model
   1. Bus 001 Device 005  04a9:2823  "Canon MF440 Series"

use the name in new quirk file at /etc/ipp-usb/quirks directory. The .conf suffix is required.

$ cat /etc/ipp-usb/quirks/canon.conf
[Canon MF440 Series]
  blacklist = true

restart ipp-usb service:

$ sudo systemctl restart ipp-usb

This quirk will deny device's support in ipp-usb and classic drivers will work.

How To Test

USB device capable of supporting IPP-over-USB is required to test this change. ipp-usb starts once IPP-over-USB device is connected and then do the following steps:

follow prerequisites mentioned in the Upgrade/compatibility impact and choose IPP-over-USB support,
open a document in applications you use for printing/scanning/fax
check whether the device is seen in the application (in print dialog, or in scanner list) - if the device is not seen, report the issue to the application's bugzilla component,
check which options are available in the dialog/settings - if some required (for your use cases) options are missing in comparison to lpoptions and scanimage outputs (details how to find out device's capabilities in Upgrade/compatibility impact), report the issue to the application's bugzilla component,
try the actions you usually do on your device (print/scan/fax) with your common options set:

in case of printers and fax if the printout is not in expected format, do report the issue to cups bugzilla component together with additional info (described here),
in case of problem with scanning output do report the issue to sane-airscan bugzilla component together with additional info acquired by following steps from this link,

once you disable the device or backend for scanning, check whether one scanner's disappeared from scanner application's dialog (simple-scan, xsane, scanimage)

In case user chooses to have classic driver support instead of driverless because driverless support does not work or it misses some options which user requires, it would be great if the user reported such case by filing an issue to golang-github-openprinting-ipp-usb bugzilla component, explaining which required options are missing or whether driverless does not print/scan at all and it will reviewed by the component's maintainer. If the model has the driverless support broken in general, the model can be disabled in ipp-usb on system level by quirk, which is located in /usr/share/ipp-usb/quirks.

Once the quirk is set and ipp-usb restarted, previously installed printers and scanners will work as before - the printing/scanning/fax will end with error otherwise.

User Experience

A new printer and a new scanner will appear in applications and settings for IPP-over-USB devices by default. Previously installed printer and discovered scanner for the device will stop working and manual intervention is required to remove the broken instances, or to create a quirk for ipp-usb.

Dependencies

Contingency Plan

Contingency mechanism: (What to do? Who will do it?) N/A (not a System Wide Change)
Contingency deadline: N/A (not a System Wide Change)
Blocks release? N/A (not a System Wide Change), Yes/No

Documentation

Printing and scanning terminology
Printing debugging
Scanning debugging
Tips and tricks
Known issues

Release Notes

Driverless USB printing/scanning/fax support is present by default with printing and scanning packages, providing the support for devices capable of using IPP-over-USB. The manual intervention is required after upgrade, which is described here.

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