[Bug 1057824]

Ubuntu Foundation's Bug Bot 1057824 at bugs.launchpad.net
Fri Sep 28 20:22:25 UTC 2012

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  USB input device interfaces compete for the same symlink name in 60

Status in “udev” package in Ubuntu:

Bug description:
  The current rules in 60-persistent-input.rules do not produce a usable
  symlink for the interface 0 device in multi-interface USB input

  These are the problematic rules:

  KERNEL=="mouse*|js*", ENV{ID_BUS}=="?*", ENV{.INPUT_CLASS}=="?*", SYMLINK+="input/by-id/$env{ID_BUS}-$env{ID_SERIAL}-$env{.INPUT_CLASS}"
  KERNEL=="event*", ENV{ID_BUS}=="?*", ENV{.INPUT_CLASS}=="?*", SYMLINK+="input/by-id/$env{ID_BUS}-$env{ID_SERIAL}-event-$env{.INPUT_CLASS}"

  The above rules can be matched by multiple devices if a USB input
  device has multiple USB interfaces (such as the Microsoft Wired
  Keyboard 600, which has two keyboard interfaces).  Because the
  generated symlink names do not include the USB interface number, the
  multiple devices will compete over the same symlink name.  According
  to the udev man page, the device that wins is undefined unless the
  devices are assigned different link_priority values (which they are

  There are other rules in 60-persistent-input.rules that do produce
  per-interface symlinks.  These rules were introduced in git commit
  5e9eb15 [1] for bug #626449.  Unfortunately, due to git commit 32567f8
  [2], a symlink for interface 0 is not produced by these per-interface
  rules.  Thus, if an interface other than 0 wins the competition for
  the colliding symlink names, there won't be a persistent symlink for
  the interface 0 device.  Even if device 0 does win the competition, it
  may change, going against the intended persistence.

  It seems like the correct fix is to give interface 0 a higher
  link_priority value than the other interfaces.  This would guarantee
  that interface 0 always wins the competition.

  [1] http://cgit.freedesktop.org/systemd/systemd/commit/?id=5e9eb156c003dc7f8f92287bfad0251d6c5d0ef9
  [2] http://cgit.freedesktop.org/systemd/systemd/commit/?id=32567f8c95290a8819c0bc7d57849b8abfba9554

  $ lsb_release -rd
  Description:    Ubuntu 12.04.1 LTS
  Release:        12.04
  $ apt-cache policy udev
    Installed: 175-0ubuntu9.1
    Candidate: 175-0ubuntu9.1
    Version table:
   *** 175-0ubuntu9.1 0
          500 http://us.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
          100 /var/lib/dpkg/status
       175-0ubuntu9 0
          500 http://us.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages

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