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[Frank Heimes <1713536@xxxxxxxxxxxxxxxxxx>]

** Changed in: ubuntu-z-systems
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1713536

Title:
  udev: boot script does not trigger subsystem coldplug

Status in Ubuntu on IBM z Systems:
  Fix Released
Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Xenial:
  Fix Released
Status in systemd source package in Zesty:
  Fix Committed
Status in systemd source package in Artful:
  Fix Released

Bug description:
  [Impact]
  subsystems udev rules are not processed on boot, thus resulting in missing devices on boot / before rootfs is mounted.

  [Solution]
  trigger udev subsystems and devices, in the initramfs, in that order.

  [Testcase]
  Boot s390x system with chzdev configured devices, and cio_ignore=all kernel command line parameter. The chzdev configured devices should still be discovered on boot.

  [Original Bug report]

  The udev initramfs-tools boot script does not trigger subsystem "add"
  uevents. As a result, udev rules that listen to subsystem "add" events
  are never activated. This problem exists on at least Ubuntu 16.04 and
  17.10.

  On s390, this results in a boot failure if the kernel is configured to
  start with an active device black list (kernel parameter
  cio_ignore=all,!condev). An example for an affected udev rule looks
  like this:

      ACTION=="add", SUBSYSTEM=="subsystem", KERNEL=="ccw",
  RUN{program}+="/bin/sh -c 'echo free 0009,ec30,ec32,f5f0-f5f2 >
  /proc/cio_ignore'"

  A proposed fix would be:

  Modify /usr/share/initramfs-tools/scripts/init-top/udev:

  Replace line
          udevadm trigger --action=add
  with
          udevadm trigger --type=subsystems --action=add
          udevadm trigger --type=devices --action=add

  This would also be consistent with the steps that the systemd udev
  coldplug unit file performs (see /lib/systemd/system/systemd-udev-
  trigger.service).

  [Regression Potential]
  More udev rules will be now triggered, earlier, during initramfs stage of boot rather than post-pivot-root. However, this is inline with current rootfs behaviour and thus should not regress behaviour - simply some rules will get triggered earlier.

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