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https://bugs.launchpad.net/bugs/1800562

Title:
  Replace "nousb" option in kdump command-line for the newer
  "usbcore.nousb"

Status in makedumpfile package in Ubuntu:
  Confirmed
Status in makedumpfile source package in Xenial:
  Confirmed
Status in makedumpfile source package in Bionic:
  Confirmed
Status in makedumpfile source package in Cosmic:
  Confirmed
Status in makedumpfile source package in Disco:
  Confirmed

Bug description:
  [Impact]
  Crash kernels come up with the usb subsystem enabled, even when it should be disabled by default.

  [Description]
  Since kernel v4.5, the correct parameter to disable USB subsystem initialization is "usbcore.nousb" always (instead of "nousb" in case the subsystem is built-in). This was changed by commit 097a9ea0e48 ("usb: make "nousb" a clear module parameter").

  We need to take this into account in kdump-tools, or else we may boot
  with USB in kdump even the command-line saying the opposite.

  This affects Xenial onwards, since the system may be running an HWE or
  other supported v4.5+ kernel.

  [Test Case]
  1) Deploy a Disco VM e.g. with uvt-kvm
  2) Install the kdump-tools package
  3) Run `kdump-config test`and check for the 'usbcore.nousb' parameter:

  $ kdump-config test
  ...
  kexec command to be used:
    /sbin/kexec -p --command-line="BOOT_IMAGE=/boot/vmlinuz-4.15.0-45-generic root=LABEL=cloudimg-rootfs ro console=tty1 console=ttyS0 nr_cpus=1 systemd.unit=kdump-tools.service irqpoll nousb ata_piix.prefer_ms_hyperv=0" /var/lib/kdump/vmlinuz

  [Regression Potential]
  The regression potential is very low, since it doesn't need any changes in makedumpfile and we're only adding a parameter on the crashkernel cmdline.
  According to kernel documentation [0], unknown parameters will be ignored if they contain a dot (usbcore.nousb), so this change should have no impact on v4.4 and earlier kernels.
  Nonetheless, the fix will be tested with autopkgtests and normal kdump use-case scenarios.

  [0] https://www.kernel.org/doc/Documentation/admin-guide/kernel-
  parameters.rst

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