Thanks for bringing that up, Cascardo. That was one scenario we didn't
consider, and you're right about it causing problems for users with
encrypted systems.

It does seem more sensible to just remove the 'nousb' option in this case, 
since this parameter has no effect in recent kernels. I'll respin the patches 
and change this LP to better reflect this.
Thanks!

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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:
  Opinion
Status in makedumpfile source package in Xenial:
  In Progress
Status in makedumpfile source package in Bionic:
  In Progress
Status in makedumpfile source package in Cosmic:
  In Progress
Status in makedumpfile source package in Disco:
  Opinion

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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