[Bug 1800562] [NEW] Remove obsolete "nousb" option in kdump command-line for newer kernels

[Launchpad Bug Tracker]

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[Impact]
* Kdump command-line include an obsolete "nousb" parameter by default, which can cause a misimpression: users will think they are not booting with USB, but they are.

* 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").

* USB may be pretty essential in case for example kdump users need to
decrypt a disk under LUKS, and there's only an USB keyboard connected to
the system. Given the option is innocuous since Bionic, we should just
drop it to prevent confusion.


[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 '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 extremely low, since the "nousb" parameter
is not used since Bionic although is there. Any bugs we would have by
changing this are still valid by not removing the option - the semantics
with or without "nosub" is the same since from Bionic.

NOTICE we won't change Xenial, it can use kernel 4.4 which indeed
disables USB by taking the "nousb" parameter.

** Affects: makedumpfile (Ubuntu)
     Importance: Medium
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: Confirmed

** Affects: kdump-tools (Ubuntu Xenial)
     Importance: Undecided
         Status: New

** Affects: makedumpfile (Ubuntu Xenial)
     Importance: Medium
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: Won't Fix

** Affects: kdump-tools (Ubuntu Bionic)
     Importance: Undecided
         Status: New

** Affects: makedumpfile (Ubuntu Bionic)
     Importance: Medium
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: Confirmed

** Affects: kdump-tools (Ubuntu Eoan)
     Importance: Undecided
         Status: New

** Affects: makedumpfile (Ubuntu Eoan)
     Importance: Medium
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: Won't Fix

** Affects: kdump-tools (Ubuntu Focal)
     Importance: Undecided
         Status: New

** Affects: makedumpfile (Ubuntu Focal)
     Importance: Medium
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: Confirmed

** Affects: kdump-tools (Ubuntu Groovy)
     Importance: Undecided
         Status: New

** Affects: makedumpfile (Ubuntu Groovy)
     Importance: Medium
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: Won't Fix


** Tags: patch seg
-- 
Remove obsolete "nousb" option in kdump command-line for newer kernels
https://bugs.launchpad.net/bugs/1800562
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