Remove obsolete "nousb" option in kdump command-line for newer kernels

[Guilherme G. Piccoli]

[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.

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "debdiff for disco" seems to be a debdiff. The ubuntu-sponsors team has been subscribed to the bug report so that they can review and hopefully sponsor the debdiff. If the attachment isn't a patch, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are member of the ~ubuntu-sponsors, unsubscribe the team.

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[Thadeu Lima de Souza Cascardo (cascardo)]

Have you seen this cause any issue when kdumping from bionic or any releases later than xenial?

Because we should not disable usb, and I would apply the opposite fix and just remove "nousb" from the command line.

The reason for this is supporting kdump on encrypted systems, where the user must type a password and use a USB keyboard.

Cascardo.

[Heitor Alves de Siqueira (halves)]

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!

[Simon Quigley (tsimonq2)]

Unsubscribing the Ubuntu Sponsors Team as there is nothing to sponsor.

[Guilherme G. Piccoli (gpiccoli)]

This is the debdiff containing the proposed solution for this LP.
I'd like to thanks specially Cascardo and Heitor for the fruitful discussions with regards the direction we should take in this LP.

[Steve Langasek (vorlon)]

Ubuntu 19.04 reached end of life on January 23, 2020. I am therefore marking this bug 'wontfix' for that release.

[Brian Murray (brian-murray)]

The Eoan Ermine has reached end of life, so this bug will not be fixed for that release

[Brian Murray (brian-murray)]

The Groovy Gorilla has reached end of life, so this bug will not be fixed for that release

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "lp1800562_eoan.debdiff" seems to be a debdiff. The ubuntu-sponsors team has been subscribed to the bug report so that they can review and hopefully sponsor the debdiff. If the attachment isn't a patch, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are member of the ~ubuntu-sponsors, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issue please contact him.]

[Graham Inggs (ginggs)]

"patch" flag removed from the attachment
"patch" tag removed
~ubuntu-sponsors unsubscribed