[Bug 1838525] Re: LVM setup fails to install grub on virtio storage

[Rafael David Tinoco]

Reproducer:

#!/bin/bash
  
device_to_disk () {
    echo "$1" | \
        sed 's:\(/dev/[a-z]\+\).*:\1:'
}

device_to_disk /dev/mapper/vgubuntu-root

So device_to_disk() is doing what it is supposed to do and there was NO
CHANGE to it (as it appears).

I guess using grub-install at /dev/vda was allowed before (instead of
the LVM PV ?), so there wasn't a need to use /dev/mapper/vgubuntu-root
as the argument for grub-installer.

It is either that OR the "/dev/mapper" section of this same script,
related to:

case $prefix in
...
    /dev/mapper)
    disc_offered_devfs=...
...

couldn't deal with virtio disks on top of LVM (my next task here) as it
should.

Simply using:

----

#!/bin/bash

device_to_disk () {
    echo "$1" | \
        sed 's:\(/dev/mapper/.*\+\|/dev/[a-z]\+\).*:\1:'
}

device_to_disk /dev/mapper/vgubuntu-root
device_to_disk /dev/something/else

$ ./temp.sh 
/dev/mapper/vgubuntu-root
/dev/something
----

instead, keeps the same behavior for everything else AND fixes usage
case where device is "/dev/mapper/XXXXX". This is ONE WAY of fixing
this, BUT I guess the /dev/mapper section should also work for LVM w/
virtio disks, as stated in the script, so I'm investigating this.

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https://bugs.launchpad.net/bugs/1838525

Title:
  LVM setup fails to install grub on virtio storage

Status in debian-installer package in Ubuntu:
  New
Status in grub-installer package in Ubuntu:
  Triaged
Status in debian-installer source package in Eoan:
  New
Status in grub-installer source package in Eoan:
  Triaged
Status in debian-installer package in Debian:
  New

Bug description:
  The Eoan debian-installer ISO fails to install GRUB on LVM installs
  with virtio storage, as it runs grub-install with /dev/mapper as a
  target (a directory), even if instructed to target a device.

  The following steps to reproduce have been prepared running the
  20190730 build, but this has been broken since about June 18, 2019.
  Steps to reproduce:

  $ md5sum eoan-server-amd64.iso
  f591e30485e5f0b5117f6c116e538c42  eoan-server-amd64.iso
  $ qemu-img create -f raw disk1.img 8G
  Formatting 'disk1.img', fmt=raw size=8589934592
  $ kvm -m 1024 -boot d -cdrom eoan-server-amd64.iso -drive file=disk1.img,if=virtio

  Proceed with all the defaults. In the "Partition disk" step select
  "Guided - use entire disk and set up LVM". Go ahead accepting the
  defaults. At the "Install the GRUB boot loader" step select "/dev/vda"
  as the target device. The installer will actually run `grub-install
  --force /dev/mapper` and fail after a while. The wrong command is
  visible both in the d-i screen and by running `ps` on a different
  console.

  Full installer syslog: http://paste.ubuntu.com/p/qtZy86dTp6/

  It's interesting how this doesn't happen when not using virtio. If
  from the commands above the "if=virtio" option is dropped then
  everything works as expected. In this case the target block device is
  called /dev/sda instead of /dev/vda.

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