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

[Rafael David Tinoco]

When zeroing debconf value, I was able to see that grub-installer
populates it again (grub-installer/bootdev with the wrong value
"/dev/mapper"). The code that db_sets it again is:

    elif [ "$(device_to_disk "$cdsrc")" = "$default_bootdev" ] || \
       ([ -n "$hdsrc" ] && [ "$(device_to_disk "$hdsrc")" = "$default_bootdev" ]) || \
       ([ "$default_bootdev" = '(hd0)' ] && \
        (([ -n "$cdfs" ] && [ "$cdfs" != "iso9660" ]) || \
         [ "$hybrid" = true ])) || \
       ([ "$default_bootdev" != '(hd0)' ] && \
        ! partmap "$default_bootdev" >/dev/null && \
        ! grub_probe -t fs -d "$default_bootdev" >/dev/null); then
        db_fget grub-installer/bootdev seen
        if [ "$RET" != true ]; then
            bootfs=$(findfs /boot)
            [ "$bootfs" ] || bootfs="$(findfs /)"
            disk=$(device_to_disk "$bootfs")
            db_set grub-installer/bootdev "$disk" ---------- HERE
            state=2
        fi
    fi
    ;;

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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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