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

[Rafael David Tinoco]

SUMMARY Of the problem (or a HUGE TL;DR):

- Installer depends on "grub-mkdevice --no-floppy -m -" command to get bootable devices ordering.
- grub-mkdevice was dropped upstream and it is included in grub2 by a quilt patch.
- grub-mkdevice orders everything that is in /dev/disk/by-id/* excluding, in this order, everything containing "-part", "dm-" and "md-". 
- LVM partitions are added to /dev/disk/by-id, but not the entire disk (as the PV is the partition itself).
- UDEV creates /dev/disk/by-id depending on 60-persistent-storage.rules:

# virtio-blk
KERNEL=="vd*[!0-9]", ATTRS{serial}=="?*", ENV{ID_SERIAL}="$attr{serial}", SYMLINK+="disk/by-id/virtio-$env{ID_SERIAL}"
KERNEL=="vd*[0-9]", ATTRS{serial}=="?*", ENV{ID_SERIAL}="$attr{serial}", SYMLINK+="disk/by-id/virtio-$env{ID_SERIAL}-part%n"

- So, LVM puts ID_SERIAL in LVM partitions, they get added to /dev/disk
/by-id and installer is lost when trying to order it, as LVM partition
gets into 1st position of choice, instead of the full disk (for hd0,
hd1, ... grub setup).

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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:
  Comment #26 has the TL;DR version of the problem.
  https://bugs.launchpad.net/ubuntu/+source/debian-installer/+bug/1838525/comments/26

  [Original 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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