Comment 0 for bug 1838525

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.