[Bug 1788775] Re: updating grub can end up with loopback devices in grub.cfg

[Phillip Susi]

How is this something relied on for building images?  As it stands, such
a boot entry is non functional since it doesn't tell grub to set up a
loop mapping to the underlying file so the "disk" won't be found.  If
you are building an image and later transferring that image to bare
metal, then it would work ( who does this? ), but does that use case
only need to get the running system set up, or does it also need to be
able to have os-prober add entries for other installations too?

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Title:
  updating grub can end up with loopback devices in grub.cfg

Status in grub2 package in Ubuntu:
  Triaged

Bug description:
  I had (I think, I can't quite remember) the filesystem.squashfs from a
  live server ISO mounted when the kernel was updated. A menu entry for
  this OS-resembling device is now in my grub.cfg:

  menuentry 'Ubuntu 18.04.1 LTS (18.04) (on /dev/loop35p1)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'osprober-gnulinux-simple-cf05f674-791e-48eb-9b42-1bb903f4d024' {
          insmod part_msdos
          insmod ext2
          if [ x$feature_platform_search_hint = xy ]; then
            search --no-floppy --fs-uuid --set=root  cf05f674-791e-48eb-9b42-1bb903f4d024
          else
            search --no-floppy --fs-uuid --set=root cf05f674-791e-48eb-9b42-1bb903f4d024
          fi
          linux /boot/vmlinuz-4.15.0-29-generic root=UUID=cf05f674-791e-48eb-9b42-1bb903f4d024 ro
          initrd /boot/initrd.img-4.15.0-29-generic
  }

  I didn't select it :)

  Something in this setup should be skipping loopback devices, surely?

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