Comment 13 for bug 1838525

## SUMMARY OF THE ISSUE ##

After reading the grub-installer script, and following execution flow:

...

if [ "$found" = "0" ] && type lvdisplay >/dev/null 2>&1 && \
     (lvdisplay "$disc_offered" | grep -q 'LV Name' 2>/dev/null || \
      [ -e "$(dirname "$disc_offered")/control" ]); then
 # Don't set frdev/frdisk here, otherwise you'll end up in different
 # code paths below ...
 frtype=lvm
fi

...

default_bootdev_os="$($chroot $ROOT grub-mkdevicemap --no-floppy -m - | head -n1 | cut -f2)"
if [ "$default_bootdev_os" ]; then
 default_bootdev="$($chroot $ROOT readlink -f "$default_bootdev_os")"
 if db_get grub-installer/bootdev && [ "$RET" = '(hd0)' ]; then
  db_set grub-installer/bootdev "$default_bootdev"
 fi
else
 default_bootdev="(hd0)"
fi

DEBUG:

default_bootdev_os=/dev/disk/by-id/lvm-pv-uuid-IKvzNq-IRE5-arLC-hSS1-jDU2-ZSKA-90lATY
and bootdev wasn't set to anything because it isn't '(hd0)'.

...

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"
  state=2
 fi
fi

DEBUG:

bootdev=/dev/mapper after disk=$(device_to_disk bootfs)
since bootfs is bootfs=/dev/mapper/vgubuntu-root
and device_to_disk will remove last part from /dev/mapper/XXX.

bootfs is /dev/mapper/vgubuntu-root BECAUSE:

rootfs=$(findfs /)
bootfs=$(findfs /boot
[ -n "$bootfs" ] || bootfs="$rootfs"

so, device_to_disk() has cut "vgubuntu-root" from the string and that is how bootdev has become "/dev/mapper" only.

----

Testing with a SCSI disk, I got the exact same DEBUG output, BUT ...

I was able to see that the INITIAL value for:

grub-installer/bootdev WAS "/dev/sda"

but, after purging it with "debconf-set grub-installer/bootdev ''", I could NOT repopulate db variable again by executing only "grub-installer /target", DIFFERENTLY than when executing "grub-installer /target" in a /dev/vda based LVM, when it ALWAYS gets populated like described above (with /dev/mapper).

TODO:

discover why grub-installer/bootdev isn't populated back when re-executing "grub-installer /target" after purging the original (right after installation) value. Whenever bootdev defaults to /dev/mapper/XXXX, bootdev should be replaced with /dev/sdXXX or /dev/vdXXX, one of the LVM PV disks of under laying volume group (to confirm).