[Bug 1247905] [NEW] update-grub fails in the face of overlayroot

[Mike Purvis]

Public bug reported:

Info on overlayroot: http://blog.dustinkirkland.com/2012/08/introducing-
overlayroot-overlayfs.html

Mount configuration for an overlayroot-configured box:

$ mount
overlayroot on / type overlayfs (rw,errors=remount-ro)
/dev/sda5 on /media/root-ro type ext3 (ro,relatime,errors=continue,user_xattr,acl,barrier=1,data=ordered)
/dev/sda6 on /media/root-rw type ext3 (rw,relatime,errors=continue,user_xattr,acl,barrier=1,data=ordered)
/dev/sda1 on /boot type ext3 (rw)

When attempting to update-grub:

$ sudo update-grub
[sudo] password for administrator: 
/usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).

The issue comes about in this line of the /usr/sbin/grub-mkconfig
script:

GRUB_DEVICE="`${grub_probe} --target=device /`"

In the short term, I'm hacking that script to pass in a value for
GRUB_DEVICE, but the ideal would be to have the grub-probe binary detect
when an overlayfs is / and return the device which is the bottom of the
overlay.

** Affects: grub2 (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1247905

Title:
  update-grub fails in the face of overlayroot

Status in “grub2” package in Ubuntu:
  New

Bug description:
  Info on overlayroot: http://blog.dustinkirkland.com/2012/08
  /introducing-overlayroot-overlayfs.html

  Mount configuration for an overlayroot-configured box:

  $ mount
  overlayroot on / type overlayfs (rw,errors=remount-ro)
  /dev/sda5 on /media/root-ro type ext3 (ro,relatime,errors=continue,user_xattr,acl,barrier=1,data=ordered)
  /dev/sda6 on /media/root-rw type ext3 (rw,relatime,errors=continue,user_xattr,acl,barrier=1,data=ordered)
  /dev/sda1 on /boot type ext3 (rw)

  When attempting to update-grub:

  $ sudo update-grub
  [sudo] password for administrator: 
  /usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).

  The issue comes about in this line of the /usr/sbin/grub-mkconfig
  script:

  GRUB_DEVICE="`${grub_probe} --target=device /`"

  In the short term, I'm hacking that script to pass in a value for
  GRUB_DEVICE, but the ideal would be to have the grub-probe binary
  detect when an overlayfs is / and return the device which is the
  bottom of the overlay.

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