[Bug 1815002] Re: quick-boot-lvm.patch caused regression - menu always appear if root is on Btrfs

[Steve Langasek]

On February 15, 2019 4:08:36 AM PST, RussianNeuroMancer <1815002 at bugs.launchpad.net> wrote:
>> Nevertheless, this configuration does NOT reliably allow the user to
>reach the boot menu with the default timeout of 0.
>
>Could you please clarify under which circumstances this configuration
>does not reliably allow user reach boot menu? I asking because I never
>seen situation where this menu wasn't reachable on dozens/hundreds
>different devices with / on btrfs, from 7 inch tablets to two-socket
>servers.
>
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>Title:
> quick-boot-lvm.patch caused regression - menu always appear if root is
>  on Btrfs
>
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Under UEFI, there is no way for grub to detect a modifier key being held
down; instead of holding shift at boot to get to the menu, you have to
press the shift key at the right moment.

If you have a boot timeout of 0, that means grub waits 0 seconds for you
to press the shift key before booting.

That means the window in which you can press the shift key to get to the
boot menu is 0 seconds.

If you miss the window, your only option is to reboot and try again.

If you reboot before the boot finishes, then grub will show you the boot
menu by default with a timeout.

But if /boot is on btrfs, then grub has no way to record that a boot was
attempted, which means it will not know that you rebooted before the
boot finished.  And you will never reliably get the boot menu.

-- 
Steve Langasek

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https://bugs.launchpad.net/bugs/1815002

Title:
  quick-boot-lvm.patch caused regression - menu always appear if root is
  on Btrfs

Status in grub2 package in Ubuntu:
  Confirmed

Bug description:
  Comments about this regression:

  https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1800722/comments/12
  https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1800722/comments/13

  In my case menu starting to always appear on various devices from
  small tablets to workstations. First time it happened with laptop
  https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/736743/comments/95
  and since then more devices became affected. I not 100% sure, but
  seems like at least one unsuccessfully boot is required to reproduce
  this issue, but maybe I am mistake here and issue starting to happen
  for all Btrfs users.

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