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

[Mathieu Trudel-Lapierre]

I'm not convinced the keypress is 100% reliable. It does get better all
the time, but there are still systems on which it's just not possible to
get it working reliably, and sometimes not at all - you'll press
consistantly "too late" or "to early" and GRUB won't notice, so you
won't get the menu.

AIUI, the issue came from EFI timers being odd, but I can't qualify
that: TSC calibration isn't done using the EFI timer first -- we first
look at pmtimer and PIT before we use the EFI timers.

As for / on btrfs, I agree it's a side-effect of the check_writable()
call, but it does seem to still be "up to date" at first glance: it's
*supposed* to be affected the same way: if you're on a system on which
the keypress doesn't get you the menu (this is system-specific), *and*
you're set up with /boot on btrfs (which doesn't have write support as
far as I can tell), then a failing boot won't get you the menu
automatically. So... three machines is good, but if they're all the same
kind (all Dell, all AMI, etc.) then it might not be a good sample.

I think the point is that we need a better idea of exactly which systems
are affected, to try and tell how many people it really affects. Let's
try to get that now.

Steve, do we have a good list of exactly which systems we've seen the
LVM issues on?

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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:
  Opinion

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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