[Bug 1848180] Re: LVM initrd fails to activate btrfs multidevice root

[Steve Dodd]

OK, attached are some initramfs scripts:

local-top.hook -> /etc/initramfs-tools/hooks/btrfs-lvm
local-top.script -> /etc/initramfs-tools/scripts/local-top/btrfs-lvm

I've tried to make them reasonably generic, the root fs is examined on
initramfs creation, component btrfs devices extracted and tested to see
if they are LVM LVs, and if so added to a config file inside them
initramfs. Then on boot all those LVs are activated before attempting to
mount root.

** Attachment added: "/etc/initramfs-tools/hooks/btrfs-lvm"
   https://bugs.launchpad.net/ubuntu/+source/lvm2/+bug/1848180/+attachment/5447425/+files/local-top.hook

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Title:
  LVM initrd fails to activate btrfs multidevice root

Status in lvm2 package in Ubuntu:
  Confirmed

Bug description:
  I have two lvm volumes (/dev/mapper/raid-btrfs and /dev/mapper/fast-
  btrfs) in two different volume groups. I have created a btrfs (raid1)
  filesystem on top of them and that's my root filesystem.

  If i define it by UUID in the root= kernel argument, i just hit bug
  #1574333. Forcing my root to "/dev/mapper/fast-btrfs" by defining
  GRUB_DEVICE in /etc/default/grub works around that bug.

  The problem now is that initrd is only activating the device given as
  root= argument, leaving the other inactive; consequently the btrfs
  mount fails to find its second device and the system fails to boot
  giving up at initramfs prompt.

  Manually adding a line to activate also 2nd device at the bottom of
  /usr/share/initramfs-tools/scripts/local-top/lvm2 and rebuilding the
  initramfs works around this issue too, but i suppose my mods will be
  washed away by next package upgrade.

  Here is the result:
  > activate "$ROOT"
  > activate "$resume"
  > activate "/dev/mapper/raid-btrfs"

  Proposed solution:
  I understand this is an uncommon setup and correctly handling multidevice LVM roots is complicated, please just add a configuration option to manually define/append the list of volume groups to be activated at initrd time.

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