Installation with btrfs ends in "initramfs" after final installation-reboot

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Problem Description
=============================================
When installing with / on btrfs file system, the first boot (after the installation process is finished) ends in "initramfs". Installed system does not come up.

Installation under z/VM

following partition layout during installation:

dasda1 /boot ext3
dasda2 / btrfs
dasda3 swap

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[Ubuntu Foundations Team Bug Bot (crichton)]

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------- Comment From <email address hidden> 2016-04-01 07:59 EDT-------
Still broken in beta and in kernel 4.4.0-16 (installer 443). Raising severity to ship issue - or it needs to be documented in release notes!

[Dimitri John Ledkov (xnox)]

I have been debugging this yesterday, the generated /etc/fstab is correct, however instead of mounting @ subvolume the btrfs root group is mounted in /root. It would indicate that zipl-installer support for btrfs is non-existent. It does not seem like this ever worked, thus we can add an errata to the beta release notes until this is fixed. However, this is not a regression.

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------- Comment From <email address hidden> 2016-04-01 09:30 EDT-------
I agree to document this in release notes, as I already suggested. When it is available in release notes, we will revert severity again.

[Launchpad Janitor (janitor)]

This bug was fixed in the package zipl-installer - 0.0.33ubuntu1

---------------
zipl-installer (0.0.33ubuntu1) xenial; urgency=medium

  * Merge from Debian, remaining changes:
    - Enable crashkernel=128M paramemter for d-i installs by default.
    - Apply ubuntu branding.

zipl-installer (0.0.33) unstable; urgency=medium

  * Query /target's btrfs subvolume and correctly add rootfs subvol flag
    to the kernel arguments in the generated zipl.conf. LP: #1557329.

 -- Dimitri John Ledkov <email address hidden> Fri, 01 Apr 2016 15:48:03 +0100

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------- Comment From <email address hidden> 2016-04-06 06:23 EDT-------
Successfully verified with installer 445 (after working around other problems, caused by LTC 139323 - LP1559193). Closed.