[Bug 1265402] Re: Unity calls mapdevfs with wrong number of args on btrfs raid1

[dododge]

I ran into the same problem trying to use a raid1 btrfs for "/" in the
14.04 Xubuntu installer.  Just like above, I tracked it down to grub-
installer, patched it almost the exact same way, and then after the
installation finished it wouldn't boot.

Somewhere else in the installer it uses a grub-probe device scan to
populate the kernel options in the grub configuration, and again the
installer assumes that grub-probe only ever returns one device.  When I
went into the grub menu and viewed the entry, I found that it had listed
both of my btrfs devices on the kernel command line, separated by a line
break (which is just how grub-probe outputs them):

      linux /vmlinuz-3.13.0-20-generic.efi.signed root=/dev/mapper/vg-root1
  /dev/mapper/vg-root2 ro rootflags=subvol=@ quiet splash $vt_handoff

After editing that to remove the extra device it did get farther into
the boot.

In my case it still failed: I'm trying to use logical volumes for the
btrfs devices which are allocated from a volume group built from
encrypted partitions.  The resulting initramfs neverf asked for the
encryption passphrase(s), so it still couldn't find the root device and
dropped me into an initramfs shell.  For a more normal setup with just
plain btrfs partitions, editing the kernel line in the grub menu might
be enough to get it to boot.

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https://bugs.launchpad.net/bugs/1265402

Title:
  Unity calls mapdevfs with wrong number of args on btrfs raid1

Status in “ubiquity” package in Ubuntu:
  Triaged

Bug description:
  Trying to install Saucy on a KVM vm. The filesystem is /vda1 mounted
  on /boot, vda2 and vdb1 ate btrfs raid1 swap is on vda. Installer
  always says it can't install bootloader on vda, pick another device.
  But no device works. I'v tried many time with different configurations
  of the virtual disks, always ends the same.

  Thanks,
  Barry

  ProblemType: Bug
  DistroRelease: Ubuntu 13.10
  Package: ubiquity 2.15.26
  ProcVersionSignature: Ubuntu 3.11.0-12.19-generic 3.11.3
  Uname: Linux 3.11.0-12-generic x86_64
  ApportVersion: 2.12.5-0ubuntu2
  Architecture: amd64
  CasperVersion: 1.336ubuntu1
  Date: Wed Jan  1 19:19:46 2014
  InstallCmdLine: file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd.lz quiet splash -- maybe-ubiquity
  LiveMediaBuild: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
  MarkForUpload: True
  ProcEnviron:
   TERM=linux
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
  SourcePackage: grub-installer
  UpgradeStatus: No upgrade log present (probably fresh install)

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