Bug#686097: possible solution

[Daniel Pocock <daniel@pocock.com.au>]

Suggested that any enhancement to support this for wheezy must be
non-disruptive and must not require changes to any strings that would
need to be translated.

The only way I see of supporting that for wheezy is described below:



Concept:

  * user can specify two partitions with the same mount point,
    provided they are both btrfs
  * partman-btrfs will recognise this special case and assume
    that RAID1 is desired
  * due to the requirement to avoid changing any text strings,
    this will happen silently and the user will not be
    prompted to choose RAID level or other possible choices
  * if filesystems are not btrfs, the normal error will appear


package partman-target
----------------------

  check.d/
    proper_mountpoints
    duplicate_labels
        same_mountpoint and same_label errors must be suppressed when
        this special case is detected

package partman-btrfs
---------------------

  commit.d/
    format_btrfs
        * must do a pre-screening of all filesystem specs
          and identify those that need RAID
        * format the normal filesystems first, and the RAID ones in a
          second pass

  fstab.d/
    btrfs
        * must do a pre-screening of all filesystem specs
          and identify those that need RAID
        * output the normal filesystems first
        * for the RAID filesystems, must mount by UUID= syntax
          (due to bug #612402)
          http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=612402
        * one possible technique is to just check UUID of each
          filesystem, and parse the resulting fstab output via uniq