[bug #43874] wrong interpretation of btrfs(-default)-subvolume

[Florian]

URL:
  <http://savannah.gnu.org/bugs/?43874>

                 Summary: wrong interpretation of btrfs(-default)-subvolume
                 Project: GNU GRUB
            Submitted by: ikcalb
            Submitted on: Tue 23 Dec 2014 12:23:57 PM GMT
                Category: Filesystem
                Severity: Major
                Priority: 5 - Normal
              Item Group: Software Error
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: Florian Kerle
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 
                 Release: 2.02~beta1
         Reproducibility: Every Time
         Planned Release: None

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Details:

SETUP:
=====

* OS-partition is BTRFS on  /dev/sda OR (hd0,msdos1)
   (only subvolumes in the root of this partition!)
* I have a fresh install of Debian8 on the subvolume /root.
  (GRUB's config is in /root/boot/grub)
* I put an old ubuntu installation on the subvolume /ubuntu_root.

subvolume /root was default, but reverted to ` btrfs su set 0 /`
(as well as subvolid=5 respectively; does not change anything)


OBSERVED BEHAVIOR:
=================

I cannot configure grub to boot from another subvolume, where the config is
located.

in the grub> console:

#1: check root-var
grub> echo $root
hd0,msdos1

#2: showing my subvoumes:
grub> ls (hd0,msdos1)
btrfs volume; UUID=...
grub> ls (hd0,msdos1)/
/root    /ubuntu_root

#3: houston, we've got a problem
# '(hd0,msdos1)/root/'  is listed here!
ls root
/bin    /boot ... /vmlinuz

SUMMARY: I can correctly list my subvolumes, as in 2). When setting the
(necessray) root-var, some magic seems to happen, as in 3). I cannot specify
the subvolume (hence the correct path) to root, kernel or initrd.

#4: When entering commands manually
# I can at least boot into initramfs...
grub> linux (hd0,msdos1)/ubuntu_root/vmlinuz root=UUID...
rootflags=subvol=/ubuntu_root
grub> initrd (hd0,msdos1)/ubuntu_root/initrd.img

!!! sidenote only !!!
Idk why, but 3 days (and some updates) ago, `update-grub` was able to find the
ubuntu-installation.
!!! the config was not bootable though !!!


EXPECTED BEHAVIOR:
=================
Either:
1. add the option to specify a *subvolume* for a menuentry, and use relative
paths from within the subvolume
(which would be benefitial, when i.e. booting some other [backup]snapshot.
only the subvolume needs to be changed)
2. use full paths again (including the subvolume in the path)

additionally: automatically recognize linux-installations on other subvolumes




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