[sles-beta] default btrfs subvolumes under / in SLES 12

[Johannes Meixner]

Hello,

On Jun 27 15:25 Wendy Palm wrote (excerpt):
> In the default installation of SLES 12, these btrfs subvolumes
> are created underneath /.

What exactly do you mean with "underneath /"?
In particular what exactly do you mean with '/' here?

In other words:
>From what point of view is '/' the root of exactly what in SLE12?

On my SLES12-beta8 installation with default partitioning and
default filesystem (btrfs with our default subvolumes) I get:
-------------------------------------------------------------------------
# btrfs subvolume list -a /
ID 257 gen 487 top level 5 path <FS_TREE>/@
ID 258 gen 396 top level 257 path @/boot/grub2/i386-pc
ID 259 gen 396 top level 257 path @/boot/grub2/x86_64-efi
ID 260 gen 396 top level 257 path @/home
ID 261 gen 396 top level 257 path @/opt
ID 262 gen 396 top level 257 path @/srv
ID 263 gen 486 top level 257 path @/tmp
ID 264 gen 408 top level 257 path @/usr/local
ID 265 gen 396 top level 257 path @/var/crash
ID 266 gen 396 top level 257 path @/var/lib/mailman
ID 267 gen 396 top level 257 path @/var/lib/named
ID 268 gen 396 top level 257 path @/var/lib/pgqsl
ID 269 gen 487 top level 257 path @/var/log
ID 270 gen 396 top level 257 path @/var/opt
ID 271 gen 491 top level 257 path @/var/spool
ID 272 gen 486 top level 257 path @/var/tmp
ID 276 gen 486 top level 257 path @/.snapshots
ID 277 gen 55 top level 276 path <FS_TREE>/@/.snapshots/1/snapshot
ID 278 gen 56 top level 276 path <FS_TREE>/@/.snapshots/2/snapshot

# btrfs subvolume get-default /
ID 257 gen 487 top level 5 path @

# mount | grep btrfs
/dev/sda2 on / type btrfs (rw,relatime,space_cache)
/dev/sda2 on /.snapshots type btrfs (rw,relatime,space_cache)
/dev/sda2 on /var/tmp type btrfs (rw,relatime,space_cache)
/dev/sda2 on /var/spool type btrfs (rw,relatime,space_cache)
/dev/sda2 on /var/opt type btrfs (rw,relatime,space_cache)
/dev/sda2 on /var/log type btrfs (rw,relatime,space_cache)
/dev/sda2 on /var/lib/mailman type btrfs (rw,relatime,space_cache)
/dev/sda2 on /srv type btrfs (rw,relatime,space_cache)
/dev/sda2 on /usr/local type btrfs (rw,relatime,space_cache)
/dev/sda2 on /var/lib/named type btrfs (rw,relatime,space_cache)
/dev/sda2 on /var/lib/pgqsl type btrfs (rw,relatime,space_cache)
/dev/sda2 on /tmp type btrfs (rw,relatime,space_cache)
/dev/sda2 on /var/crash type btrfs (rw,relatime,space_cache)
/dev/sda2 on /opt type btrfs (rw,relatime,space_cache)
/dev/sda2 on /boot/grub2/x86_64-efi type btrfs (rw,relatime,space_cache)
/dev/sda2 on /home type btrfs (rw,relatime,space_cache)
/dev/sda2 on /boot/grub2/i386-pc type btrfs (rw,relatime,space_cache)

# mkdir /tmp/btrfs-default

# mount -t btrfs /dev/sda2 /tmp/btrfs-default

# ls /tmp/btrfs-default
bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run
   sbin  selinux  .snapshots  srv  sys  tmp  usr  var

# ls /
bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run
   sbin  selinux  .snapshots  srv  sys  tmp  usr  var

# mkdir /tmp/btrfs-toplevel

# mount -t btrfs -o subvolid=0 /dev/sda2 /tmp/btrfs-toplevel/

# ls /tmp/btrfs-toplevel/
@

# ls /tmp/btrfs-toplevel/@
bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run
   sbin  selinux  .snapshots  srv  sys  tmp  usr  var

# mount | grep tmp/btrfs
/dev/sda2 on /tmp/btrfs-toplevel type btrfs (rw,relatime,space_cache)
/dev/sda2 on /tmp/btrfs-default type btrfs (rw,relatime,space_cache)
-------------------------------------------------------------------------

Note our special '<FS_TREE>/@' btrfs default subvolume and its
matching '<FS_TREE>/@' directory which makes it ambiguous what '/' means.

Therefore my above question:
>From what point of view means '/' the root of exactly what in SLE12?


Kind Regards
Johannes Meixner
-- 
SUSE LINUX Products GmbH -- Maxfeldstrasse 5 -- 90409 Nuernberg -- Germany
HRB 16746 (AG Nuernberg) GF: Jeff Hawn, Jennifer Guild, Felix Imendoerffer