[systemd-devel] systemd and nested Btrfs subvolumes

[Chris Murphy]

On Sun, Mar 22, 2015 at 10:53 PM, Lennart Poettering
<mzerqung at 0pointer.de> wrote:
> On Fri, 20.03.15 18:08, Chris Murphy (lists at colorremedies.com) wrote:
>
>> Sure but now it's missing if you do a rollback, or if you mount any
>> different root tree, so immediately special handling is needed.
>>
>> If machines is a subvolume at the top level, it can always be mounted
>> at /var/lib/machines regardless of which root is used.
>>
>> I also think this is more consistent with
>> http://0pointer.net/blog/revisiting-how-we-put-together-linux-systems.html
>> specifically the section "What We Propose" when it comes to the
>> location and naming convention for Btrfs subvolumes.
>
> containers are recursively stackable, hence having toplevel subvolumes
> doesn't work, since the containers should be able to have
> subcontainers of their own...
>
> Also, it kinda defeats the whole point of btrfs' subvolume concept,
> where subvolumes are little more than special directories.

They're much more than that, they're a separate fs tree. They're maybe
something between a completely separate filesystem volume, and a
directory. They each have their own inodes, so it's possible (if not
likely) that on a Btrfs volume an inode will point to multiple files
in different subvolumes.

http://marc.info/?l=linux-btrfs&m=137462926329422&w=2

-- 
Chris Murphy