Re: [systemd-devel] [HEADS-UP] Discoverable Partitions Spec

[Chris Mason <clm@fb.com>]

On 03/10/2014 07:45 PM, Lennart Poettering wrote:
> On Mon, 10.03.14 23:39, Goffredo Baroncelli (kreijack@libero.it) wrote:
>
>>> Well, the name is property of the admin really. There needs to be a way
>>> how the admin can label his subvolumes, with a potentially localized
>>> name. This makes it unsuitable for our purpose, we cannot just take
>>> possession of this and leave the admin with nothing.
>>
>> Instead of the name we can use the xattr to store these information.
>
> Ah, using xattrs for this is indeed an option. That way we should be able
> attach any kind of information we like to a subvolume.
>
> Hmm, I figure though that there is no way currently to read xattrs off a
> subvolume without first mounting them individually? Having to mount all
> subvolumes before we can make sense of them and mount them to the right
> place certainly sounds less than ideal...

Ok, are we hoping to pull the xattrs off the disk before mounting 
anything?  Or can we do a mount in a side directory first to scan for 
subvols?

I like the idea of something like this:

mount device on /search_for_fstab
cd /search_for_fstab/<some_magic_directory_name_option_in_systemd>

read xattrs on directories it finds to see where they should be mounted 
in the FS.  xattrs may include mount options and special flags.

mount the things you find

umount /search_for_fstab

I like that it's not actually btrfs specific, since the bind mounts will 
work for any FS.  But it naturally fits the /@ namespace that we seem to 
be favoring as a collection point for snapshots and subvolumes.

-chris