On 19.12.2012 12:25, Miao Xie wrote:

Hi, everyone.

As we know, there is no backup function for qgroup. when the problem
occurs, the users must recover qgroup configuration manually, it is not
convenient. And besides that, some users might want to import an existed
qgroup configuration into a new filesystem. Btrfs does not have such a
function,it can only be done manually.

So we want to implement btrfs qgroup import/export commands.
1)'btrfs qgroup export' commands will export qgroup tree
  into a user's specified file.(stdout by default)

2)user may modify the configuration file firstly and then
  import it into the filesystem.(by 'btrfs qgroup import' command)

The file may be formated as the following:

Qgroupid     is_compressed     is_exclusive   limited_size    parent
----------------------------------------------------------------------
 0/1            0                 0              10G            1/0
 1/0            1                 1              20G            ---
  
 If 'is_exclusive' is set, 'limited_size' corresponds to max exlusive size,
 else max referenced size. Here 'parent' exclude ancestral qgroups. 

Is there any comment about this idea? 

The configuration only really makes sense in combination with the existing
subvolumes. Even if the target has subvolumes under the same name, they
might have different internal IDs. So it might make more sense to address
the level 0 qgroups by name.
Also it might be misleading to apply a configuration to an existing fs, as
it currently is not possible get a correct accounting if the fs is not
empty. Rescan is not yet implemented.
So instead of just saving and restoring the qgroup config, it might make
more sense to create a new filesystem including all subvolumes and quota
config from a config file.
But, I'm not completely convinced that this is a features that is needed
frequently. If I want a standard deployment, I simple write a script that
creates the fs + subvol + quota.

-Arne

Thanks
Miao