Add Btrfs quotas to the Partitioner UI

[ancorgs]

Problem

We want to add support for Btrfs quotas to the Partitioner. See Jira entry SLE-7742

This is the second part of https://trello.com/c/Ypt6X2VA/2118-3-partitioner-support-for-btrfs-quotas (the first part was #1163).

Solution

• In the form to edit a Btrfs file system (not to be confused with the form to edit a block device), a new "Enable Subvolumes Quota" is added.
  Click here to see two screenshots about it

  
  

• In the form to edit a Btrfs subvolume, a "Limit Size" widget is added.
  Click here to see two screenshots about it

  
  
  Note: the help text was extended in 167bcff

• The columns in the Btrfs section of the Partitioner are reorganized to show that limit and also, if known, the space used by each subvolume.
  Click here to see two screenshots about it

  
  
  Note: the help texts were slightly modified in 167bcff

• As a bonus, when subvolumes with a quota are displayed in a general table with more devices, the size limit is displayed in the column "Size".

Testing

• Manually tested
• Added unit tests

[joseivanlopez]

I am not sure whether to use the first block device is a good idea in case of a multi-device Btrfs. Why not something like filesystem.blk_devices.map(&:size).min ?

[joseivanlopez]

BTW, what happens when the limit is bigger than the size of the filesystem? Is there something like thin provisioning?

[ancorgs]

There is nothing like thin provisioning. But that's not a problem here. It's a max quota in a subdirectory. It implies no promises about that subdirectory being bigger than the container file system.

[ancorgs]

I mean, adding a max quota of 100GiB in a subdirectory of a partition that is only 50GiB will give me no extra space. :-)

[joseivanlopez]

NP: I understood we prefer to use Yast2::Popup in the new code.

[ancorgs]

Well, for very simple cases like this, the old API is more straightforward... and we have another 27 usages of Yast::Popup in the Partitioner anyways.

[joseivanlopez]

LGTM

[coveralls]

Coverage decreased (-0.05%) to 97.605% when pulling 167bcff on ancorgs:ui_snap_experiment2 into 5caf727 on yast:btrfs_subvols.