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Message-ID: <514C33A2.9050709@oracle.com>
Date: Fri, 22 Mar 2013 11:34:10 +0100
From: Koen De Wit <koen.de.wit@oracle.com>
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To: linux-btrfs@vger.kernel.org
Subject: Adding a non-empty subvol to a qgroup
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All,

When adding a subvolume to a qgroup, pre-existing files in that 
subvolume are not counted in the referenced/exclusive space of the 
qgroup. Is this intended behavior ?

I create a subvol with one file:

   # mkfs.btrfs /dev/sdg
   # mount /dev/sdg /mnt/fulldisk
   # cd /mnt/fulldisk
   # btrfs quota enable ./
   # btrfs sub create sub1
   # dd if=/dev/zero of=sub1/file1 bs=100000 count=1
   # sync
   # btrfs qgroup show ./
   0/257 106496 106496

Now I create a new qgroup on level 1 and add the qgroup of sub1 to it :

   # btrfs qgroup create 1/0 ./
   # btrfs qgroup assign 0/257 1/0 ./
   # sync
   # btrfs fi sync ./
   # btrfs quota rescan ./
   # btrfs quota rescan ./sub1
   # btrfs qgroup show ./
   0/257 106496 106496
   1/0 0 0

The pre-existing file does not contribute to the space numbers.

Let's create a new file:

   # dd if=/dev/zero of=sub1/file2 bs=50000 count=1
   # sync
   # btrfs qgroup show ./
   0/257 159744 159744
   1/0 53248 53248

We see that only the new file is included in the space numbers.

Now I remove the first file:

   # rm -f sub1/file1
   # sync
   # btrfs qgroup show ./
   0/257 57344 57344
   1/0 -49152 -49152

The space numbers go below zero. Even if the behavior above is intended, 
the removal of the pre-existing file should not result in negative space 
numbers.

Koen.