tree de483837504aa33c429cca2812c5828076938180
parent 8465ecec9611d60cbbc8e374ecf68453e0dd5b50
author Qu Wenruo <quwenruo@cn.fujitsu.com> 1425025463 +0800
committer Chris Mason <clm@fb.com> 1428936774 -0700

btrfs: Don't allow subvolid >= (1 << BTRFS_QGROUP_LEVEL_SHIFT) to be created

Btrfs will create qgroup on subvolume creation if quota is enabled, but
qgroup uses the high bits(currently 16 bits) as level, to build the
inheritance.

However it is fully possible a subvolume can be created with a
subvolumeid larger than 1 << BTRFS_QGROUP_LEVEL_SHIFT, so it will be
considered as level 1 and can't be assigned to other qgroup in level 1.

This patch will prevent such things so qgroup inheritance will not be
screwed up.
The downside is very clear, btrfs subvolume number limit will decrease
from (u64 max - 256(fisrt free objectid) - 256(last free objectid)) to
(u48 max -256(first free objectid)).
But we still have near u48(that's 15 digits in dec), so that should not
be a huge problem.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>