btrfs subvolume result in wrong disk calculation

[imlonghao]

My VPS only has 20G disk

Device     Start      End  Sectors Size Type
/dev/vda1   2048     4095     2048   1M BIOS boot
/dev/vda2   4096 41943006 41938911  20G Linux filesystem

But yabs.sh said I got 60G

Disk       : 60.0 GiB

# df -t simfs -t ext2 -t ext3 -t ext4 -t btrfs -t xfs -t vfat -t ntfs -t swap --total 2>/dev/null
Filesystem     1K-blocks     Used Available Use% Mounted on
/dev/vda2       20969452 12098376   7625576  62% /nix
/dev/vda2       20969452 12098376   7625576  62% /persist
/dev/vda2       20969452 12098376   7625576  62% /boot
total           62908356 36295128  22876728  62% -

# mount | fgrep vda2
/dev/vda2 on /nix type btrfs (rw,relatime,compress-force=zstd:3,space_cache=v2,subvolid=259,subvol=/@nix)
/dev/vda2 on /persist type btrfs (rw,relatime,compress-force=zstd:3,space_cache=v2,subvolid=260,subvol=/@persist)
/dev/vda2 on /boot type btrfs (rw,relatime,compress-force=zstd:3,space_cache=v2,subvolid=258,subvol=/@boot)

[masonr]

This is a known issue affecting certain filesystem types during the size calculation when using df. ZFS is another filesystem that this also affects (see #35). I don't currently have a good way currently of fixing this issue without overly complex logic to handle all the different fs types and edge cases, so for now this will left as a known bug without resolution. Appreciate the bug report!