Bug#600190: linux-image-2.6.32-5-amd64: btrfs filesystem df doesn't work because of missing ioctl
The btrfs tool, which is the canonical tool for btrfs handling, doesn't
have a useful output for btrfs filesystem df because the necessay ioctl
isn't available in 2.6.32. Would you consider adding it?
1406e4327be3a533a2b18582f715ce2cfbcf6804 is the relevant commit id.
(7fde62bffb576d384ea49a3aed3403d5609ee5bc further modifies the ioctl
function to buffer the output)