Revert to using df to get free space for btrfs pools

[JorgeB]

I believe it was used before but due to unreliable values it stopped being used, on newer kernels it should work reliably, and better than current method for some situations.

 

There are frequent posts on the forum from users using two different size devices in a pool, because free space is incorrectly reported and they run out of it, e.g. a pool made of 32GB + 64GB devices default raid1

 

 

Usable space will be around 32GB, GUI reports 47GB, df reports correctly:

 

Also starting with even newer kernels, like the one on v6.9-beta1 is started correctly reporting free space for raid5/6 profiles, pool made of four 64GB devices using raid6

 

 

With df:

 

Please change this for v6.9, with multiple pools it will likely affect more users.

 

[bonienl]

For better visibility, can you create (move to) a bug report.

[JorgeB]

Can't move posts to the bug reports section (or don't know how to) but copied it there.