My application needs to know the free space on a APFS volume.
It seems the operating system can 'reserve' purgeable disk space, starting from macOS High Sierra and APFS.
When using NSFileManager function, it only returns 'real' free space:
NSDictionary* pathAttrs = [[NSFileManager defaultManager] fileSystemAttributesAtPath: path];
NSNumber* pathSize = pathAttrs[ NSFileSystemSize];
NSNumber* pathFreeSize = pathAttrs[ NSFileSystemFreeSize];
My question: how to compute or estimate this 'purgeable' free space?