Re: [Bug-tar] Detection of sparse files is broken on btrfs

[Paul Eggert]

On 01/18/2018 02:33 AM, Joerg Schilling wrote:
> Returning a value for st_blocks, that changes with the phases of the moon while
> the content of that file is not changed is another unexpected behavior.

Not at all. It's completely expected nowadays, for the same reason that 
invoking statvfs twice on the same file might return different results, 
even if no application has made any change to any file. Nothing in POSIX 
says or implies that an implementation cannot spontaneously change the 
amount of available space in a file system, or that it cannot 
spontaneously change the amount of space that a file is using.