BIO_DELETE equivalent for file on FFS filesystem

[Wojciech Puchar]

>> file to take 900MB or... can i call some system function to "punch"
>> holes?
>
> I think you can only truncate the file at this time, pretty much like
> brk() works for memory.


BAD. suppose i keep windoze VM image on filesystem which takes 10GB but 
uses 5GB.

i could write simple program to find out what blocks are unused and 
then...do nothing.