Re: Q: sparse file creation in existing data?

[Daniel Phillips <phillips@bonn-fries.net>]

On Friday 29 June 2001 14:55, Ph. Marek wrote:
> Hmmm, on second thought ... But I'd like it better to have a fcntl for
> hole-making :-)
> Maybe I'll implement this myself.

A far superior interface would be:

    ssize_t sys_clear(unsigned int fd, size_t count)

A stub implementation would just write zeroes.  You would need a generic way 
of determining whether holes are supported for a particular file - this is 
where an fcntl would be appropriate.  It would also be nice to know this 
before opening/creating a file, perhaps by fcntling the directory.

But don't expect to have a real, hole-creating implementation any time soon.  
Taming the truncate races is hard enough as it is with a single boundary at 
the end of a file.  Taking care of multiple boundaries inside the file is 
far, far harder.  Talk to Al Viro or the Ext3 team if you want the whole ugly 
story.

--
Daniel