Re: Is there a "make hole" (truncate in middle) syscall?

[Mike Fedyk]

On Thu, Dec 04, 2003 at 02:32:23PM -0600, Rob Landley wrote:
> You can make a file with a hole by seeking past it and never writing to that 
> bit, but is there any way to punch a hole in a file after the fact?  (I mean 
> other with lseek and write.  Having a sparse file as the result....)
> 

No, Linux doesn't have this feature.

> What are the downsides of holes?  (How big do they have to be to actually save 
> space, is there a performance penalty to having a file with 1000 4k holes in 
> it, etc...)

When you copy them, you need to use tools that know about sparse files and
how to deal with them.  Also, you will only save space on block aligned
contiguous zeros at least the length of one block.
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