How are 'files with holes' stored?

[Larry McVoy]

I don't remember how UFS did this but I could go figure it out in 10 or 20 
minutes if that helped.  ext* - no idea.  I'd expect that your "block number
is 0" is a darn good guess, that's what I would do.  That or -1.

On Wed, Oct 15, 2008 at 03:43:10AM +0200, Carlo Wood wrote:
> Hi, I don't know how to call them, but it seems
> that ext3 grep allows files to be stored that
> have a very large size (when doing an 'ls -l')
> but do not actually allocate all blocks.
> 
> I assume this is achieved by using 0 as blocknumber
> for indirect blocks.
> 
> What are the exact requirements for such files?
> Is it allowed to have a double indirect block
> that exists entirely of zeroes? Is it possible
> there is are 0 entries in the tripple indirect
> block? Etc.
> 
> -- 
> Carlo Wood <carlo at alinoe.com>
> 
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-- 
---
Larry McVoy                lm at bitmover.com           http://www.bitkeeper.com