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-   -   How are 'files with holes' stored? (http://www.linux-archive.org/ext3-users/176500-how-files-holes-stored.html)

Carlo Wood 10-15-2008 01:43 AM

How are 'files with holes' stored?
 
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@alinoe.com>

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10-15-2008 01:47 AM

How are 'files with holes' stored?
 
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@alinoe.com>
>
> _______________________________________________
> Ext3-users mailing list
> Ext3-users@redhat.com
> https://www.redhat.com/mailman/listinfo/ext3-users

--
---
Larry McVoy lm at bitmover.com http://www.bitkeeper.com

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