How are 'files with holes' stored?

Carlo Wood carlo at
Wed Oct 15 01:43:10 UTC 2008

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>

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