index directories in ext2 / ext3

Gaëtan Podevijn gpodevij at
Mon Feb 8 20:59:57 UTC 2010

Hello Everyone,

I am a Belgian student in computer sciences at the Free University of
Brussels ( ULB ).

I am currently working on a little article. I would like to explain the
differences between ext2, ext3 and ext4.

During my researches, I read that ext2's directories are implemented with a
linked-list structure. I also read Daniel Phillips's article "A Directory
index for ext2" (2002) and I'm a bit troubled.

Indeed, I see that the HTree data structure was developed for ext2 but I
cannot see anywhere that the current ext2 implementation uses that data

I opened the dir.c file from ext2 on the last stable kernel sources and I do
not see anything about HTree, but the dir.c file from ext3 uses it, if I do
not go wrong.

Could you explain me why people talk about "index directories for ext2" but
there's no ext2 implementation that uses the HTree structure ? Is it only
for ext3 ? Since when ? Could you give me some source that explain when was
implemented HTree in ext{2,3} ?

Thanks a lot.
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