From: Avi Deitcher <avi@deitcher.net>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: linux-ext4@vger.kernel.org
Subject: Re: algorithm for half-md4 used in htree directories
Date: Tue, 12 Oct 2021 19:20:26 -0700 [thread overview]
Message-ID: <CAF1vpkidOGm0OmRac+OqaXcnJptn1O22OLHXJZoPfEbhxb3Ttw@mail.gmail.com> (raw)
In-Reply-To: <YWXGRgfxJZMe9iut@mit.edu>
Yep, right here
https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/tree/lib/ext2fs/dirhash.c
Hey, that's your name on it, Ted!
I am close, must be messing it up somehow. I literally copied the
majority of that (actually, some slight variant, but basically the
same) into a standalone main.c, removed any library dependencies by
copying those in so I can get a standalone, and I still am not quite
getting it. Maybe I am messing up the seed?
dump2fs of the superblock shows:
Default directory hash: half_md4
Directory Hash Seed: d64563bc-ea93-4aaf-a943-4657711ed153
and debugfs of the hash tree shows:
Root node dump:
Reserved zero: 0
Hash Version: 1
Info length: 8
Indirect levels: 1
Flags: 0
Number of entries (count): 2
Number of entries (limit): 123
Checksum: 0x49f0afdc
Entry #0: Hash 0x00000000, block 124
Entry #1: Hash 0x78b6e3b8, block 128
Entry #0: Hash 0x00000000, block 124
Number of entries (count): 113
Number of entries (limit): 126
Checksum: 0x78407270
Entry #0: Hash 0x00000000, block 1
Entry #1: Hash 0x00f48688, block 193
...
So it has the hash version correct (I also gdb-ed through my little
program. Maybe I am getting the u32 order wrong in the seed? Or the
endianness?
I should just create a gist with this, shouldn't I?
On Tue, Oct 12, 2021 at 10:30 AM Theodore Ts'o <tytso@mit.edu> wrote:
>
> On Mon, Oct 11, 2021 at 07:58:00PM -0700, Avi Deitcher wrote:
> > Aha. I missed that the seed is injected into buf before passing it
> > into half_md4_transform. I was looking at it as just the empty buffer
> > before the first iteration of the loop (or, in my case, since I was
> > testing with a 6 char filename, the only iteration).
> >
> > I will repeat my experiment with that and see if I can tease it out.
>
> BTW, if you are looking for a userspace implementation of the hash,
> it's available in libext2fs in e2fsprogs.
>
> Cheers,
>
> - Ted
--
Avi Deitcher
avi@deitcher.net
Follow me http://twitter.com/avideitcher
Read me http://blog.atomicinc.com
next prev parent reply other threads:[~2021-10-13 2:20 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-01 11:49 algorithm for half-md4 used in htree directories Avi Deitcher
2021-10-03 12:47 ` Avi Deitcher
2021-10-03 16:43 ` Andreas Dilger
2021-10-04 7:57 ` Avi Deitcher
2021-10-11 15:30 ` Avi Deitcher
2021-10-11 20:20 ` Theodore Ts'o
2021-10-12 2:58 ` Avi Deitcher
2021-10-12 17:30 ` Theodore Ts'o
2021-10-13 2:20 ` Avi Deitcher [this message]
2021-10-15 18:43 ` Avi Deitcher
2021-10-15 19:10 ` Theodore Ts'o
2021-10-15 19:43 ` Avi Deitcher
2021-10-15 20:30 ` Theodore Ts'o
2021-10-15 19:50 ` Theodore Ts'o
2021-10-18 16:56 ` Avi Deitcher
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