linux-kernel - Re: If not readdir() then what?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <b6c5339f0704101457x294d36bfg11088f807e9e2c48@mail.gmail.com>
Date:	Tue, 10 Apr 2007 17:57:37 -0400
From:	"Bob Copeland" <me@...copeland.com>
To:	"Neil Brown" <neilb@...e.de>
Cc:	"Trond Myklebust" <trond.myklebust@....uio.no>,
	"Theodore Tso" <tytso@....edu>,
	"Jörn Engel" <joern@...ybastard.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Christoph Hellwig" <hch@...radead.org>,
	"Ulrich Drepper" <drepper@...il.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: If not readdir() then what?

On 4/10/07, Neil Brown <neilb@...e.de> wrote:
> 2/ Some data structure using an ordered search key that is based on
>   the filename (e.g. a B-tree with a search key that is a hash of the
>   filename).
>
> In the first case, you just use a fixed opaque cookie for location in
> a directory.
> In the second you use the filename.  If the file has been deleted,
> that shouldn't stop you finding the place where it would have been in
> the overall sort order.

I can think of one (admittedly insane) FS that is between those two:

3/ an unsorted hash table, where each directory entry has an indirect
pointer to its neighbor in case of hash collisions.

   a
   b -> d -> c -> e
   g
   f -> x

Given 'c' as the "last" thing returned, you can hash c to find out
that you are in the bucket with 'b', but if 'c' was deleted, the best
you can do is return b twice or skip the chain entirely.  I maintain
an out-of-tree driver for such an fs (I promise I did not invent it);
the best I could come up with is to encode the hash chain index in the
top byte of f_pos.   Needless to say, readdir is very not performant
with all the seeking this hash scheme entails.

-Bob
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/