From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932408AbWF2U1E (ORCPT ); Thu, 29 Jun 2006 16:27:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932413AbWF2U1E (ORCPT ); Thu, 29 Jun 2006 16:27:04 -0400 Received: from mail.clusterfs.com ([206.168.112.78]:47541 "EHLO mail.clusterfs.com") by vger.kernel.org with ESMTP id S932408AbWF2U1C (ORCPT ); Thu, 29 Jun 2006 16:27:02 -0400 Date: Thu, 29 Jun 2006 14:27:00 -0600 From: Andreas Dilger To: Daniel Phillips Cc: Johann Lombardi , sho@tnes.nec.co.jp, cmm@us.ibm.com, ext2-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [RFC 1/2] ext3: enlarge blocksize and fix rec_len overflow Message-ID: <20060629202700.GD5318@schatzie.adilger.int> Mail-Followup-To: Daniel Phillips , Johann Lombardi , sho@tnes.nec.co.jp, cmm@us.ibm.com, ext2-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org References: <20060628205238sho@rifu.tnes.nec.co.jp> <20060628155048.GG2893@chiva> <20060628202421.GL5318@schatzie.adilger.int> <44A417A3.80001@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <44A417A3.80001@google.com> User-Agent: Mutt/1.4.1i X-GPG-Key: 1024D/0D35BED6 X-GPG-Fingerprint: 7A37 5D79 BF1B CECA D44F 8A29 A488 39F5 0D35 BED6 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Jun 29, 2006 11:10 -0700, Daniel Phillips wrote: > Andreas Dilger wrote: > >On Jun 28, 2006 17:50 +0200, Johann Lombardi wrote: > >>ext2/ext3_dir_entry_2 has a 16-bit entry(rec_len) and it would overflow > >>with 64KB blocksize. This patch prevent from overflow by limiting > >>rec_len to 65532. > > > >Having a max rec_len of 65532 is rather unfortunate, since the dir > >blocks always need to filled with dir entries. 65536 - 65532 = 4, and > >the minimum ext3_dir_entry size is 8 bytes. I would instead make this > >maybe 64 bytes less so that there is room for a filename in the "tail" > >dir_entry. > > Then why not introduce a little symmetry by making max rec_len 2**15 and > treat big directory blocks as an array of smaller ones? I dimly recall > the page-cache oriented Ext2 dir code already does this. I have no objection to this at all, but I think it will lead to a slightly more complex implementation. We even discussed in the distant past to make large directories a series of 4kB "chunks", for fs blocksize >= 4kB. This has negative implications for large filenames because the internal free space fragmentation is high, but has the advantage that it might eventually still be usable if we can get blocksize > PAGE_SIZE. The difficulty is that when freeing dir entires you would have to be concerned with a merging a dir_entry that is spanning the middle of a 2^16 block. Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc.