From: Niraj Kulkarni Subject: Re: Need of revoke mechanism in JBD Date: Sat, 30 Apr 2011 07:36:49 +0530 Message-ID: <4DBB6EB9.40100@gmail.com> References: <4DB68257.4070407@gmail.com> <20110426122558.GF9486@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Ted Ts'o , Ding Dinghua , Yongqiang Yang , linux-ext4@vger.kernel.org To: Amir Goldstein Return-path: Received: from mail-pv0-f174.google.com ([74.125.83.174]:33945 "EHLO mail-pv0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754379Ab1D3CG6 (ORCPT ); Fri, 29 Apr 2011 22:06:58 -0400 Received: by pvg12 with SMTP id 12so2515450pvg.19 for ; Fri, 29 Apr 2011 19:06:58 -0700 (PDT) In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: On Saturday 30 April 2011 01:15 AM, Amir Goldstein wrote: > On Tue, Apr 26, 2011 at 3:25 PM, Ted Ts'o wrote: >> On Tue, Apr 26, 2011 at 05:23:21PM +0800, Ding Dinghua wrote: >>> I think it's not only a performance issue but more important, a >>> correctness issue. >>> Revoke table is used for preventing the wrong replay of journal which >>> cause data corruption: >>> If block A has been journalled its modification, committed to journal >>> and hasn't been checkpointed, >>> and in later transactions block A is freed and reused for data in >>> no-journalled-data mode, then If >>> we don't have revoke table which recording the releasing event, replay >>> of journal will overwrite the new data, >>> which causing data corruption. >> Yes, this is correct. It should be covered fairly well in Stephen >> Tweedie's, "Journaling the ext2fs file system" paper, which you can >> find at: >> >> https://ext4.wiki.kernel.org/index.php/Publications > Actually, the original paper has no mention of revoke records. > I went out to look for useful documentation on journal forget/revoke > and came back empty handed as well. > >> if you'd like more details. >> >> Hope this helps! >> >> - Ted >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Yes, I tried some other papers too, but no use. Anyway I've figured out that for my change, I dont need any kind of journalling related facilities, so I am going to bypass it completely. Niraj