From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marco Stornelli Subject: Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem Date: Thu, 25 Jun 2009 08:32:08 +0200 Message-ID: <2ea1731b0906242332n305a8ebbgf37b259171741ea8@mail.gmail.com> References: <2ea1731b0906212333r20deb71q2f021fc79bcc8a8e@mail.gmail.com> <4A3FBFF0.40006@am.sony.com> <20090622173704.GC21299@elf.ucw.cz> <4A3FC84A.6060608@gmail.com> <20090622204031.GA24236@elf.ucw.cz> <4A3FFC89.4070006@am.sony.com> <20090622215753.GA25434@elf.ucw.cz> <4A4119DB.4030203@gmail.com> <20090623182941.GA2045@elf.ucw.cz> <20090624174700.GI14121@shareable.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Pavel Machek , Tim Bird , Linux Embedded , Linux Kernel , Linux FS Devel , Daniel Walker To: Jamie Lokier Return-path: Received: from mail-bw0-f213.google.com ([209.85.218.213]:59851 "EHLO mail-bw0-f213.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751192AbZFYGcH convert rfc822-to-8bit (ORCPT ); Thu, 25 Jun 2009 02:32:07 -0400 In-Reply-To: <20090624174700.GI14121@shareable.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: 2009/6/24 Jamie Lokier : > Pavel Machek wrote: >> On Tue 2009-06-23 20:07:23, Marco wrote: >> > You are talked about journaling. This schema works well for a disk= , but >> > what about a piece of ram? What about a crazy kernel that write in= that >> > area for a bug? Do you remember for example the e1000e bug? It's n= ot >> >> I believe you need both journaling *and* write protection. How do yo= u >> handle power fault while writing data? > > I think this is basically right. > > write protection for the crazy kernels, and journalling for > powerfail/crash during updates. > > Journalling can be extremely simple. =A0It can be just one memory blo= ck > at a fixed location, double-buffering all writes. > > Pramfs already has checksums, which makes that easier. =A0You just wr= ite > to the buffer area first, with checksum, then write to the final area= =2E > Mount looks at the buffer area, and if the checksum is fine, copies > the contents to the destination block. > > That's all it takes to be resistant against power failures and crashe= s > during writes. =A0Probably <100 lines of code. > > -- Jamie > It seems a reasonable request. Marco -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html