From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp1040.oracle.com ([156.151.31.81]:34632 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751871AbdGLSrb (ORCPT ); Wed, 12 Jul 2017 14:47:31 -0400 Date: Wed, 12 Jul 2017 11:46:29 -0600 From: Liu Bo To: dsterba@suse.cz, linux-btrfs@vger.kernel.org Subject: Re: [PATCH] Btrfs: report errors when checksum is not found Message-ID: <20170712174628.GB4268@localhost.localdomain> Reply-To: bo.li.liu@oracle.com References: <20170711204316.11283-1-bo.li.liu@oracle.com> <20170712144036.GC2866@twin.jikos.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170712144036.GC2866@twin.jikos.cz> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Wed, Jul 12, 2017 at 04:40:36PM +0200, David Sterba wrote: > On Tue, Jul 11, 2017 at 02:43:16PM -0600, Liu Bo wrote: > > When btrfs fails the checksum check, it'll fill the whole page with > > "1". > > One could ask, why is the page filled with 1s. Brought by commit > 07157aacb1ecd394a54949 from 2007, without mentioning any justification. > I'm more inclined to revisit this behaviour and drop it eventually. > > > However, if %csum_expected is 0 (which means there is no checksum), then > > for some unknown reason, we just pretend that the read is correct, so > > userspace would be confused about the dilemma that read is successful but > > getting a page with all content being "1". > > Here 'no checksum' means that no checksum was found but was expected, > right? Yes, no checksum was found. > An EIO would fail the read, I don't see a reason why the page > needs to be "zeroed". The contents would be inaccessible anyway. > Right, resetting page's content is needed when we return 0 instead of -EIO. I guess it was introduced for testing. So yes, I'm glad to remove that part, will do in a v2. > > This can happen due to a bug in btrfs-convert. > > > > This fixes it by always returning errors if checksum doesn't match. > > Independent of the above, this fix makes sense. > > Reviewed-by: David Sterba Thank you for the comments. Thanks, -liubo