From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 031C4C433E2 for ; Tue, 8 Sep 2020 16:20:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9F70F2065E for ; Tue, 8 Sep 2020 16:20:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599582023; bh=v2zsVbidV/dpXBuxnNOOWyBxJCinNIceKjsE+Knsapc=; h=Subject:From:To:Cc:Date:In-Reply-To:References:List-ID:From; b=SiEpjGVRL3D8qhvH5ZfWkR2tA07Meo7i06T5UdVyIqGXdaP+ZAR9YWTAajczKyTd7 k30NF5tkVMoaufhpxRiBd29jMWo8S24SIPnsm9R+vnfufQstDF7pClh/8Jh5/nVAKF VdczxWeC1qDi3bgLzk/y0pNeLEvWqWs80mPMus6M= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731876AbgIHQUU (ORCPT ); Tue, 8 Sep 2020 12:20:20 -0400 Received: from mail.kernel.org ([198.145.29.99]:59170 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731843AbgIHQUH (ORCPT ); Tue, 8 Sep 2020 12:20:07 -0400 Received: from tleilax.poochiereds.net (68-20-15-154.lightspeed.rlghnc.sbcglobal.net [68.20.15.154]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F28EC205CB; Tue, 8 Sep 2020 16:10:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599581448; bh=v2zsVbidV/dpXBuxnNOOWyBxJCinNIceKjsE+Knsapc=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=qcRMUHSfIbb1We5HAkPbiDyxoStGFeeDjZQINQRCiB02sz2KJR+wSF9e8rh2hFWX/ pRdR7L5L4Ji67IrqudFk9FYmW37g7LVLBI5MLHW7kGBwH6bYgz6ktZzXzMdso0klAC fZP1Nr1+cyUG5NNMwSPOjPXC4hfYj4cgJjooh2u8= Message-ID: Subject: Re: [PATCH] fsync.2: ERRORS: add EIO and ENOSPC From: Jeff Layton To: Jan Kara , "Michael Kerrisk (man-pages)" Cc: milan.opensource@gmail.com, lkml , Andrew Morton , "linux-fsdevel@vger.kernel.org" Date: Tue, 08 Sep 2020 12:10:46 -0400 In-Reply-To: <20200908112742.GA2956@quack2.suse.cz> References: <1598685186-27499-1-git-send-email-milan.opensource@gmail.com> <20200908112742.GA2956@quack2.suse.cz> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5 (3.36.5-1.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, 2020-09-08 at 13:27 +0200, Jan Kara wrote: > Added Jeff to CC since he has written the code... > > On Mon 07-09-20 09:11:06, Michael Kerrisk (man-pages) wrote: > > [Widening the CC to include Andrew and linux-fsdevel@] > > [Milan: thanks for the patch, but it's unclear to me from your commit > > message how/if you verified the details.] > > > > Andrew, maybe you (or someone else) can comment, since long ago your > > > > commit f79e2abb9bd452d97295f34376dedbec9686b986 > > Author: Andrew Morton > > Date: Fri Mar 31 02:30:42 2006 -0800 > > > > included a comment that is referred to in stackoverflow discussion > > about this topic (that SO discussion is in turn referred to by > > https://bugzilla.kernel.org/show_bug.cgi?id=194757). > > > > The essence as I understand it, is this: > > (1) fsync() (and similar) may fail EIO or ENOSPC, at which point data > > has not been synced. > > (2) In this case, the EIO/ENOSPC setting is cleared so that... > > (3) A subsequent fsync() might return success, but... > > (4) That doesn't mean that the data in (1) landed on the disk. > > Correct. > > > The proposed manual page patch below wants to document this, but I'd > > be happy to have an FS-knowledgeable person comment before I apply. > > Just a small comment below: > > > On Sat, 29 Aug 2020 at 09:13, wrote: > > > From: Milan Shah > > > > > > This Fix addresses Bug 194757. > > > Ref: https://bugzilla.kernel.org/show_bug.cgi?id=194757 > > > --- > > > man2/fsync.2 | 13 +++++++++++++ > > > 1 file changed, 13 insertions(+) > > > > > > diff --git a/man2/fsync.2 b/man2/fsync.2 > > > index 96401cd..f38b3e4 100644 > > > --- a/man2/fsync.2 > > > +++ b/man2/fsync.2 > > > @@ -186,6 +186,19 @@ In these cases disk caches need to be disabled using > > > or > > > .BR sdparm (8) > > > to guarantee safe operation. > > > + > > > +When > > > +.BR fsync () > > > +or > > > +.BR fdatasync () > > > +returns > > > +.B EIO > > > +or > > > +.B ENOSPC > > > +any error flags on pages in the file mapping are cleared, so subsequent synchronisation attempts > > > +will return without error. It is > > > +.I not > > > +safe to retry synchronisation and assume that a non-error return means prior writes are now on disk. > > > .SH SEE ALSO > > > .BR sync (1), > > > .BR bdflush (2), > > So the error state isn't really stored "on pages in the file mapping". > Current implementation (since 4.14) is that error state is stored in struct > file (I think this tends to be called "file description" in manpages) and > so EIO / ENOSPC is reported once for each file description of the file that > was open before the error happened. Not sure if we want to be so precise in > the manpages or if it just confuses people. Anyway your takeway that no > error on subsequent fsync() does not mean data was written is correct. > > Honza > Yep. My only comment is that there is nothing special about EIO and ENOSPC. All errors are the same in this regard. Basically, issuing a new fsync after a failed one doesn't do any good. You need to redirty the pages first. -- Jeff Layton