From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out1-smtp.messagingengine.com ([66.111.4.25]:56329 "EHLO out1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965026AbdIYUBm (ORCPT ); Mon, 25 Sep 2017 16:01:42 -0400 From: Nikolaus Rath To: Maxim Patlasov Cc: mszeredi@redhat.com, fuse-devel@lists.sourceforge.net, linux-fsdevel Subject: Re: [fuse-devel] [fuse] getattr() results ignored when writeback cache is active References: <87zi9pk2ra.fsf@vostro.rath.org> <87vakdjsjj.fsf@vostro.rath.org> <87y3p8uzpw.fsf@vostro.rath.org> <11acc9f1-12e5-9806-48ff-de261acae979@virtuozzo.com> <87wp4s9bva.fsf@vostro.rath.org> <97fa18f6-84ab-7723-42a8-84e2bc2d92ed@virtuozzo.com> <87o9q3aop8.fsf@vostro.rath.org> <87lgl7ame3.fsf@vostro.rath.org> Date: Fri, 22 Sep 2017 10:34:15 +0100 In-Reply-To: (Maxim Patlasov's message of "Thu, 21 Sep 2017 12:44:58 -0700") Message-ID: <87shffyt48.fsf@vostro.rath.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Sep 21 2017, Maxim Patlasov wrote: > Oh, I understand now. Your example actually demonstrates that > FUSE_WRITEBACK_CACHE must not be used if it's possible to modify > underlying data (/tmp/issue_93/file_1) externally w.r.t fuse > filesystem. That's correct. But initial statement: > >> this mode of operation is not suitable for any network filesystem=20 >> even if no write operations are actually carried out > > is not, because it's not impossible to protect underlying data against > such an external change somehow. A network filesystem is not obliged > to keep transparent correspondence like /tmp/issue_93_mnt/file_1 <-->=20 > /tmp/issue_93/file_1. It can keep all user data (and metadata) in > internal structures making any external modifications > impossible. Then, implementing exclusive write semantics would make > using FUSE_WRITEBACK_CACHE safe. Agree? I agree with what you're saying, but I don't agree that this should go into the documentation for which the sentence in dispute was intended :-). I think in 93% of all cases, the simplified statement will be more helpful to a potential FUSE user than the correct one. If this bothers you a lot, can we compromise and just be a little more vague overall? I.e., | This mode of operation is therefore generally not suitable for | filesystems where modifications may not come through the (local) FUSE | layer (i.e, most network filesystems). Best, -Nikolaus --=20 GPG Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F =C2=BBTime flies like an arrow, fruit flies like a Banana.=C2= =AB