Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8F3A1C433F5 for ; Wed, 1 Dec 2021 23:23:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240529AbhLAX0y (ORCPT ); Wed, 1 Dec 2021 18:26:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56802 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232038AbhLAX0u (ORCPT ); Wed, 1 Dec 2021 18:26:50 -0500 Received: from mail-il1-x129.google.com (mail-il1-x129.google.com [IPv6:2607:f8b0:4864:20::129]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AB842C061574; Wed, 1 Dec 2021 15:23:28 -0800 (PST) Received: by mail-il1-x129.google.com with SMTP id s11so19965880ilv.3; Wed, 01 Dec 2021 15:23:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Af3RlAsLkBfp1bcElgEIL/uV/0nmFtZn2QzPrICGZJc=; b=KTF5cCZkcyKB8kh4XpQbQwXfGXimMLisrHNjl73Lc21ru4fUBu8Zy8O6dZQD6GT1Zj +G9Hqk7mmNnS8jKGSbdiN0H9dIZa7u3cQuTsePDq9TbgQ64uUn75+NZqIGA6bkDhckdk g9rHEfkp9H1Go0/hhVRryCZt+fVVmSHCgj74H5DGpQpM+oStsgMWIPMWu+Abti0pAxPK 62ocDpeb8rZvFhpIxhgsyqkxQjFnQyfx7w4qxf/ZZoXy2ZetH1n12RbnB3p1ZcmHtnQ3 +Q92UdUomWOK8TMs5b6VhuYV643jMH4E3XQrvXENqlK0pEWRLe8chFZWu9GkHd4kV4OP zWsA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Af3RlAsLkBfp1bcElgEIL/uV/0nmFtZn2QzPrICGZJc=; b=BINApKAA63FTVqPBPWLMulN/X3nuO98O7N58uznFYGRN1HQ/ozeZuIX8D8KZJnrTFY pibUcxL6oR2U7eR3Q0HrbS3yP5BTOmBjrWx2Y8va1ckHR5cfiR9091+E0eljqfGiqtfY RrJllWPXNE86lA+oMi0bQ5n7EAyrgaxo7tobuiaEonuP1mkRTF38qqTu+7PdIOJr2a8D C87U5J0fv3ccaxA0XJHxTY3ZjPH7JmHZgsb31H/eHr2BUYPGiuy1serGSOUqhhr1bJmL UEkHK//csxI2f5m6DHfdmWVAGTxLwTASa/in4k4DLZfzOIhoMSL9VN3Jmz166mZ1nLLC kz+g== X-Gm-Message-State: AOAM530PcS4rfZj8JynS4kjsPzK+fyQl+/uIuYUyriHIlDu0XFKH1v4Y NKJs6TdTrMbMDSYP3DCfHGaDGO4PfylxhMiE3MQ= X-Google-Smtp-Source: ABdhPJzXU3YvqHPX90w9ejT7eu7mqKFglskeupNE5LeOcrNMt3JV9VU9GfMbF9oO3F+ly0PBAiW/fQZfXXCC1vfjpw4= X-Received: by 2002:a05:6e02:f81:: with SMTP id v1mr14402482ilo.107.1638401008111; Wed, 01 Dec 2021 15:23:28 -0800 (PST) MIME-Version: 1.0 References: <20211118112315.GD13047@quack2.suse.cz> <17d32ecf46e.124314f8f672.8832559275193368959@mykernel.net> <20211118164349.GB8267@quack2.suse.cz> <17d36d37022.1227b6f102736.1047689367927335302@mykernel.net> <20211130112206.GE7174@quack2.suse.cz> <17d719b79f9.d89bf95117881.5882353172682156775@mykernel.net> <17d73da701b.e571c37220081.6904057835107693340@mykernel.net> <17d74b08dcd.c0e94e6320632.9167792887632811518@mykernel.net> <20211201134610.GA1815@quack2.suse.cz> <17d76cf59ee.12f4517f122167.2687299278423224602@mykernel.net> In-Reply-To: From: Amir Goldstein Date: Thu, 2 Dec 2021 01:23:17 +0200 Message-ID: Subject: Re: ovl_flush() behavior To: Chengguang Xu Cc: Jan Kara , Miklos Szeredi , linux-fsdevel , overlayfs , linux-kernel , ronyjin , charliecgxu , Vivek Goyal Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > > > To be honest I even don't fully understand what's the ->flush() logic in overlayfs. > > Why should we open new underlying file when calling ->flush()? > > Is it still correct in the case of opening lower layer first then copy-uped case? > > > > The semantics of flush() are far from being uniform across filesystems. > most local filesystems do nothing on close. > most network fs only flush dirty data when a writer closes a file > but not when a reader closes a file. > It is hard to imagine that applications rely on flush-on-close of > rdonly fd behavior and I agree that flushing only if original fd was upper > makes more sense, so I am not sure if it is really essential for > overlayfs to open an upper rdonly fd just to do whatever the upper fs > would have done on close of rdonly fd, but maybe there is no good > reason to change this behavior either. > On second thought, I think there may be a good reason to change ovl_flush() otherwise I wouldn't have submitted commit a390ccb316be ("fuse: add FOPEN_NOFLUSH") - I did observe applications that frequently open short lived rdonly fds and suffered undesired latencies on close(). As for "changing existing behavior", I think that most fs used as upper do not implement flush at all. Using fuse/virtiofs as overlayfs upper is quite new, so maybe that is not a problem and maybe the new behavior would be preferred for those users? Thanks, Amir.