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=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 E688DC433E0 for ; Mon, 15 Feb 2021 01:26:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 910BA64DB1 for ; Mon, 15 Feb 2021 01:26:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229994AbhBOB0f (ORCPT ); Sun, 14 Feb 2021 20:26:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56136 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229875AbhBOB02 (ORCPT ); Sun, 14 Feb 2021 20:26:28 -0500 Received: from mail-vs1-xe2d.google.com (mail-vs1-xe2d.google.com [IPv6:2607:f8b0:4864:20::e2d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 58183C061574 for ; Sun, 14 Feb 2021 17:25:48 -0800 (PST) Received: by mail-vs1-xe2d.google.com with SMTP id x201so2595012vsc.0 for ; Sun, 14 Feb 2021 17:25:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=nqWxVX3tai8d6xQXNuc7CwStRoLgRKEWoNr21bE/mSo=; b=QOpoZzZaeSCQbZPr1cTUfUvf2158J9Niprw8W19J41RTckcu2Nv8IiqjG1ZyyfpZBP CxrzJD6dUjPg7Wd3LyI9B4r194w2v0RhKtJ7jd+Ocsy+T54GULfQKFE7NdL5uDGYBx4x buYdYsItgZcFvPSVhd2I1nKFsc9X5Cha3B9jU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=nqWxVX3tai8d6xQXNuc7CwStRoLgRKEWoNr21bE/mSo=; b=VXXL4Kt6jre+zudKISTvs+6JAqg4LQtan279z4rmDLluapF39LQwQUNjiGV3JV+nok zEvJbyZpDypmQzwzBZ1S6PhOT5eRTcyQuSRBw3Hul+87k1mGZw8SPCYlRigM965822CJ yHbnH/ZlLZTfpuSyi4PC2OxEwEzEdXRYzuR/h5wgemaerUsRpNo4bTzEXj9v6Y96kOck YLmcGZVnuKHIa/pEA16ekrqNK7wy7w8/uHaCCYwcE8z+w0vspYgDWXa97fObzJaoWAT5 XUyMY4kbr+mIQkTpzw96AfWQ6Tag7M6IT/sLt1Nl31L1Vc1JiC7iputmnKv4/kAT/Vqo gEHw== X-Gm-Message-State: AOAM532FGdIfewWvbd0ZroPrg0oL80XY+/l9rTIO/7A341oQHP+8eEIC 2Cy1TxiYdMnZF65BRp+SBX3M1tUTzcNrPpegimHvGA== X-Google-Smtp-Source: ABdhPJwxzNCcjBfqsq4WyT6GHAU2U4lh0z0W/tdmtYIKR51lPejDwZXlP7EQG7k4rpH4++0lqRrO0kdZtEA/IDdAV2E= X-Received: by 2002:a67:e119:: with SMTP id d25mr7271805vsl.16.1613352347038; Sun, 14 Feb 2021 17:25:47 -0800 (PST) MIME-Version: 1.0 References: <20210212124354.1.I7084a6235fbcc522b674a6b1db64e4aff8170485@changeid> <20210212230346.GU4626@dread.disaster.area> <20210212232726.GW4626@dread.disaster.area> <20210212235448.GH7187@magnolia> <20210215003855.GY4626@dread.disaster.area> In-Reply-To: From: Nicolas Boichat Date: Mon, 15 Feb 2021 09:25:36 +0800 Message-ID: Subject: Re: [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated To: Ian Lance Taylor Cc: Dave Chinner , "Darrick J. Wong" , Greg KH , Alexander Viro , Luis Lozano , linux-fsdevel@vger.kernel.org, lkml Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 15, 2021 at 9:12 AM Ian Lance Taylor wrote: > > On Sun, Feb 14, 2021 at 4:38 PM Dave Chinner wrote: > > > > On Fri, Feb 12, 2021 at 03:54:48PM -0800, Darrick J. Wong wrote: > > > On Sat, Feb 13, 2021 at 10:27:26AM +1100, Dave Chinner wrote: > > > > > > > If you can't tell from userspace that a file has data in it other > > > > than by calling read() on it, then you can't use cfr on it. > > > > > > I don't know how to do that, Dave. :) > > > > If stat returns a non-zero size, then userspace knows it has at > > least that much data in it, whether it be zeros or previously > > written data. cfr will copy that data. The special zero length > > regular pipe files fail this simple "how much data is there to copy > > in this file" check... > > This suggests that if the Go standard library sees that > copy_file_range reads zero bytes, we should assume that it failed, and > should use the fallback path as though copy_file_range returned > EOPNOTSUPP or EINVAL. This will cause an extra system call for an > empty file, but as long as copy_file_range does not return an error > for cases that it does not support we are going to need an extra > system call anyhow. > > Does that seem like a possible mitigation? That is, are there cases > where copy_file_range will fail to do a correct copy, and will return > success, and will not return zero? I'm a bit worried about the sysfs files that report a 4096 bytes file size, for 2 reasons: - I'm not sure if the content _can_ actually be longer (I couldn't find a counterexample) - If you're unlucky enough to have a partial write in the output filesystem, you'll get a non-zero return value and probably corrupted content. > > Ian