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=-0.9 required=3.0 tests=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 F27A4C33CB3 for ; Wed, 15 Jan 2020 20:55:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C8A272077B for ; Wed, 15 Jan 2020 20:55:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="NZk0qML9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729335AbgAOUzQ (ORCPT ); Wed, 15 Jan 2020 15:55:16 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:47554 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729066AbgAOUzN (ORCPT ); Wed, 15 Jan 2020 15:55:13 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579121711; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Sya8hiKE3seQ7JhwAaYjNxPWsTZ5VsWtEdoIS+CdCAk=; b=NZk0qML9cKEAJvP99gMHmL46K2Gb7WgviYEW5uGeT37/duWLiLlStTjbLxvkSTEIsVk/tn joRH2gruSTyrI8RHu0kF5NgXakgEw5MIqImJowTxmMFOxZEttbW33d0sD8LcIdWXQ8+Vpk DqfM2CEt/bio7qWNhRWxlme4KmmQhX0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-156-1MIDawWYPTKnKF8DxbpAWA-1; Wed, 15 Jan 2020 15:55:08 -0500 X-MC-Unique: 1MIDawWYPTKnKF8DxbpAWA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DCFD81800D48; Wed, 15 Jan 2020 20:55:05 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-120-52.rdu2.redhat.com [10.10.120.52]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0E8B9166B1; Wed, 15 Jan 2020 20:55:02 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <4467.1579020509@warthog.procyon.org.uk> <00fc7691-77d5-5947-5493-5c97f262da81@gmx.com> <27181AE2-C63F-4932-A022-8B0563C72539@dilger.ca> <20200115133101.GA28583@lst.de> To: Andreas Dilger Cc: dhowells@redhat.com, Christoph Hellwig , Qu Wenruo , linux-fsdevel , Al Viro , "Theodore Y. Ts'o" , "Darrick J. Wong" , Chris Mason , Josef Bacik , David Sterba , linux-ext4 , linux-xfs , linux-btrfs , Linux Kernel Mailing List Subject: Re: Problems with determining data presence by examining extents? MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <23761.1579121702.1@warthog.procyon.org.uk> Date: Wed, 15 Jan 2020 20:55:02 +0000 Message-ID: <23762.1579121702@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Andreas Dilger wrote: > I think what is needed here is an fadvise/ioctl that tells the filesystem > "don't allocate blocks unless actually written" for that file. Yeah - and it would probably need to find its way onto disk so that its effect is persistent and visible to out-of-kernel tools. It would also have to say that blocks of zeros shouldn't be optimised away. David