From nobody Tue Apr 23 22:45:16 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1562851847; cv=none; d=zoho.com; s=zohoarc; b=L6DxRzRDEZFJzNnFJZKGvkF1ndBa0+j3OE/kjjzbWsZ7jmMZAbRsHiMt9wZWbpqJzjdcFgHlMStXkJVCInnZ7YjYfCfjXYm1y5uKFL0MBJtZrLdPXefAiA9RfHCP2LvJpsYAO7FdZWxl3t3PLg9VIxlQTKSH47IN847qqBoI2tE= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; s=zohoarc; t=1562851847; h=Content-Transfer-Encoding:Cc:Date:From:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:Sender:Subject:To:ARC-Authentication-Results; bh=AiIdURcLupjIYzCrSAhp4PwzN2+NDTeIB7sZJYd4Tqs=; b=kkr6I+RX/0AcPnDrPRg2YhCezsRK7Paaa/kGXznozdO1uBNSItPizwYyEFjwUjILfJNKseB1EYVnDiXFNv6j7J2djvhc3r5bgZtj1N6oUURcJDB4LJXLTP8QOGb+7csoENkozuJNOFjQD/a9e/ThKeUZy3QEQTKN+1FRs3wacxs= ARC-Authentication-Results: i=1; mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1562851847458837.0341727821357; Thu, 11 Jul 2019 06:30:47 -0700 (PDT) Received: from localhost ([::1]:41810 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hlZ9n-00071e-CJ for importer@patchew.org; Thu, 11 Jul 2019 09:30:43 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42898) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hlZ8o-0005ok-3a for qemu-devel@nongnu.org; Thu, 11 Jul 2019 09:29:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hlZ8m-0002oq-W1 for qemu-devel@nongnu.org; Thu, 11 Jul 2019 09:29:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50532) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hlZ8k-0002jy-GI; Thu, 11 Jul 2019 09:29:38 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CA5FC356E4; Thu, 11 Jul 2019 13:29:37 +0000 (UTC) Received: from localhost (unknown [10.40.205.198]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 60C6A60185; Thu, 11 Jul 2019 13:29:37 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org Date: Thu, 11 Jul 2019 15:29:35 +0200 Message-Id: <20190711132935.13070-1-mreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Thu, 11 Jul 2019 13:29:37 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH] doc: Preallocation does not require writing zeroes X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , =?UTF-8?q?Daniel=20P=20=2E=20Berrang=C3=A9?= , Markus Armbruster , qemu-devel@nongnu.org, Maxim Levitsky , Max Reitz Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Type: text/plain; charset="utf-8" When preallocating an encrypted qcow2 image, it just lets the protocol driver write data and then does not mark the clusters as zero. Therefore, reading this image will yield effectively random data. As such, we have not fulfilled the promise of always writing zeroes when preallocating an image in a while. It seems that nobody has really cared, so change the documentation to conform to qemu's actual behavior. Signed-off-by: Max Reitz Reviewed-by: Daniel P. Berrang=C3=A9 Reviewed-by: Eric Blake Reviewed-by: Maxim Levitsky --- qapi/block-core.json | 9 +++++---- docs/qemu-block-drivers.texi | 4 ++-- qemu-img.texi | 4 ++-- 3 files changed, 9 insertions(+), 8 deletions(-) diff --git a/qapi/block-core.json b/qapi/block-core.json index 0d43d4f37c..a4363b84d2 100644 --- a/qapi/block-core.json +++ b/qapi/block-core.json @@ -5167,10 +5167,11 @@ # @off: no preallocation # @metadata: preallocate only for metadata # @falloc: like @full preallocation but allocate disk space by -# posix_fallocate() rather than writing zeros. -# @full: preallocate all data by writing zeros to device to ensure disk -# space is really available. @full preallocation also sets up -# metadata correctly. +# posix_fallocate() rather than writing data. +# @full: preallocate all data by writing it to the device to ensure +# disk space is really available. This data may or may not be +# zero, depending on the image format and storage. +# @full preallocation also sets up metadata correctly. # # Since: 2.2 ## diff --git a/docs/qemu-block-drivers.texi b/docs/qemu-block-drivers.texi index 91ab0eceae..c02547e28c 100644 --- a/docs/qemu-block-drivers.texi +++ b/docs/qemu-block-drivers.texi @@ -31,8 +31,8 @@ Supported options: @item preallocation Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}= ). @code{falloc} mode preallocates space for image by calling posix_fallocate= (). -@code{full} mode preallocates space for image by writing zeros to underlyi= ng -storage. +@code{full} mode preallocates space for image by writing data to underlying +storage. This data may or may not be zero, depending on the storage locat= ion. @end table =20 @item qcow2 diff --git a/qemu-img.texi b/qemu-img.texi index c8e9bba515..b5156d6316 100644 --- a/qemu-img.texi +++ b/qemu-img.texi @@ -666,8 +666,8 @@ Supported options: @item preallocation Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}= ). @code{falloc} mode preallocates space for image by calling posix_fallocate= (). -@code{full} mode preallocates space for image by writing zeros to underlyi= ng -storage. +@code{full} mode preallocates space for image by writing data to underlying +storage. This data may or may not be zero, depending on the storage locat= ion. @end table =20 @item qcow2 --=20 2.21.0