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=-12.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 DA576C433DB for ; Fri, 5 Feb 2021 08:20:48 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 331E964F99 for ; Fri, 5 Feb 2021 08:20:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 331E964F99 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:55642 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l7wMA-0008S7-VA for qemu-devel@archiver.kernel.org; Fri, 05 Feb 2021 03:20:46 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:48988) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l7wKZ-0007Y2-PG for qemu-devel@nongnu.org; Fri, 05 Feb 2021 03:19:07 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:36854) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l7wKX-0005OI-QP for qemu-devel@nongnu.org; Fri, 05 Feb 2021 03:19:07 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612513144; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NgJdrjlDwBQwDdtQsxBsLjeP9JHE6jIC5JgrAb3+3Pk=; b=Y5fttuktPyGUsaFWBiEkJnTSUM0hAQUiOc6iq9nroZuTGduvcMBwQ0Rel2tZqfh63eS5n3 xpYgldwiJ+ZJUxRrVokCDCl+ZprxhWyhTmi89tf1BZW0PYt2MrkysrEh6zhJveXrYXsxeW LeqV7lvnjFPkoivE/C1H4zbic+CiPMA= 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-280-lAk3lKsNP9iU_n34NFgABg-1; Fri, 05 Feb 2021 03:19:01 -0500 X-MC-Unique: lAk3lKsNP9iU_n34NFgABg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BC042C7401; Fri, 5 Feb 2021 08:19:00 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-114-18.ams2.redhat.com [10.36.114.18]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 686E260C6C; Fri, 5 Feb 2021 08:18:59 +0000 (UTC) Subject: Re: [PATCH] qemu-img: add seek and -n option to dd command To: Peter Lieven , Eric Blake , qemu-block@nongnu.org References: <20210128140704.6547-1-pl@kamp.de> <99982043-ed89-5fbe-afe2-691a9c19280d@redhat.com> <567ab8bb-b452-d6c2-dec7-bc2cf1e34ec8@kamp.de> From: Max Reitz Message-ID: Date: Fri, 5 Feb 2021 09:18:57 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <567ab8bb-b452-d6c2-dec7-bc2cf1e34ec8@kamp.de> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.351, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.182, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: kwolf@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 04.02.21 21:09, Peter Lieven wrote: > Am 02.02.21 um 16:51 schrieb Eric Blake: >> On 1/28/21 8:07 AM, Peter Lieven wrote: >>> Signed-off-by: Peter Lieven >> Your commit message says 'what', but not 'why'. Generally, the one-line >> 'what' works well as the subject line, but you want the commit body to >> give an argument why your patch should be applied, rather than blank. >> >> Here's the last time we tried to improve qemu-img dd: >> https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg02618.html > > > I was not aware of that story. My use case is that I want to be > > able to "patch" an image that Qemu is able to handle by overwriting > > certain sectors. And I especially do not want to "mount" that image > > via qemu-nbd because I might not trust it. I totally want to avoid that the host > > system tries to analyse that image in terms of scanning the bootsector, partprobe, > > lvm etc. pp. qemu will have FUSE exporting as of 6.0 (didn’t quite make it into 5.2), so you can do something like this: $ qemu-storage-daemon \ --blockdev node-name=export,driver=qcow2,\ file.driver=file,file.filename=image.qcow2 \ --export fuse,id=fuse,node-name=export,mountpoint=image.qcow2 This exports the image on image.qcow2 (i.e., on itself) and so by accessing the image file you then get raw access to its contents (so you can use system tools like dd). Doesn’t require root rights, and shouldn’t make the kernel scan anything, because it’s exported as just a regular file. Max