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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]:52264 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l7xFc-0001mR-9s for qemu-devel@archiver.kernel.org; Fri, 05 Feb 2021 04:18:04 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:33980) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l7xE7-0000qc-CS for qemu-devel@nongnu.org; Fri, 05 Feb 2021 04:16:32 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:42733) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l7xDw-0006kn-Tl for qemu-devel@nongnu.org; Fri, 05 Feb 2021 04:16:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612516578; 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=YI+YqU+G+gZbRF6/T+tFq4PSSEF9Vx22rw17/Sxc3Dg=; b=PLOZHaVDbqwZQk8d74iCWlqws5oC+b9U+h0qKUxvhntdibI/iS7o6aFiXsz09Hx60TwBfS 1ZO1rISU8vDfBcS/pcG6bS2ZfUvRXF2kIzvQ0TBqGGb4feoRfWxHZDqZMsUDnPKsHBu9Cs SwJa9wFFZitdInBH+s2DQJ9mBCtU1Ow= 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-316-2CWI3_H1ODulGOiFruMYBw-1; Fri, 05 Feb 2021 04:16:16 -0500 X-MC-Unique: 2CWI3_H1ODulGOiFruMYBw-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 812C1801975; Fri, 5 Feb 2021 09:16:15 +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 5B16F2B175; Fri, 5 Feb 2021 09:16:14 +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> <70e0dbc0-4770-a409-945e-c31e0d93081b@kamp.de> From: Max Reitz Message-ID: <50cb6864-b0a9-c1dc-2cba-9a35a2970ba2@redhat.com> Date: Fri, 5 Feb 2021 10:16:12 +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: <70e0dbc0-4770-a409-945e-c31e0d93081b@kamp.de> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 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 05.02.21 09:47, Peter Lieven wrote: > Am 05.02.21 um 09:18 schrieb Max Reitz: >> 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. > > > Okay, but that is still more housekeeping than just invoking a single command. Yes, but I personally see this as much better than copying all of dd’s functionality into qemu-img. My personal complaint is only that it’s a pain in the ass to invoke QSD this way. It would be nice to have a script that does the same via $ qemu-blk-fuse-export image.qcow2 Would probably be trivial to write, but well, first we gotta do it, and have justification to keep it as part of qemu... And if that’s still too much housekeeping, we could even write a qemu-dd script that scans all file arguments for non-raw images, launches a QSD instance to present them as raw, and then invokes dd. All much simpler and much more feature-complete than to add more dd functionality to qemu-img. > Would it be an option to extend qemu-io to write data at a certain offset which it reads from STDIN? You mean read the data from stdin? Isn’t that what “write -s ” does? Max