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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]:33084 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l7y64-0008M8-Ah for qemu-devel@archiver.kernel.org; Fri, 05 Feb 2021 05:12:16 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:43828) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l7y0n-0003aU-IG for qemu-devel@nongnu.org; Fri, 05 Feb 2021 05:06:51 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:39445) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l7y0j-0004I4-OZ for qemu-devel@nongnu.org; Fri, 05 Feb 2021 05:06:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612519604; 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; 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Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <50cb6864-b0a9-c1dc-2cba-9a35a2970ba2@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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: multipart/mixed; boundary="------------F781D1628F9E471D6DCC934B" Content-Language: en-US Received-SPF: pass client-ip=216.205.24.124; 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_H3=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" This is a multi-part message in MIME format. --------------F781D1628F9E471D6DCC934B Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit On 05.02.21 10:16, Max Reitz wrote: > 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. Since today’s Day of Learning at Red Hat, I decided to have some fun writing a qemu-dd.py script. Max --------------F781D1628F9E471D6DCC934B Content-Type: text/x-python; charset=UTF-8; name="qemu-dd.py" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="qemu-dd.py" #!/usr/bin/python import json import os import subprocess import sys from typing import Optional images = {} for arg in sys.argv[1:]: if arg.startswith('if=') or arg.startswith('of='): filename = arg[3:] # Ignore non-existing files, the user probably wants to make # dd create them (as raw images) if not os.path.exists(filename): continue qemu_img = subprocess.Popen(('qemu-img', 'info', filename), stdout=subprocess.PIPE, universal_newlines=True) output: str = qemu_img.communicate()[0] if qemu_img.returncode != 0: sys.exit(os.EX_NOINPUT) fmt_line = next(line for line in output.split('\n') if line.startswith('file format: ')) fmt = fmt_line.split(': ', 1)[1] if fmt != 'raw': images[filename] = fmt qsd: Optional[subprocess.Popen] = None if images: args = ['qemu-storage-daemon', '--chardev', 'stdio,id=monitor', '--monitor', 'monitor'] for i, (image, fmt) in enumerate(images.items()): args += ['--blockdev', f'{fmt},node-name=export{i},' + f'file.driver=file,file.filename={image}', '--export', f'fuse,id=fuse{i},node-name=export{i},' + f'mountpoint={image},writable=on'] qsd = subprocess.Popen(args, stdin=subprocess.PIPE, stdout=subprocess.PIPE, universal_newlines=True) assert qsd.stdin is not None assert qsd.stdout is not None # Do some QMP communication so we know for sure that the exports # are up qmp_line = json.loads(qsd.stdout.readline()) if 'QMP' in qmp_line: qsd.terminate() qsd.wait() sys.stderr.write('The QEMU storage daemon did not provide ' + 'a QMP monitor\n') sys.exit(os.EX_SOFTWARE) qsd.stdin.write('{ "execute": "qmp_capabilities" }') qsd.stdin.flush() # qmp_capabilities response if json.loads(qsd.stdout.readline()) != {'return': {}}: qsd.terminate() qsd.wait() sys.stderr.write('Communication error with the QEMU storage daemon\n') sys.exit(os.EX_SOFTWARE) while True: qsd.stdin.write('{ "execute": "query-block-exports" }') qsd.stdin.flush() exports = json.loads(qsd.stdout.readline())['return'] if exports is None or len(exports) > len(images): qsd.terminate() qsd.wait() sys.stderr.write('Communication error with the ' + 'QEMU storage daemon\n') sys.exit(os.EX_SOFTWARE) if len(exports) == len(images): break subprocess.Popen(['dd'] + sys.argv[1:]).wait() if qsd is not None: qsd.terminate() qsd.wait() --------------F781D1628F9E471D6DCC934B--