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=-5.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 5FB79C4363A for ; Tue, 20 Oct 2020 14:45:17 +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 B654E2224B for ; Tue, 20 Oct 2020 14:45:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="JAeN9Po5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B654E2224B 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]:54904 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kUssz-0003Fp-VX for qemu-devel@archiver.kernel.org; Tue, 20 Oct 2020 10:45:13 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:47252) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kUsqO-0000rw-CJ for qemu-devel@nongnu.org; Tue, 20 Oct 2020 10:42:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:57217) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kUsqJ-0002Fm-LU for qemu-devel@nongnu.org; Tue, 20 Oct 2020 10:42:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603204944; 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=cyHVh5UNAJnlZVWe1WuMTVBLHHRV+vwMiv5b/10uRLA=; b=JAeN9Po5nAoHRs2zmiRm8C3Qji8ZEMAQ+P+24NDQ8hUiceR0u/pFq8uAtg0dCANRdnm7BL sCM5F1ULC6RgOIxtMwKowOjkXnb0rEaU8AzbJcFk5JMP6TDlMhATgXJhc9D2f0ARyPWR5I a3AwFpmp9b+hZD0EKxGsATgW/zrRDoo= 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-231-JxUzIVRPNSKkFWPE4ClX5A-1; Tue, 20 Oct 2020 10:42:20 -0400 X-MC-Unique: JxUzIVRPNSKkFWPE4ClX5A-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 250B561266; Tue, 20 Oct 2020 14:42:19 +0000 (UTC) Received: from localhost (ovpn-114-98.ams2.redhat.com [10.36.114.98]) by smtp.corp.redhat.com (Postfix) with ESMTP id C092F5B4C5; Tue, 20 Oct 2020 14:42:18 +0000 (UTC) Date: Tue, 20 Oct 2020 15:42:17 +0100 From: "Richard W.M. Jones" To: Eric Blake Subject: Re: Question on Compression for Raw Image Message-ID: <20201020144217.GT30079@redhat.com> References: <516589845d6f42d0b00784d16b59b5dc@intel.com> <20201020080051.GA4452@merkur.fritz.box> <6124d55766e4477299a5796a002276a0@intel.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=rjones@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/20 01:16:16 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: Kevin Wolf , "qemu-block@nongnu.org" , "qemu-devel@nongnu.org" , "mreitz@redhat.com" , "Wang, Wei W" , "lersek@redhat.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Oct 20, 2020 at 09:32:23AM -0500, Eric Blake wrote: > On 10/20/20 9:22 AM, Wang, Wei W wrote: > > On Tuesday, October 20, 2020 4:01 PM, Kevin Wolf wrote: > >> Am 20.10.2020 um 03:31 hat Wang, Wei W geschrieben: > >>> Hi, > >>> > >>> Does anyone know the reason why raw-format.c doesn't have > >> compression > >>> support (but qcow has the supported added)? For example, raw image > >>> backup with compression, "qemu-img convert -c -O raw origin.img > >>> dist.img", doesn't work. > >> > >> A raw image is by definition a file that contains the exact same sequence of > >> bytes as the guest sees, without any additional information or encoding. If > >> you compress a raw file, the guest will see compressed data on its hard disk > >> instead of the real data. > > > > Ok, thanks. I'm thinking QEMU could do decompression of the compressed data in raw.img when guest reads data. > > > >> > >> Anything you could do to add transparent compression to it would mean that > >> it's not a raw image any more, but a new image format. > >> > > Yes, decompression makes it transparent to the guest. Would you think it's good to reuse the raw image implementation, just add the compress/decompress option? > > My recommendation would be implementing a new BDS filter that does > uncompression. Then, you could do things like: > > raw -> decompress -> file.xz > > or even > > qcow2 -> decompress -> file.qcow2.xz > > By the way, the notion of filters is already possible in other ways. > For example, you can point qemu to read from an NBD server, and then use > nbdkit to do the decompression with its filters: > > nbdkit --filter=xz file file.xz > raw -> nbd://localhost:10809 nbdkit can already act as a front-end to qemu-nbd, allowing you to use the rich nbdkit filter ecosystem with qemu block devices. There are some examples in the link below, but --filter=xz could also be used here: https://libguestfs.org/nbdkit-nbd-plugin.1.html#Use-qemu-nbd-to-open-a-qcow2-file > Also note that serving a decompressed view of a compressed image tends > to be a read-only proposition (you really CAN'T write to the image > without recompressing, but even if recompression has been blocked for > parallelism, you would end up writing far more of the file after > recompression than the amount of data written by a guest). Yup! Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v