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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id B7E89EF9002 for ; Wed, 4 Mar 2026 16:13:28 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vxoqY-0006jW-A7; Wed, 04 Mar 2026 11:13:14 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vxoqW-0006j2-2G for qemu-devel@nongnu.org; Wed, 04 Mar 2026 11:13:12 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vxoqU-0001zH-FT for qemu-devel@nongnu.org; Wed, 04 Mar 2026 11:13:11 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1772640788; 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=PePA3EoSGToggFlcdZD+7pDBcMe+mF8ho6FoB7AFscA=; b=MI4D0jecZEP7ckc2SINslZvc/t/wI55fo+Hep2UGSdlzMQ/OYwKmdPAkArwLf0rhtwm4OA WZieQf0ch3TgaBDmD5TCjabCeUJ3PXPNyAUp0eq5T1wIXLuVXIR5B736TLKAwd4z+3R8nt jZT7+vysjw5rJ9BEMz35YMy2jj8DA/4= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-602-RhLB3DobOaSOQ8p35lVSmQ-1; Wed, 04 Mar 2026 11:13:05 -0500 X-MC-Unique: RhLB3DobOaSOQ8p35lVSmQ-1 X-Mimecast-MFC-AGG-ID: RhLB3DobOaSOQ8p35lVSmQ_1772640785 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9B92C1956050; Wed, 4 Mar 2026 16:13:04 +0000 (UTC) Received: from redhat.com (unknown [10.44.32.201]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4365730002D2; Wed, 4 Mar 2026 16:13:03 +0000 (UTC) Date: Wed, 4 Mar 2026 17:13:00 +0100 From: Kevin Wolf To: Hanna Czenczek Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org Subject: Re: [PATCH 2/5] block: Introduce BDRV_O_NO_DATA_{WRITE,RESIZE} Message-ID: References: <20260205144737.31131-1-hreitz@redhat.com> <20260205144737.31131-3-hreitz@redhat.com> <83ed45e5-b1f5-447a-8489-6f13edb2372c@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <83ed45e5-b1f5-447a-8489-6f13edb2372c@redhat.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 33 X-Spam_score: 3.3 X-Spam_bar: +++ X-Spam_report: (3.3 / 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.703, RCVD_IN_VALIDITY_SAFE_BLOCKED=1.386, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 04.03.2026 um 15:20 hat Hanna Czenczek geschrieben: > On 02.03.26 15:30, Kevin Wolf wrote: > > Am 05.02.2026 um 15:47 hat Hanna Czenczek geschrieben: > > > Add BDS flags that prevent taking WRITE and/or RESIZE permissions on > > > pure data (no metadata) children. These are going to be used by qcow2 > > > during formatting, when we need write access to format the metadata > > > file, but no write access to an external data file. This will allow > > > creating a qcow2 image for a raw image while the latter is currently in > > > use by the VM. > > > > > > Signed-off-by: Hanna Czenczek > > > --- > > > include/block/block-common.h | 11 +++++++++++ > > > block.c | 15 +++++++++++++++ > > > 2 files changed, 26 insertions(+) > > > > > > diff --git a/include/block/block-common.h b/include/block/block-common.h > > > index c8c626daea..504f6aa113 100644 > > > --- a/include/block/block-common.h > > > +++ b/include/block/block-common.h > > > @@ -245,6 +245,17 @@ typedef enum { > > > #define BDRV_O_CBW_DISCARD_SOURCE 0x80000 /* for copy-before-write filter */ > > > +/* > > > + * Promise not to write any data to pure (non-metadata-bearing) data storage > > > + * children, so we don't need the WRITE permission for them. > > > + * For image creation, formatting requires write access to the image, but not > > > + * necessarily to its pure storage children. This allows creating an image on > > > + * top of an existing raw storage image that is already attached to the VM. > > > + */ > > > +#define BDRV_O_NO_DATA_WRITE 0x100000 > > Can't we just use BDRV_O_NO_IO for this one? It is stricter because it > > doesn't allow reading either, but I don't think image creation ever > > requires reading from the image? > > How would qcow2 set it?  It opens the qcow2 image, so it can only set the > flag on the qcow2 BDS (via a BlockBackend), but BDRV_O_NO_IO needs to go on > the data-file child.  Maybe we can construct the graph manually…? It would > be quite painful, I imagine, but I haven’t tried yet. Why should it go on the data-file child? The child permissions are defined by the qcow2 node. If the caller promises not to do any I/O (and I'm fairly sure that apart from preallocation, creating the image doesn't involve any I/O on the qcow2 node, just on the primary child), then qcow2 doesn't need any permissions on data-file. Or am I missing a reason why BDRV_O_NO_IO can't be set for the qcow2 node? Kevin