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 78622ECE579 for ; Mon, 9 Sep 2024 15:42:44 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sngXB-0005vd-2a; Mon, 09 Sep 2024 11:42:33 -0400 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 1sngX9-0005n5-WD for qemu-devel@nongnu.org; Mon, 09 Sep 2024 11:42:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sngX8-000413-95 for qemu-devel@nongnu.org; Mon, 09 Sep 2024 11:42:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1725896549; 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=QwKEHGp6ByZ7EpqsMvWZHKTnJ5RyEHMaR8tEmjcvLXA=; b=FhpphffrDHHiVPasc6X2hmsVnw6gSixIxzBCiP76UsjBgpJaGWHmiWoNz065dYOxJAPf1G NuHw+DzDbwbiyzZDDfcEFhV84Ky6mHnZla8ZpKMtVKKE2ugrikjRtcZu/zwiogLDZgmGBO 8nkT2/0wVjrf8NYn+TJy99qbg9eaGC0= Received: from mx-prod-mc-05.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-147-wHd4IjKwPni36hRlAI0DAA-1; Mon, 09 Sep 2024 11:42:26 -0400 X-MC-Unique: wHd4IjKwPni36hRlAI0DAA-1 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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 85EE7195608C; Mon, 9 Sep 2024 15:42:24 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.47]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 27B6D300147D; Mon, 9 Sep 2024 15:42:17 +0000 (UTC) Date: Mon, 9 Sep 2024 17:42:15 +0200 From: Kevin Wolf To: Joelle van Dyne Cc: qemu-devel@nongnu.org, Hanna Reitz , Eric Blake , Markus Armbruster , Peter Maydell , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Akihiko Odaki , Gerd Hoffmann , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , "open list:Block layer core" Subject: Re: [PATCH] block: support locking on change medium Message-ID: References: <20240909015847.40377-1-j@getutm.app> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.141, 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_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: 2.1.29 Precedence: list List-Id: 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 09.09.2024 um 16:25 hat Joelle van Dyne geschrieben: > On Mon, Sep 9, 2024 at 2:56 AM Kevin Wolf wrote: > > > > Am 09.09.2024 um 03:58 hat Joelle van Dyne geschrieben: > > > New optional argument for 'blockdev-change-medium' QAPI command to allow > > > the caller to specify if they wish to enable file locking. > > > > > > Signed-off-by: Joelle van Dyne > > > > I feel once you need to control such details of the backend, you should > > really use a separate 'blockdev-add' commannd. > > > > If it feels a bit too cumbersome to send explicit commands to open the > > tray, remove the medium, insert the new medium referencing the node you > > added with 'blockdev-add' and then close the tray again, I can > > understand. Maybe what we should do is extend 'blockdev-change-medium' > > so that it doesn't only accept a filename to specify the new images, but > > alternatively also a node-name. > > > > > + switch (file_locking_mode) { > > > + case BLOCKDEV_CHANGE_FILE_LOCKING_MODE_AUTO: > > > + break; > > > + > > > + case BLOCKDEV_CHANGE_FILE_LOCKING_MODE_OFF: > > > + qdict_put_str(options, "file.locking", "off"); > > > + break; > > > + > > > + case BLOCKDEV_CHANGE_FILE_LOCKING_MODE_ON: > > > + qdict_put_str(options, "file.locking", "on"); > > > + break; > > > + > > > + default: > > > + abort(); > > > + } > > > > Using "file.locking" makes assumptions about what the passed filename > > string would result in. There is nothing that guarantees that the block > > driver even has a "file" child, or that the "file" child is referring > > to a file-posix driver rather than using a different protocol or being a > > filter driver above yet another node. It also doesn't consider backing > > files and other non-primary children of the opened node. > > > > So this is not correct, and I don't think there is any realistic way of > > making it correct with this approach. > > The existence of "filename" already makes this assumption that the > input is a file child. No. Try using something like "blkdebug::image.iso" or "nbd://localhost". In the former case, you get another layer and the "file" child would be a blkdebug node. To turn off locking on the file-posix block driver you'd need to set "file.file.locking" in this case. And the latter doesn't have any file-posix involved, it goes straight to the NBD block driver. > While I agree with you that there are better ways to solve this > problem, ultimately "blockdev-change-medium" will have to be > deprecated when this hypothetical "better" way of referencing a node > added with blockdev-add is introduced. This is not a hypothetical better way. It is how you can achieve this today. Extending blockdev-change-medium to alternatively accept a node-name would just introduce a convenience shortcut (as is the whole command) that doesn't require you to send four QMP commands (blockdev-open-tray, blockdev-remove-medium, blockdev-insert-medium and blockdev-close-tray). There is no need to deprecate blockdev-change-medium with a filename any more than there is a need to deprecate -hda on the command line. We could do it because there are alternatives that provide a strict superset of functionality, but we don't have to. Kevin