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 C34E8CCA47F for ; Mon, 11 Jul 2022 11:12:17 +0000 (UTC) Received: from localhost ([::1]:56196 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oArKq-0002sb-OC for qemu-devel@archiver.kernel.org; Mon, 11 Jul 2022 07:12:16 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57854) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oArI3-0008RW-L0 for qemu-devel@nongnu.org; Mon, 11 Jul 2022 07:09:23 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:27026) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oArHq-0003oi-AH for qemu-devel@nongnu.org; Mon, 11 Jul 2022 07:09:21 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1657537748; h=from:from:reply-to: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=4A7pSfFON7ys5BQH/RZIJDGQIcBwKDXbGc2X7Ns/bYs=; b=LNr2UJee/wzeZ79P8ExOe2pcpIXhEIIt9YrubAo0EUtZxW5q1J5fUftnO7lswZULoD0kHp tbzHW2iY33wMzBZhSjbOB3PMDagiCGddfqim8W5WMVm0hHG4f/E1iD959Tk/LHgz3/UJG0 NJORi/uu9g06/B2fSM82UZ9CQL7FzVE= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-665-LXHRyxWaO6-32qqLKTrF8A-1; Mon, 11 Jul 2022 07:09:05 -0400 X-MC-Unique: LXHRyxWaO6-32qqLKTrF8A-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 231323C01DF2; Mon, 11 Jul 2022 11:09:05 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.95]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 47AEB40D2827; Mon, 11 Jul 2022 11:09:04 +0000 (UTC) Date: Mon, 11 Jul 2022 12:09:01 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Maydell Cc: Markus Armbruster , qemu-devel@nongnu.org, kwolf@redhat.com, hreitz@redhat.com Subject: Re: [RFC PATCH] qobject: Rewrite implementation of QDict for in-order traversal Message-ID: References: <20220705095421.2455041-1-armbru@redhat.com> <87wncqmq2t.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.6 (2022-06-05) X-Scanned-By: MIMEDefang 2.84 on 10.11.54.2 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@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=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jul 11, 2022 at 11:32:35AM +0100, Peter Maydell wrote: > On Fri, 8 Jul 2022 at 12:01, Daniel P. Berrangé wrote: > > What alternative options do we have for addressing this scenario. > > > > I can think of > > > > - Auto-create array elements, if seeing an element set before length. > > > > This is based on the theory that 'len-PROP' field is largely > > redundant. It is only needed if you want to create a sparse > > array, with empty elements /after/ the last one explicitly > > set, or if you want to get error reporting for an app setting > > element 3 after saying it wanted a 2 element list. IMHO the > > error reporting benefit is dubious, because the error scenario > > only exists because we made the app set this redundant 'len-PROP' > > attribute. Does anything actually need the 'sparse array' > > facility ? > > I'm pretty sure that nothing needs sparse array elements like > that. The major reason for the len-PROP field is an implementation > one: because there is currently no way for a QOM object to > say "call this method if somebody tries to set a non-existent > property", the way array properties work is that the 'set' > method for the len-PROP property is the place where we then > add the PROP[0], PROP[1], ... properties. Ahhh, I see what you mean. I totally missed this subtle detail. IIUC, there's essentially no such thing as array properties in QOM. 'prop[0]', 'prop[1]', 'prop[2]', etc are all simply scalar properties from QOM's, that just happen to follow a common naming scheme, but QOM doesn't care about that. > If we either had a "call this for any property set/get attempt > where there is no specific method set" or else had array > properties supported by the core QOM code, we could avoid > having to set len-PROP first. Techically arrays are already supported at the core QOM level, because you can use any QAPI type as a property. The authz/list.c object has a 'rules' property that is an array of QAuthzListRule objects: { 'struct': 'AuthZListProperties', 'data': { '*policy': 'QAuthZListPolicy', '*rules': ['QAuthZListRule'] } } At the time I wrote that, we couldn't express it on the CLI though, without using JSON syntax for -object. I don't think we've ever made it possible to use the opts_visitor with non-scalar properties though. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|