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=-12.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 9C71FC4361B for ; Wed, 16 Dec 2020 11:14:11 +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 EE46523124 for ; Wed, 16 Dec 2020 11:14:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EE46523124 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]:38644 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kpUkz-0008PE-FH for qemu-devel@archiver.kernel.org; Wed, 16 Dec 2020 06:14:09 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:57894) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kpUjp-0007xa-Nl for qemu-devel@nongnu.org; Wed, 16 Dec 2020 06:12:57 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:30683) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kpUjn-0005Fh-Bz for qemu-devel@nongnu.org; Wed, 16 Dec 2020 06:12:56 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1608117174; 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=jm8BXxaF+xaTS8wsfjDfaxPUFM8OLPKVCVAlUIN52dQ=; b=gyiwdv/qxRqjsKllE/TyFoMHSzoGILdFfHV2PBWj56MSWXRiEFIBwiogFr2uZoAsJnHZC0 R5PiBw4q3gzqYp3q67AlYuQosJUfcrHqfUiXnoMmRNAXORafS2cOq27NizXpOPWvcUp1Xx D/Ev+qUfWfq+UcHsdWHPL7wwh9dmxYY= 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-261-nwEQnt-aNzOzHFrN2EETgA-1; Wed, 16 Dec 2020 06:12:50 -0500 X-MC-Unique: nwEQnt-aNzOzHFrN2EETgA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 347C1192D787 for ; Wed, 16 Dec 2020 11:12:49 +0000 (UTC) Received: from redhat.com (ovpn-115-177.ams2.redhat.com [10.36.115.177]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5A3F318017; Wed, 16 Dec 2020 11:12:44 +0000 (UTC) Date: Wed, 16 Dec 2020 11:12:42 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Gerd Hoffmann Subject: Re: [PATCH v2 8/9] vnc: add support for extended desktop resize Message-ID: <20201216111242.GG189795@redhat.com> References: <20201208115737.18581-1-kraxel@redhat.com> <20201208115737.18581-9-kraxel@redhat.com> <20201208181328.GW3136942@redhat.com> <20201215101503.obaq7ycm2zdxcnq5@sirius.home.kraxel.org> <20201215102040.GH121272@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201215102040.GH121272@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com 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_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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Dec 15, 2020 at 10:20:40AM +0000, Daniel P. Berrangé wrote: > On Tue, Dec 15, 2020 at 11:15:03AM +0100, Gerd Hoffmann wrote: > > On Tue, Dec 08, 2020 at 06:13:28PM +0000, Daniel P. Berrangé wrote: > > > On Tue, Dec 08, 2020 at 12:57:36PM +0100, Gerd Hoffmann wrote: > > > > The extended desktop resize encoding adds support for (a) clients > > > > sending resize requests to the server, and (b) multihead support. > > > > > > > > This patch implements (a). All resize requests are rejected by qemu. > > > > Qemu can't resize the framebuffer on its own, this is in the hands of > > > > the guest, so all qemu can do is forward the request to the guest. > > > > Should the guest actually resize the framebuffer we can notify the vnc > > > > client later with a separate message. > > > > > > > > This requires support in the display device. Works with virtio-gpu. > > > > > > > > https://github.com/rfbproto/rfbproto/blob/master/rfbproto.rst#extendeddesktopsize-pseudo-encoding > > > > > > The spec says > > > > > > "The server must send an ExtendedDesktopSize rectangle in response > > > to a FramebufferUpdateRequest with incremental set to zero, assuming > > > the client has requested the ExtendedDesktopSize pseudo-encoding > > > using the SetEncodings message. This requirement is needed so that > > > the client has a reliable way of fetching the initial screen > > > configuration, and to determine if the server supports the > > > SetDesktopSize message. > > > > > > A consequence of this is that a client must not respond to an > > > ExtendedDesktopSize rectangle by sending a FramebufferUpdateRequest > > > with incremental set to zero. Doing so would make the system go into > > > an infinite loop." > > > > > > Historically gtk-vnc always sets incremental=0 after a resize message, > > > so it should trigger an infinite loop. This doesn't happen with QEMU's > > > impl, so I think QEMU isn't correctly following the sec here. IIUC, > > > tt needs to force send an ExtendedDesktopSize message every time > > > incremental=0, not merely when a resize happens. > > > > There are three cases where qemu sends an ExtendedDesktopSize message: > > > > (1) during the initial handshake (to cover the feature detection). > > (2) as response to a SetDesktopSize request, and > > (3) when an resize happens. > > > > So, yes, I skimmed the spec a bit to fast and didn't implement it > > correctly. Which also explains why you can't trigger the infinite > > loop issue. > > > > > Having said that, I find this part of the spec rather crazy. I dont > > > see why clients need more than the first ExtendedDesktopSize message > > > in order to detect the feature, rather than after every single > > > incremental=0 update request. > > > > Yes, it doesn't make much sense. > > > > > None the less the spec says we should get an infinite loop and with > > > my intentional attempt to cause this, QEMU doesn't play ball. > > > > Not fully sure I should consider this a bug or a feature. > > This patch doesn't conform to the spec. > > But it clearly is more robust ... > > I'm going to propose a spec change and see what response it gets I ended up opening an issue to query the spec instead: https://github.com/rfbproto/rfbproto/issues/37 Also, I've proposed a spec update to make the interaction between ExtendedDesktopSize and WMVi encodings explicit: https://github.com/rfbproto/rfbproto/pull/36 QEMU is already in compliance with this clarification, I just wanted to make it explicitly required. 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 :|