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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 0755EC433B4 for ; Tue, 4 May 2021 14:30:11 +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 A9254613B3 for ; Tue, 4 May 2021 14:30:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A9254613B3 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]:47036 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ldw3t-0005uS-JB for qemu-devel@archiver.kernel.org; Tue, 04 May 2021 10:30:09 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57790) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ldw2s-00055A-0M for qemu-devel@nongnu.org; Tue, 04 May 2021 10:29:06 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:54544) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ldw2n-0000wL-Rg for qemu-devel@nongnu.org; Tue, 04 May 2021 10:29:04 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620138541; 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=uwRYgiUOircZKd6MDaHCe9AHunH4mtIXAUDZll6DHjU=; b=UoCCVC/oTrFQCv5VzQBIBj9J5ZH8JZ6WRqQgmwFJiIM01NllC0dFQ0GvQ7miEaQf1IJFmC +Eg8Rgsvp4snGWubnnCB3ePYqmLlQtQmFeRmagk/Xqx11P6errlymX+/6SLdANP9epaxu6 9kwq+tcWRd1LEPBAfkp6YEV8FVJBzVY= 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-356-tK27bWu9M_yCpt83uda8bw-1; Tue, 04 May 2021 10:28:59 -0400 X-MC-Unique: tK27bWu9M_yCpt83uda8bw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F17A5801817; Tue, 4 May 2021 14:28:57 +0000 (UTC) Received: from localhost (ovpn-115-110.ams2.redhat.com [10.36.115.110]) by smtp.corp.redhat.com (Postfix) with ESMTP id E2F1B5D9D5; Tue, 4 May 2021 14:28:50 +0000 (UTC) Date: Tue, 4 May 2021 15:28:49 +0100 From: Stefan Hajnoczi To: Eduardo Habkost Subject: Re: [PATCH] virtio-blk: drop deprecated scsi=on|off property Message-ID: References: <20210429155221.1226561-1-stefanha@redhat.com> <20210429180352.ohhfz4kwyxapbiyl@habkost.net> MIME-Version: 1.0 In-Reply-To: <20210429180352.ohhfz4kwyxapbiyl@habkost.net> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="nQhmgPCngL/7jJAt" Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.697, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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 , Peter Krempa , qemu-block@nongnu.org, "Michael S. Tsirkin" , libvir-list@redhat.com, Markus Armbruster , qemu-devel@nongnu.org, Max Reitz , Christoph Hellwig , "Dr . David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --nQhmgPCngL/7jJAt Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Apr 29, 2021 at 02:03:52PM -0400, Eduardo Habkost wrote: > On Thu, Apr 29, 2021 at 04:52:21PM +0100, Stefan Hajnoczi wrote: > > The scsi=3Don|off property was deprecated in QEMU 5.0 and can be remove= d > > completely at this point. > >=20 > > Drop the scsi=3Don|off option. It was only available on Legacy virtio-b= lk > > devices. Linux v5.6 already dropped support for it. > >=20 > > Remove the hw_compat_2_4[] property assignment since scsi=3Don|off no > > longer exists. Old guests with Legacy virtio-blk devices no longer see > > the SCSI host features bit. > >=20 >=20 > This means pc-2.4 will now break guest ABI if using virtio-blk > devices, correct? Yes. However, this feature was only enabled on Linux hosts, so cross-host OS migration was always broken and no one noticed. Maybe that configuration is too niche and QEMU never supported cross-host OS migration, but it still means that the "pc-2.4" ABI was never solid to begin with :). >=20 > > Live migrating old guests from an old QEMU with the SCSI feature bit > > enabled will fail with "Features 0x... unsupported. Allowed features: > > 0x...". We've followed the QEMU deprecation policy so users have been > > warned... > >=20 >=20 > Were they really warned, though? People running > "-machine pc-i440fx-2.4" might be completely unaware that it was > silently enabling a deprecated feature. >=20 > Can we have this documented in a more explicit way? Maybe just a > comment at hw_compat_2_4 would be enough, to warn people doing > backports and rebases downstream. >=20 > Can we make QEMU refuse to start if using pc-2.4 + virtio-blk > together, just to be sure? >=20 > An alternative would be keeping the property (and the > hw_compat_2_4 entry) just to keep pc-2.4 working (until pc-2.4 is > deprecated and removed), but refusing to realize the device if > the feature is enabled. Yes, the least invasive approach is to leave the property in place but refuse to realize the virtio-blk device when scsi=3Don. The cost is more cruft, including a useless scsi=3Doff command-line option that will continue to show up in libvirt-generated QEMU command-lines. The cautious approach makes sense to me and I'll send a new revision. Stefan --nQhmgPCngL/7jJAt Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmCRWiEACgkQnKSrs4Gr c8jCjAf+PNF2dJCvDznYk1b7YhiNPqqLz1i8hyhNG2l78hKDrvvzSTvDbMtQ4lXu 5zFL2Incm8IuTqp0VNts2VzvSqk1O/tlPNdFEj3GDJ/UFQ2mToCCYXtB91eIZANJ 8ky6LrNa1ptxZ7jYYt8fC1OzWoM2k2JVhOrbDBVx9wdYkc8fj7jjeNeUb0vIcmUi CINm2XWv7ALCFWI86K5NuKxfSu/AQB2JRVNrYuJirb0giVmgxlZUt9EOT/3HMAyE QHhu+h2HUeZrOQQsi1P6woJ5L8l8LLCHr4A8Srk+AymLn2/e2/Qa7mZEYOVtxf0R MpS3Bc0nlCkzZQYb57/ZCxXT5EtEwA== =X/54 -----END PGP SIGNATURE----- --nQhmgPCngL/7jJAt--