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=-0.8 required=3.0 tests=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 7EC13C433DF for ; Thu, 25 Jun 2020 10:32:58 +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 1AF1C2053B for ; Thu, 25 Jun 2020 10:32:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="bWryAwbS" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1AF1C2053B 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]:37844 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1joPBh-0008IR-0H for qemu-devel@archiver.kernel.org; Thu, 25 Jun 2020 06:32:57 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:38702) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1joPAh-00075c-Hn for qemu-devel@nongnu.org; Thu, 25 Jun 2020 06:31:55 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:37147 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1joPAf-0000Ry-Pl for qemu-devel@nongnu.org; Thu, 25 Jun 2020 06:31:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1593081112; 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=ecfE+8Xcpj03hl/wlcmxokH/IaYLvXQTdQbVjwczAvc=; b=bWryAwbSZgfhwOcPJzgqtjamj/NHXqkRB4aevd2fbQbS1tE69zlJEEy7IOuHwWQoNiO1Vi mHL3ZvrvCv6Lgjpmr4RhzEgakkHMHIyu7YAA05Qt8KVhAoZcaK5J2e1xeZRJX7Pe0LWxar jlzAlhJzKu4XmCDeWgNIOX0e4cvygx0= 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-138-9A8QywsdPFCD0H6XSQ5lZg-1; Thu, 25 Jun 2020 06:31:50 -0400 X-MC-Unique: 9A8QywsdPFCD0H6XSQ5lZg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D4DCE1800D4A; Thu, 25 Jun 2020 10:31:49 +0000 (UTC) Received: from gondolin (ovpn-112-36.ams2.redhat.com [10.36.112.36]) by smtp.corp.redhat.com (Postfix) with ESMTP id D5B42101E662; Thu, 25 Jun 2020 10:31:38 +0000 (UTC) Date: Thu, 25 Jun 2020 12:31:36 +0200 From: Cornelia Huck To: "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" Subject: Re: [RFC 0/4] Enable virtio-fs on s390x Message-ID: <20200625123136.2c3c0ebe.cohuck@redhat.com> In-Reply-To: <20200625101935.GF1009994@redhat.com> References: <20200625100430.22407-1-mhartmay@linux.ibm.com> <20200625101935.GF1009994@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=205.139.110.61; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/25 00:45:15 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: "Michael S. Tsirkin" , qemu-devel@nongnu.org, Halil Pasic , Marc Hartmayer , Stefan Hajnoczi , =?UTF-8?B?TWFyYy1BbmRyw6k=?= Lureau Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 25 Jun 2020 11:19:35 +0100 Daniel P. Berrang=C3=A9 wrote: > On Thu, Jun 25, 2020 at 12:04:26PM +0200, Marc Hartmayer wrote: > > This RFC is about enabling virtio-fs on s390x. For that we need > > + some shim code (first patch), and we need > > + libvhost-user to deal with virtio endiannes as mandated by the spec. > > =20 > > The second part is trickier, because unlike QEMU we are not certain > > about the guest's native endianness, which is needed to handle the > > legacy-interface appropriately. In fact, this is the reason why just > > RFC. > >=20 > > One of the open questions is whether to build separate versions, one > > for guest little endian and one for guest big endian, or do we want > > something like a command line option? (Digression on the libvirt > > modeling) =20 >=20 > When you talk about big vs little endian, are you referring to TCG > scenarios with mixed host/guest arch, or arches which can support > either endianess, or both ? i guess it doesn't matter actually, as > I think the latter forces a specific answer. >=20 > Considering that some architectures allow the guest OS to flip between > big & little endian as they boot, libvirt cannot know what endianess > the guest is using when it launches virtiofsd. It thus cannot pick > between two different endianness builds of virtiofsd automatically. > This would force the user to tell libvirt what arch the guest is using > at the time they define the guest. This is an undesirable restriction > for use cases where the admin of the guest OS has no direct control > over the host config. Right, but that is in practice only a problem for legacy devices, isn't it? The standard says that non-legacy devices use little-endian everywhere; it's the legacy 'device endian' that is causing us headaches. Which leads to the question: Do we really need to support legacy virtio-fs devices, or can we just force virtio-1, as many (most?) newer virtio devices do? >=20 > IOW, I think the only practical answer is to have a single binary that > automagically does the right thing at runtime according to guest > endianess that currently is in use. >=20 > Regards, > Daniel