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=-5.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 395D8C433ED for ; Wed, 5 May 2021 17:56:26 +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 A9F03613EA for ; Wed, 5 May 2021 17:56:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A9F03613EA 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]:41042 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1leLl2-0003wP-Ka for qemu-devel@archiver.kernel.org; Wed, 05 May 2021 13:56:24 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:39716) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1leLjJ-00033b-6r for qemu-devel@nongnu.org; Wed, 05 May 2021 13:54:37 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:21301) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1leLjF-0000nr-MG for qemu-devel@nongnu.org; Wed, 05 May 2021 13:54:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620237272; 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=NdW9Zi1T+f3fzX2fRJLE/kim+RxVMv4R5nc9KJjrpJ8=; b=CrJFczoY2ZZM+fGXFpkpM8UBe+sbvP4X/cuoz1mBrD1SjOwfhQumTpWsJRmAeg3GpVemU6 Z/uMzg93lgx8xQmGy7QbqtKwCNzikyZNczde8Tz9h3hOETwZa5z6X83mqTBRku8U8t/NlM u13f9jTfaF7/sNe1QFkuz/XmG3oakg0= 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-252-FmyHM5CEP8m6oIaMXOo4MQ-1; Wed, 05 May 2021 13:54:30 -0400 X-MC-Unique: FmyHM5CEP8m6oIaMXOo4MQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 76626106BB24; Wed, 5 May 2021 17:54:29 +0000 (UTC) Received: from work-vm (ovpn-115-97.ams2.redhat.com [10.36.115.97]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 566C060864; Wed, 5 May 2021 17:54:19 +0000 (UTC) Date: Wed, 5 May 2021 18:54:16 +0100 From: "Dr. David Alan Gilbert" To: =?iso-8859-1?Q?Marc-Andr=E9?= Lureau Subject: Re: vhost-user payload union restrictions ? Message-ID: References: MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.0.6 (2021-03-06) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@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=-0.693, 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=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: , Cc: QEMU , Stefan Hajnoczi , vgoyal@redhat.com, "Michael S. Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Marc-André Lureau (marcandre.lureau@gmail.com) wrote: > Hi > > On Wed, May 5, 2021 at 4:38 PM Dr. David Alan Gilbert > wrote: > > > (Resend, remembering to add list) > > Hi, > > I'm trying to understand what restrictions there are on the > > payload that's part of VhostUserMsg; and am confused by > > inconsistencies. > > > > Lets start with this version: > > > > subprojects/libvhost-user/libvhost-user.h : > > typedef struct VhostUserMsg { > > int request; > > > > #define VHOST_USER_VERSION_MASK (0x3) > > #define VHOST_USER_REPLY_MASK (0x1 << 2) > > #define VHOST_USER_NEED_REPLY_MASK (0x1 << 3) > > uint32_t flags; > > uint32_t size; /* the following payload size */ > > > > union { > > #define VHOST_USER_VRING_IDX_MASK (0xff) > > #define VHOST_USER_VRING_NOFD_MASK (0x1 << 8) > > uint64_t u64; > > struct vhost_vring_state state; > > struct vhost_vring_addr addr; > > VhostUserMemory memory; > > VhostUserMemRegMsg memreg; > > VhostUserLog log; > > VhostUserConfig config; > > VhostUserVringArea area; > > VhostUserInflight inflight; > > } payload; > > > > int fds[VHOST_MEMORY_BASELINE_NREGIONS]; > > int fd_num; > > uint8_t *data; > > } VU_PACKED VhostUserMsg; > > > > note the 'fds' array after the payload but before > > the end of the structure. > > > > But then there's the version in: > > hw/virtio/vhost-user.c > > typedef union { > > #define VHOST_USER_VRING_IDX_MASK (0xff) > > #define VHOST_USER_VRING_NOFD_MASK (0x1<<8) > > uint64_t u64; > > struct vhost_vring_state state; > > struct vhost_vring_addr addr; > > VhostUserMemory memory; > > VhostUserMemRegMsg mem_reg; > > VhostUserLog log; > > struct vhost_iotlb_msg iotlb; > > VhostUserConfig config; > > VhostUserCryptoSession session; > > VhostUserVringArea area; > > VhostUserInflight inflight; > > } VhostUserPayload; > > > > typedef struct VhostUserMsg { > > VhostUserHeader hdr; > > VhostUserPayload payload; > > } QEMU_PACKED VhostUserMsg; > > > > which hasn't got the 'fds' section. > > Yet they're both marked as 'packed'. > > > > They are packed, because both are used to serialize/deserialize the stream. The header is (de)serialized and the payload is; but we don't ever try and deal with both at the same time do we ? We read the header, check the length, read the payload; so isn't it really each part is packed and not the whole? > > > That's a bit unfortunate for two structures with the same name. > > > > > Yes, maybe it's time to have a canonical system header used by both? Any idea where that would live? I think the problem is that in some respects the libvhost_user.h is the right place, but it's now formally a separate/sub project. > > Am I right in thinking that the vhost-user.c version is sent over > > the wire, while the libvhost-user.h one is really just an interface? > > > > > I believe the extra fields are not used for serializing the message, but > just a convenient way to group related data. OK > > Is it safe for me to add a new, larger entry in the payload union > > without breaking existing clients? > > > > It should be. Good. > > I ended up at this question after trying to add a variable length > > entry to the union: > > > > typedef struct { > > VhostUserFSSlaveMsg fs; > > VhostUserFSSlaveMsgEntry entries[VHOST_USER_FS_SLAVE_MAX_ENTRIES]; > > } QEMU_PACKED VhostUserFSSlaveMsgMax; > > > > ... > > union .... > > VhostUserFSSlaveMsg fs; > > VhostUserFSSlaveMsgMax fs_max; /* Never actually used */ > > } VhostUserPayload; > > > > and in the .h I had: > > typedef struct { > > /* Generic flags for the overall message */ > > uint32_t flags; > > /* Number of entries */ > > uint16_t count; > > /* Spare */ > > uint16_t align; > > > > VhostUserFSSlaveMsgEntry entries[]; > > } VhostUserFSSlaveMsg; > > > > union { > > ... > > VhostUserInflight inflight; > > VhostUserFSSlaveMsg fs; > > } payload; > > > > which is apparently OK in the .c version, and gcc is happy with the same > > in the libvhost-user.h version; but clang gets upset by the .h > > version because it doesn't like the variable length structure > > before the end of the struct - which I have sympathy for. > > > > > Indeed, we probably want to allocate the message separately then. I'm thinking that wecould change the libvhost-user.h to be: (as the C file) typedef struct VhostUserMsg { VhostUserHeader hdr; VhostUserPayload payload; } VU_PACKED VhostUserMsgWire; typedef struct VhostUserMsgExt { int fds[VHOST_MEMORY_BASELINE_NREGIONS]; int fd_num; uint8_t *data; VhostUserMsgWire msg; } VhostUserMsg; Dave > thanks > > -- > Marc-André Lureau -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK