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 0C004C433ED for ; Wed, 5 May 2021 12:38:17 +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 8134C613BF for ; Wed, 5 May 2021 12:38:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8134C613BF 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]:39880 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1leGn9-0002H0-Eq for qemu-devel@archiver.kernel.org; Wed, 05 May 2021 08:38:15 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41656) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1leGlm-00010M-9b for qemu-devel@nongnu.org; Wed, 05 May 2021 08:36:51 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:21276) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1leGlf-0008Qt-AM for qemu-devel@nongnu.org; Wed, 05 May 2021 08:36:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620218202; 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; bh=pCkXBlBCAP9nOrfqwMkc4sYlP1KthdCG0pkc92qsntM=; b=XYQSwn2uPYHaFvJ1oOQvJjPlo7qpU5N/zGBJ1SyhF9gXvV2uyIBT/QV4YjrDBergV5OH8B ilzkeYAYKYyn/5kg8XpNisgp5oTlyy+yl7kSlnMZQD7iVHs7GStDTJuUbp1EBjHnWKM0zp hHyaolS/p8f6Z48cuUZZGYrWSdU3R4A= 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-543-uJYFgnYzN1ayyJIn7DiWxQ-1; Wed, 05 May 2021 08:36:39 -0400 X-MC-Unique: uJYFgnYzN1ayyJIn7DiWxQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C1C67107ACCA for ; Wed, 5 May 2021 12:36:38 +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 902F370C24; Wed, 5 May 2021 12:36:37 +0000 (UTC) Date: Wed, 5 May 2021 13:36:34 +0100 From: "Dr. David Alan Gilbert" To: marcandre.lureau@redhat.com, mst@redhat.com Subject: vhost-user payload union restrictions ? Message-ID: MIME-Version: 1.0 User-Agent: Mutt/2.0.6 (2021-03-06) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 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=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; 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: vgoyal@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" (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'. That's a bit unfortunate for two structures with the same name. 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? Is it safe for me to add a new, larger entry in the payload union without breaking existing clients? 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. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK