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=-2.0 required=3.0 tests=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 A75DDC433E0 for ; Wed, 10 Jun 2020 03:23:39 +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 7539220737 for ; Wed, 10 Jun 2020 03:23:39 +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="crPl57Et" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7539220737 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]:47004 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jirL0-0001yd-Pc for qemu-devel@archiver.kernel.org; Tue, 09 Jun 2020 23:23:38 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55812) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jirJl-0001EF-4m for qemu-devel@nongnu.org; Tue, 09 Jun 2020 23:22:21 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:50380 helo=us-smtp-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 1jirJj-0004fk-KU for qemu-devel@nongnu.org; Tue, 09 Jun 2020 23:22:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1591759335; 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=giGNkMug9B13IF80bioDjaMMNFrcJCoFvN4ZnxVNpeA=; b=crPl57EtYfoOCCiELQwuuDtif0r2gGwNYFGtwYkIE6n+/aLwup+ykw8KVWabyUiO2brXFe NBQifz8GfzEPxDxOUlIm2khvKU7bNYLKNpYHy9t1NkewZp0CKUQjMRU+NKAW7n9SNUfntT oYuoWGGAwQ5IvtAMAKBHVMo+QbBXRgI= 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-125-yBR4QoG0PbSmWlShHbMs6w-1; Tue, 09 Jun 2020 23:22:13 -0400 X-MC-Unique: yBR4QoG0PbSmWlShHbMs6w-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 19D5C107ACF2; Wed, 10 Jun 2020 03:22:12 +0000 (UTC) Received: from [10.72.13.194] (ovpn-13-194.pek2.redhat.com [10.72.13.194]) by smtp.corp.redhat.com (Postfix) with ESMTP id B621661983; Wed, 10 Jun 2020 03:21:52 +0000 (UTC) Subject: Re: [PATCH v2 4/7] vhost: involve device backends in feature negotiation To: "Michael S. Tsirkin" , Stefan Hajnoczi References: <20200609170218.246468-1-stefanha@redhat.com> <20200609170218.246468-5-stefanha@redhat.com> <20200609135007-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <37ac3fbb-9a9b-9290-abee-a8603c81925c@redhat.com> Date: Wed, 10 Jun 2020 11:21:50 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200609135007-mutt-send-email-mst@kernel.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=jasowang@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/09 21:17:20 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: Kevin Wolf , Fam Zheng , Thomas Huth , Eduardo Habkost , qemu-block@nongnu.org, Laurent Vivier , cohuck@redhat.com, qemu-devel@nongnu.org, Raphael Norwitz , "Gonglei \(Arei\)" , Gerd Hoffmann , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Paolo Bonzini , Max Reitz , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/6/10 上午2:07, Michael S. Tsirkin wrote: >> +/* >> + * Default vhost_get_features() feature bits for existing device types that do >> + * not define their own. >> + * >> + * This is a workaround for existing device types, do not use this in new vhost >> + * device types. Explicitly define a list of feature bits instead. >> + * >> + * The following feature bits are excluded because libvhost-user device >> + * backends did not advertise them for a long time. Therefore we cannot detect >> + * their presence. Instead we assume they are always supported by the device >> + * backend: >> + * VIRTIO_F_NOTIFY_ON_EMPTY >> + * VIRTIO_F_ANY_LAYOUT >> + * VIRTIO_F_VERSION_1 >> + * VIRTIO_RING_F_INDIRECT_DESC >> + * VIRTIO_RING_F_EVENT_IDX > Weird. I remember that it's common for vhost-user not to set > VIRTIO_RING_F_INDIRECT_DESC - they have huge queues so > don't need it and inline descriptors give them better > performance. > > So what's going on here? I guess one reason is to support live migration between vhost-user and vhost-net. Thanks