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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,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 F1970C433B4 for ; Wed, 14 Apr 2021 08:20:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C931260BBB for ; Wed, 14 Apr 2021 08:20:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349913AbhDNIS5 (ORCPT ); Wed, 14 Apr 2021 04:18:57 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:54034 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231223AbhDNISy (ORCPT ); Wed, 14 Apr 2021 04:18:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618388311; 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=drGuROoG7lj2vDETDU9JDvj19d1vG70cVaZLfEDasfQ=; b=eng9jP2F8WIvEVqjIHcrtypbkDa0bReMJI2sovQ9ju6aGAoJhVd2xavUMFgQRObkGPK1TA zG20mQeSxpQ28JcLiYKL6XcsdA+M80AdNX7W0Bh+0qyOiWtruxL13xmouwavbQFAg67nAn 4/y1crStaHgijUC1goWLNQJGuTg4NEI= 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-442-BEpTz7kFPZK4thdSD3eoIQ-1; Wed, 14 Apr 2021 04:18:28 -0400 X-MC-Unique: BEpTz7kFPZK4thdSD3eoIQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 74FE91883527; Wed, 14 Apr 2021 08:18:26 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-13-33.pek2.redhat.com [10.72.13.33]) by smtp.corp.redhat.com (Postfix) with ESMTP id B882B16ED7; Wed, 14 Apr 2021 08:18:13 +0000 (UTC) Subject: Re: [PATCH v6 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace To: Yongji Xie Cc: "Michael S. Tsirkin" , Stefan Hajnoczi , Stefano Garzarella , Parav Pandit , Christoph Hellwig , Christian Brauner , Randy Dunlap , Matthew Wilcox , viro@zeniv.linux.org.uk, Jens Axboe , bcrl@kvack.org, Jonathan Corbet , =?UTF-8?Q?Mika_Penttil=c3=a4?= , Dan Carpenter , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <20210331080519.172-1-xieyongji@bytedance.com> <20210331080519.172-10-xieyongji@bytedance.com> <091dde74-449b-385c-0ec9-11e4847c6c4c@redhat.com> <0f386dfe-45c9-5609-55f7-b8ab2a4abf5e@redhat.com> From: Jason Wang Message-ID: <51cd2e3a-5b76-a6f5-da59-b118a7e13923@redhat.com> Date: Wed, 14 Apr 2021 16:18:11 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 在 2021/4/13 下午12:28, Yongji Xie 写道: > On Tue, Apr 13, 2021 at 11:35 AM Jason Wang wrote: >> >> 在 2021/4/12 下午5:59, Yongji Xie 写道: >>> On Mon, Apr 12, 2021 at 5:37 PM Jason Wang wrote: >>>> 在 2021/4/12 下午4:02, Yongji Xie 写道: >>>>> On Mon, Apr 12, 2021 at 3:16 PM Jason Wang wrote: >>>>>> 在 2021/4/9 下午4:02, Yongji Xie 写道: >>>>>>>>>>> +}; >>>>>>>>>>> + >>>>>>>>>>> +struct vduse_dev_config_data { >>>>>>>>>>> + __u32 offset; /* offset from the beginning of config space */ >>>>>>>>>>> + __u32 len; /* the length to read/write */ >>>>>>>>>>> + __u8 data[VDUSE_CONFIG_DATA_LEN]; /* data buffer used to read/write */ >>>>>>>>>> Note that since VDUSE_CONFIG_DATA_LEN is part of uAPI it means we can >>>>>>>>>> not change it in the future. >>>>>>>>>> >>>>>>>>>> So this might suffcient for future features or all type of virtio devices. >>>>>>>>>> >>>>>>>>> Do you mean 256 is no enough here？ >>>>>>>> Yes. >>>>>>>> >>>>>>> But this request will be submitted multiple times if config lengh is >>>>>>> larger than 256. So do you think whether we need to extent the size to >>>>>>> 512 or larger? >>>>>> So I think you'd better either: >>>>>> >>>>>> 1) document the limitation (256) in somewhere, (better both uapi and doc) >>>>>> >>>>> But the VDUSE_CONFIG_DATA_LEN doesn't mean the limitation of >>>>> configuration space. It only means the maximum size of one data >>>>> transfer for configuration space. Do you mean document this? >>>> Yes, and another thing is that since you're using >>>> data[VDUSE_CONFIG_DATA_LEN] in the uapi, it implies the length is always >>>> 256 which seems not good and not what the code is wrote. >>>> >>> How about renaming VDUSE_CONFIG_DATA_LEN to VDUSE_MAX_TRANSFER_LEN? >>> >>> Thanks, >>> Yongji >> >> So a question is the reason to have a limitation of this in the uAPI? >> Note that in vhost-vdpa we don't have such: >> >> struct vhost_vdpa_config { >> __u32 off; >> __u32 len; >> __u8 buf[0]; >> }; >> > If so, we need to call read()/write() multiple times each time > receiving/sending one request or response in userspace and kernel. For > example, > > 1. read and check request/response type > 2. read and check config length if type is VDUSE_SET_CONFIG or VDUSE_GET_CONFIG > 3. read the payload > > Not sure if it's worth it. > > Thanks, > Yongji Right, I see. So I'm fine with current approach. Thanks >