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=-8.7 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=unavailable 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 566F9C07E96 for ; Mon, 5 Jul 2021 03:36:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3DD0F613E2 for ; Mon, 5 Jul 2021 03:36:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229823AbhGEDjJ (ORCPT ); Sun, 4 Jul 2021 23:39:09 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:35821 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229728AbhGEDjG (ORCPT ); Sun, 4 Jul 2021 23:39:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1625456190; 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=PNRaRFhxCfnbw9LvPZ80acVFOHmYfRIDpgg4dy1jTTw=; b=aNN86Z9WBpniD+7U7SY/V3S5RduvyFy/H0esuq2+YMvYI0WVUSpe69toHpxn9aqlaP+/qx wW4Tcw4m57vdC7OCW/1Ro/TnlcTHJtA3Zkjfy75pT0VTL5Abg4AcGzjMnkA2SEfg9tde8j TR8hAf7P1NodVXl2uaITDQ4PqU3FoDI= Received: from mail-pg1-f198.google.com (mail-pg1-f198.google.com [209.85.215.198]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-9-zru_N9AGOTCvyYmwaxjReA-1; Sun, 04 Jul 2021 23:36:29 -0400 X-MC-Unique: zru_N9AGOTCvyYmwaxjReA-1 Received: by mail-pg1-f198.google.com with SMTP id p2-20020a63e6420000b02902271082c631so12611874pgj.5 for ; Sun, 04 Jul 2021 20:36:29 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=PNRaRFhxCfnbw9LvPZ80acVFOHmYfRIDpgg4dy1jTTw=; b=SSoFkGF83FDJrzDjk1tO4/Q/GkJaZF8FICiKZyogxVIOl1mosZe87POj3eksSoJ+bL ShDA/ZdrepNRXHyQmhMjzR9g71xn5/akLeJPG3P9GkDoEyqBTGfKOkDi1Ncg7VSFuHpU TiPKCq3qH9iQm5yk6hWAa+i9JfbsHf52uf6zHTGTpxvwAjJkgX2D1a/IG1L1lrrX9SLv vOFiDJrhuJVj6scEAemrMUeHnGUx0x2FFm1xVUY7OrrWxi6E3aAVD7RGgG88YmunToGU CnidLPPF9CSKjQ7SNcns4yPgW7xMYEpF4WjpAVH4e/Cu7dD4bt2rfb806/DBRLEvaTrt aKwA== X-Gm-Message-State: AOAM530EWuSdfLI5Bq9tCIXRis6ikFOySpd6eaw401Yix+Rm2IVClnY1 BE4CeSAQCd/YWE9BhUpNk+WwiK76kqpdMPwMkNAbr2QaX7s1I+pzWz7fWnRm5+LxqCBsSp6b2Rk pz+qSBglwaKKGnOqG1B7gQy/RUJdyjJzno/Ka+84T4OFby7u4moHLZdZljTBTC1UCQDLk39XP+w 1w X-Received: by 2002:a62:b502:0:b029:2ec:a539:e29b with SMTP id y2-20020a62b5020000b02902eca539e29bmr12907052pfe.37.1625456187966; Sun, 04 Jul 2021 20:36:27 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxU1ORvJgRFvEdcSUoAIpBbFs4fUYC6vc+xVQFL1exU5Y4g4vdf/8e25LPd+joB4XFQ5Hj+PQ== X-Received: by 2002:a62:b502:0:b029:2ec:a539:e29b with SMTP id y2-20020a62b5020000b02902eca539e29bmr12907014pfe.37.1625456187646; Sun, 04 Jul 2021 20:36:27 -0700 (PDT) Received: from wangxiaodeMacBook-Air.local ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id u13sm10509834pfi.54.2021.07.04.20.36.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 04 Jul 2021 20:36:27 -0700 (PDT) Subject: Re: [PATCH v8 10/10] Documentation: Add documentation for VDUSE To: Yongji Xie , Stefan Hajnoczi Cc: "Michael S. Tsirkin" , Stefano Garzarella , Parav Pandit , Christoph Hellwig , Christian Brauner , Randy Dunlap , Matthew Wilcox , Al Viro , Jens Axboe , bcrl@kvack.org, Jonathan Corbet , =?UTF-8?Q?Mika_Penttil=c3=a4?= , Dan Carpenter , joro@8bytes.org, Greg KH , songmuchun@bytedance.com, virtualization , netdev@vger.kernel.org, kvm , linux-fsdevel@vger.kernel.org, iommu@lists.linux-foundation.org, linux-kernel References: <20210615141331.407-1-xieyongji@bytedance.com> <20210615141331.407-11-xieyongji@bytedance.com> From: Jason Wang Message-ID: <8320d26d-6637-85c6-8773-49553dfa502d@redhat.com> Date: Mon, 5 Jul 2021 11:36:15 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2021/7/4 下午5:49, Yongji Xie 写道: >>> OK, I get you now. Since the VIRTIO specification says "Device >>> configuration space is generally used for rarely-changing or >>> initialization-time parameters". I assume the VDUSE_DEV_SET_CONFIG >>> ioctl should not be called frequently. >> The spec uses MUST and other terms to define the precise requirements. >> Here the language (especially the word "generally") is weaker and means >> there may be exceptions. >> >> Another type of access that doesn't work with the VDUSE_DEV_SET_CONFIG >> approach is reads that have side-effects. For example, imagine a field >> containing an error code if the device encounters a problem unrelated to >> a specific virtqueue request. Reading from this field resets the error >> code to 0, saving the driver an extra configuration space write access >> and possibly race conditions. It isn't possible to implement those >> semantics suing VDUSE_DEV_SET_CONFIG. It's another corner case, but it >> makes me think that the interface does not allow full VIRTIO semantics. Note that though you're correct, my understanding is that config space is not suitable for this kind of error propagating. And it would be very hard to implement such kind of semantic in some transports.  Virtqueue should be much better. As Yong Ji quoted, the config space is used for "rarely-changing or intialization-time parameters". > Agreed. I will use VDUSE_DEV_GET_CONFIG in the next version. And to > handle the message failure, I'm going to add a return value to > virtio_config_ops.get() and virtio_cread_* API so that the error can > be propagated to the virtio device driver. Then the virtio-blk device > driver can be modified to handle that. > > Jason and Stefan, what do you think of this way? I'd like to stick to the current assumption thich get_config won't fail. That is to say, 1) maintain a config in the kernel, make sure the config space read can always succeed 2) introduce an ioctl for the vduse usersapce to update the config space. 3) we can synchronize with the vduse userspace during set_config Does this work? Thanks > 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,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 9599AC07E95 for ; Mon, 5 Jul 2021 03:36:38 +0000 (UTC) Received: from smtp2.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (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 42A8D610E6 for ; Mon, 5 Jul 2021 03:36:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 42A8D610E6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; 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auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jasowang@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Cc: kvm , "Michael S. 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Sun, 04 Jul 2021 20:36:27 -0700 (PDT) Received: from wangxiaodeMacBook-Air.local ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id u13sm10509834pfi.54.2021.07.04.20.36.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 04 Jul 2021 20:36:27 -0700 (PDT) Subject: Re: [PATCH v8 10/10] Documentation: Add documentation for VDUSE To: Yongji Xie , Stefan Hajnoczi References: <20210615141331.407-1-xieyongji@bytedance.com> <20210615141331.407-11-xieyongji@bytedance.com> From: Jason Wang Message-ID: <8320d26d-6637-85c6-8773-49553dfa502d@redhat.com> Date: Mon, 5 Jul 2021 11:36:15 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jasowang@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Cc: kvm , "Michael S. Tsirkin" , virtualization , Christian Brauner , Jonathan Corbet , joro@8bytes.org, Matthew Wilcox , Christoph Hellwig , Dan Carpenter , Al Viro , songmuchun@bytedance.com, Jens Axboe , Greg KH , Randy Dunlap , linux-kernel , iommu@lists.linux-foundation.org, bcrl@kvack.org, netdev@vger.kernel.org, linux-fsdevel@vger.kernel.org, =?UTF-8?Q?Mika_Penttil=c3=a4?= X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: base64 Content-Type: text/plain; charset="utf-8"; Format="flowed" Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" CuWcqCAyMDIxLzcvNCDkuIvljYg1OjQ5LCBZb25namkgWGllIOWGmemBkzoKPj4+IE9LLCBJIGdl dCB5b3Ugbm93LiBTaW5jZSB0aGUgVklSVElPIHNwZWNpZmljYXRpb24gc2F5cyAiRGV2aWNlCj4+ PiBjb25maWd1cmF0aW9uIHNwYWNlIGlzIGdlbmVyYWxseSB1c2VkIGZvciByYXJlbHktY2hhbmdp bmcgb3IKPj4+IGluaXRpYWxpemF0aW9uLXRpbWUgcGFyYW1ldGVycyIuIEkgYXNzdW1lIHRoZSBW RFVTRV9ERVZfU0VUX0NPTkZJRwo+Pj4gaW9jdGwgc2hvdWxkIG5vdCBiZSBjYWxsZWQgZnJlcXVl bnRseS4KPj4gVGhlIHNwZWMgdXNlcyBNVVNUIGFuZCBvdGhlciB0ZXJtcyB0byBkZWZpbmUgdGhl IHByZWNpc2UgcmVxdWlyZW1lbnRzLgo+PiBIZXJlIHRoZSBsYW5ndWFnZSAoZXNwZWNpYWxseSB0 aGUgd29yZCAiZ2VuZXJhbGx5IikgaXMgd2Vha2VyIGFuZCBtZWFucwo+PiB0aGVyZSBtYXkgYmUg ZXhjZXB0aW9ucy4KPj4KPj4gQW5vdGhlciB0eXBlIG9mIGFjY2VzcyB0aGF0IGRvZXNuJ3Qgd29y ayB3aXRoIHRoZSBWRFVTRV9ERVZfU0VUX0NPTkZJRwo+PiBhcHByb2FjaCBpcyByZWFkcyB0aGF0 IGhhdmUgc2lkZS1lZmZlY3RzLiBGb3IgZXhhbXBsZSwgaW1hZ2luZSBhIGZpZWxkCj4+IGNvbnRh aW5pbmcgYW4gZXJyb3IgY29kZSBpZiB0aGUgZGV2aWNlIGVuY291bnRlcnMgYSBwcm9ibGVtIHVu cmVsYXRlZCB0bwo+PiBhIHNwZWNpZmljIHZpcnRxdWV1ZSByZXF1ZXN0LiBSZWFkaW5nIGZyb20g dGhpcyBmaWVsZCByZXNldHMgdGhlIGVycm9yCj4+IGNvZGUgdG8gMCwgc2F2aW5nIHRoZSBkcml2 ZXIgYW4gZXh0cmEgY29uZmlndXJhdGlvbiBzcGFjZSB3cml0ZSBhY2Nlc3MKPj4gYW5kIHBvc3Np Ymx5IHJhY2UgY29uZGl0aW9ucy4gSXQgaXNuJ3QgcG9zc2libGUgdG8gaW1wbGVtZW50IHRob3Nl Cj4+IHNlbWFudGljcyBzdWluZyBWRFVTRV9ERVZfU0VUX0NPTkZJRy4gSXQncyBhbm90aGVyIGNv cm5lciBjYXNlLCBidXQgaXQKPj4gbWFrZXMgbWUgdGhpbmsgdGhhdCB0aGUgaW50ZXJmYWNlIGRv ZXMgbm90IGFsbG93IGZ1bGwgVklSVElPIHNlbWFudGljcy4KCgpOb3RlIHRoYXQgdGhvdWdoIHlv dSdyZSBjb3JyZWN0LCBteSB1bmRlcnN0YW5kaW5nIGlzIHRoYXQgY29uZmlnIHNwYWNlIAppcyBu b3Qgc3VpdGFibGUgZm9yIHRoaXMga2luZCBvZiBlcnJvciBwcm9wYWdhdGluZy4gQW5kIGl0IHdv dWxkIGJlIHZlcnkgCmhhcmQgdG8gaW1wbGVtZW50IHN1Y2gga2luZCBvZiBzZW1hbnRpYyBpbiBz b21lIHRyYW5zcG9ydHMuwqAgVmlydHF1ZXVlIApzaG91bGQgYmUgbXVjaCBiZXR0ZXIuIEFzIFlv bmcgSmkgcXVvdGVkLCB0aGUgY29uZmlnIHNwYWNlIGlzIHVzZWQgZm9yIAoicmFyZWx5LWNoYW5n aW5nIG9yIGludGlhbGl6YXRpb24tdGltZSBwYXJhbWV0ZXJzIi4KCgo+IEFncmVlZC4gSSB3aWxs IHVzZSBWRFVTRV9ERVZfR0VUX0NPTkZJRyBpbiB0aGUgbmV4dCB2ZXJzaW9uLiBBbmQgdG8KPiBo YW5kbGUgdGhlIG1lc3NhZ2UgZmFpbHVyZSwgSSdtIGdvaW5nIHRvIGFkZCBhIHJldHVybiB2YWx1 ZSB0bwo+IHZpcnRpb19jb25maWdfb3BzLmdldCgpIGFuZCB2aXJ0aW9fY3JlYWRfKiBBUEkgc28g dGhhdCB0aGUgZXJyb3IgY2FuCj4gYmUgcHJvcGFnYXRlZCB0byB0aGUgdmlydGlvIGRldmljZSBk cml2ZXIuIFRoZW4gdGhlIHZpcnRpby1ibGsgZGV2aWNlCj4gZHJpdmVyIGNhbiBiZSBtb2RpZmll ZCB0byBoYW5kbGUgdGhhdC4KPgo+IEphc29uIGFuZCBTdGVmYW4sIHdoYXQgZG8geW91IHRoaW5r IG9mIHRoaXMgd2F5PwoKCkknZCBsaWtlIHRvIHN0aWNrIHRvIHRoZSBjdXJyZW50IGFzc3VtcHRp b24gdGhpY2ggZ2V0X2NvbmZpZyB3b24ndCBmYWlsLiAKVGhhdCBpcyB0byBzYXksCgoxKSBtYWlu dGFpbiBhIGNvbmZpZyBpbiB0aGUga2VybmVsLCBtYWtlIHN1cmUgdGhlIGNvbmZpZyBzcGFjZSBy ZWFkIGNhbiAKYWx3YXlzIHN1Y2NlZWQKMikgaW50cm9kdWNlIGFuIGlvY3RsIGZvciB0aGUgdmR1 c2UgdXNlcnNhcGNlIHRvIHVwZGF0ZSB0aGUgY29uZmlnIHNwYWNlLgozKSB3ZSBjYW4gc3luY2hy b25pemUgd2l0aCB0aGUgdmR1c2UgdXNlcnNwYWNlIGR1cmluZyBzZXRfY29uZmlnCgpEb2VzIHRo aXMgd29yaz8KClRoYW5rcwoKCj4KCl9fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fX19fClZpcnR1YWxpemF0aW9uIG1haWxpbmcgbGlzdApWaXJ0dWFsaXphdGlvbkBs aXN0cy5saW51eC1mb3VuZGF0aW9uLm9yZwpodHRwczovL2xpc3RzLmxpbnV4Zm91bmRhdGlvbi5v cmcvbWFpbG1hbi9saXN0aW5mby92aXJ0dWFsaXphdGlvbg==