From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932634AbeDWWkM (ORCPT ); Mon, 23 Apr 2018 18:40:12 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:34674 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932558AbeDWWkI (ORCPT ); Mon, 23 Apr 2018 18:40:08 -0400 Subject: Re: [Xen-devel] [PATCH 0/1] drm/xen-zcopy: Add Xen zero-copy helper DRM driver To: Oleksandr Andrushchenko , Wei Liu Cc: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , jgross@suse.com, Artem Mygaiev , Dongwon Kim , konrad.wilk@oracle.com, airlied@linux.ie, "Oleksandr_Andrushchenko@epam.com" , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, "Potrola, MateuszX" , xen-devel@lists.xenproject.org, daniel.vetter@intel.com References: <5d8fec7f-956c-378f-be90-f45029385740@gmail.com> <20180416192905.GA18096@downor-Z87X-UD5H> <20180417075928.GT31310@phenom.ffwll.local> <20180417205744.GA15930@downor-Z87X-UD5H> <41487acb-a67a-8933-d0c3-702c19b0938e@gmail.com> <20180418073508.ptvntwedczpvl7bx@MacBook-Pro-de-Roger.local> <20180418101058.hyqk3gr3b2ibxswu@MacBook-Pro-de-Roger.local> <20180420071914.GG31310@phenom.ffwll.local> <76cdc65a-7bb1-9377-7bc5-6164e32f7b5d@gmail.com> <20180423115242.ywdwqblj2aseu3fr@citrix.com> <61105351-8896-072b-abf0-757c7f6c0edf@gmail.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <61105351-8896-072b-abf0-757c7f6c0edf@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8872 signatures=668698 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1804230222 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/23/2018 08:10 AM, Oleksandr Andrushchenko wrote: > On 04/23/2018 02:52 PM, Wei Liu wrote: >> On Fri, Apr 20, 2018 at 02:25:20PM +0300, Oleksandr Andrushchenko wrote: >>>>>      the gntdev. >>>>> >>>>> I think this is generic enough that it could be implemented by a >>>>> device not tied to Xen. AFAICT the hyper_dma guys also wanted >>>>> something similar to this. >>>> You can't just wrap random userspace memory into a dma-buf. We've >>>> just had >>>> this discussion with kvm/qemu folks, who proposed just that, and >>>> after a >>>> bit of discussion they'll now try to have a driver which just wraps a >>>> memfd into a dma-buf. >>> So, we have to decide either we introduce a new driver >>> (say, under drivers/xen/xen-dma-buf) or extend the existing >>> gntdev/balloon to support dma-buf use-cases. >>> >>> Can anybody from Xen community express their preference here? >>> >> Oleksandr talked to me on IRC about this, he said a few IOCTLs need to >> be added to either existing drivers or a new driver. >> >> I went through this thread twice and skimmed through the relevant >> documents, but I couldn't see any obvious pros and cons for either >> approach. So I don't really have an opinion on this. >> >> But, assuming if implemented in existing drivers, those IOCTLs need to >> be added to different drivers, which means userspace program needs to >> write more code and get more handles, it would be slightly better to >> implement a new driver from that perspective. > If gntdev/balloon extension is still considered: > > All the IOCTLs will be in gntdev driver (in current xen-zcopy > terminology): >  - DRM_ICOTL_XEN_ZCOPY_DUMB_FROM_REFS >  - DRM_IOCTL_XEN_ZCOPY_DUMB_TO_REFS >  - DRM_IOCTL_XEN_ZCOPY_DUMB_WAIT_FREE > > Balloon driver extension, which is needed for contiguous/DMA > buffers, will be to provide new *kernel API*, no UAPI is needed. > So I am obviously a bit late to this thread, but why do you need to add new ioctls to gntdev and balloon? Doesn't this driver manage to do what you want without any extensions? -boris